Abstract: The impact of internal combustion engines and the environmental situation. Environmental problems of heat use

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SEROV METALLURGICAL COLLEGE

abstract

on Ecological bases of nature management

on the topic:Environmental problems associated with the development of energy

Fulfilleda: student

correspondence department

IVcourse TiTO group

Sochneva Natalia

Checked by: teacher

Chernysheva N.G.

Introduction

1. Environmental problems of thermal power engineering

2. Environmental problems of hydropower

3. Problems of nuclear power

4. Some ways to solve the problems of modern energy

Conclusion

List of used literature

Introduction

There is a figurative expression that we live in the era of three "E": economy, energy, ecology. At the same time, ecology as a science and a way of thinking attracts more and more close attention of mankind.

Ecology is considered as a science and academic discipline, which is designed to study the relationship between organisms and the environment in all their diversity. At the same time, the environment is understood not only as the world of inanimate nature, but also as the impact of some organisms or their communities on other organisms and communities. Ecology is sometimes associated only with the study of habitat or environment. The latter is fundamentally correct, with the essential correction, however, that the environment cannot be considered in isolation from organisms, just as organisms outside their habitat cannot be considered. These are the constituent parts of a single functional whole, which is emphasized by the above definition of ecology as the science of the relationship between organisms and the environment.

Energy ecology is a branch of production that is developing at an unprecedented pace. If the population in the conditions of the modern population explosion doubles in 40-50 years, then in the production and consumption of energy this happens every 12-15 years. With such a ratio of population and energy growth rates, the energy supply increases like an avalanche not only in total terms, but also per capita.

Currently, energy needs are met mainly by three types of energy resources: organic fuel, water and the atomic nucleus. Water energy and atomic energy are used by man after turning it into electrical energy. At the same time, a significant amount of energy contained in organic fuel is used in the form of thermal energy, and only part of it is converted into electrical energy. However, in both cases, the release of energy from organic fuel is associated with its combustion, and, consequently, with the release of combustion products into the environment.

The purpose of this work is to study the impact on the environment of different types of energy (thermal power, hydropower, nuclear power) and consider ways to reduce emissions and pollution from energy facilities. When writing this essay, I set myself the task of identifying ways to solve the problems of each of the considered types of energy.

1. Ecologistscal problems of thermal power engineering

The impact of thermal power plants on the environment largely depends on the type of fuel burned (solid and liquid).

When burning solid fuel fly ash with particles of unburned fuel, sulfurous and sulfuric anhydrides, nitrogen oxides, a certain amount of fluorine compounds, as well as gaseous products of incomplete combustion of fuel enter the atmosphere. Fly ash in some cases contains, in addition to non-toxic components, more harmful impurities. So, in the ash of Donetsk anthracites, arsenic is contained in small quantities, and in the ash of Ekibastuz and some other deposits - free silicon dioxide, in the ash of shales and coals of the Kansk-Achinsk basin - free calcium oxide.

Coal - the most abundant fossil fuel on our planet. Experts believe that its reserves will last for 500 years. In addition, coal is more evenly distributed throughout the world and is more economical than oil. Synthetic liquid fuel can be obtained from coal. The method of obtaining fuel by processing coal has long been known. However, the cost of such products was too high. The process takes place at high pressure. This fuel has one indisputable advantage - it has a higher octane rating. This means that it will be more environmentally friendly.

Peat. There are a number of negative environmental impacts associated with the energy use of peat as a result of peat mining on a large scale. These include, in particular, violation of the regime of water systems, changes in the landscape and soil cover in peat extraction sites, deterioration in the quality of local fresh water sources and pollution of the air basin, and a sharp deterioration in the living conditions of animals. Significant environmental difficulties also arise in connection with the need to transport and store peat.

When burning liquid fuel(fuel oil) with flue gases into the atmospheric air enter: sulfurous and sulfuric anhydrides, nitrogen oxides, vanadium compounds, sodium salts, as well as substances removed from the surface of boilers during cleaning. From an environmental standpoint, liquid fuels are more “hygienic”. At the same time, the problem of ash dumps completely disappears, which occupy large areas, exclude their useful use and are a source of constant atmospheric pollution in the station area due to the removal of part of the ash with the winds. There is no fly ash in the combustion products of liquid fuels.

Natural gas. When natural gas is burned, nitrogen oxides are a significant air pollutant. However, the emission of nitrogen oxides when natural gas is burned at thermal power plants is on average 20% lower than when coal is burned. This is due not to the properties of the fuel itself, but to the peculiarities of the combustion processes. The excess air ratio for coal combustion is lower than for natural gas combustion. Thus, natural gas is the most environmentally friendly type of energy fuel in terms of the release of nitrogen oxides during combustion.

The complex impact of thermal power plants on the biosphere as a whole is illustrated in Table. one.

Thus, coal, oil and oil products, natural gas and, less commonly, wood and peat are used as fuel in thermal power plants. The main components of combustible materials are carbon, hydrogen and oxygen, sulfur and nitrogen are contained in smaller amounts, traces of metals and their compounds (most often oxides and sulfides) are also present.

In the thermal power industry, the source of massive atmospheric emissions and large-tonnage solid waste are thermal power plants, enterprises and installations of steam power facilities, i.e. any enterprises whose work is associated with fuel combustion.

Along with gaseous emissions, thermal power engineering produces huge masses of solid waste. These include ash and slag.

Waste coal preparation plants contain 55-60% SiO 2 , 22-26% Al 2 O 3 , 5-12% Fe 2 O 3 , 0.5-1% CaO, 4-4.5% K 2 O and Na 2 O and up to 5% C. They enter the dumps, which produce dust, smoke and drastically worsen the state of the atmosphere and adjacent territories.

Life on Earth originated in a reducing atmosphere, and only much later, after about 2 billion years, did the biosphere gradually transform the reducing atmosphere into an oxidizing one. At the same time, living matter previously removed various substances from the atmosphere, in particular carbon dioxide, forming huge deposits of limestone and other carbon-containing compounds. Now our technogenic civilization has generated a powerful flow of reducing gases, primarily due to the burning of fossil fuels in order to obtain energy. For 30 years, from 1970 to 2000, about 450 billion barrels of oil, 90 billion tons of coal, 11 trillion. m 3 of gas (Table 2).

Air emissions from a 1,000 MW/year power plant (tonnes)

The main part of the emission is occupied by carbon dioxide - about 1 million tons in terms of carbon 1 Mt. With wastewater from a thermal power plant, 66 tons of organic matter, 82 tons of sulfuric acid, 26 tons of chlorides, 41 tons of phosphates and almost 500 tons of suspended particles are annually removed. Ash from power plants often contains elevated concentrations of heavy, rare earth and radioactive substances.

A coal-fired power plant requires 3.6 million tons of coal, 150 m 3 of water and about 30 billion m 3 of air annually. These figures do not take into account environmental disturbances associated with the extraction and transportation of coal.

Considering that such a power plant has been actively operating for several decades, then its impact can be compared with that of a volcano. But if the latter usually throws out the products of volcanism in large quantities at a time, then the power plant does this all the time. For tens of millennia, volcanic activity has not been able to noticeably affect the composition of the atmosphere, and human economic activity has caused such changes over some 100-200 years, mainly due to the burning of fossil fuels and emissions of greenhouse gases by destroyed and deformed ecosystems.

The efficiency of power plants is still low and amounts to 30-40%, most of the fuel is burned in vain. The received energy is used in one way or another and eventually turns into heat, i.e., in addition to chemical pollution, thermal pollution enters the biosphere.

Pollution and waste from energy facilities in the form of gas, liquid and solid phases are distributed into two streams: one causes global changes, and the other causes regional and local ones. The same is true in other sectors of the economy, but still energy and fossil fuel combustion remain a source of major global pollutants. They enter the atmosphere, and due to their accumulation, the concentration of small gas components of the atmosphere, including greenhouse gases, changes. In the atmosphere, gases appeared that were practically absent in it before - chlorofluorocarbons. These are global pollutants that have a high greenhouse effect and at the same time participate in the destruction of the stratospheric ozone screen.

Thus, it should be noted that at the present stage, thermal power plants emit about 20% of the total amount of all hazardous industrial waste into the atmosphere. They significantly affect the environment of the area of their location and the state of the biosphere as a whole. The most harmful are condensing power plants operating on low-grade fuels. So, when burning at the station for 1 hour 1060 tons of Donetsk coal, 34.5 tons of slag is removed from the furnaces of boilers, 193.5 tons of ash is removed from the bunkers of electrostatic precipitators that clean gases by 99%, and 10 million m 3 are emitted into the atmosphere through pipes flue gases. These gases, in addition to nitrogen and oxygen residues, contain 2350 tons of carbon dioxide, 251 tons of water vapor, 34 tons of sulfur dioxide, 9.34 tons of nitrogen oxides (in terms of dioxide) and 2 tons of fly ash not “caught” by electrostatic precipitators.

Waste water from thermal power plants and storm water from their territories, contaminated with waste from technological cycles of power plants and containing vanadium, nickel, fluorine, phenols and oil products, when discharged into water bodies, can affect water quality and aquatic organisms. A change in the chemical composition of certain substances leads to a violation of the habitat conditions established in the reservoir and affects the species composition and abundance of aquatic organisms and bacteria, and ultimately can lead to violations of the processes of self-purification of water bodies from pollution and to a deterioration in their sanitary condition.

The so-called thermal pollution of water bodies with diverse violations of their condition is also dangerous. Thermal power plants produce energy using turbines driven by heated steam. During the operation of turbines, it is necessary to cool the exhaust steam with water, therefore, a stream of water continuously leaves the power plant, usually heated by 8-12 ° C and discharged into a reservoir. Large thermal power plants need large volumes of water. They discharge 80-90 m 3 /s of water in a heated state. This means that a powerful stream of warm water is continuously flowing into the reservoir, approximately on the scale of the Moscow River.

The heating zone, formed at the confluence of a warm "river", is a kind of section of the reservoir, in which the temperature is maximum at the spillway point and decreases with distance from it. The heating zones of large thermal power plants occupy an area of several tens of square kilometers. In winter, polynyas form in the heated zone (in the northern and middle latitudes). During the summer months, the temperatures in the heated zones depend on the natural temperature of the intake water. If the water temperature in the reservoir is 20 °C, then in the heating zone it can reach 28-32 °C.

As a result of an increase in temperatures in a reservoir and a violation of their natural hydrothermal regime, the processes of “blooming” of water are intensified, the ability of gases to dissolve in water decreases, the physical properties of water change, all chemical and biological processes occurring in it are accelerated, etc. In the heating zone the transparency of water decreases, pH increases, the rate of decomposition of easily oxidized substances increases. The rate of photosynthesis in such water is markedly reduced.

2. Environmental problems of hydropower

The most important feature of hydropower resources in comparison with fuel and energy resources is their continuous renewal. The lack of need for fuel for HPPs determines the low cost of electricity generated at HPPs. Therefore, the construction of HPPs, despite significant specific capital investments per 1 kW of installed capacity and long construction periods, has been and is being given great importance, especially when it is associated with the location of electrically intensive industries.

A hydroelectric power plant is a complex of structures and equipment by means of which the energy of the flow of water is converted into electrical energy. The hydroelectric power station consists of a series of hydraulic structures that provide the necessary concentration of water flow and create pressure, and power equipment that converts the energy of water moving under pressure into mechanical rotational energy, which, in turn, is converted into electrical energy.

Despite the relative cheapness of energy obtained from hydro resources, their share in the energy balance is gradually decreasing. This is due both to the exhaustion of the cheapest resources and to the large territorial capacity of lowland reservoirs. It is believed that in the future, the world production of hydroelectric energy will not exceed 5% of the total.

One of the most important reasons for the decrease in the share of energy received at HPPs is the powerful impact of all stages of the construction and operation of hydraulic structures on the environment (Table 3).

According to various studies, one of the most important impacts of hydropower on the environment is the alienation of large areas of fertile (floodplain) land for reservoirs. In Russia, where no more than 20% of electrical energy is produced through the use of hydro resources, at least 6 million hectares of land were flooded during the construction of hydroelectric power stations. Natural ecosystems have been destroyed in their place.

Significant areas of land near reservoirs are experiencing flooding as a result of rising groundwater levels. These lands, as a rule, go into the category of wetlands. In flat conditions, flooded lands can be 10% or more of the flooded. The destruction of lands and their ecosystems also occurs as a result of their destruction by water (abrasion) during the formation of the coastline. Abrasion processes usually last for decades, resulting in the processing of large masses of soil, water pollution, siltation of reservoirs. Thus, the construction of reservoirs is associated with a sharp violation of the hydrological regime of rivers, their ecosystems, and the species composition of hydrobionts.

In reservoirs, the warming of waters sharply increases, which intensifies the loss of oxygen and other processes caused by thermal pollution. The latter, together with the accumulation of biogenic substances, creates conditions for the overgrowth of water bodies and the intensive development of algae, including poisonous blue-green ones. For these reasons, as well as due to the slow renewal of waters, their ability to self-purify is sharply reduced.

The deterioration of water quality leads to the death of many of its inhabitants. The incidence of fish stocks is increasing, especially the susceptibility to helminths. The taste qualities of the inhabitants of the aquatic environment are reduced.

Fish migration routes are being disrupted, forage grounds, spawning grounds, etc. are being destroyed. The Volga has largely lost its significance as a spawning ground for Caspian sturgeons after the construction of a hydroelectric power station cascade on it.

Ultimately, the river systems blocked by reservoirs turn from transit systems into transit-accumulation systems. In addition to biogenic substances, heavy metals, radioactive elements and many pesticides with a long life span are accumulated here. Accumulation products make it problematic to use the territories occupied by reservoirs after their liquidation.

Reservoirs have a significant impact on atmospheric processes. For example, in arid (arid) regions, evaporation from the surface of reservoirs exceeds evaporation from an equal land surface by tens of times.

A decrease in air temperature and an increase in foggy phenomena are associated with increased evaporation. The difference between the thermal balances of reservoirs and the adjacent land determines the formation of local winds such as breezes. These, as well as other phenomena, result in a change in ecosystems (not always positive), a change in the weather. In some cases, in the area of reservoirs, it is necessary to change the direction of agriculture. For example, in the southern regions of our country, some heat-loving crops (melons) do not have time to ripen, the incidence of plants increases, and the quality of products deteriorates.

The costs of hydraulic construction for the environment are noticeably lower in mountainous regions, where reservoirs are usually small in area. However, in seismic mountainous areas, reservoirs can provoke earthquakes. The likelihood of landslides and the likelihood of disasters as a result of the possible destruction of dams is increasing. Thus, in 1960, in India (the state of Gunjarat), as a result of a dam breakthrough, water claimed 15,000 lives.

Due to the specifics of the technology of using water energy, hydropower facilities transform natural processes for very long periods. For example, a hydroelectric power station reservoir (or a system of reservoirs in the case of a hydroelectric power station cascade) can exist for tens and hundreds of years, while in place of a natural watercourse a man-made object arises with artificial regulation of natural processes - a natural-technical system (NTS). In this case, the task is reduced to the formation of such a PTS that would ensure the reliable and environmentally safe formation of the complex. At the same time, the ratio between the main subsystems of the PTS (man-made object and the natural environment) can be significantly different depending on the chosen priorities - technical, environmental, socio-economic, etc., and the principle of environmental safety can be formulated, for example, as maintaining a certain stable state of the created PTS.

An effective way to reduce the flooding of territories is to increase the number of HPPs in a cascade with a decrease in pressure at each stage and, consequently, a reservoir surface.

Another environmental problem of hydropower is related to the assessment of the quality of the aquatic environment. The current water pollution is caused not by the technological processes of generating electricity at hydroelectric power plants (the volume of pollution coming from wastewater from hydroelectric power plants is an insignificantly small proportion of the total mass of pollution of the economic complex), but by the poor quality of sanitary and technical work during the creation of reservoirs and the discharge of untreated effluents into water objects.

Most of the nutrients brought by rivers are retained in reservoirs. In warm weather, algae are able to multiply in masses in the surface layers of a nutrient-rich, or eutrophic, reservoir. During photosynthesis, algae consume nutrients from the reservoir and produce large amounts of oxygen. Dead algae give water an unpleasant odor and taste, cover the bottom with a thick layer and prevent people from resting on the banks of reservoirs.

In the first years after the reservoir is filled, a lot of decomposed vegetation appears in it, and the “new” soil can dramatically reduce the level of oxygen in the water. The rotting of organic matter can lead to the release of huge amounts of greenhouse gases - methane and carbon dioxide.

Considering the impact of HPPs on the environment, one should still note the life-saving function of HPPs. Thus, the generation of each billion kWh of electricity at hydroelectric power plants instead of thermal power plants leads to a decrease in mortality by 100-226 people per year.

3. Problems of nuclear power

Nuclear power can currently be considered as the most promising. This is due both to the relatively large reserves of nuclear fuel and to the gentle impact on the environment. The advantages also include the possibility of building a nuclear power plant without being tied to resource deposits, since their transportation does not require significant costs due to small volumes. Suffice it to say that 0.5 kg of nuclear fuel allows you to get as much energy as burning 1000 tons of coal.

It is known that the processes underlying the production of energy at nuclear power plants - the reactions of fission of atomic nuclei - are much more dangerous than, for example, combustion processes. That is why, for the first time in the history of industrial development, nuclear energy implements the principle of maximum safety at the highest possible productivity when generating energy.

Many years of experience in the operation of nuclear power plants in all countries shows that they do not have a significant impact on the environment. By 2000, the average NPP operation time was 20 years. The reliability, safety and economic efficiency of nuclear power plants is based not only on the strict regulation of the operation of nuclear power plants, but also on the reduction to an absolute minimum of the impact of nuclear power plants on the environment.

In table. 4 presents comparative data of nuclear power plants and thermal power plants on fuel consumption and environmental pollution for the year at a power of 1000 MW.

Fuel consumption and environmental pollution

During normal operation of nuclear power plants, releases of radioactive elements into the environment are extremely insignificant. On average, they are 2-4 times less than from thermal power plants of the same capacity.

By May 1986, 400 power units operating in the world and providing more than 17% of electricity increased the natural background of radioactivity by no more than 0.02%. Before the Chernobyl disaster in our country, no industry had a lower level of industrial injuries than nuclear power plants. 30 years before the tragedy, 17 people died in accidents, and even then not for radiation reasons. After 1986, the main environmental hazard of nuclear power plants began to be associated with the possibility of an accident. Although their probability at modern nuclear power plants is low, it is not excluded. The largest accidents of this kind include the accident that occurred at the fourth unit of the Chernobyl nuclear power plant.

According to various sources, the total release of fission products from those contained in the reactor ranged from 3.5% (63 kg) to 28% (50 tons). For comparison, it should be noted that the bomb dropped on Hiroshima yielded only 740 g of radioactive material.

As a result of the accident at the Chernobyl nuclear power plant, a territory within a radius of more than 2 thousand km, covering more than 20 states, was subjected to radioactive contamination. Within the boundaries of the former USSR, 11 regions were affected, where 17 million people live. The total area of contaminated territories exceeds 8 million hectares, or 80,000 km 2 . In Russia, the Bryansk, Kaluga, Tula and Oryol regions suffered the most. There are spots of pollution in Belgorod, Ryazan, Smolensk, Leningrad and other regions. As a result of the accident, 31 people died and more than 200 people received a dose of radiation that led to radiation sickness. 115 thousand people were evacuated from the most dangerous (30 km) zone immediately after the accident. The number of victims and the number of evacuated residents is increasing, the zone of contamination is expanding as a result of the movement of radioactive substances by wind, fires, transport, etc. The consequences of the accident will affect the lives of several generations.

After the Chernobyl accident in many states, at the request of the public, nuclear power plant construction programs were temporarily stopped or curtailed, but nuclear energy continued to develop in 32 countries.

Now the discussions on the acceptability or unacceptability of nuclear energy have begun to decline, it has become clear that the world cannot once again plunge into darkness or come to terms with the extremely dangerous effects on the atmosphere of carbon dioxide and other fossil fuel combustion products harmful to humans. Already during 1990, 10 new nuclear power plants were connected to the grid. The construction of nuclear power plants does not stop: as of the end of 1999, there were 436 nuclear power units in operation in the world, compared with 434 registered in 1998. The total electric power of the power units operating in the world is about 335 GW (1 GW = 1000 MW = 10 9 W ). Operating nuclear power plants cover 7% of the world's energy needs, and their share in the world's electricity production is 17%. Only in Western Europe, nuclear power plants produce on average about 50% of all electricity.

If we now replace all the nuclear power plants operating in the world with thermal ones, the global economy, our entire planet and each person individually, would suffer irreparable damage. This conclusion is based on the fact that the generation of energy at nuclear power plants simultaneously prevents the annual release of up to 2300 million tons of carbon dioxide, 80 million tons of sulfur dioxide and 35 million tons of nitrogen oxides into the Earth's atmosphere by reducing the amount of fossil fuel burned at thermal power plants. In addition, when burning, organic fuel (coal, oil) releases into the atmosphere a huge amount of radioactive substances containing mainly radium isotopes with a half-life of about 1600 years! In this case, it would not be possible to extract all these hazardous substances from the atmosphere and protect the population of the Earth from their impact. Here is just one specific example. The closure of the Barsebæk-1 nuclear power plant in Sweden led to the fact that Sweden began to import electricity from Denmark for the first time in the last 30 years. The environmental consequences of this are as follows: at coal-fired power plants in Denmark, an additional almost 350 thousand tons of coal from Russia and Poland were burned, which led to an increase in carbon dioxide emissions by 4 million tons (!) per year and a significant increase in the amount of acid rain falling in the entire southern part of Sweden.

The construction of nuclear power plants is carried out at a distance of 30-35 km from large cities. The site should be well ventilated, not flooded during the flood. Around the nuclear power plant, a place is provided for a sanitary protection zone in which the population is prohibited from living.

In the Russian Federation, 29 power units are currently in operation at nine nuclear power plants with a total installed electrical capacity of 21.24 GW. In 1995-2000 nuclear power plants in Russia generated more than 13% of the total electricity production in the country, now - 14.4%. In terms of the total installed capacity of nuclear power plants, Russia ranks fifth after the USA, France, Japan and Germany. Currently, more than 100 billion kWh generated by the country's nuclear power units make a significant and necessary contribution to the energy supply of its European part - 22% of all electricity generated. Electricity produced at nuclear power plants is more than 30% cheaper than at thermal power plants using fossil fuels.

The safety of operating NPPs is one of the most important tasks of the Russian nuclear power industry. All plans for the construction, reconstruction and modernization of nuclear power plants in Russia are implemented only taking into account modern requirements and standards. A study of the state of the main equipment of operating Russian NPPs has shown that it is quite possible to extend its service life by at least another 5-10 years. Moreover, thanks to the implementation of an appropriate set of works for each power unit, while maintaining a high level of safety.

To ensure the further development of nuclear energy in Russia in 1998, the “Program for the Development of Nuclear Energy in the Russian Federation for 1998-2000” was adopted. and for the period up to 2010”. It notes that in 1999, Russian NPPs generated 16% more energy than in 1998. To produce this amount of energy at TPPs, 36 billion m 3 of gas worth $ 2.5 billion in export prices would be required. A 90% increase in energy consumption in the country was ensured by its generation at nuclear power plants.

Assessing the prospects for the development of the world nuclear energy, most of the authoritative international organizations involved in the study of global fuel and energy problems suggest that after 2010-2020. in the world, the need for large-scale construction of nuclear power plants will again increase. According to the realistic version, it is predicted that in the middle of the XXI century. about 50 countries will have nuclear power. At the same time, the total installed electric capacity of nuclear power plants in the world will almost double by 2020, reaching 570 GW, and by 2050, 1100 GW.

4. Some ways to solve the problems of modern energy

Undoubtedly, in the near future, thermal energy will remain dominant in the energy balance of the world and individual countries. There is a high probability of an increase in the share of coal and other types of less clean fuel in energy production. In this regard, we will consider some ways and methods of their use, which can significantly reduce the negative impact on the environment. These methods are based mainly on the improvement of fuel preparation technologies and hazardous waste capture. Among them are the following:

1. Use and improvement of cleaning devices. Currently, many thermal power plants capture mainly solid emissions using various types of filters. Sulfur dioxide, the most aggressive pollutant, is not captured at many TPPs or is captured in limited quantities. At the same time, there are thermal power plants (USA, Japan), which carry out almost complete purification from this pollutant, as well as from nitrogen oxides and other harmful pollutants. For this, special desulphurization (to capture sulfur dioxide and trioxide) and denitrification (to capture nitrogen oxides) installations are used. The most widely captured oxides of sulfur and nitrogen is carried out by passing flue gases through an ammonia solution. The end products of such a process are ammonium nitrate, used as a mineral fertilizer, or sodium sulfite solution (raw material for the chemical industry). Such installations capture up to 96% of sulfur oxides and more than 80% of nitrogen oxides. There are other methods of purification from these gases.

2. Reducing the entry of sulfur compounds into the atmosphere through preliminary desulfurization (desulfurization) of coal and other fuels (oil, gas, oil shale) by chemical or physical methods. These methods make it possible to extract from 50 to 70% of sulfur from the fuel before its combustion.

3. Great and real opportunities to reduce or stabilize the flow of pollution into the environment are associated with energy savings. Such possibilities are especially great due to the reduction in the energy intensity of the products obtained. For example, in the United States, an average of 2 times less energy was spent per unit of output than in the former USSR. In Japan, this consumption was three times less. Energy savings are no less real by reducing the metal consumption of products, improving their quality and increasing the life expectancy of products. It is promising to save energy by switching to science-intensive technologies associated with the use of computer and other low-current devices.

4. No less significant are the possibilities for saving energy in everyday life and at work by improving the insulating properties of buildings. Real energy savings comes from replacing incandescent lamps with an efficiency of about 5% with fluorescent lamps, the efficiency of which is several times higher. It is extremely wasteful to use electrical energy to produce heat. It is important to keep in mind that the production of electrical energy at thermal power plants is associated with a loss of approximately 60-65% of thermal energy, and at nuclear power plants - at least 70% of energy. Energy is also lost when it is transmitted over wires over a distance. Therefore, direct combustion of fuel to produce heat, especially gas, is much more efficient than turning it into electricity and then back into heat.

5. The efficiency of the fuel is also noticeably increased when it is used instead of a thermal power plant at a thermal power plant. In the latter case, the objects of obtaining energy are closer to the places of its consumption, and thereby the losses associated with transmission over a distance are reduced. Along with electricity, heat is used in CHP plants, which is captured by cooling agents. This significantly reduces the likelihood of thermal pollution of the aquatic environment. It is most economical to obtain energy in small CHP plants (iogenation) directly in buildings. In this case, the loss of heat and electricity is reduced to a minimum. Such methods in individual countries are increasingly used.

Conclusion

So, I tried to cover all aspects of such a topical issue today as "Environmental problems associated with the development of energy." I already knew something from the presented material, but I encountered something for the first time.

In conclusion, I would like to add that environmental problems are among the global problems of the world. The political, economic, ideological, military dictatorships were replaced by a more cruel and merciless dictatorship - the dictatorship of the limited resources of the biosphere. Borders in a changed world today are determined not by politicians, not by border patrols and not by the customs service, but by regional environmental patterns.

Withlist of used literature

1. Akimova T.A. Ecology. - M.: "UNITI", 2000

2. Dyakov A.F. The main directions of development of energy in Russia. - M.: "Phoenix", 2001

3. Kiselev G.V. The problem of development of nuclear energy. - M.: "Knowledge", 1999.

4. Hwang T.A. Industrial ecology. - M.: "Phoenix", 2003

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Ministry of Science of the Russian Federation

Samara State Aerospace University named after Academician S.P. Queen

Department of Ecology

Environmental problems of internal combustion engines and ways to solve them

Student R.A. Ignatenko, gr. 233

Teacher V.N. Vyakin

Samara 2004

Introduction

Fuel treatment devices

Taming the internal combustion engine

That strange word "hybrid"

dimethyl ether

Conclusion

Introduction

hydrocarbon diesel motor vehicle fuel

Today, one of the urgent environmental problems is the problem of motor transport, since internal combustion engines running on refined products have the greatest anthropogenic impact on the environment. Every year, 250 million tons of fine aerosols are emitted into the Earth's atmosphere. Now the biosphere contains about 3 million chemical compounds that have never been found in nature before.

The problem of environmental safety in the operation of internal combustion engines requires the development of environmentally friendly motor fuels.

Environmental problems of using hydrocarbon fuels

Exhaust gases of internal combustion engines are a source of such organic toxicants as phenanthrene, anthracene, fluoranthene, pyrene, chrysene, dibenzpyrilene, etc., which have strong carcinogenic activity, as well as irritating the skin and mucous membranes of the respiratory tract.

An analysis of the mechanisms of chemical reactions taking place inside the engine during fuel combustion showed that the main reason for the formation of organic toxicants is incomplete combustion of fuel:

in the process of fuel combustion, the metals that make up the alloy of the engine are catalysts for many chemical processes leading to the formation of condensing aromatic compounds and their derivatives;

the formation of soot during incomplete combustion of fuel contributes to the aromatization of hydrocarbons;

the chemical composition of gasoline significantly determines the concentration of condensed compounds formed.

The greatest danger is catalytic reforming gasoline, due to the high unsaturation of its constituent hydrocarbons and the high content of aromatic hydrocarbons.

Catalytic cracking gasoline is less dangerous, although it has a lower calorific value.

Emissions of organic toxicants formed during the combustion of hydrocarbon fuels can be reduced in several ways:

increase the supply of oxygen to the fuel combustion chamber, which will increase the percentage of combustion of organic substances;

to suppress the catalytic activity of nickel and iron, which are part of the alloy structure of the combustion chamber, by introducing a small amount of metallic lead, which is a catalytic poison for these metals;

use fuel, which is dominated by saturated hydrocarbons, natural gas, petroleum ether, synthetic gasoline.

Modern methods for improving the quality of diesel fuels

Obtaining diesel fuels that meet modern requirements is possible by improving the quality of oil refining and introducing a package of additives for various purposes.

The main advantages of diesel engines in comparison with other internal combustion engines are efficiency and comparative cheapness of fuel, so their use is constantly expanding. The dieselization of cars and trucks, which is growing all over the world, including in Russia, requires an urgent solution to the issues of improving the quality of fuels, since the exhaust gases of internal combustion engines have become the main source of air pollution.

The governments of industrialized countries and a number of international organizations have carried out fundamental studies to determine the influence of the most significant quality factors of diesel fuels (DF) on the performance of engines and environmental pollution by combustion products. These works culminated in the adoption of new standards for diesel fuel. In particular, the World Fuel Charter and the European standard EN 590, which, unlike the current Russian GOST 305-82, severely limit the content of sulfur, aromatic and polyaromatic hydrocarbons in the fuel, introduce a new indicator "fuel lubricity" and set a significantly higher level of cetane number .

Automobiles are the main cause of smog in large cities. The share of exhaust gases reaches 4/5 of the total amount of harmful emissions into the atmosphere.

GOST 305-82 has ceased to meet modern requirements for the indicators listed above, which is already affecting the state of the air basin and the health of Russians. There is a need to adopt a new, mandatory, Russian standard, perhaps even more stringent than the European one. This development seems inevitable. Although the production of new fuel requires significant efforts from refiners, this will largely solve the problems of environmental safety and high-quality operation of diesel engines.

If today the bulk of domestic diesel fuel, in fact, is a product of atmospheric distillation of oil hydrotreated to a sulfur content of 0.2%, then obtaining modern environmentally friendly diesel fuel is a technologically more difficult task, and achieving such indicators as cetane number, lubricity, pour point today it is impossible without the introduction of appropriate additives.

One of the main indicators of the quality of diesel fuel is the cetane number (CN), which serves as a criterion for the self-ignition of fuel, determines the durability and efficiency of the engine, the completeness of fuel combustion and, in many respects, the smoke and composition of exhaust gases.

The struggle to reduce vehicle emissions of the most dangerous pollutant - sulfur dioxide, has led to the appearance on the market of deeply hydrotreated low-sulphur diesel fuel. However, in practice it turned out that their use quickly disables diesel fuel equipment (fuel pumps, injectors), because. with a decrease in sulfur content below 0.1% as a result of hydrotreatment, the lubricating properties of the fuel, due to the natural heteroatomic organic compounds present in it, drop sharply. In practice, the lubricity of diesel fuel is determined by the diameter of the wear scar on a special ball friction machine or as a result of bench tests on full-scale units or directly on engines. By the way, it deteriorates noticeably when some cetane-boosting and depressant additives are introduced into diesel fuel due to the peculiarities of their chemical structure.

Improving the environmental performance of diesel fuel is also possible with the help of anti-smoke additives, which reduce the amount of one of the most toxic components of the exhaust gases of diesel engines - soot with carcinogenic polyaromatic compounds adsorbed on it. The effectiveness of anti-smoke additives depends on the type of engine and its mode of operation. The domestic range of anti-smoke additives is represented mainly by fuel-soluble barium compounds: IHP-702, IHP-706, EFAP-B, ECO-1. They are used at a concentration of 0.05-0.2%, possibly in combination with cetane-enhancing additives (CPP) or other additives. Abroad, recently they refuse to use barium-containing additives due to a certain toxicity of the carried out barium oxide.

The application was found by the so-called. combustion modifiers (catalysts), which are fuel-soluble complexes of transition metals (primarily iron), which reduce not only the content of soot, toxic carbon and nitrogen oxides in exhaust gases, but also fuel consumption. In Russia, additives for diesel fuels FK-4, Angarad-2401 and "0010" based on complex iron compounds are approved for use.

An analysis of the main trends in the development of oil refining shows that one of the most effective ways to obtain modern environmentally friendly diesel fuels, along with deep hydrotreating, is the use of various mutually compatible additives of the latest generation, as a rule, as part of a package.

Fuel treatment devices

You can regularly check and adjust the "exhaust" at service stations.

For many years, Russian scientists have been working on the problem of improving the environmental friendliness of internal combustion engines using petroleum products (gasoline, diesel fuel, fuel oil, kerosene) as fuel. During numerous studies, scientists noticed that the fuel changes its characteristics under the influence of an electric field. The test results of the "modified" fuel showed that it is able to significantly reduce the content of harmful substances in exhaust gases - and not only. Further tests showed that the experimental fuel has several other positive qualities: it reduces fuel consumption, increases engine power, reduces engine noise and makes it easier to start in cold weather, cleans the combustion chambers and increases the life of the power unit.

After the technology was patented, the Russian company A.M.B. Sphere” has developed industrial samples of a new fuel processing device, which have successfully passed independent bench and operational tests in leading research institutes in Russia and neighboring countries. After that, the devices, which received the brand name "Sphere 2000", were tested in real conditions on cars when driving in various cycles (urban, suburban and mixed). The tests involved new and used trucks and cars manufactured by the largest domestic and foreign automakers: MAZ, VAZ, GAZ, KamAZ, Ikarus, Mercerdes-Benz, Nissan, etc.

Of course, no one expected phenomenal results, but the demonstrated qualities allow us to speak about the real efficiency of the Sfera 2000 fuel treatment device:

reduction in fuel consumption for gasoline engines by 2-7%, for diesel engines - by 5-15%;

engine power increase up to 5%;

reduction of exhaust gas toxicity on gasoline engines CO by 20-60%, CH by 40-50%, on diesel engines CO up to 48%, CH up to 50% and NOx up to 17%.

Taming the internal combustion engine

However, making a car "green" is not so easy. Take, for example, the internal combustion engine - the main source of automotive environmental problems. It seems that, despite all attempts, it will not be possible to find an equivalent replacement for him in the near future. And this means that in order to create a "friendly" car, you need to create, first of all, a "friendly" internal combustion engine. Judging by what could be seen in Frankfurt, the world's leading automakers are working - and not without success - in this direction. Modern technology allows you to make car engines more powerful, economical and environmentally friendly. This applies to both petrol and diesel engines. An example of this is the HDi family of diesel engines developed by Peugeot-Citroen specialists and the GDI series gasoline engines from Mitsubishi, which significantly reduce fuel consumption and improve the environmental parameters of the car.

Some manufacturers have gone even further, replacing liquid fuels with liquefied or compressed gas. BMW, for example, and a number of other companies already mass-produce such cars. But, firstly, gas is also an irreplaceable resource, and, secondly, it is also impossible to completely avoid environmental pollution, although, of course, a gas engine is “cleaner” than a gasoline or diesel one. As you can see, the first steps towards curbing the "predator" have already been taken. However, no matter how you feed the wolf, he still looks into the forest, and it is clear to everyone that it is practically impossible to completely abandon the use of natural fuel in internal combustion engines or make its exhausts absolutely harmless. And if so, then we have to admit that the creation of a "friendly" internal combustion engine is by no means a solution to the problem as a whole, but only a delay, more or less significant.

Today it is fashionable to talk and write about alternative engines. One of them is traditionally considered electric. But even here everything is far from being as clear as it might seem at first glance. Indeed, the electric motor itself does not pollute the atmosphere, and besides, its use makes it possible to avoid many purely engineering problems associated with the operation of vehicles. But such a motor, unfortunately, cannot radically solve environmental problems. Suffice it to recall that the generation of electricity today is a rather “dirty” business. The production of batteries is also associated with the use of irreplaceable resources and pollution - and how much! -- Environment. If we add to this the inconvenience associated with the limited capacity of currently existing batteries, the problems of recharging them, as well as the recycling of batteries that have served their time, it becomes clear that the electric motor is in fact no alternative, but another palliative. Of course, cars equipped with electric motors will appear more and more often in the near future, but they will most likely occupy only a certain and rather narrow niche. In particular, electric vehicles are quite appropriate in the role of urban transport. In Frankfurt, for example, the Japanese automakers presented the urban electric concept car Carro to the public. Its main consumers should be the disabled and the elderly, who are unable to use a conventional car. The power of the Kappo electric motor is only 0.6 kW, which does not allow the machine to reach high speeds, thus providing additional security measures.

That strange word "hybrid"

The so-called "hybrid" or "mixed" power plants are much more intended to make the car "native and close". This idea is not new. Back at the beginning of the century, young Ferdinand Porsche successfully worked on such a machine at Lohner. The principle of "hybrid" is that the machine itself is driven by an electric motor, and the energy for it is generated by a generator driven by an internal combustion engine. The second option is also possible - both motors work to set the car in motion. It would seem, what good is there: the shortcomings of the electric motor multiply by the disadvantages of the internal combustion engine. However, do not rush to conclusions. Here, as in mathematics, multiplying "minus" by "minus" gives a plus. The fact is that the internal combustion engine that drives the electric generator operates all the time in the same mode, and, as you know, it is changes in the engine operating mode that lead to an increase in fuel consumption and emissions of harmful substances into the atmosphere. In addition, ICE, as we have already seen, can be quite economical and environmentally friendly. So "hybrids" are also a step forward. A number of Frankfurt novelties were equipped with just such power plants. Suffice it to mention the Mitsubishi SUW Advance hybrid concept car, which consumes only 3.6 liters of fuel per 100 kilometers. (Imagine how much emissions are reduced!) Attracted the attention of visitors and the new Honda Insight, and specially prepared for Europe, the world's first serial "hybrid" Toyota Prius, which, by the way, has already won recognition in its homeland.

As for the Honda Insight, this car went on sale at the end of last year. The car is equipped with a one-liter three-cylinder engine that consumes only 3.4 liters of fuel per 100 km. According to a company representative, this is the lowest fuel consumption of mass-produced mass-produced engines. At the same time, the emission of carbon dioxide into the atmosphere is 80 g per one kilometer of run, which is also a record. And the speed of the Insight is quite decent - up to 180 km / h.

But the most tempting thing would be to simultaneously abandon the consumption of fossil fuels and completely eliminate harmful emissions. To do this, you just need to use an oxygen-hydrogen mixture in the internal combustion engine. Then the engine works quite efficiently, and harmless water vapor is released into the atmosphere. A sufficient amount of the necessary gases can be obtained by electrolysis, decomposing water into its components. But the energy for electrolysis should ideally be provided by solar panels. By the way, several stands in the expositions of Daimler-Benz and BMW were devoted to this problem in Frankfurt. These firms have already created "oxygen-hydrogen" cars, which are successfully being tested.

Well, the last "squeak" in the fight for a "clean" car, of course, are fuel cells, or, as they are also called in the English manner, fuel cells. According to experts, this is a fantastically promising source of energy - a kind of small-sized chemical power plant, where electricity is produced as a result of the decomposition of methanol into oxygen and hydrogen. The process is very complex, requiring the use of the most modern technologies and materials, and therefore quite expensive. But the game, as they say, is worth the candle, because as a result of the use of fuel cells, carbon dioxide emissions into the atmosphere are halved, and nitrogen oxides are not emitted at all in reactions of this kind.

The problem of vehicle emissions in urban environments and aspects of solving this problem

The state of ecology is one of the most important problems of our time. As a result of its life activity, mankind constantly violates the ecological balance, this happens during the extraction of minerals, in the production of material and energy resources. The situation is aggravated by the fact that a significant proportion of pollutants and CO is emitted into the atmosphere during the operation of internal combustion engines used in all spheres of our life.

In the EEC countries, motor transport accounts for up to 70% of carbon monoxide emissions, up to 50% of nitrogen oxides, up to 45% of hydrocarbons and up to 90% of lead, and this is with stringent environmental requirements for transport and fuels used (Euro 1-4) .

In Russia, motor transport accounts for more than half of all harmful emissions into the environment, which in large cities are the main source of air pollution. The exhaust gases of engines contain about 280 components. On average, with a run of 15 thousand km per year, each car burns 2 tons of fuel and about 20-30 tons of air, including 4.5 tons of oxygen. At the same time, the car emits into the atmosphere (kg / t): carbon monoxide - 700, nitrogen dioxide - 40, unburned hydrocarbons - 230 and solids - 2-5. In addition, due to the use of leaded gasoline, many lead compounds that are very hazardous to health are emitted; in the EEC countries, other antiknock agents are added to high-octane gasolines to solve this problem.

The situation in our country is aggravated by the fact that the lion's share of transport operated by enterprises has an extreme physical wear and tear. For a number of objective factors, there is no moral renewal of the rolling stock. This is due, first of all, to the economic situation of enterprises, the fact that the domestic car ferry produces outdated models that do not shine with efficiency, environmental and sanitary safety, and foreign brands are not available because of the price.

An electric car is not a luxury, but a means of survival

An electric car is a vehicle whose driving wheels are driven by an electric motor powered by batteries. It first appeared in England and France in the early 80s of the nineteenth century, that is, before cars with internal combustion engines. The traction motor in such machines was powered by lead-acid batteries with an energy capacity of only 20 watt-hours per kilogram. In general, to power an engine with a power of 20 kilowatts for an hour, a lead battery weighing 1 ton was required. Therefore, with the invention of the internal combustion engine, the production of cars began to rapidly gain momentum, and electric vehicles were forgotten until serious environmental problems arose. Firstly, the development of the greenhouse effect with subsequent irreversible climate change and, secondly, the decrease in the immunity of many people due to the violation of the foundations of genetic heredity.

These problems were provoked by toxic substances, which are contained in sufficiently large quantities in the exhaust gases of an internal combustion engine. The solution to the problems lies in reducing the level of toxicity of exhaust gases, especially carbon monoxide and carbon dioxide, despite the fact that the volume of car production is growing.

Scientists, having conducted a series of studies, have outlined several directions for solving these problems, one of which is the production of electric vehicles. It is, in fact, the first technology to officially achieve zero emission status and is already on the market.

Concern General Motors was one of the first to start selling mass-produced mass-produced electric vehicles. The impetus for this was the California legislation, according to which automakers wishing to be present in the California market must supply 2% of vehicles with zero emissions.

In our country, the Volga Automobile Plant is mainly engaged in the development of electric vehicles, not counting design firms. In his arsenal are VAZ-2109E, VAZ-2131E, Elf, Rapan, and the Golf family of electric vehicles. It must be said that the operating costs in an electric car are significantly less than in a standard car, which requires the cost of maintaining cooling, power, and exhaust systems. The durability of the electric motor is approximately ten thousand hours.

Thus, the number of operations for the maintenance of the electric motor is reduced to a minimum. For example, a DC motor only needs periodic brush changes, while more modern three-phase motors and AC synchronous motors require virtually no maintenance.

If we talk about electric vehicles of VAZ production, then two DC motors are used as a power unit: a power of 25 kW with a torque of 110 N * m and a power of 40 kW with a torque of 190 N * m. Engines of the first type, as a rule, are installed on light electric vehicles, such as Golf, Oka Electro, Elf, and more powerful ones on cars of the VAZ-2108, VAZ-2109, and Niva families.

Why, despite the quietness, ease of operation and zero emissions, the electric car did not become a mass means of transportation? The main problem is the imperfection of batteries: low mileage from a single charge, long recharge cycles and high price. Currently, they rely on nickel-metal hydride and lithium-ion batteries. Russia has already begun the production of pilot batches of nickel-metal hydride batteries, but so far only experimental work is underway with lithium-ion batteries.

Despite these shortcomings, Europeans believe in electric vehicles as a way to clean heavily polluted streets. Whether the electric car will become a real alternative to the car is another question. But its use in megacities, resorts, parks, that is, in areas with increased environmental requirements, is fully justified.

dimethyl ether

One of the most acute environmental problems of large cities is the progressive pollution of their air basin by harmful emissions from internal combustion engines (in Moscow in 1986 - 870 thousand tons, in 1995 - 1.7 million tons). Known methods for reducing the toxicity of engines, such as the use of catalytic treatment of exhaust gases, the use of alternative fuels such as methanol, ethanol, natural gas do not lead to a radical solution to this problem.

One of the solutions could be the adaptation of engines to work on a new alternative fuel - dimethyl ether (DME). Its favorable physico-chemical parameters contribute to the complete elimination of exhaust smoke and reduce their toxicity (as well as noise).

Dimethyl ether (CH3-O-CH3) has very important properties - it is gaseous under normal conditions and its molecules do not have carbon-carbon chemical bonds that contribute to soot formation during combustion. At present, DME is mainly used as a propellant in aerosol cans.

At present, methods of adapting engines to work on DME are being worked out in a number of countries. For example, in Denmark, operational tests of city buses adapted to work on DME are already being carried out. In our country, work on the conversion of diesel engines to DME has been carried out on an initiative basis since 1996 at NIID, which has many years of experience in creating special-purpose diesel engines. It is expected that as a result of this work, a radical reduction in the toxicity of automobile engines to the level of foreign standards for 2000 will be ensured.

To create an environmentally friendly car, "AMO ZIL" 5301 ("Bull") with a D-245.12 diesel engine manufactured by the Minsk Motor Plant was used. The engine equipped with a turbocharger has a rated power of 80 kW at a speed of 2400 rpm.

Exhaust gas toxicity standards according to UNECE Regulation 49:

Name	CO, g/kWh	CH, g/kWh	NOx, g/kWh	PT (particles), g/kWh	Introduction date

Emissions indicators when working according to the external characteristic:

The power and efficiency (in energy equivalent) of the engine when powered by DME and diesel fuel turned out to be almost the same. In all modes, including start-up and idle, the engine stably worked on DME with completely smokeless exhaust (optical density coefficient K = 0), while when operating on diesel fuel, a typical diesel smoke level of exhaust gases was observed, corresponding to K = 17 ...28%.

The level of absolute and specific harmful emissions during operation on DME, estimated according to the methodology of UNECE Regulation No. 49-02, had the following features:

The level of emissions of nitrogen oxides (NOx) in all modes was significantly less than in diesel fuel. A particularly significant difference - a decrease by 2 ... 3 times - was observed in the most loaded modes Ne = 50 ... 100%.

At load Ne=50...100% at the maximum torque mode (n=1600 rpm), the level of emissions of unburned hydrocarbons (CH) decreased by 20...70% compared to diesel fuel, and at low load modes (Ne =10...20%) significantly exceeded the level on diesel fuel, reaching 2000...3000 ppm.

The level of carbon monoxide (CO) emissions during operation on DME in all modes exceeded the corresponding values on diesel fuel, reaching 1000 ppm.

Compared to natural gas, the operation of the engine in the external characteristic modes on DME provided a reduction in NOx emissions - by 2.5 ... 3.0 times, CO - by 5 ... 6 times, and CH - by 3.0 ... 3.5 times.

Natural gas as a fuel for a transport engine (without the use of a converter) has advantages only in comparison with gasoline. Therefore, the programs for converting engines and switching to gas fuel provide for the use of 3-stage catalytic converters, for example, from J. Matthey with a degree of gas purification: from NOx - 35 ... 80%, from CO - 85 ... 95%, from CH - 50...80%. And only in this case, the level of harmful emissions approaches that achieved when working on DME without additional purification of exhaust gases.

The reduction in CO and CH emissions recorded in experiments with DME at low loads can be achieved by optimizing the fuel and air supply. The use of a catalytic converter when the engine is running on DME will lead to the almost complete elimination of harmful emissions.

In terms of the first measures to improve the working process at low load modes, where an increased level of CO and CH emissions is observed, an experimental design of the engine exhaust route has been prepared for testing, bypassing part of the exhaust gases past the turbocharger. In addition, the fuel system of the truck is being further improved.

The conducted studies have shown that the most difficult environmental problem of significantly reducing nitrogen oxide emissions and smoke with the transfer of a diesel engine to work on DME is completely solved. Experts believe that the new stringent exhaust gas standards (ULEV, EURO-3) cannot be achieved without the use of DME.

Conclusion

Today, large Russian cities, especially metropolitan areas such as Moscow, St. Petersburg, Yekaterinburg and others, suffocate in the stench of exhaust gases emitted by cars and trucks. How to solve this problem? Radical measures - a complete ban on the movement of cars - will lead to a violation of the industrial and cultural ties of cities and therefore are not acceptable. One of the ways out is the creation of environmentally friendly urban transport.

The possibility of overcoming the impasse by switching the city's fleet to electric traction is not a solution to the problem, since the overall coefficient of performance (COP) of an electric vehicle (if we count it from the moment electricity is received to the fact that electric transport moves) is about half as much as the efficiency of a modern car equipped with internal combustion engine. Thus, to enable the movement of urban transport based on electric vehicles, it will be necessary to burn twice as much fossil fuel as is required to enable the movement of a modern fleet of cars. To date, the only rational way to solve the current problem is to create machines with an internal combustion engine operating in the mode of the lowest possible fuel consumption with minimal exhaust toxicity. At the same time, of course, all the necessary performance indicators of the transport unit must be maintained, whether it be a passenger taxi or a heavy truck.

To solve the environmental problem of transport, it is necessary to create a power plant (PP), including an internal combustion engine (ICE) and ensuring the ability of the internal combustion engine to operate in a constant mode of minimum specific fuel consumption with minimum exhaust toxicity. Traditional vehicles with a stepwise transfer of energy from the power plant to the drive wheels cannot fundamentally solve the problem, since the speed control of such vehicles is carried out by switching the internal combustion engine to partial modes with the obligatory departure from the work area with minimal fuel consumption and minimal exhaust toxicity. Most of the continuously variable transmissions used also do not radically solve the problem. The most well-known in engineering practice hydromechanical transmission, as well as mechanical, provides control of the vehicle speed by switching the internal combustion engine to partial modes with a departure from the zone of minimum fuel consumption and minimum toxicity. In addition, a somewhat lower efficiency of such transmissions leads to a slight increase in fuel consumption in comparison with a stepped mechanical transmission.

List of sources used

1. Spectrophotometric determination of trace amounts of lead (II) in aerosol emissions from motor vehicles and roadside deposits, G.I. Savenko, N.M. Malakhov, A.N. Chebotarev, M.G. Torosyan, N.Kh. Kopyt, A.I. Struchaev / Bulletin of the Engineering Academy of Ukraine, 1998. Special issue "Inzhstrategiya-97". - pp.76-78.

2. Sablina Z.A., Gureev A.A. Additives for motor fuels. - M.: Chemistry, 1988.- 472 p.

3. Malakhova N.M., Nikipelova E.M., Savenko G.I. Photometric determination of lead (II) in natural objects with its preliminary sorption concentration // Chemistry and technology of water. - 1990. -T. 12, no. 7. - S. 627 - 629.

4. Maximum permissible concentrations of harmful substances in air and water. - L .: Chemistry, 1985.-456s.

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Fuel combustion products have a decisive influence on the energy and environmental performance of various heat engineering installations. However, in addition to these products, a number of other substances are formed during combustion, which, due to their small amount, are not taken into account in energy calculations, but determine the environmental performance of furnaces, furnaces, heat engines and other devices of modern heat engineering.

First of all, the so-called toxic substances that have negative effects on the human body and the environment should be attributed to the number of environmentally harmful products of combustion. The main toxic substances are nitrogen oxides (NOx), carbon monoxide (CO), various hydrocarbons (CH), soot and compounds containing lead and sulfur.

Nitrogen oxides are formed as a result of the chemical interaction of nitrogen and atmospheric oxygen if the temperature exceeds 1500 K. During the combustion of fuels, mainly nitric oxide NO is formed, which is then oxidized to NO2 in the atmosphere. The formation of NO increases with increasing gas temperature and oxygen concentration. The dependence of NO formation on temperature creates certain difficulties in terms of increasing the thermal efficiency of a heat engine. For example, with an increase in the maximum cycle temperature from 2000 K to 3000 K, the thermal efficiency of the Carnot cycle increases 1.5 times and reaches a value of 0.66, but the calculated maximum concentration of NO in the combustion products increases 10 times and reaches 1.1% by volume. .

NO2 in the atmosphere is a reddish-brown gas, which in high concentrations has a suffocating odor that is harmful to the mucous membranes of the eyes.

Carbon monoxide (CO) is formed during combustion in the absence of oxygen. Carbon monoxide is a colorless and odorless gas. When inhaled together with air, it intensively combines with blood hemoglobin, which reduces its ability to supply the body with oxygen. Symptoms of carbon monoxide poisoning include headache, palpitations, shortness of breath and nausea.

Hydrocarbons (CH) consist of original or decayed fuel molecules that did not take part in combustion. Hydrocarbons appear in the exhaust gases (EG) of internal combustion engines due to the extinguishing of the flame near the relatively cold walls of the combustion flame. In diesel engines, hydrocarbons are formed in the over-enriched zones of the mixture, where the pyrolysis of fuel molecules occurs. If, during the expansion process, these zones do not receive enough oxygen, then CH will end up in the composition of the exhaust gas. Hydrocarbons under the action of sunlight can interact with NOx, forming biologically active substances that irritate the respiratory tract and cause the appearance of the so-called smog.

Emissions of benzene, toluene, polycyclic automatic hydrocarbons (PAHs) and, first of all, benzpyrene have a particular impact. PAHs are so-called carcinogens; they are not excreted from the human body, but accumulate in it over time, contributing to the formation of malignant tumors.

Soot is a solid product consisting mainly of carbon. In addition to carbon, soot contains 1–3% (by mass) of hydrogen. Soot is formed at temperatures above 1500 K as a result of thermal decomposition (pyrolysis) with a strong lack of oxygen. The presence of soot in the exhaust gases causes black smoke at the outlet.

Soot is a mechanical pollutant of the nasopharynx and lungs. A great danger is associated with the property of soot to accumulate carcinogenic substances on the surface of its particles and serve as their carrier.

Some toxic substances, after they enter the atmosphere as part of the products of combustion, undergo further transformations. For example, in the presence of hydrocarbons, nitrogen oxides and carbon monoxide in the atmosphere, intense ultraviolet radiation from the sun produces ozone (O3), which is the strongest oxidizing agent and, at an appropriate concentration, causes a deterioration in people's well-being.

With a high content of NO2, Oz and CH in a sedentary and humid atmosphere, a brown fog arises, which is called "smog" (from the English "smoke" - smoke and "fog" - fog). Smog is a mixture of liquid and gaseous components, it irritates the eyes and mucous membranes, impairs visibility on the roads.

The main sources of emission of toxic products of combustion are cars, industry, thermal and power plants. In some cities, the content of toxic products of combustion in the atmosphere exceeds the maximum permissible concentration by several tens of times.

To combat this evil, in most countries of the world, relevant laws have been adopted that limit the content of toxic substances in combustion products emitted into the atmosphere.

The fulfillment of the norms of permitted normal emissions prescribed by the relevant laws has become one of the central tasks of heat engineering. In many cases, the operation of industrial heat engineering facilities is controlled in such a way as to provide the required compromise between their energy, economic and environmental performance. In many cases, the level of economic performance achieved in this way exceeds that permitted by modern standards. Therefore, the neutralization and purification of combustion products before their release into the atmosphere has become of great importance. For this purpose, various neutralizers and filters are used. At the same time, the composition of hydrocarbon fuels is improving (reducing the content of the sphere, lead, aromatic hydrocarbons), and the use of gas fuels is expanding. In the future, the use of hydrogen as a fuel will completely exclude the content of CO, CH and other toxic carbon-containing components in the combustion products.

INTERNAL COMBUSTION ENGINES AND ECOLOGY.

1.3. Alternative fuels

1.5. Neutralization

Bibliography

INTERNAL COMBUSTION ENGINES AND ECOLOGY

1.1. Harmful emissions in the composition of exhaust gases and their impact on wildlife

With the complete combustion of hydrocarbons, the final products are carbon dioxide and water. However, complete combustion in reciprocating internal combustion engines is technically impossible to achieve. Today, about 60% of the total amount of harmful substances emitted into the atmosphere of large cities is accounted for by road transport.

The composition of the exhaust gases of internal combustion engines includes more than 200 different chemicals. Among them:

products of incomplete combustion in the form of carbon monoxide, aldehydes, ketones, hydrocarbons, hydrogen, peroxide compounds, soot;
products of thermal reactions of nitrogen with oxygen - nitrogen oxides;
compounds of inorganic substances that are part of the fuel - lead and other heavy metals, sulfur dioxide, etc.;
excess oxygen.

The amount and composition of exhaust gases are determined by the design features of the engines, their operating mode, technical condition, quality of road surfaces, weather conditions. On fig. 1.1 shows the dependences of the content of basic substances in the composition of exhaust gases.

In table. 1.1 shows the characteristics of the urban rhythm of the car and the average values of emissions as a percentage of their total value for a full cycle of conventional urban traffic.

Carbon monoxide (CO) is formed in engines during the combustion of enriched air-fuel mixtures, as well as due to the dissociation of carbon dioxide, at high temperatures. Under normal conditions, CO is a colorless, odorless gas. The toxic effect of CO lies in its ability to convert part of the hemoglobin in the blood into carbo-xyhemoglobin, which causes a violation of tissue respiration. Along with this, CO has a direct effect on tissue biochemical processes, resulting in a violation of fat and carbohydrate metabolism, vitamin balance, etc. The toxic effect of CO is also associated with its direct effect on the cells of the central nervous system. When exposed to a person, CO causes headache, dizziness, fatigue, irritability, drowsiness, and pain in the region of the heart. Acute poisoning is observed when air is inhaled with a CO concentration of more than 2.5 mg/l for 1 hour.

Table 1.1

Characteristics of the urban rhythm of the car

Nitrogen oxides in exhaust gases are formed as a result of the reversible oxidation of nitrogen with atmospheric oxygen under the influence of high temperatures and pressure. As the exhaust gases cool and dilute them with atmospheric oxygen, nitrogen oxide turns into dioxide. Nitric oxide (NO) is a colorless gas, nitrogen dioxide (NO 2) is a red-brown gas with a characteristic odor. Nitrogen oxides, when ingested, combine with water. At the same time, they form compounds of nitric and nitrous acid in the respiratory tract. Nitrogen oxides irritate the mucous membranes of the eyes, nose, and mouth. Exposure to NO 2 contributes to the development of lung diseases. Symptoms of poisoning appear only after 6 hours in the form of coughing, suffocation, and increasing pulmonary edema is possible. NOX is also involved in the formation of acid rain.

Nitrogen oxides and hydrocarbons are heavier than air and can accumulate near roads and streets. In them, under the influence of sunlight, various chemical reactions take place. The decomposition of nitrogen oxides leads to the formation of ozone (O 3). Under normal conditions, ozone is unstable and quickly decomposes, but in the presence of hydrocarbons, the process of its decay slows down. It actively reacts with moisture particles and other compounds, forming smog. In addition, ozone corrodes the eyes and lungs.

Individual hydrocarbons CH (benzapyrene) are the strongest carcinogens, the carriers of which can be soot particles.

When the engine is running on leaded gasoline, particles of solid lead oxide are formed due to the decomposition of tetraethyl lead. In the exhaust gases, they are contained in the form of tiny particles with a size of 1–5 microns, which remain in the atmosphere for a long time. The presence of lead in the air causes serious damage to the digestive organs, central and peripheral nervous system. The effect of lead on the blood is manifested in a decrease in the amount of hemoglobin and the destruction of red blood cells.

The composition of the exhaust gases of diesel engines differs from gasoline engines (Table 10.2). In a diesel engine, fuel combustion is more complete. This produces less carbon monoxide and unburned hydrocarbons. But, at the same time, due to the excess air in the diesel engine, a greater amount of nitrogen oxides is formed.

In addition, the operation of diesel engines in certain modes is characterized by smoke. Black smoke is a product of incomplete combustion and consists of carbon particles (soot) 0.1–0.3 µm in size. White smoke, mainly generated when the engine is idling, consists mainly of aldehydes, which have an irritating effect, particles of evaporated fuel and water droplets. Blue smoke is formed when exhaust gases are cooled in air. It consists of droplets of liquid hydrocarbons.

A feature of the exhaust gases of diesel engines is the content of carcinogenic polycyclic aromatic hydrocarbons, among which dioxin (cyclic ether) and benzapyrene are the most harmful. The latter, like lead, belongs to the first hazard class of pollutants. Dioxins and related compounds are many times more toxic than poisons such as curare and potassium cyanide.

Table 1.2

The amount of toxic components (in g),

formed during the combustion of 1 kg of fuel

Acreolin was also found in the exhaust gases (especially when diesel engines are running). It has the smell of burnt fats and, at levels above 0.004 mg/l, causes irritation of the upper respiratory tract, as well as inflammation of the mucous membrane of the eyes.

Substances contained in car exhaust gases can cause progressive damage to the central nervous system, liver, kidneys, brain, genital organs, lethargy, Parkinson's syndrome, pneumonia, endemic ataxia, gout, bronchial cancer, dermatitis, intoxication, allergies, respiratory and other diseases. . The probability of occurrence of diseases increases as the time of exposure to harmful substances and their concentration increases.

1.2. Legislative restrictions on emissions of harmful substances

The first steps to limit the amount of harmful substances in exhaust gases were made in the United States, where the problem of gas pollution in large cities became the most urgent after World War II. In the late 60s, when the megacities of America and Japan began to suffocate from smog, the government commissions of these countries took the initiative. Legislative acts on the mandatory reduction of toxic emissions from new cars have forced manufacturers to improve engines and develop neutralization systems.

In 1970, a law was passed in the United States, according to which the level of toxic components in the exhaust gases of 1975 model year cars was to be less than that of 1960 cars: CH - by 87%, CO - by 82% and NOx - by 24%. Similar requirements have been legalized in Japan and in Europe.

The development of pan-European rules, regulations and standards in the field of automotive ecology is carried out by the Inland Transport Committee within the framework of the United Nations Economic Commission for Europe (UNECE). The documents issued by it are called the UNECE Rules and are obligatory for the countries-participants of the 1958 Geneva Agreement, to which Russia has also joined.

According to these rules, permissible emissions of harmful substances since 1993 have been limited: for carbon monoxide from 15 g/km in 1991 to 2.2 g/km in 1996, and for the sum of hydrocarbons and nitrogen oxides from 5.1 g/km in 1991 to 0.5 g/km in 1996. In 2000, even more stringent standards were introduced (Fig. 1.2). A sharp tightening of the standards is also provided for diesel trucks (Fig. 1.3).

Rice. 1.2. Emission limits dynamics

for vehicles weighing up to 3.5 tons (gasoline)

The standards introduced for cars in 1993 were called EBPO-I, in 1996 - EURO-II, in 2000 - EURO-III. The introduction of such norms brought European regulations to the level of US standards.

Along with the quantitative tightening of the norms, their qualitative change is also taking place. Instead of restrictions on smoke, rationing of solid particles has been introduced, on the surface of which aromatic hydrocarbons dangerous to human health, in particular benzapyrene, are adsorbed.

Particulate emission regulation limits the amount of particulate matter to a much greater extent than smoke limiting, which allows only such amount of particulate matter to be estimated that makes the exhaust gases visible.

Rice. 1.3. Dynamics of harmful emission limits for diesel trucks with a gross weight of more than 3.5 tons established by the EEC

In order to limit the emission of toxic hydrocarbons, standards are being introduced for the content of the methane-free group of hydrocarbons in the exhaust gases. It is planned to introduce restrictions on the release of formaldehyde. Limitation of fuel evaporation from the power supply system of cars with gasoline engines is provided.

Both in the USA and in the UNECE Rules, the mileage of cars (80 thousand and 160 thousand km) is regulated, during which they must comply with the established toxicity standards.

In Russia, standards limiting the emission of harmful substances by motor vehicles began to be introduced in the 70s: GOST 21393-75 “Cars with diesel engines. Exhaust smoke. Norms and methods of measurements. Safety requirements” and GOST 17.2.1.02-76 “Nature protection. Atmosphere. Emissions from engines of cars, tractors, self-propelled agricultural and road-building machines. Terms and Definitions".

In the eighties, GOST 17.2.2.03-87 “Nature Protection. Atmosphere. Norms and methods for measuring the content of carbon monoxide and hydrocarbons in the exhaust gases of vehicles with gasoline engines. Safety requirements” and GOST 17.2.2.01-84 “Nature protection. Atmosphere. Diesels are automobile. Exhaust smoke. Norms and methods of measurements”.

The norms, in accordance with the growth of the fleet and the orientation towards similar UNECE Regulations, were gradually tightened. However, already from the beginning of the 90s, Russian standards in terms of rigidity began to be significantly inferior to the standards introduced by the UNECE.

The reasons for the backlog are the unpreparedness of the infrastructure for the operation of automotive and tractor equipment. For the prevention, repair and maintenance of vehicles equipped with electronics and neutralization systems, a developed network of service stations with qualified personnel, modern repair equipment and measuring equipment, including in the field, is required.

GOST 2084-77 is in force, providing for the production in Russia of gasolines containing lead tetraethylene. Transportation and storage of fuel do not guarantee that leaded residues will not get into unleaded gasoline. There are no conditions under which owners of cars with neutralization systems would be guaranteed against refueling with gasoline with lead additives.

Nevertheless, work is underway to tighten environmental requirements. The Decree of the State Standard of the Russian Federation dated April 1, 1998 No. 19 approved the “Rules for carrying out work in the system of certification of motor vehicles and trailers”, which determine the temporary procedure for the application in Russia of UNECE Rules No. 834 and No. 495.

On January 1, 1999, GOST R 51105.97 “Fuels for internal combustion engines. Unleaded gasoline. Specifications”. In May 1999, Gosstandart adopted a resolution on the enactment of state standards that limit the emission of pollutants by cars. The standards contain authentic text with UNECE Regulations No. 49 and No. 83 and come into force on July 1, 2000. In the same year, the standard GOST R 51832-2001 “Gasoline-powered positive-ignition internal combustion engines and motor vehicles” was adopted. with a gross weight of more than 3.5 tons, equipped with these engines. Emissions of harmful substances. Technical requirements and test methods”. On January 1, 2004, GOST R 52033-2003 “Vehicles with gasoline engines. Emissions of pollutants with exhaust gases. Norms and methods of control in assessing the technical condition”.

In order to comply with increasingly stringent standards for the emission of pollutants, manufacturers of automotive equipment are improving power and ignition systems, using alternative fuels, neutralizing exhaust gases, and developing combined power plants.

1.3. Alternative fuels

All over the world, much attention is paid to replacing liquid petroleum fuels with liquefied hydrocarbon gas (propane-butane mixture) and compressed natural gas (methane), as well as alcohol-containing mixtures. In table. 1.3 shows comparative indicators of emissions of harmful substances during the operation of internal combustion engines on various fuels.

Table 1.3

The advantages of gas fuel are a high octane number and the possibility of using converters. However, when using them, the engine power decreases, and the large mass and dimensions of the fuel equipment reduce the performance of the vehicle. The disadvantages of gaseous fuels also include high sensitivity to fuel equipment adjustments. With unsatisfactory manufacturing quality of fuel equipment and with a low operating culture, the toxicity of exhaust gases of an engine running on gas fuel may exceed the values of the gasoline version.

In countries with a hot climate, cars with engines running on alcohol fuels (methanol and ethanol) have become widespread. The use of alcohols reduces the emission of harmful substances by 20-25%. The disadvantages of alcohol fuels include a significant deterioration in the starting qualities of the engine and the high corrosiveness and toxicity of methanol itself. In Russia, alcohol fuels for cars are not currently used.

Increasing attention, both in our country and abroad, is being paid to the idea of using hydrogen. The prospects of this fuel are determined by its environmental friendliness (for cars running on this fuel, the emission of carbon monoxide is reduced by 30–50 times, nitrogen oxides by 3–5 times, and hydrocarbons by 2–2.5 times), unlimitedness and renewability of raw materials. However, the introduction of hydrogen fuel is constrained by the creation of energy-intensive hydrogen storage systems on board the car. Currently used metal hydride batteries, methanol decomposition reactors and other systems are very complex and expensive. Considering also the difficulties associated with the requirements of a compact and safe generation and storage of hydrogen on board a car, cars with a hydrogen engine do not yet have any noticeable practical application.

As an alternative to internal combustion engines, electric power plants using electrochemical energy sources, batteries and electrochemical generators are of great interest. Electric vehicles are distinguished by good adaptability to variable modes of urban traffic, ease of maintenance and environmental friendliness. However, their practical application remains problematic. First, there are no reliable, light and sufficiently energy-intensive electrochemical current sources. Secondly, the transition of the car fleet to power electrochemical batteries will lead to the expenditure of a huge amount of energy on their recharging. Most of this energy is generated in thermal power plants. At the same time, due to the multiple conversion of energy (chemical - thermal - electrical - chemical - electrical - mechanical), the overall efficiency of the system is very low and the environmental pollution of the areas around the power plants will many times exceed the current values.

1.4. Improving power and ignition systems

One of the disadvantages of carburetor power systems is the uneven distribution of fuel over the engine cylinders. This causes uneven operation of the internal combustion engine and the impossibility of depleting the carburetor adjustments due to the over-depletion of the mixture and the cessation of combustion in individual cylinders (an increase in CH) with an enriched mixture in the rest (a high content of CO in the exhaust gases). To eliminate this shortcoming, the order of operation of the cylinders was changed from 1-2-4-3 to 1-3-4-2 and the shape of the intake pipelines was optimized, for example, the use of receivers in the intake manifold. In addition, various dividers were installed under the carburetors, directing the flow, and the intake pipeline is heated. In the USSR, an autonomous idle system (XX) was developed and introduced into mass production. These measures made it possible to meet the requirements for the XX regimes.

As mentioned above, during the urban cycle up to 40% of the time, the car operates in forced idle mode (PHX) - engine braking. At the same time, under the throttle valve, the vacuum is much higher than in the XX mode, which causes the re-enrichment of the air-fuel mixture and the cessation of its combustion in the engine cylinders, and the amount of harmful emissions increases. To reduce emissions in the PHH modes, throttle damping systems (openers) and EPHH forced idle economizers were developed. The first systems, by slightly opening the throttle, reduce the vacuum under it, thereby preventing the over-enrichment of the mixture. The latter block the flow of fuel into the engine cylinders in the PXC modes. PECH systems can reduce the amount of harmful emissions by up to 20% and increase fuel efficiency by up to 5% in urban operation.

Emissions of nitrogen oxides NOx were fought by lowering the combustion temperature of the combustible mixture. For this, the power systems of both gasoline and diesel engines were equipped with exhaust gas recirculation devices. The system, at certain engine operating modes, passed part of the exhaust gases from the exhaust to the intake pipeline.

The inertia of fuel dosing systems does not allow creating a carburetor design that fully meets all the requirements for dosing accuracy for all engine operating modes, especially transient ones. To overcome the shortcomings of the carburetor, so-called "injection" power systems were developed.

At first, these were mechanical systems with a constant supply of fuel to the intake valve area. These systems made it possible to meet the initial environmental requirements. Currently, these are electronic-mechanical systems with phrased injection and feedback.

In the 1970s, the main way to reduce harmful emissions was to use increasingly leaner air-fuel mixtures. For their uninterrupted ignition, it was necessary to improve the ignition systems in order to increase the power of the spark. The restraining fakir in this was the mechanical break of the primary circuit and the mechanical distribution of high-voltage energy. To overcome this shortcoming, contact-transistor and non-contact systems have been developed.

Today, non-contact ignition systems with static distribution of high-voltage energy under the control of an electronic unit, which simultaneously optimizes fuel supply and ignition timing, are becoming more common.

In diesel engines, the main direction of improving the power system was to increase the injection pressure. Today, the norm is the injection pressure of about 120 MPa, for promising engines up to 250 MPa. This allows more complete combustion of fuel, reducing the content of CH and particulate matter in the exhaust gases. As well as for gasoline, for diesel power systems, electronic engine control systems have been developed that do not allow engines to enter smoke modes.

Various exhaust gas aftertreatment systems are being developed. For example, a system has been developed with a filter in the exhaust tract, which retains particulate matter. After a certain operating time, the electronic unit gives a command to increase the fuel supply. This leads to an increase in the temperature of the exhaust gases, which, in turn, leads to soot burning and filter regeneration.

1.5. Neutralization

In the same 70s, it became clear that it was impossible to achieve a significant improvement in the situation with toxicity without the use of additional devices, since a decrease in one parameter entails an increase in others. Therefore, they actively engaged in the improvement of exhaust gas aftertreatment systems.

Neutralization systems have been used in the past for automotive and tractor equipment operating in special conditions, such as tunneling and mine development.

There are two basic principles for constructing converters - thermal and catalytic.

Thermal converter is a combustion chamber, which is located in the exhaust tract of the engine for afterburning the products of incomplete combustion of fuel - CH and CO. It can be installed in place of the exhaust pipeline and perform its functions. The oxidation reactions of CO and CH proceed quite quickly at temperatures above 830 °C and in the presence of unbound oxygen in the reaction zone. Thermal converters are used on engines with positive ignition, in which the temperature necessary for the effective flow of thermal oxidation reactions is provided without the supply of additional fuel. The already high exhaust gas temperature of these engines rises in the reaction zone as a result of the burning out of part of CH and CO, the concentration of which is much higher than that of diesel engines.

The thermal neutralizer (Fig. 1.4) consists of a housing with inlet (outlet) pipes and one or two flame tube inserts made of heat-resistant sheet steel. Good mixing of the additional air required for the oxidation of CH and CO with the exhaust gases is achieved by intense vortex formation and turbulence of gases as they flow through the holes in the pipes and as a result of changing the direction of their movement by a baffle system. For effective afterburning of CO and CH, a sufficiently long time is required, therefore, the speed of gases in the converter is set low, as a result of which its volume is relatively large.

Rice. 1.4. Thermal converter

To prevent a drop in the temperature of the exhaust gases as a result of heat transfer to the walls, the exhaust pipeline and the converter are covered with thermal insulation, heat shields are installed in the exhaust channels, and the converter is placed as close as possible to the engine. Despite this, it takes a significant amount of time to warm up the thermal converter after starting the engine. To reduce this time, the temperature of the exhaust gases is increased, which is achieved by enriching the combustible mixture and reducing the ignition timing, although both of these increase fuel consumption. Such measures are resorted to to maintain a stable flame during transient engine operation. The flame insert also contributes to a decrease in the time until the effective oxidation of CH and CO begins.

catalytic converters– devices containing substances that accelerate reactions, – catalysts . Catalytic converters can be "single-way", "two-way" and "three-way".

One-component and two-component oxidizing-type neutralizers afterburn (re-oxidize) CO (one-component) and CH (two-component).

2CO + O 2 \u003d 2CO 2(at 250–300°С).

C m H n + (m + n/4) O 2 \u003d mCO 2 + n / 2H 2 O(over 400°С).

The catalytic converter is a stainless steel housing included in the exhaust system. The carrier block of the active element is located in the housing. The first neutralizers were filled with metal balls coated with a thin layer of catalyst (see Fig. 1.5).

Rice. 1.5. Catalytic converter device

As active substances were used: aluminum, copper, chromium, nickel. The main disadvantages of the first generation neutralizers were low efficiency and short service life. Catalytic converters based on noble metals - platinum and palladium - proved to be the most resistant to the "poisonous" effects of sulfur, organosilicon and other compounds formed as a result of the combustion of fuel and oil contained in the engine cylinder.

The carrier of the active substance in such neutralizers is special ceramics - a monolith with many longitudinal honeycombs. A special rough substrate is applied to the surface of the honeycombs. This makes it possible to increase the effective contact area of the coating with exhaust gases up to ~20 thousand m 2 . The amount of noble metals deposited on the substrate in this area is 2–3 grams, which makes it possible to organize the mass production of relatively inexpensive products.

Ceramics can withstand temperatures up to 800–850 °C. Malfunctions of the power supply system (difficult start) and prolonged operation on a re-enriched working mixture lead to the fact that excess fuel will burn in the converter. This leads to melting of the cells and the failure of the converter. Today, metal honeycombs are used as carriers of the catalytic layer. This makes it possible to increase the area of the working surface, obtain less back pressure, accelerate the heating of the converter to the operating temperature, and expand the temperature range to 1000–1050 °C.

Reducing media catalytic converters, or three-way neutralizers, are used in exhaust systems, both to reduce CO and CH emissions, and to reduce emissions of nitrogen oxides. The catalytic layer of the converter contains, in addition to platinum and palladium, the rare earth element rhodium. As a result of chemical reactions on the surface of a catalyst heated to 600-800 ° C, CO, CH, NOx contained in the exhaust gases are converted into H 2 O, CO 2, N 2:

2NO + 2CO \u003d N 2 + 2CO 2.

2NO + 2H 2 \u003d N 2 + 2H 2 O.

The efficiency of a three-way catalytic converter reaches 90% under real operating conditions, but only on condition that the composition of the combustible mixture differs from the stoichiometric one by no more than 1%.

Due to changes in engine parameters due to its wear, operation in non-stationary modes, drift of power system settings, it is not possible to maintain the stoichiometric composition of the combustible mixture only due to the design of carburetors or injectors. Feedback is needed that would evaluate the composition of the air-fuel mixture entering the engine cylinders.

To date, the most widely used feedback system using the so-called oxygen sensor(lambda probe) based on zirconium ceramics ZrO 2 (Fig. 1.6).

The sensitive element of the lambda probe is a zirconium cap 2 . The inner and outer surfaces of the cap are covered with thin layers of platinum-rhodium alloy, which act as the outer 3 and domestic 4 electrodes. With threaded part 1 the sensor is installed in the exhaust tract. In this case, the outer electrode is washed by the processed gases, and the inner one - by atmospheric air.

Rice. 1.6. The design of the oxygen sensor

Zirconium dioxide at temperatures above 350°C acquires the property of an electrolyte, and the sensor becomes a galvanic cell. The EMF value on the sensor electrodes is determined by the ratio of oxygen partial pressures on the inner and outer sides of the sensing element. In the presence of free oxygen in the exhaust gases, the sensor generates an EMF of the order of 0.1 V. In the absence of free oxygen in the exhaust gases, the EMF increases almost abruptly to 0.9 V.

The composition of the mixture is controlled after the sensor has warmed up to operating temperatures. The composition of the mixture is maintained by changing the amount of fuel supplied to the engine cylinders at the boundary of the probe EMF transition from low to high voltage level. To reduce the time to reach the operating mode, electrically heated sensors are used.

The main disadvantages of systems with feedback and a three-way catalytic converter are: the impossibility of running the engine on leaded fuel, a rather low resource of the converter and lambda probe (about 80,000 km) and an increase in the resistance of the exhaust system.

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