A heat engine is a device capable of converting the received amount of heat into mechanical work. Mechanical work in heat engines is performed in the process of expansion of a substance called the working fluid. Gaseous substances (gasoline vapor, air, water vapor) are usually used as the working fluid. The working fluid receives (or gives) thermal energy in the process of heat exchange with bodies that have a large supply of internal energy.
ECOLOGICAL CRISIS, a disruption of relationships within an ecosystem or irreversible phenomena in the biosphere caused by anthropogenic activities and threatening the existence of humans as a species. According to the degree of threat to natural human life and the development of society, an unfavorable environmental situation, an environmental disaster and an environmental catastrophe are distinguished
Pollution from heat engines:
1. Chemical.
2. Radioactive.
3. Thermal.
Heat engine efficiency< 40%, в следствии чего больше 60% теплоты двигатель отдаёт холодильнику.
When burning fuel, oxygen from the atmosphere is used, as a result of which the oxygen content in the air gradually decreases
The combustion of fuel is accompanied by the release of carbon dioxide, nitrogen, sulfur and other compounds into the atmosphere.
Pollution prevention measures:
1.Decrease harmful emissions.
2. Exhaust gas monitoring, filter modification.
3.Comparison of efficiency and environmental friendliness various types fuel, transfer of transport to gas fuel.
The main toxic emissions from a car include: exhaust gases, crankcase gases and fuel fumes. Exhaust gases emitted by the engine contain carbon monoxide, hydrocarbons, nitrogen oxides, benzopyrene, aldehydes and soot. On average, when a car runs 15 thousand km per year, it burns more than 2 tons of fuel and consumes about 30 tons of air. At the same time, about 700 kg of carbon monoxide (CO), 400 kg of nitrogen dioxide, 230 kg of hydrocarbons and other pollutants, the total amount of which is more than 200 items, are released into the atmosphere. Every year in atmospheric air About 1 million tons of pollutants are emitted with exhaust gases from mobile sources.
Some of these substances, for example, heavy metals and certain organochlorine compounds, persistent organic pollutants accumulate in the natural environment and pose a serious threat to both environment, and people's health. If the current growth rate of the car fleet is maintained, it is predicted that by 2015 the volume of emissions of pollutants into the atmospheric air will increase to 10% or more.
An electric car could radically solve the problem of air pollution from transport. Today, electric locomotives are most widely used in railway transport.
2. From an environmental point of view, hydrogen is best suited as a fuel for cars, which, moreover, is the most calorific.
3. Attempts are being made to create engines using air, alcohol, biofuel, etc. as fuel. But, unfortunately, for now all these engines can rather be called experimental models. But science does not stand still, let’s hope that the process of creating an environmentally friendly car is not “just around the corner”
Causes of air pollution from exhaust gases
cars.
The main cause of air pollution is incomplete and uneven combustion of fuel. Only 15% of it is spent on moving the car, and 85% “flies to the wind.” In addition, the combustion chambers of a car engine are a kind of chemical reactor that synthesizes toxic substances and releases them into the atmosphere. Even innocent nitrogen from the atmosphere, entering the combustion chamber, turns into toxic nitrogen oxides.
The exhaust gases of an internal combustion engine (ICE) contain over 170 harmful components, of which about 160 are hydrocarbon derivatives, which are directly due to the incomplete combustion of fuel in the engine. The presence of harmful substances in exhaust gases is ultimately determined by the type and conditions of fuel combustion.
Exhaust gases, wear products from mechanical parts and tires of a car, as well as road surfaces account for about half of atmospheric emissions of anthropogenic origin. The most studied are engine and crankcase emissions. These emissions, in addition to nitrogen, oxygen, carbon dioxide and water, include harmful components such as oxides. Moving at an average speed of 80-90 km/h, a car converts as much oxygen into carbon dioxide as 300-350 people. But it's not just about carbon dioxide. The annual exhaust of one car is 800 kg of carbon monoxide, 40 kg of nitrogen oxides and more than 200 kg of various hydrocarbons. Carbon monoxide is very insidious in this set. Due to its high toxicity, its permissible concentration in atmospheric air should not exceed 1 mg/m3. There are known cases of tragic deaths of people who started car engines with the garage door closed. In a single-occupancy garage, lethal concentrations of carbon monoxide occur within 2-3 minutes after the starter is turned on. In the cold season, when stopping for the night on the side of the road, inexperienced drivers sometimes turn on the engine to heat the car. Due to the penetration of carbon monoxide into the cabin, such an overnight stay may be the last.
Nitrogen oxides are toxic to humans and, in addition, have an irritating effect. A particularly dangerous component of exhaust gases are carcinogenic hydrocarbons, found primarily at intersections near traffic lights (up to 6.4 μg/100 m3, which is 3 times more than in the middle of the quarter).
When using leaded gasoline, a car engine emits lead compounds. Lead is dangerous because it can accumulate, both in external environment, and in the human body.
The level of gas pollution on highways and highway areas depends on the intensity of vehicle traffic, the width and topography of the street, wind speed, the share of freight transport and buses in the total flow and other factors. With a traffic intensity of 500 transport units per hour, the concentration of carbon monoxide in an open area at a distance of 30-40 m from the highway decreases by 3 times and reaches the norm. It is difficult to disperse vehicle emissions in tight streets. As a result, almost all city residents experience the harmful effects of polluted air.
Of the metal compounds that make up solid emissions from automobiles, the most studied are lead compounds. This is due to the fact that lead compounds, entering the human body and warm-blooded animals with water, air and food, have the most harmful effect on it. Up to 50% of the daily intake of lead into the body comes from the air, of which a significant proportion is made up of vehicle exhaust gases.
Hydrocarbons enter the atmospheric air not only during the operation of cars, but also during gasoline spills. According to American researchers, about 350 tons of gasoline evaporate into the air in Los Angeles per day. And it is not so much the car that is to blame for this, but the person himself. They spilled a little while pouring gasoline into the tank, forgot to close the lid tightly during transportation, splashed it on the ground while refueling at a gas station, and various hydrocarbons were released into the air.
Every motorist knows: it is almost impossible to pour all the gasoline into the tank from a hose; some part of it from the barrel of the “gun” will inevitably splash out onto the ground. A little. But how many cars do we have today? And every year their number will grow, which means that harmful fumes into the atmosphere will also increase. Only 300 g of gasoline spilled when refueling a car pollutes 200 thousand cubic meters of air. The easiest way to solve the problem is to create new design refueling machines that do not allow even one drop of gasoline to spill on the ground.
Conclusion
It can be said without exaggeration that heat engines are currently the main converters of fuel into other types of energy, and without them progress in the development of modern civilization would be impossible. However, all types of heat engines are sources of environmental pollution. (Kostryukov Denis)
The environmental impact of thermal power plants largely depends on the type of fuel burned (solid and liquid).
When burning solid fuel Fly ash with particles of unburned fuel, sulfur dioxide and sulfuric anhydrides, nitrogen oxides, a certain amount of fluoride compounds, as well as gaseous products of incomplete combustion of fuel enter the atmosphere. In some cases, fly ash contains, in addition to non-toxic components, more harmful impurities. Thus, the ash of Donetsk anthracites contains arsenic in small quantities, and the ash of Ekibastuz and some other deposits contains free silicon dioxide, and the ash of shale and coal of the Kansk-Achinsk basin contains 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 around the world and is more economical than oil. Coal can be used to produce synthetic liquid fuel. The method of obtaining fuel by processing coal has been known for a long time. However, the cost of such products was too high. The process occurs at high pressure. This fuel has one undeniable advantage - it has a higher octane number. This means that it will be more environmentally friendly.
Peat. When using peat for energy, there are a number of negative consequences for the environment that arise as a result of peat extraction on a large scale. These include, in particular, disruption of the regime of water systems, changes in the landscape and soil cover in areas of peat extraction, deterioration in the quality of local sources fresh water and air pollution, a sharp deterioration in the living conditions of animals. Significant environmental difficulties also arise due to the need to transport and store peat.
When burning liquid fuel(fuel oil) with flue gases the following enter the atmospheric air: sulfur dioxide and sulfuric anhydrides, nitrogen oxides, vanadium compounds, sodium salts, as well as substances removed from the surface of boilers during cleaning. From an environmental point of view, liquid fuel is more “hygienic”. At the same time, the problem of ash dumps, which occupy large areas, eliminates them completely beneficial use and are a source of constant air pollution in the area of the station due to the removal of part of the ash by 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 pollutant of the atmosphere. However, the emission of nitrogen oxides when burning natural gas at thermal power plants is on average 20% lower than when burning coal. This is explained not by the properties of the fuel itself, but by the characteristics of the combustion processes. The excess air coefficient when burning coal is lower than when burning natural gas. 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 enterprises on the biosphere as a whole is illustrated in Table. 1.
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; smaller quantities contain sulfur and nitrogen; traces of metals and their compounds (most often oxides and sulfides) are also present.
In thermal power engineering, the source of massive atmospheric emissions and large-scale solid waste are thermal power plants, enterprises and steam power plants, i.e., any enterprises whose work involves burning fuel.
Along with gaseous emissions, thermal power generation produces huge amounts of solid waste. These include ash and slag.
Waste from coal preparation plants contains 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 end up in dumps, which generate dust, smoke and dramatically worsen the condition of the atmosphere and surrounding areas.
Life on Earth arose under conditions of a reducing atmosphere, and only much later, after about 2 billion years, the biosphere gradually transformed 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 formed a powerful flow of reducing gases, primarily due to the combustion of fossil fuels to produce 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 1000 MW power plant per year (tonnes)
The main part of the emission is carbon dioxide - about 1 million tons in terms of carbon 1 Mt. Co wastewater The thermal power plant annually removes 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. 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. The above figures do not take into account environmental disturbances associated with coal mining and transportation.
If we consider that such a power plant has been actively operating for several decades, its impact can be compared to the effect of a volcano. But if the latter usually releases volcanic products in large quantities one-time, then the power plant does this constantly. For tens of thousands of years, volcanic activity has not been able to have any noticeable effect on the composition of the atmosphere, and economic activity humans over the course of some 100-200 years caused such changes, mainly due to the burning of fossil fuels and emissions of greenhouse gases from destroyed and deformed ecosystems.
Coefficient useful action of power plants is still small and amounts to 30-40%, most of the fuel is burned in vain. The resulting energy is used in one way or another and is ultimately converted 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 divided into two streams: one causes global changes, and the other causes regional and local ones. The situation is the same in other sectors of the economy, but still energy and the burning of fossil fuels remain the source of the main global pollutants. They enter the atmosphere, and due to their accumulation, the concentration of trace gas components of the atmosphere, including greenhouse gases, changes. Gases appeared in the atmosphere that were previously practically absent in it - chlorofluorocarbons. These are global pollutants that have a high greenhouse effect and at the same time participate in the destruction of the ozone layer of the stratosphere.
Thus, it should be noted that on modern 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 where they are located and the state of the biosphere as a whole. The most harmful are condensation power stations operating on low-grade fuels. Thus, when burning 1060 tons of Donetsk coal at the station in 1 hour, 34.5 tons of slag are removed from the boiler furnaces, 193.5 tons of ash are removed from the bunkers of electric precipitators that purify gases by 99%, and 10 million m3 are released through pipes into the atmosphere. 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 electric precipitators.
Wastewater 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 petroleum products, when discharged into water bodies, can affect the quality of water and aquatic organisms. A change in the chemical composition of certain substances leads to a disruption of the established living conditions in a reservoir and affects the species composition and number of aquatic organisms and bacteria and can ultimately lead to disruptions in the processes of self-purification of reservoirs from pollution and to a deterioration in their sanitary condition.
The so-called thermal pollution of water bodies with various violations of their condition also poses a danger. Thermal power plants produce energy using turbines driven by heated steam. When turbines operate, it is necessary to cool the exhaust steam with water, so a stream of water continuously leaves the power plant, usually heated by 8-12 °C and discharged into a reservoir. Large thermal power plants require large volumes of water. They discharge 80-90 m3/s of water in a heated state. This means that a powerful stream continuously enters the reservoir warm water approximately the same size as the Moscow River.
The heating zone, formed at the confluence of a warm “river,” is a kind of section of a 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 cover an area of several tens of square kilometers. In winter, polynyas form in the heating zone (in northern and middle latitudes). IN summer months temperatures in the heating zones depend on the natural temperature of the taken 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 intensify, the ability of gases to dissolve in water decreases, and changes physical properties water, all chemical and biological processes occurring in it are accelerated, etc. In the heating zone, the transparency of the water decreases, the pH increases, and the rate of decomposition of easily oxidized substances increases. The rate of photosynthesis in such water decreases noticeably.
Among other social dangers, one of the first places is occupied by those associated with the use of heat engines.
What do heat engines mean to us?
Every day we deal with engines that power cars, ships, industrial equipment, railway locomotives and aircraft. It was the advent and widespread use of heat engines that rapidly advanced industry.
The environmental problem of using heat engines is that emissions of thermal energy inevitably lead to heating of surrounding objects, including the atmosphere. Scientists have long been struggling with the problem of rising sea levels, considering human activity to be the main influencing factor. Changes in nature will lead to changes in our living conditions, but despite this, energy consumption increases every year.
Where are heat engines used?
Millions of vehicles powered by internal combustion engines transport passengers and cargo. By railways There are powerful diesel locomotives and motor ships along water routes. Airplanes and helicopters are equipped with piston, turbojet and turboprop engines. Rocket engines are "pushed" into space stations, ships and satellites of the Earth. Internal combustion engines in agriculture are installed on combines, pumping stations, tractors and other objects.
Environmental problem of using heat engines
Machines used by humans, heat engines, automobile production, the use of gas turbine propulsion systems, aviation and launch vehicles, pollution of the aquatic environment by ships - all this has a catastrophically destructive effect on the environment.
Firstly, when coal and oil are burned, nitrogen and sulfur compounds are released into the atmosphere, which are harmful to humans. Secondly, the processes use atmospheric oxygen, the content of which in the air decreases because of this.
Emissions into the atmosphere are not the only factor in the influence of thermal engines on nature. Manufacturing of mechanical and electrical energy cannot be carried out without releasing significant amounts of heat into the environment, which cannot but lead to an increase in the average temperature on the planet.
It is aggravated by the fact that burned substances increase the concentration of carbon dioxide in the atmosphere. This, in turn, leads to the emergence of the “greenhouse effect”. Global warming is becoming a real danger.
The environmental problem of using heat engines is that fuel combustion cannot be complete, and this leads to the release of ash and soot flakes into the air we breathe. According to statistics, all over the world, power plants annually discharge more than 200 million tons of ash and more than 60 million tons of sulfur oxide into the air.
All civilized countries are trying to solve environmental problems associated with the use of heat engines. The latest energy-saving technologies are being introduced to improve heat engines. As a result, energy consumption for the production of the same product is significantly reduced, reducing the harmful effect on the environment.
Thermal power plants, internal combustion engines of cars and other machines discharge large quantities into the atmosphere and then into the soil waste harmful to all living things, for example, chlorine, sulfur compounds (during the combustion of coal), carbon monoxide CO, nitrogen oxides, etc. Car engines emit about three tons of lead into the atmosphere every year.
At nuclear power plants, another environmental problem with the use of thermal engines is the safety and disposal of radioactive waste.
Due to incredibly high energy consumption, some regions have lost the ability to clean their own airspace. The operation of nuclear power plants has helped to significantly reduce harmful emissions, but the operation requires huge amounts of water and large ponds to cool the waste steam.
Solutions
Unfortunately, humanity is unable to abandon the use of heat engines. Where is the way out? In order to consume an order of magnitude less fuel, that is, reduce energy consumption, the engine efficiency should be increased to carry out the same work. The only way to combat the negative consequences of using heat engines is to increase the efficiency of energy use and switch to energy-saving technologies.
In general, it would be wrong to say that the global environmental problem of using heat engines is not being solved. All large quantity electric locomotives are being replaced by conventional trains; Battery-powered cars are becoming popular; Energy-saving technologies are being introduced into industry. There is hope that environmentally friendly aircraft and rocket engines will appear. The governments of many countries are implementing international programs on environmental protection, aimed against pollution of the Earth.
INTERNAL COMBUSTION ENGINES AND ECOLOGY.
1.3. Alternative fuels
1.5. Neutralization
Bibliography
INTERNAL COMBUSTION ENGINES AND ECOLOGY
1.1. Harmful emissions from exhaust gases and their impact on wildlife
When hydrocarbons are completely burned, the end products are carbon dioxide and water. However, complete combustion in piston internal combustion engines is technically impossible to achieve. Today, about 60% of the total amount of harmful substances emitted into the atmosphere major cities, accounts for road transport.
The exhaust gases of internal combustion engines contain 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;
- connections inorganic substances that are part of the fuel - lead and other heavy metals, sulfur dioxide, etc.;
- excess oxygen.
The quantity and composition of exhaust gases are determined by the design features of engines, their operating mode, technical condition, quality of road surfaces, and weather conditions. In Fig. Figure 1.1 shows the dependences of the content of main substances in the exhaust gases.
In table 1.1 shows the characteristics of the urban rhythm of vehicle movement and the average values of emissions as a percentage of their total value for full cycle conditional 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 carboxyhemoglobin, which causes disruption of tissue respiration. Along with this, CO has a direct effect on tissue biochemical processes, leading to disruption 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 humans, CO causes headache, dizziness, fatigue, irritability, drowsiness, and pain in the heart area. Acute poisoning occurs when air with a CO concentration of more than 2.5 mg/l is inhaled for 1 hour.
Table 1.1
Characteristics of the urban rhythm of car movement
Nitrogen oxides in exhaust gases are formed as a result of the reversible reaction of nitrogen oxidation by atmospheric oxygen under the influence of high temperatures and pressure. As the exhaust gases cool and are diluted with oxygen from the air, 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. When nitrogen oxides enter the human body, they 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. NO X also participates in the formation of acid rain.
Nitrogen oxides and hydrocarbons are heavier than air and can accumulate near roads and streets. They are under the influence sunlight undergo various chemical reactions. The decomposition of nitrogen oxides leads to the formation of ozone (O 3). Under normal conditions, ozone is unstable and decays quickly, 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.
Certain CH hydrocarbons (benzapyrene) are the strongest carcinogenic substances, the carriers of which can be soot particles.
When an engine runs on leaded gasoline, solid lead oxide particles are formed due to the decomposition of tetraethyl lead. In exhaust gases they are contained in the form of tiny particles 1–5 microns in size, 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 systems. 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 exhaust gases from diesel engines differs from gasoline engines (Table 10.2). In a diesel engine, fuel is burned more completely. This produces less carbon monoxide and unburned hydrocarbons. But, at the same time, due to excess air in the diesel engine, more nitrogen oxides are 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 microns in size. White smoke, which is produced mainly when the engine is idling, consists mainly of irritating aldehydes, 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 diesel engine exhaust gases is the content of carcinogenic polycyclic aromatic hydrocarbons, among which the most harmful are dioxin (cyclic ether) and benzopyrene. The latter, like lead, belongs to the first class of hazardous pollutants. Dioxins and related compounds are many times more toxic than poisons such as curare and potassium cyanide.
Table 1.2
Amount of toxic components (in g),
formed during the combustion of 1 kg of fuel
Acreolin was also found in exhaust gases (especially when operating diesel engines). It has the smell of burnt fats and at a content of more than 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 vehicle 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 likelihood of developing 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 taken in the United States, where the problem of gas pollution in major cities became most relevant after the Second World War. At the end of the 60s, when the megacities of America and Japan began to choke on smog, government commissions of these countries took the initiative. Legislative acts the mandatory reduction of toxic emissions from new cars 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 cars of the 1975 model year had to be less than that of cars of the 1960 model year: CH - by 87%, CO - by 82% and NOx - by 24%. Similar requirements have been legalized in Japan and Europe.
The Inland Transport Committee operating within the United Nations Economic Commission for Europe (UNECE) is developing pan-European rules, regulations and standards in the field of environmental protection of automotive vehicles. The documents it issues are called the UNECE Rules and are binding on countries participating in the 1958 Geneva Agreement, to which Russia also joined.
According to these rules, permissible emissions of harmful substances have been limited since 1993: 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 standards is also provided for diesel engines in trucks (Fig. 1.3).
Rice. 1.2. Dynamics of emissions restrictions
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 standards brought European rules to the level of US standards.
Simultaneously with the quantitative tightening of standards, their qualitative change occurs. Instead of restrictions on smoke, standardization of solid particles has been introduced, on the surface of which aromatic hydrocarbons hazardous to human health, in particular benzopyrene, are adsorbed.
Standardization of particulate emissions limits the amount of particulate matter to a much greater extent than with smoke control, which allows you to estimate only the amount of particulate matter 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 methane-free hydrocarbons in exhaust gases. It is planned to introduce restrictions on formaldehyde emissions. Provision is made for limiting fuel evaporation from the power supply system of vehicles with gasoline engines.
Both in the USA and the UNECE Rules regulate vehicle mileage (80 thousand and 160 thousand km), during which they must comply with established toxicity standards.
In Russia, standards limiting the emission of harmful substances from motor vehicles began to be introduced in the 70s: GOST 21393-75 “Cars with diesel engines. Smokiness of exhaust gases. Norms and methods of measurement. Safety requirements” and GOST 17.2.1.02-76 “Nature conservation. Atmosphere. Emissions from engines of cars, tractors, self-propelled agricultural and road construction vehicles. Terms and Definitions".
In the eighties, GOST 17.2.2.03-87 “Nature conservation” was adopted. Atmosphere. Standards and methods for measuring the content of carbon monoxide and hydrocarbons in the exhaust gases of cars with gasoline engines. Safety requirements” and GOST 17.2.2.01-84 “Nature conservation. Atmosphere. Automotive diesels. Smokiness of exhaust gases. Norms and methods of measurement.”
The standards, in accordance with the growth of the fleet and the orientation towards similar UNECE Rules, 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 lag are the unprepared 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 is required, including on site.
GOST 2084-77 is in force, providing for the production in Russia of gasoline containing lead tetraethylethylene. Transportation and storage of fuel does not guarantee against leaded residues getting into unleaded gasoline. There are no conditions under which owners of cars with neutralization systems would be guaranteed against refueling with gasoline containing lead additives.
Nevertheless, work is underway to tighten environmental requirements. Resolution of the State Standard of the Russian Federation dated April 1, 1998 No. 19 approved the “Rules for carrying out work in the certification system of motor vehicles and trailers,” which determine the temporary procedure for the application of UNECE Rules No. 834 and No. 495 in Russia.
On January 1, 1999, GOST R 51105.97 “Fuels for internal combustion engines” was introduced. Unleaded gasoline. Specifications" In May 1999, Gosstandart adopted a resolution introducing state standards limiting the emission of pollutants from 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 GOST R 51832-2001 standard “Internal combustion engines with forced ignition, running on gasoline, 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 “Cars with gasoline engines” came into force. Emissions of pollutants from exhaust gases. Standards and methods of control when assessing technical condition.”
To comply with increasingly stringent standards for the emission of pollutants, automotive manufacturers 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 Table 1.3 shows comparative indicators of emissions of harmful substances when operating internal combustion engines on various fuels.
Table 1.3
The advantages of gas fuel are its high octane number and the possibility of using neutralizers. However, when using them, engine power decreases, and the large weight and dimensions of the fuel equipment reduce the performance of the vehicle. The disadvantages of gaseous fuels also include high sensitivity to adjustments of fuel equipment. If the manufacturing quality of the fuel equipment is unsatisfactory and the operating culture is poor, the toxicity of the exhaust gases of an engine running on gas fuel may exceed the values of the gasoline version.
In countries with hot climates, 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 engine starting performance and the high corrosiveness and toxicity of methanol itself. In Russia, alcohol fuels are not currently used for cars.
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, emissions of carbon monoxide are reduced by 30–50 times, nitrogen oxides by 3–5 times and hydrocarbons by 2–2.5 times), the unlimited and renewable nature of raw materials. However, the introduction of hydrogen fuel is hampered by the creation of energy-intensive on-vehicle hydrogen storage systems. Currently used metal hydride batteries, methanol decomposition reactors and other systems are very complex and expensive. Taking into account also the difficulties associated with the requirements for compact and safe generation and storage of hydrogen on board a car, cars with a hydrogen engine do not yet have any significant 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 their good adaptability to variable urban traffic conditions, ease of maintenance and environmental friendliness. However, their practical application remains problematic. Firstly, there are no reliable, lightweight and sufficiently energy-intensive electrochemical current sources. Secondly, switching the vehicle fleet to be powered by electrochemical batteries will lead to the consumption of a huge amount of energy during recharging. This energy is mostly produced in thermal power plants. At the same time, due to multiple energy conversion (chemical - thermal - electrical - chemical - electrical - mechanical), the overall efficiency of the system is very low and environmental pollution areas around power plants will be many times higher than current values.
1.4. Improving power and ignition systems
One of the disadvantages of carburetor power systems is the uneven distribution of fuel among the engine cylinders. This causes uneven operation of the internal combustion engine and the impossibility of depleting the carburetor adjustments due to the leanness of the mixture and the cessation of combustion in some cylinders (increase in CH) with an enriched mixture in the rest ( great content in exhaust gases CO). To eliminate this drawback, the operating order of the cylinders was changed from 1–2–4–3 to 1–3–4–2 and the shape of the intake pipes was optimized, for example, the use of receivers in the intake manifold. In addition, various dividers were installed under the carburetors, flow guides were installed, and the intake pipeline was heated. In the USSR, an autonomous idle system (IAC) was developed and introduced into mass production. These measures made it possible to meet the requirements for the 20th regime.
As mentioned above, during the urban cycle, up to 40% of the time the car operates in the forced idle mode (FID) - engine braking. At the same time, the vacuum under the throttle valve is much higher than in idle mode, which causes the air-fuel mixture to become over-enriched and its combustion in the engine cylinders to stop, and the amount of harmful emissions increases. To reduce emissions in IPH modes, throttle valve damping systems (openers) and EPH forced idle economizers were developed. The first systems, by slightly opening the throttle valve, reduce the vacuum under it, thereby preventing the mixture from becoming over-rich. The second ones block the flow of fuel into the engine cylinders in IPH modes. PECH systems can reduce harmful emissions by up to 20% and increase fuel efficiency by up to 5% in urban operating conditions.
Emissions of nitrogen oxides NOx were combated by lowering the combustion temperature of the combustible mixture. To achieve this, the power systems of both gasoline and diesel engines were equipped with exhaust gas recirculation devices. The system, at certain engine operating modes, transferred part of the exhaust gases from the exhaust to the intake manifold.
The inertia of fuel metering systems does not allow creating a carburetor design that fully meets all the requirements for metering accuracy for all engine operating modes, especially transitional ones. To overcome the disadvantages 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 70s, the main way to reduce harmful emissions was to use increasingly lean air-fuel mixtures. For their uninterrupted ignition, it was necessary to improve the ignition systems in order to increase the spark power. The restraining factor in this was the mechanical rupture of the primary circuit and the mechanical distribution of high-voltage energy. To overcome this disadvantage, contact-transistor and contactless systems have been developed.
Today, contactless ignition systems with static distribution of high-voltage energy controlled by an electronic unit, which simultaneously optimizes fuel supply and ignition timing, are becoming increasingly widespread.
For diesel engines, the main direction of improving the power supply system was to increase the injection pressure. Today, the norm is injection pressure of about 120 MPa, with promising engines up to 250 MPa. This allows fuel to be burned more completely, reducing the content of CH and particulate matter in the exhaust gases. Just like for gasoline power systems, electronic engine control systems have been developed for diesel power systems that do not allow engines to reach smoking modes.
Various exhaust gas neutralization systems are being developed. For example, a system has been developed with a filter in the exhaust tract that retains particulate matter from the exhaust. 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, we actively began to improve exhaust gas aftertreatment systems.
Neutralization systems have previously been used for automotive vehicles operating in special conditions, such as tunneling and mine development.
There are two main principles for constructing neutralizers - thermal and catalytic.
Thermal neutralizer is a combustion chamber that 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 neutralizers are used on engines with forced ignition, in which the temperature necessary for the effective occurrence of thermal oxidation reactions is provided without the supply of additional fuel. The already high temperature of the exhaust gases of these engines increases in the reaction zone as a result of the afterburning 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 additional air required for the oxidation of CH and CO with the exhaust gases is achieved by intense vortex formation and turbulization of gases when flowing through holes in the pipes and as a result of changing the direction of their movement by a system of partitions. For effective combustion of CO and CH, sufficient big time, therefore, the speed of gases in the neutralizer is set low, as a result of which its volume is relatively large.
Rice. 1.4. Thermal neutralizer
To prevent a drop in the temperature of the exhaust gases as a result of heat transfer into 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 to the engine as possible. Despite this, it takes considerable 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 operating conditions. The heat insert also helps reduce the time before effective oxidation of CH and CO begins.
Catalytic converters– devices containing substances that accelerate reactions, – catalysts . Catalytic converters can be “one-way,” “two-way,” or “three-way.”
One-component and two-component oxidative-type neutralizers burn out (re-oxidize) CO (one-component) and CH (two-component).
2CO + O 2 = 2CO 2(at 250–300°C).
C m H n + (m + n/4) O 2 = mCO 2 + n/2H 2 O(over 400°C).
The neutralizer is a stainless steel housing included in the exhaust system. The housing contains the active element carrier unit. 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 substance used: aluminum, copper, chromium, nickel. The main disadvantages of the first generations of neutralizers were low efficiency and short service life. 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 turned out to be catalytic converters based on noble metals - platinum and palladium.
The carrier of the active substance in such neutralizers is special ceramics - a monolith with many longitudinal honeycomb cells. A special rough substrate is applied to the surface of the honeycomb. This makes it possible to increase the effective contact area of the coating with exhaust gases to ~20 thousand m2. The amount of noble metals deposited on the substrate in this area is 2–3 grams, which makes it possible to organize mass production of relatively inexpensive products.
Ceramics can withstand temperatures up to 800–850 °C. Malfunctions of the power system (difficulty starting) and prolonged operation on an over-enriched working mixture lead to the fact that excess fuel will burn in the neutralizer. This leads to melting of the honeycombs and failure of the neutralizer. Today, metal honeycombs are used as carriers of the catalytic layer. This allows you to increase the area work surface, obtain less back pressure, speed up the heating of the converter to operating temperature and expand the temperature range to 1000–1050 °C.
Catalytic converters with reducing environment, or three-component neutralizers, are used in exhaust gas systems, both to reduce CO and CH emissions, and to reduce nitrogen oxide emissions. The catalytic layer of the neutralizer contains, in addition to platinum and palladium, the rare earth element rhodium. As a result chemical reactions on the surface of a catalyst heated to 600–800 °C, CO, CH, Nox contained in the exhaust gases are converted into H2O, CO2, N2:
2NO + 2CO = N 2 + 2CO 2.
2NO + 2H 2 = N 2 + 2H 2 O.
The efficiency of a three-component catalytic converter reaches 90% under real operating conditions, but only under the 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 wear, operation in unsteady modes, and drift of power system settings, it is not possible to maintain the stoichiometric composition of the combustible mixture only through the design of carburetors or injectors. Feedback is needed that would evaluate the composition of the air-fuel mixture entering the engine cylinders.
Today, the most widely used feedback system is 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 coated with thin layers of platinum-rhodium alloy, which act as the outer 3 and internal 4 electrodes. With threaded part 1 The sensor is installed in the exhaust tract. In this case, the outer electrode is washed with processed gases, and the inner electrode with atmospheric air.
Rice. 1.6. Oxygen sensor design
At temperatures above 350°C, zirconium dioxide acquires the properties of an electrolyte, and the sensor becomes a galvanic element. The magnitude of the EMF at the sensor electrodes is determined by the ratio of the partial pressures of oxygen on the inner and outer sides of the sensitive 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 practically jumps to 0.9 V.
The mixture composition is controlled after the sensor warms 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 it takes to reach operating mode, electrically heated sensors are used.
The main disadvantages of systems with feedback and a three-component catalytic converter are: the inability to operate the engine on leaded fuel, the rather low service life of the converter and lambda probe (about 80,000 km) and an increase in the resistance of the exhaust system.
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