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Research on Vehicle Emission Control Technology

Author: China introduced …

This paper analyzes the relationship between automobile emission pollution and human living environment, and introduces some measures that should be taken from aspects of engine combustion, structural design, fuel supply, etc., such as strengthening automobile maintenance, developing new environmentally-friendly vehicles, etc., to control automobile emission and reduce air pollution. Keywords: automobile emission control pollution gasoline engine With the continuous development of automobile industry, the number of automobiles is increasing day by day, which not only brings convenience to human beings, but also harms people's health and social environment. With the sustained and rapid development of China's national economy, the problem of atmospheric environmental pollution in big cities has become increasingly prominent. In Beijing, Guangzhou, Shanghai, Chongqing and other big cities, bicycle emissions are relatively large, leading to the primary pollution source of urban air pollution. According to the research results of environmental protection department, the sharing rates of CO, HC and NO in air pollutants emitted by motor vehicles in Beijing are 63.4%, 73.5% and 46% respectively. The contribution rates of motor vehicle emissions to CO, HC and NO in the atmosphere in the downtown area of Shanghai are 86%, 96% and 56% respectively. In many countries, more than 50% of air pollution in large and medium-sized cities comes from automobile exhaust. The living environment of human beings has been seriously polluted, and the ecological balance is deteriorating day by day, which directly harms people's health, and cars have become the main pollution source. Therefore, automobile emission pollution must be strictly controlled, and the research on prevention and control technology of automobile emission pollution has become an important topic at present. Here are some technical measures to control automobile emission pollution. 1 The emission control technology of gasoline engine is facing increasingly strict emission regulations, and the development of automobile emission treatment technology is also changing with each passing day. The emission control technologies of gasoline engines mainly include the following. 1. 1 cold machine, the catalyst activity is poor, which is not conducive to reducing HC emissions. At this time, reducing HC emissions has become a major problem. Among the methods adopted, lean-burn technology is the most effective. In order to ensure the lean air-fuel ratio (A/F), a swirl control valve is set at the air inlet to improve the intake system of the engine and the charging efficiency. Improve the engine combustion system, reasonably organize the gas flow in the combustion chamber, promote the flame propagation, improve the ignition stability, and keep the engine burning stably under the lean mixture, thus reducing HC emissions. 1.2 Reduce the area between the first ring ridge of the unburned HC piston (the area between the first ring groove and the piston top) and the cylinder wall, and the unburned HC in this area can be directly discharged out of the cylinder. Increasing the position of the first piston ring, that is, reducing the height of the first piston ring group, can reduce the volume between the piston ring and the cylinder wall, thus reducing the emission of unburned HC. In order to reduce the wear of piston ring groove, aluminum oxide coating is usually coated on the piston surface, but many fine holes are easily formed on the piston surface, so the adsorbed HC is discharged from the engine during the exhaust stroke. In order to solve this contradiction, when the aluminum oxide coating is applied to the piston surface, only the piston ring groove is treated, and the top surface of the piston is not treated, which is beneficial to further reducing HC emission. It is an effective way to reduce unburned HC by using 1.3 to adsorb and purify unburned HC, using boiling foam stone as HC adsorbent and adsorbing HC before catalyst activation. The most important performance of adsorbent is the adsorption rate of HC. The more carbon atoms in the adsorbent, the better the adsorption rate. For HC adsorption layer, HC adsorption catalyst can be coated on the three-way catalytic layer, and the adsorbed HC will be automatically separated with the increase of exhaust temperature and purified by the surface catalytic layer. At present, the initial temperature of HC desorption from adsorption layer is lower than the active temperature of catalytic layer, so it is difficult to purify HC in the initial stage of desorption, and its purification performance needs to be further improved by improving materials, structure and temperature rise characteristics in the future. 1.4 Improving the early activity of the catalyst In order to promote the early activity of the catalyst, the effective method is to improve its heating characteristics and reduce its activity temperature. The main method to improve the temperature rise characteristics is to use double exhaust pipes and "thin-walled" catalyst carriers. Reasonable selection of precious metals with good low temperature characteristics, such as increasing platinum content in the catalyst and improving air-fuel ratio dilution, is an effective means to reduce the active temperature of the catalyst. The forced heating of 1.5 catalyst is to use the heat generated by the electric heating catalyst (EHC) and the combustion of exhaust gas in the exhaust pipe to promote the temperature rise of the catalyst, that is, the exhaust burner (EGC) can further improve the early activity of the catalyst. EHC adopts the method of current preheating, which can make the metal-loaded catalyst reach the light-off temperature of the catalyst within 5 ~ 10s after the engine is started, thus reducing the emission of harmful substances in the first few minutes after the engine is started. EHC has reached the practical level, but its electrical system is more complicated. The principle of EGC is that after the engine is started, combustible components such as CO generated in a rich air-fuel ratio are mixed with oxygen supplied by secondary air to form a combustible mixture. An exhaust burner is arranged in the exhaust system, and the unburned mixture is ignited by a spark plug ignition device, so that the early activity of the catalyst is improved by using the heat generated by combustion, and the unburned HC component is combusted and purified after the engine is started. Although EGC technology is in the development stage, its catalytic conversion efficiency is high, which is likely to exceed EHC. 1.6 exhaust gas recirculation exhaust gas recirculation (EGR) is one of the commonly used effective measures to control the emission of nitrogen oxides from internal combustion engines. It introduces a certain amount of exhaust gas into the intake system of the engine, which increases the proportion of inert gases (H2O, N2 and CO2) in the engine mixture. Due to the high specific heat of these inert gases, the specific heat of the mixed gas diluted by recycled exhaust gas increases, resulting in the decrease of the maximum combustion temperature of the engine. Because the recycled exhaust gas dilutes the new mixed gas and the oxygen concentration in the mixed gas decreases, the recycling of exhaust gas destroys the conditions for the formation of nitrogen oxides, thus effectively inhibiting the formation of nitrogen oxides. This exhaust purification technology is also suitable for diesel engines.