Technical paper on automobile pollution 1 automobile pollution and its prevention and control technology
Abstract: With the increase of the number of cars, the impact of exhaust pollution on urban environment is becoming more and more obvious. This paper analyzes the present situation of automobile pollution and discusses the measures and methods to control automobile emissions.
Keywords: automobile pollutants, hazards and control measures
Automobile pollution is mainly composed of noise pollution and harmful emissions pollution. With the rapid development of China's economy and the continuous improvement of people's living standards, China's automobile sales have increased at an alarming rate. In 20 1 1 year, the number of cars in China will exceed 75 million, surpassing Japan to become the second in the world, and the ensuing environmental protection has become an urgent and important issue. Let people enjoy the transportation convenience brought by the development of science and technology, solve the harm of automobile pollution to people's living environment, and become scientific and technological workers and environmentalists.
First, automobile noise pollution.
1. 1 noise source
Automobile noise mainly includes aerodynamic noise, mechanical noise and combustion noise.
When the intake, exhaust system and cooling system are working, the vibration caused by the pressure generated by the airflow is called aerodynamic noise. In practice, aerodynamic noise mainly shows medium frequency characteristics and low frequency characteristics.
During engine operation, crank connecting rod, piston, valve train, gear transmission system and other accessory parts. Due to frequent friction and collision between parts caused by high-speed operation, the noise generated by exciting structural vibration is called mechanical noise.
The combustible mixture enters the cylinder, and the rapid combustion makes the pressure in the combustion chamber change sharply, which leads to the strong vibration of the cylinder liner, engine block, cylinder head and other auxiliary parts. The generated high-frequency noise is called combustion noise.
1.2 Measures to eliminate noise
The fundamental measure to eliminate noise is to reduce vibration as much as possible. The following methods are usually adopted:
(1) Optimize the combustion process, adjust the injection advance angle and postpone the combustion. Fuel injection is accurate, timely and appropriate, reducing the concentration of mixed gas in the cylinder during non-ignition period.
(2) adopt new materials, improve the structure of the machine body and various components, reduce the weight as much as possible, enhance the vibration and weaken the vibration on the premise of ensuring the standard stiffness and quality.
(3) Improve the processing technology to reduce the sealing performance of piston cylinder liner and the clearance of bearing gear assembly. Check the working condition of lubrication system in time to reduce the impact force between components.
(4) Learn to introduce foreign advanced technology, improve the muffler assembly in structure, and adopt new materials to reduce noise. The optimal valve timing is studied by experiments to reduce unnecessary work of engine cooling system and aerodynamic noise.
(5) Install the engine balance bar to reduce the vibration and noise of the engine, and install sound insulation sponge or other materials with good sound absorption in the hood to block the spread of sound and reduce noise.
Second, the harmful emissions of automobiles.
Harmful substances emitted by automobiles include carbon monoxide, nitrogen oxides, hydrocarbons and inhalable particles. It is mainly discharged in three ways: fuel evaporation, crankcase blowby and tail gas.
Carbon monoxide is a colorless and odorless toxic gas, which is produced by incomplete combustion of combustible mixture in cylinder. The main reason is related to the uneven distribution of air-fuel ratio and combustible mixture in the cylinder. HC is unburned hydrocarbon, the product of decomposition. The reason of HC is that the engine can't burn completely because of too much fuel injection. The so-called nitrogen oxides are mainly NO, which needs to be produced at high temperature, and its emission is the result of the combined action of oxygen concentration and reaction time.
2. 1 Methods of controlling harmful automobile emissions
The simplest, most extensive and fastest way to reduce the pollutants emitted by automobiles is to improve refining technology, unify refining standards, improve oil quality and reduce the emission of harmful substances in tail gas.
Considering the use area and driving conditions, there are many vehicles in the urban area and the road conditions are complicated. Generally, vehicles are running at low speed, and the fuel cannot be fully burned, which not only causes economic waste, but also does great harm to the environment. It is found that methanol, natural gas and liquefied petroleum gas are more economical, the engine runs smoothly, and the low-speed driving is better than gasoline engine and diesel engine, which is suitable for urban traffic. We can consider promoting fossil fuel -CNG dual-fuel vehicles in these areas to reduce vehicle emissions.
The development of automobile emission control regulations puts forward higher requirements for automobile emissions in the future. At present, the Euro IV standard adopted abroad requires diesel vehicles to emit no more than 250 mg of nitrogen oxides per kilometer. The emission of nitrogen oxides per kilometer of vans and SUVs shall not exceed 390 mg. It is reported that the Euro VI standard implemented from 2065438 to September 2004 is more stringent. This puts forward higher requirements for automobile production enterprises in scientific and technological creation. At present, the Prius hybrid vehicle developed and produced by Toyota in Japan can travel 38 kilometers per liter of gasoline, which has high fuel efficiency and reduces the emission of harmful pollutants.
Learn from the advanced experience of foreign automobile management, speed up the formulation of corresponding laws and regulations, and adopt the policy of not leaving the factory, not selling or licensing new cars with substandard emissions. Improve the automobile after-sales service system, and regularly remind customers to carry out regular maintenance of motor vehicles. In addition, strengthen and improve the vehicle exhaust detection system, adopt strict scrapping standards, and force the vehicles with serious hazards to be scrapped.
At the technical level, the mainstream idea now is to adopt internal control method and external control method to improve automobile pollutant emission. The research shows that the pollutants in the exhaust gas can be reduced by about 70% by using the internal control generator alone and by about 80% by secondary purification. Therefore, it is necessary to combine internal and external control to minimize pollutant emissions.
2. 1. 1 internal control method
The factors that affect the engine combustion process are 1. Coordination between injection quantity and injection time, in-cylinder airflow speed and combustion chamber shape; 2. Engine load, speed, fuel supply advance angle and exhaust gas recirculation system. Therefore, the intake system of the engine, the shape of the combustion chamber, the valve timing and the design and processing of the internal components of the engine cylinder have been improved accordingly. For example, turbocharging technology, mechanical supercharging technology, gasoline direct injection technology, * * * rail diesel injection system and flexible variable displacement system are relatively mature now.
2. 1.2 Off-site control mode
Adopting low-pollution power plant and various measures to promote combustion are the fundamental measures to solve exhaust pollution. Generally speaking, we use:
The engine pretreatment includes: intake air temperature control and mixed preheating system, crankcase forced ventilation closed system, oil and gas adsorption device and exhaust gas recirculation device.
Exhaust aftertreatment is equipped with a regeneration device with an oxidation catalytic convert, a three-way catalytic converter and a diesel particulate filt. Diesel engines, in particular, should learn to use foreign combustion methods, such as water injection, emulsification and fumigation. Strengthen the research and application of related sensors, and feedback control the ignition sequence and ignition time of the engine.
Third, the end.
The development of automobile pollutant emission control requires economy, power and emission to be as efficient as possible. At the same time, efforts should be made to improve the design level of automobiles, refine processing technology, strengthen scientific research and development, and strengthen the strict requirements of environmental protection laws and regulations. According to the development trend of emission standards at home and abroad, it is urgent to research and develop zero-emission vehicles.
Reference: [1] Zhou Qinghui. Modern automobile emission control technology [M]. Beijing: Peking University Publishing House, 20 10[2], Highway Department of Ministry of Communications, practical technology of automobile emission control [M]. Beijing: People's Communications Press, 2004[3] Dong Jing, Zhuang Zhi, Chang.
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