Technical analysis of automobile pollution treatment

. The automobile emission exceeds the standard problem, is a world subject, only has the technical analysis to be able to obtain the effective management. In the vehicle aftermarket, vehicle maintenance is the main way to control vehicle exhaust exceeding the standard. Vehicle design and manufacturing factory with technical performance, with the vehicle running time, load changes constantly, the parts of the wear, deformation, aging, loss of function and other phenomena, the vehicle technical performance far less than the factory design requirements, will cause vehicle emissions seriously exceed the standard, serious air pollution. We must carefully analyze the vehicle technical conditions, find the crux of the problem can be very good maintenance management.


Vehicle emission pollution control technology analysis is a requirement of air pollution control
"Air pollution has become an inescapable fact of life for city dwellers all over the world."Since the reform and opening up, China has experienced the rapid development of "getting rich" for several decades.Although it has created huge wealth for us and made great progress in industrial civilization and urban development, it has discharged billions of tons of waste gases and wastes into the atmosphere, bringing a huge impact on the living environment of human beings.Therefore, the prevention and control of air pollution is related to everyone's vital interests, and is of great significance for improving urban air quality and improving the well-being of the general public.In recent years, with the increasing number of cars in use in China, vehicle emissions have become one of the important sources of urban air pollution, and the PM2.5 and other particles and NOx produced by vehicle emissions are far higher than those of developed countries in Europe and the United States.
On May 10, Li Jiangping, director of the Traffic Management Bureau of the Ministry of Public Security, said at a press conference that the number of motor vehicles in China has reached 380 million, of which 30 million are trucks, accounting for 7.9 percent of the total, the largest in the world.The per capita share of motor vehicles in China is less than one car for every four people, and the per capita share will be higher in some large and mediumsized cities. Analysis of PM2.5 sources in 15 cities including Beijing, Tianjin and Shanghai shows that the contribution of mobile sources to PM2.5 concentration ranges from 13.5% to 52.1%.According to China Mobile Source Environmental Management Annual Report (2019), in 2018, the total emission of four pollutants including carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) and particulate matter (PM) from motor vehicles in China was initially calculated to be 40,653,000 tons, among which, carbon monoxide (CO) was 30,894,000 tons.Hydrocarbon (HC) was 3.688 million tons, nitrogen oxide (NOx) was 5.629 million tons, and particulate matter (PM) was 442,000 million tons.Automobiles are the main contributor to air pollution emissions from motor vehicles, with more than 90% of CO, NOx and PM emissions and more than 80% of HC emissions.About 85% of diesel trucks pass the regular emissions tests at one time.Some vehicles with excessive emissions have not been repaired and treated.Instead, they have passed the emissions tests by means of temporary replacement of pollution control devices and falsification of emission test results, which has not fundamentally solved the problem of excessive emissions.China's three-year action plan to win the battle to keep the blue sky clear goals, "Diesel truck pollution control action plan", requires that we must pay attention to the control of vehicle emissions pollution.

Vehicle emission pollution control technology analysis is the requirement of vehicle technical performance changes
In the process of continuous use of the car, it is easy to produce mechanical wear and aging, so that emissions and fuel consumption seriously exceed the standard, only through the maintenance and management of M station, in order to make emissions exceed the standard of vehicles to restore good technical conditions, reduce emissions pollution, to achieve energy saving and emission reduction.
For gasoline engine, through the analysis of carbon monoxide (CO), hydrocarbon (HC), carbon dioxide (CO2), nitrogen oxides (NOx), sulfur compounds (SO) in the tail gas, can judge whether the mixture is too thick or too thin.Spark plug, engine combustion chamber carbon deposit is too much (too much can cause cannot ignite mixture formation or spontaneous combustion, ignition disorders, work is not normal, increase output power reduction, sewage), cylinder, piston ring for wear (wear can cause compression severely malnourished, channeling gas, burning machine oil lamp), ternary catalytic converters is failure, whether the sensor failure, etc.
For diesel engine, due to the low flash point of diesel, gas, compressed to a certain degree will be an explosion, burning into, pressure, make, work process, easy to cause combustion insufficient, lead to low combustion efficiency, and low diesel cetane number, ignition delay period is long, easy to cause large amounts of carbon deposit combustion system, exhaust system, smoke, increased pollution, Forming a large number of particulate matter (PM), through the adjustment of the oil pump can only change the size of the oil supply problem, can't solve the problem of black smoke.It needs to analyze the particulate matter (PM) and nitrogen oxides (NOx) in its exhaust.In view of the emergence of the above problems, it is necessary to go through serious technical analysis, identify the root cause of the problem, in order to get effective governance.

Vehicle emission pollution control technology analysis is a requirement of vehicle emission control
Under the premise of the inherent performance function of the vehicle when leaving the factory, how to solve the excessive emission or reduce the emission pollution, only by increasing the post-treatment system.Emission post-treatment technology refers to the technology for proper treatment of exhaust gas emitted by engines in order to reduce environmental pollution.The international internal combustion engine industry develops from Europe Ⅲ to Europe, there are two basic systems.In general, Europe prefers SCR (selective catalytic reduction) systems, which use urea solution to treat NOx in exhaust gas.The United States and Japan favor EGR (exhaust gas recirculation) systems, in which particles produced by combustion are treated with a particle trap or a particle catalytic converter (DPF).Because of different national conditions, enterprises in different countries have different tendencies to choose technology.
Diesel vehicles are fitted with a particulate filter (DOF), which intercepts 70 to 90 percent of PM particles in the exhaust through a filter made of metal fiber felt.Add selective catalytic reducer (SCR), is a process of diesel vehicle exhaust NOx emissions, used to purify the nitrogen oxide in the exhaust, that is, under the action of a catalyst, spray into reducing agent ammonia or urea, the NOx in the tail gas reduction into N2 and H2O.You can say how well they work, and only if the technical analysis is right, governance is much easier.

Technical analysis and treatment of emission pollution caused by vehicles in use
The core technology of the automobile is the engine technology.Only by mastering the basic structure and working principle of the engine can we use it correctly and maintain it in time to ensure the good technical condition of the vehicle.The main content includes: the basic knowledge of the automobile, the overall structure and working principle of the automobile engine, the crank linkage mechanism, the gas distribution mechanism, the fuel supply system, the ignition system (gasoline engine), the lubrication system, the cooling system, the starting system.The engine is through fuel and air mixing, compression ignition (diesel engine is compressed) chemical energy into heat energy, through two institutions and several systems of continuous work, the heat energy into mechanical energy, that is, the linear motion of the piston into the crankshaft rotating motion, generating power output.
The technical analysis of the emission pollution caused by gasoline vehicles in the use process is mainly the technical analysis of the intake -compression -work -exhaust system, the intake is the fuel in the tank, through the filter -oil pump -injector and air mixtureintake branch pipe, through the valve of the distribution mechanism into the cylinder on time, Through the crankshaft connecting rod mechanism to compress the fuel mixture gas, the ignition system on time completes the work, the crankshaft connecting rod mechanism produces the power output, and the waste gas produced at the same time is discharged from the exhaust valve -exhaust branch pipe -exhaust muffler.
Through the above analysis can be seen, analysis management should grasp not only every technical link.Also see: one is the fuel operator does not meet the requirements of the vehicle instruction manual, do not meet the requirements will cause incomplete combustion, power decline, fuel consumption increases, emissions exceed the standard, the management method is to replace the fuel in time; Two is to see whether the oil tank cap, tubing, air filter is blocked, gasoline pump, injector is working normally, otherwise easy to cause the mixture is too thick or too thin, too thick will cause a lot of black smoke, emissions exceed the standard, the management method is to check one by one elimination; Three is to look at the distribution phase is accurate, also is the valve opening and closing, the rotation of the crank shaft Angle, we now use the four stroke engine, to complete a work, four times the pistons run up and down through the connecting rod crank shaft to rotate 720 degrees, into the exhaust valve open and close abnormal directly cause inadequate intake, exhaust, generally with gas phase is good factory Settings, But because the wear of timing gear and camshaft will affect the distribution phase, the treatment method is to carry out the corresponding maintenance and replacement of accessories through detection; Four is to see whether the spark plug, combustion chamber carbon deposition is too much, spark plug carbon deposition is too much, cause the spark is too weak or even break the fire, work disorder, combustion chamber carbon deposition is too much, resulting in combustion chamber volume is too small, easy to spontaneous combustion, resulting in ignition disorder, power reduction, pollution increase, the treatment method is to replace the spark plug in time to remove carbon deposition; Five is to see if the exhaust pipe has the blue smoke phenomenon, check the abrasion of the cylinder and piston ring, piston ring and the presence of dislocation, adhesion, no stretch, etc., caused by the phenomenon of gas burning oil, gas channeling crankcase pressure increases, the mixture pressure is insufficient, the combustion efficiency decline and burning oil, lead to excessive emissions, governance approach is depending on the situation of engine repair, Replace the corresponding accessories; Six is to see whether the electronic control injection system is working normally, mainly to see the intake of air, throttle position, idle control valve, etc., transmitted to the electronic control unit through the sensor, it issues an instruction signal, control the amount of oil injection, directly affect the mixture is too thick or too thin and ignition time, you can determine the management through the fault indicator light.Diesel vehicles do not have ignition system, it is compression combustion, engine combustion pollutants are mainly particles (PM) and nitrogen oxides (NOx), working conditions can refer to gasoline vehicles, but mainly depends on the post-treatment system governance.

Three-way catalytic converter
The HC and CO produced by the abnormal combustion of the car are toxic gases, and excessive inhalation will lead to death, while NOx will directly lead to the occurrence of photochemical smog.Three-way catalytic converter is the most important external purification device installed in the automobile exhaust system.It can transform the harmful gases such as CO, HC and NOx from the automobile exhaust into harmless carbon dioxide, water and nitrogen through oxidation and reduction.When the high temperature automobile exhaust passes through the purification device, the catalyst (platinum, rhodium, palladium and other precious metals) in the three-way catalytic converter will enhance the activity of CO, HC and NOx, and promote it to carry out a certain oxidation-reduction chemical reaction, in which CO is oxidized into colorless and non-toxic carbon dioxide gas at high temperature; HC compounds oxidize at high temperatures to water (H20) and carbon dioxide; NOx reduction into nitrogen and oxygen, three kinds of harmful gases into harmless gas, so that the automobile exhaust can be purified.The ternary catalyst can only work at the lowest temperature of 350 degrees Celsius, and the conversion efficiency drops sharply when the temperature is too low.The catalyst activity temperature (the best working temperature) is about 400℃ to 800℃, too high will make the catalyst aging.The effect of catalytic conversion is also the best at the ideal air-fuel ratio (14.7:1).The performance of catalytic converter can be judged by the comparison of temperature difference because of the large amount of reaction heat generated by oxidation reaction under normal working condition.
Three-way catalytic converter in use to check the treatment method: One is to see whether the ternary catalytic temperature is too high.Because there are a large number of HC and CO in the exhaust gas after entering catalytic reactor, in which will generate excessive oxidation reaction, oxidation reaction produces a large amount of heat will lose catalytic reactor temperature causes catalyst activity and even damaged, on the other hand engine ignition time is too late or firing order confusion, fire, etc., this can be a mixture of unburned into catalytic reactor, Cause the exhaust temperature is too high, affect the efficiency of catalytic converter; The second is to see whether three catalytic chronic poisoning.Catalyst for sulfur, elements such as lead, zinc phosphate, very sensitive, sulfur and lead from gasoline, phosphorus and zinc from the lubricating oil, the four kinds of material in the engine combustion after forming oxide particles are easily adsorbed on the surface of the catalyst, the catalyst can't contact with the waste gas, thus lost the catalysis, the so-called "poisoning" phenomenon; The third is to see whether the carbon accumulation is too much.When the vehicle works at low temperature for a long time, the three-way catalytic converter cannot be started, and the charcoal smoke discharged from the engine will adhere to the surface of the catalyst, making it impossible to contact with CO and HC.In the long run, the pores of the carrier will be blocked, affecting its conversion efficiency.Fourth, it is to see whether the exhaust deteriorates.Catalytic converters have a certain limit on the conversion capacity of pollutants.If the concentration and total amount of each component of the exhaust pollutants discharged are too large, such as the excessive concentration of the mixture, the catalytic conversion capacity of catalytic converters will be affected and its conversion efficiency will be reduced.Five is to see whether the oxygen sensor fails.Best for exhaust gas catalytic rate (90%), must be installed in engine exhaust oxygen sensor and realizing the closed-loop control, its working principle is oxygen sensor to measure concentration of oxygen in flue gas, converted to electrical signals of backwardness to ECU, make the engine air-fuel ratio control in a narrow, close to the ideal area (14.7:1), if the air-fuel ratio is big, Although the conversion rate of CO and HC is slightly improved, the conversion rate of NOx drops sharply to 20%.Therefore, the best air-fuel ratio must be guaranteed.To achieve the best air-fuel ratio, the key is to ensure the normal operation of the oxygen sensor.If the fuel contains lead, silicon will cause oxygen sensor poisoning.In addition, improper use will cause carbon accumulation of oxygen sensor, ceramic fragmentation, heater resistance wire burning, internal circuit breaking and other faults.The failure of the oxygen sensor will lead to the misalignment of the air-fuel ratio, the deterioration of the exhaust condition, the reduction of the efficiency of the catalytic converter, and the service life of the catalytic converter will be reduced for a long time.
The treatment method is to replace the oxygen sensor, clean the three-way catalytic converter, and replace the three-way catalytic converter.

Diesel particulate trap (DPF)
Particle (PM) and nitrogen oxide (NOx) pollutants produced by diesel exhaust are one of the important sources of air particle pollution.Its treatment methods have been concerned by all sectors of society.For the increasingly serious particle pollution problem in recent years, from the point of view of the technical approach to reduce automobile exhaust emissions in 2013, it is necessary to meet the European Ⅳ emission standard.Generally, no longer take measures from the structure of the engine itself, but usually take the way of exhaust post-treatment to reduce the emission of pollutants.The particulate matter collection system of diesel engine DPF can reduce the emission of major pollutants by more than 95%.
Strict regulations limiting the diesel particle emission, the diesel particulate trap (DPF) is the most effective way to solve the problem of diesel exhaust particulate pollution, one of the particulate trap system is to reform the diesel exhaust systems, with honeycomb ceramic or silicon carbide of high porosity materials flow closed filtering channel carrier, filter capture exhaust particulate matter, When the particulate matter in the captured gas reaches the set level, the captured particulate matter will be oxidized through specially designed regeneration equipment to generate carbon dioxide and discharged.The technology uses an active regeneration DPF system, a diesel engine catalytic oxidant, and an auxiliary DPF regeneration scheme.When regeneration is needed, atomized diesel oil is sprayed into the exhaust pipe upstream of the DOC catalytic converter.Under the action of the catalyst, diesel oil catalyzes a reaction to release heat and raises the tail gas temperature to achieve the purpose of DPF regeneration.It is estimated that in a province of China alone, the use of this technology on the national three emission standards of yellow label vehicles for emissions purification transformation, can reduce particulate pollutants of nearly 1,000 tons per year.If rolled out nationwide, it would greatly improve the increase in fine particulate matter caused by vehicle emissions.
Inspection management method, one is through the online fault diagnosis system (OBD), for each device working condition link of the diagnosis project for fault diagnosis.Second, through the emission and power of the engine in the vehicle, the lack of power, emission difficulties, black smoke, PM exceed the standard serious phenomenon analysis and diagnosis.The third is to use a gauge lens to see whether the filter made of metal fiber felt is blocked.Mainly through the replacement of fuel, oil or cleaning, the replacement of particulate catcher to control.

Selective catalytic reduction (SCR)
Selective catalytic reduction (SCR) is an advanced automotive NOx control technology.SCR system is a process of NOx emissions from diesel vehicle exhaust, that is, to purify NOx, that is, under the action of a catalyst, spray into reducing agent ammonia or urea, to reduce the NOx in the tail gas to N2 and H2O (NOx +NH3→N2+H2O).The urea -SCR selective catalytic reduction method is the most realistic method, it can reduce the NOx in the engine exhaust by more than 50%.This technology is the exhaust gas processor of a wide range of diesel vehicles.The generation of PM particles is controlled as much as possible in the machine through chemical reactions.The complex physical and chemical reactions include the injection, atomization, evaporation, hydrolysis and pyrolysis of urea solution to generate NH3, which is used to reduce NOx and discharge N2 on the catalyst surface of SCR system.Under normal circumstances, the consumption of 100L fuel will consume 5L liquid urea aqueous solution.By optimizing the fuel injection and combustion process, try to control the generation of particles PM inside the machine, and then formed in conversion processing under the condition of rich oxygen nitrogen oxides, timely transport with urea (automotive urea decomposition at certain temperatures generated ammonia) selective catalytic reduction of nox, principle of chemical reactions in the SCR is that urea hydrolysis: Group (NH2) 2 co + H2O and nh3 2 + CO2; NOx reduction: NO+NO2+2NH3→2N2+3H2O; Ammonia oxidation: 4NH3+3O2→2N2+6H2O.SCR system can effectively save fuel consumption, meet the emission requirements, and has little impact on vehicle structure design.Domestic mainstream diesel engine manufacturers have basically reached a consensus that SCR will be the main technical direction of diesel engine emission upgrade in the future.Yuchai, Cummins and Weichai have all adopted SCR technology.
Inspection management method, one is through the online fault diagnosis system (OBD), for each device working condition link of the diagnosis project for fault diagnosis.Two is to see whether the fuel, vehicle urea is qualified, urea pump electronic control device is working normally, exhaust gas emissions big black smoke, NOx is serious exceed the standard.Mainly through the replacement of fuel or cleaning replacement catalytic reducer to control.

Conclusion
In the situation of the rapid development of motor vehicles in China, motor vehicle emission pollution problem has attracted more and more social attention and heated discussion, especially in 2020, the United Nations General Assembly put forward the goal of achieving carbon neutrality in 2060 energy saving and emission reduction, which put forward higher and stricter requirements for our motor vehicle emission control, requiring us to accurately analyze the motor vehicle emission control technology.Actively do a good job in the scientific control of emission pollution, under the premise of careful testing, the appropriate medicine, active prevention and control, motor vehicle emissions control within the scope of the ring standard.