Study On Combustion And Emission Of Natural Gas/Ethanol Combined Enjection Engine

With the increasingly stringent energy and emission regulations,it is urgent to find alternative fuels to improve combustion performance.As ethanol fuel is a kind of renewable energy and its manufacturing technology is relatively mature,it has been widely used in many countries.Natural gas storage capacity is huge,and it can also be used as an auxiliary fuel to improve the combustion performance and emission performance of the engine.In this paper,through direct injection of natural gas in cylinder and ethanol injection in intake port,not only the problem of natural gas charging efficiency can be solved,but also the stratified combustion mode with appropriate concentration can be formed in engine cylinder,which is conducive to improving combustion and reducing engine emissions.Therefore,the natural gas /ethanol combined injection engine is studied in this thesis and conclusions are as follows(1)The engine bench of ethanol inlet injection and high-pressure direct injection in cylinder based on this experiment was built,and d SPACE control platform was built.Then the stratified combustion mode of natural gas enriched in spark plug and ethanol was formed.Appropriate inlet injection and direct injection in cylinder mode were adopted to improve engine torque and reduce engine CO emission.(2)Because the lean burn limit of natural gas is better,when the excess air coefficient is larger,the stratified combustion effect formed by adding natural gas and ethanol is better,the cycle variation of the engine also decreases obviously,the optimal ignition advance angle of the engine becomes smaller,and increasing the proportion of natural gas in the case of lean burn can improve the torque of the engine and peak cylinder pressure,reduce the fast burning period,reduce CO and HC emission of engine.(3)Because the latent heat of vaporization of ethanol is relatively large,the influence of the latent heat of vaporization on the engine wall will be reduced by adding the direct injection ratio of natural gas,thus reducing the HC produced by the wall quenching and reducing the HC in the engine emission.Because the temperature of natural gas combustion is not high,increasing the direct injection ratio of natural gas will reduce the temperature of the engine,inhibit the production of NO_x and reduce the emission of NO_x.(4)When the direct injection time of natural gas is 150°CA BTDC,the stratification effect is the best,which can improve the combustion,increase the torque and cylinder pressure peak of the engine,reduce the CO and HC emissions in the engine exhaust emissions,but increase the NO_x emissions in the engine exhaust emissions.(5)The earlier ignition advance angle will increase the peak cylinder pressure and reduce the fast combustion period,but the earlier ignition advance angle will produce compression negative work and reduce the torque.Only proper ignition advance angle can reduce CO emission.For HC and NO_x,smaller ignition advance angle can reduce their emissions.(6)The increase of fuel consumption at high load will accelerate the combustion of fuel and increase the peak torque and cylinder pressure.Better combustion will reduce the emission of CO,but increase the emission of NO_x correspondingly.For HC,poor combustion at low load will cause the increase of HC.The higher the speed,the higher the fuel consumption will increase the torque,but the higher the crankshaft angle corresponding to the high speed will increase the fast burning period.Because the throttle loss and the high speed will break the stratification effect,the cylinder pressure peak value is not the maximum when the speed is high.The higher the rotational speed,the faster the oxidation of CO will be.The higher the rotational speed,the higher the formation of NO_x will be.