Ecology technologies: how toxic emissions of ICE are transformed into “violet scent”
Adsorbents and catalysts, probes and filters, tanks and ceramic honeycombs - the whole mini-enterprise for processing chemical waste hides under the hood of a modern car with a hydrocarbon-fueled engine. Today we will touch on the topic of technologies created in accordance with the requirements of rapidly changing environmental standards, we will understand how toxic exhausts of ICE are neutralized and try to assess the prospects for the survival of this segment of the car market taking into account existing global trends.
At the end of last year, the German government announced that by 2050 there would be no cars with internal combustion engines, which soon became one of the reasons for the country's accession to the international alliance ZEV (Zero-Emission Vehicle), whose ambitious goal is to drastically reduce greenhouse gas emissions gases on the scale of the planet. And for hydrocarbon-fueled car manufacturers, this is more than a clear challenge that clearly defines the key priority of survival - the development of effective means of reducing the toxicity of automobile emissions.
And why, in fact, neutralize exhaust gases - you ask? As far as is known from the school chemistry course, carbon dioxide and water are formed as a result of the combustion of any organic fuel. But carbon dioxide is not the most dangerous product of the reaction occurring in the chamber of the internal combustion engine. First: the fuel does not burn completely, and the combustion process is accompanied by the formation of a very toxic substance - carbon monoxide (CO) and, incidentally, large amounts of hydrocarbons not completely burned (from arenes to paraffins). Secondly, nitrogen (N2) from air and impurities contained in gasoline — sulfur, etc. — are actively involved in the combustion process. In turn, emissions of nitrogen oxides (NOx) cause acid rain, smog and ozone holes produced today. Byproducts of combustion containing sulfur compounds are no less dangerous to human health and all living things. Here we note that in the United States special attention in the fight against the problem is focused on the concentration of NOx in the exhaust gases that give rise to the infamous Californian photochemical smog as a result of decomposition under the influence of sunlight.
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Catalytic converter
As is known, again from the school curriculum, catalysts are substances that accelerate chemical reactions, but do not enter them. A notable example is the noble metals. A three-way catalytic converter with palladium (Pd), platinum (Pt) and rhodium (Rh) composition covers the ceramic honeycombs with the thinnest layer. At the same time, the total surface area of the coverage of such cells is, on average, up to 20,000 square meters. (!) Such an impressive area helps to improve the contact of exhaust gases with noble metals, which, per neutralizer, consumes only 2-3 grams. A unit with a neutralizer burns carbon monoxide residues and decomposes some of the unburned hydrocarbons to carbon dioxide and water. Harmful NOx oxides to atmospheric nitrogen restores rhodium.
The operating temperature of the catalytic converter is 400-800 ° C; therefore, the internal fragments of the unit's construction are made of thermally stable ceramics — silicon carbide or cordierite. The problem that engineers constantly face is determining the optimal location of the neutralizer. The fact is that the latter needs some time to reach the operating temperature, and the cold motor throws practically uncleaned mixtures into the atmosphere. The question is whether to place the neutralizer closer to the motor, where it will warm up faster, or closer to the muffler, where the device will operate in a more gentle temperature mode.
Most modern cars are equipped with neutralization systems and, therefore, you should not leave the car on a lawn with dried grass - the body of the neutralizer, red-hot after the trip, may well cause the grass to ignite with aggravating consequences. It is also not advisable to start the engine by means of towing, since this can provoke the ingress of fuel into the neutralizer, the subsequent detonation, accompanied by the destruction of the ceramic honeycombs.
Nitrogen adsorption
The neutralizer LNT (Lean NOx Trap) is one of the examples of modern systems designed to combat nitrogen oxides in diesel engine exhaust gases. The accumulation of oxides in the housing contributes to the adsorbent - barium oxide or others. At the moment when the neutralizer is completely filled, the computer gives the command to enrich the air-fuel mixture entering the combustion chambers. At first glance, this is insane, because the mixture, in which there is a lot of gasoline and little air, dramatically increases the concentration of toxic carbon monoxide in the exhaust. In reality, everything proceeds in a somewhat different scenario: inside the LNT-neutralizer, carbon monoxide reacts with nitrogen oxides, decomposing them into completely harmless molecular nitrogen N2 and conditionally harmless carbon dioxide. At the moment when the neutralizer is completely cleared of NOx, the engine goes to normal operation. As you understand, talking about the economy of periodic mixture re-enrichment would not be true, but if we are talking about such a priority as the purity of the environment, the inclusion in the working cycle of these components is justified.
What is a lambda probe
Effective neutralization implies an optimum oxygen concentration. If the mixture is excessively depleted, i.e. there is a shortage of fuel due to the prevailing air, then the concentration of NOx in the exhaust gases increases. Enrichment of the mixture under such conditions will not be accompanied by a complete burnout of the fuel, and the concentration of carbon monoxide and non-oxidized hydrocarbons will increase in the exhaust. To maintain optimal oxygen balance, a lambda sensor is used - a sensor that monitors the level of oxygen in the engine exhaust manifold.
If the coefficient of excess air, which is the ratio of the volume of air to the volume of the mixture, is λ> 1, then the mixture is “poor”, but if λ <1 is enriched. Lambda probe is a kind of fuel cell with platinum electrodes with zirconium dioxide electrolyte. One of the sensor electrodes communicates with outboard air containing an oxidizing agent (oxygen), and the other electrode communicates with exhaust gases. The “fuel” for the cell is unburned gasoline. When the mixture is enriched, the voltage on the sensor increases, which serves as a signal to the computer to give the command to impoverish the mixture.
Lambda probe - a fuel cell of two platinum electrodes and an electrolyte of zirconium dioxide. Both electrodes and electrolyte are permeable to oxygen. Air is supplied to the inside of the probe from outside, which is heated by a heating element. If the mixture is rich and the exhaust contains little oxygen, the O2 concentration inside the probe becomes much greater than the outside. Therefore, oxygen from the outboard air passes through the electrodes and the electrolyte in the form of ions, thereby causing electrical current in the external circuit. As soon as oxygen molecules appear in the exhaust (with a poor mixture), the concentration levels off and the voltage drops sharply.
Exhaust gas recirculation
Nitrogen is very inert, and in order for it to enter the desired reaction, it must either be strongly compressed or heated. Both the first and second conditions are fulfilled in the cylinder of a diesel engine (this is not relevant for gasoline units, since their compression ratio is much lower). Lowering the temperature in the cylinder may reduce the concentration of nitrogen oxides in the exhaust. This function is handled by the EGR exhaust gas recirculation system, the first modifications of which were installed back in the 1970s on diesel trucks in the USA. With the help of a special valve, the exhaust gases are mixed with exhaust air and sent back to the cylinder. Some of the heat accompanying the combustion of the mixture is assumed by inert gases, as a result of which the temperature in the combustion chamber decreases.
Urea injection
When environmental standards come into their own, urea comes to the rescue. Nitrogen oxides are excellently reduced to molecular nitrogen by reacting with ammonia (NH3). Another thing is that you cannot store toxic gas on board. As an alternative to ammonia storage, chemical engineers have suggested using urea ((NH2) 2CO), injected into the vehicle's exhaust duct in separate portions. In the “tandem” with exhaust gases, urea enters a special neutralizer, where it is converted into ammonia, which is necessary for the decomposition of NOx into nitrogen and water. The described technology is called selective catalytic reduction SCR (Selective Catalytic Reduction), and the word urea, uncomfortable for our ears, in this technology has been replaced by sonorous AdBlue. Although, if you look, AdBlue is only 32.5% pure (NH2) 2CO in distilled water.
As you can see, environmental standards turned out to be a powerful incentive in creating a whole chemical industry, and owners of urea diesel engines have to fill the car with diesel and AdBlue, whose consumption is quite tangible and amounts to 6% of the amount of fuel used.
Before a portion of the exhaust gases returns to the cylinder, it must be cooled, for which both a liquid cooling circuit and an air circuit or both can be used. The illustration shows the Scania truck recycling system.
Particulate filters
Neutralization to the accepted standards requires not only gaseous mixtures of exhaust gases, but also solid particles. Such microscopic particles of soot, ranging in size from 10 to 1 micron, are thrown out when overclocked KAMAZ trucks, which are well known to all of us, are discharged. Familiar sight. One can imagine the “healthful” effect that this intensely erupting smog has on our lungs. Soot in the exhaust, as well as NOx, is mainly a problem of diesel engines, since diesel oil is a rather heavy fraction of oil containing unsaturated compounds. This contributes to the fact that the concentration of carbon in diesel fuel is higher than in gasoline, and therefore, soot during combustion will be released more.
To cope with the problem allows resistant to high temperatures ceramics. It works like this. Up to a certain point, special DPF (Diesel Particulate Filter) ceramic filters adsorb soot from exhaust gases, and after accumulating up to a certain limit, the engine is switched to a special mode of operation in which the temperature of gases in the exhaust system rises sharply to 600 ° C, which, given the existing system oxygen allows oxidizing the soot, and then outputting it through the exhaust pipe. In order not to expose the DPF filter to the damaging effects of high temperatures, some manufacturers cover its ceramic surface with a thin layer of platinum, which serves as a catalyst. Engineers from the PSA group (Peuqeot-Citroön) suggested adding cerium (Ce) additives to diesel fuel, which allows the soot oxidation temperature to be reduced to 450 ° C. And this is quite comparable with the usual exhaust temperature. In countries where the Euro-5 standards work, since 2011 DPF filters have been installed on all diesel vehicles.
Low voltage hybrid
It is becoming increasingly difficult for owners of motor vehicles with hydrocarbon-fueled engines to squeeze in existing technological solutions into the framework of continuously tightening environmental standards. Current trends are increasingly defining the transition to hybrid solutions. One of them, based on low-voltage hybrid circuits (48V), was proposed by Bosch. And such low-voltage systems in the very near future will allow to “hybridize” many existing auto models.
Despite the attractiveness of the innovations offered by engineers from the point of view of the environmental effect, the final cost of the engine, and the car itself, “weighed down” by green technologies, is increasing significantly. Therefore, if the described trend continues, in the foreseeable future, the use of internal combustion engines against the background of popularizing and improving the infrastructure of electric vehicles will simply become ineffective.
That's all, with you there was a simple service for choosing sophisticated Dronk.Ru equipment. Do not forget to subscribe to our blog , there will be many more interesting ...
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At the end of last year, the German government announced that by 2050 there would be no cars with internal combustion engines, which soon became one of the reasons for the country's accession to the international alliance ZEV (Zero-Emission Vehicle), whose ambitious goal is to drastically reduce greenhouse gas emissions gases on the scale of the planet. And for hydrocarbon-fueled car manufacturers, this is more than a clear challenge that clearly defines the key priority of survival - the development of effective means of reducing the toxicity of automobile emissions.
And why, in fact, neutralize exhaust gases - you ask? As far as is known from the school chemistry course, carbon dioxide and water are formed as a result of the combustion of any organic fuel. But carbon dioxide is not the most dangerous product of the reaction occurring in the chamber of the internal combustion engine. First: the fuel does not burn completely, and the combustion process is accompanied by the formation of a very toxic substance - carbon monoxide (CO) and, incidentally, large amounts of hydrocarbons not completely burned (from arenes to paraffins). Secondly, nitrogen (N2) from air and impurities contained in gasoline — sulfur, etc. — are actively involved in the combustion process. In turn, emissions of nitrogen oxides (NOx) cause acid rain, smog and ozone holes produced today. Byproducts of combustion containing sulfur compounds are no less dangerous to human health and all living things. Here we note that in the United States special attention in the fight against the problem is focused on the concentration of NOx in the exhaust gases that give rise to the infamous Californian photochemical smog as a result of decomposition under the influence of sunlight.
')
Catalytic converter
As is known, again from the school curriculum, catalysts are substances that accelerate chemical reactions, but do not enter them. A notable example is the noble metals. A three-way catalytic converter with palladium (Pd), platinum (Pt) and rhodium (Rh) composition covers the ceramic honeycombs with the thinnest layer. At the same time, the total surface area of the coverage of such cells is, on average, up to 20,000 square meters. (!) Such an impressive area helps to improve the contact of exhaust gases with noble metals, which, per neutralizer, consumes only 2-3 grams. A unit with a neutralizer burns carbon monoxide residues and decomposes some of the unburned hydrocarbons to carbon dioxide and water. Harmful NOx oxides to atmospheric nitrogen restores rhodium.
The operating temperature of the catalytic converter is 400-800 ° C; therefore, the internal fragments of the unit's construction are made of thermally stable ceramics — silicon carbide or cordierite. The problem that engineers constantly face is determining the optimal location of the neutralizer. The fact is that the latter needs some time to reach the operating temperature, and the cold motor throws practically uncleaned mixtures into the atmosphere. The question is whether to place the neutralizer closer to the motor, where it will warm up faster, or closer to the muffler, where the device will operate in a more gentle temperature mode.
Most modern cars are equipped with neutralization systems and, therefore, you should not leave the car on a lawn with dried grass - the body of the neutralizer, red-hot after the trip, may well cause the grass to ignite with aggravating consequences. It is also not advisable to start the engine by means of towing, since this can provoke the ingress of fuel into the neutralizer, the subsequent detonation, accompanied by the destruction of the ceramic honeycombs.
Nitrogen adsorption
The neutralizer LNT (Lean NOx Trap) is one of the examples of modern systems designed to combat nitrogen oxides in diesel engine exhaust gases. The accumulation of oxides in the housing contributes to the adsorbent - barium oxide or others. At the moment when the neutralizer is completely filled, the computer gives the command to enrich the air-fuel mixture entering the combustion chambers. At first glance, this is insane, because the mixture, in which there is a lot of gasoline and little air, dramatically increases the concentration of toxic carbon monoxide in the exhaust. In reality, everything proceeds in a somewhat different scenario: inside the LNT-neutralizer, carbon monoxide reacts with nitrogen oxides, decomposing them into completely harmless molecular nitrogen N2 and conditionally harmless carbon dioxide. At the moment when the neutralizer is completely cleared of NOx, the engine goes to normal operation. As you understand, talking about the economy of periodic mixture re-enrichment would not be true, but if we are talking about such a priority as the purity of the environment, the inclusion in the working cycle of these components is justified.
What is a lambda probe
Effective neutralization implies an optimum oxygen concentration. If the mixture is excessively depleted, i.e. there is a shortage of fuel due to the prevailing air, then the concentration of NOx in the exhaust gases increases. Enrichment of the mixture under such conditions will not be accompanied by a complete burnout of the fuel, and the concentration of carbon monoxide and non-oxidized hydrocarbons will increase in the exhaust. To maintain optimal oxygen balance, a lambda sensor is used - a sensor that monitors the level of oxygen in the engine exhaust manifold.
If the coefficient of excess air, which is the ratio of the volume of air to the volume of the mixture, is λ> 1, then the mixture is “poor”, but if λ <1 is enriched. Lambda probe is a kind of fuel cell with platinum electrodes with zirconium dioxide electrolyte. One of the sensor electrodes communicates with outboard air containing an oxidizing agent (oxygen), and the other electrode communicates with exhaust gases. The “fuel” for the cell is unburned gasoline. When the mixture is enriched, the voltage on the sensor increases, which serves as a signal to the computer to give the command to impoverish the mixture.
Lambda probe - a fuel cell of two platinum electrodes and an electrolyte of zirconium dioxide. Both electrodes and electrolyte are permeable to oxygen. Air is supplied to the inside of the probe from outside, which is heated by a heating element. If the mixture is rich and the exhaust contains little oxygen, the O2 concentration inside the probe becomes much greater than the outside. Therefore, oxygen from the outboard air passes through the electrodes and the electrolyte in the form of ions, thereby causing electrical current in the external circuit. As soon as oxygen molecules appear in the exhaust (with a poor mixture), the concentration levels off and the voltage drops sharply.
Exhaust gas recirculation
Nitrogen is very inert, and in order for it to enter the desired reaction, it must either be strongly compressed or heated. Both the first and second conditions are fulfilled in the cylinder of a diesel engine (this is not relevant for gasoline units, since their compression ratio is much lower). Lowering the temperature in the cylinder may reduce the concentration of nitrogen oxides in the exhaust. This function is handled by the EGR exhaust gas recirculation system, the first modifications of which were installed back in the 1970s on diesel trucks in the USA. With the help of a special valve, the exhaust gases are mixed with exhaust air and sent back to the cylinder. Some of the heat accompanying the combustion of the mixture is assumed by inert gases, as a result of which the temperature in the combustion chamber decreases.
Urea injection
When environmental standards come into their own, urea comes to the rescue. Nitrogen oxides are excellently reduced to molecular nitrogen by reacting with ammonia (NH3). Another thing is that you cannot store toxic gas on board. As an alternative to ammonia storage, chemical engineers have suggested using urea ((NH2) 2CO), injected into the vehicle's exhaust duct in separate portions. In the “tandem” with exhaust gases, urea enters a special neutralizer, where it is converted into ammonia, which is necessary for the decomposition of NOx into nitrogen and water. The described technology is called selective catalytic reduction SCR (Selective Catalytic Reduction), and the word urea, uncomfortable for our ears, in this technology has been replaced by sonorous AdBlue. Although, if you look, AdBlue is only 32.5% pure (NH2) 2CO in distilled water.
As you can see, environmental standards turned out to be a powerful incentive in creating a whole chemical industry, and owners of urea diesel engines have to fill the car with diesel and AdBlue, whose consumption is quite tangible and amounts to 6% of the amount of fuel used.
Before a portion of the exhaust gases returns to the cylinder, it must be cooled, for which both a liquid cooling circuit and an air circuit or both can be used. The illustration shows the Scania truck recycling system.
Particulate filters
Neutralization to the accepted standards requires not only gaseous mixtures of exhaust gases, but also solid particles. Such microscopic particles of soot, ranging in size from 10 to 1 micron, are thrown out when overclocked KAMAZ trucks, which are well known to all of us, are discharged. Familiar sight. One can imagine the “healthful” effect that this intensely erupting smog has on our lungs. Soot in the exhaust, as well as NOx, is mainly a problem of diesel engines, since diesel oil is a rather heavy fraction of oil containing unsaturated compounds. This contributes to the fact that the concentration of carbon in diesel fuel is higher than in gasoline, and therefore, soot during combustion will be released more.
To cope with the problem allows resistant to high temperatures ceramics. It works like this. Up to a certain point, special DPF (Diesel Particulate Filter) ceramic filters adsorb soot from exhaust gases, and after accumulating up to a certain limit, the engine is switched to a special mode of operation in which the temperature of gases in the exhaust system rises sharply to 600 ° C, which, given the existing system oxygen allows oxidizing the soot, and then outputting it through the exhaust pipe. In order not to expose the DPF filter to the damaging effects of high temperatures, some manufacturers cover its ceramic surface with a thin layer of platinum, which serves as a catalyst. Engineers from the PSA group (Peuqeot-Citroön) suggested adding cerium (Ce) additives to diesel fuel, which allows the soot oxidation temperature to be reduced to 450 ° C. And this is quite comparable with the usual exhaust temperature. In countries where the Euro-5 standards work, since 2011 DPF filters have been installed on all diesel vehicles.
Low voltage hybrid
It is becoming increasingly difficult for owners of motor vehicles with hydrocarbon-fueled engines to squeeze in existing technological solutions into the framework of continuously tightening environmental standards. Current trends are increasingly defining the transition to hybrid solutions. One of them, based on low-voltage hybrid circuits (48V), was proposed by Bosch. And such low-voltage systems in the very near future will allow to “hybridize” many existing auto models.
Despite the attractiveness of the innovations offered by engineers from the point of view of the environmental effect, the final cost of the engine, and the car itself, “weighed down” by green technologies, is increasing significantly. Therefore, if the described trend continues, in the foreseeable future, the use of internal combustion engines against the background of popularizing and improving the infrastructure of electric vehicles will simply become ineffective.
That's all, with you there was a simple service for choosing sophisticated Dronk.Ru equipment. Do not forget to subscribe to our blog , there will be many more interesting ...
LetyShops cashback service sponsor . Return money for any purchases on the Internet. Read more about what a cashback service is in our article. We choose a cashback service for the 6th anniversary of Aliexpress.
Source: https://habr.com/ru/post/394073/
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