Study On Characteristics And Control Stragety Of Emissions In A Natural Gas Engine

Energy and environment are the two important problems that we face,and the continuous increase of car ownership has brought great pressure to the traditional fuel supply.The environmental pollution caused by vehicles has been paid more and more attention.Natural gas has a wide source of advantages such as less pollution,and is more and more used as engine fuel.With the increasingly strict emission regulations,it is of great significance to study the combustion and emission characteristics of natural gas engines.Through reasonable combustion in cylinder,generation of pollutant can be reduced.Combined with the conversion of three way catalytic converter,the final emissions of pollutants can be made to a very low level.The study of combustion parameters has an important guiding function in engine emission control.The stoichiometric combustion with the application of EGR technology and the three way catalytic converter is one of the main technologies of ultra low emission natural gas engine.It is an important task to realize the best performance of the catalytic converter in a scientific and reasonable combustion control mode.The engine combustion is affected by various factors such as gas composition and ignition time,the changes of these factors will make the exhaust gas composition and temperature pressure changes.The working performance of the three way catalytic converter must also take into account the inlet gas composition,operating temperature,etc..In this paper,a comparative analysis is made on the different control parameters of a turbocharged natural gas engine with equivalent air-fuel ratio combined with EGR and TWC.According to the parameters provided by the engine prototype,the simulation model of the natural gas engine was built by GT-power,and the simulation results were verified by the test data of the test bench;Based on the experimental data of catalytic performance of three way catalytic converter at different air fuel ratio,the chemical mechanism was constructed.The results showed that the catalytic conversion performance of the three way catalytic converter at different temperature and air composition was consistent with the experimental data.At the same time,this paper put forward a simulation research process,which combined the engine emission prediction with the three way catalytic converter.A complete numerical calculation process of the ultra low emission natural gas engine was formed.The combustion pressure and emission data under the initial control parameters were measured,the EGR rate and ignition strategy used in different working conditions were described in detail,and the emissions in different working conditions were analyzed.Taking three working conditions as an example,50%load of 1100r/min,50%load of 1500r/min,and 100%load of 1500r/min,the effects of three factors,namely,air fuel ratio,EGR ratio and ignition advance angle,on the generation of CO,HC,NOx and the effects on the catalytic performance of three way catalytic converter were compared and analyzed.The effects of different independent control parameters on the three kinds of emissions were obtained from the simulation result.What was more,the DOE simulation was used to obtain the comprehensive effects of the three parameters of air fuel ratio,EGR ratio and ignition advance angle on emission and catalysis.According to the influence of three kinds of control parameters on emission and catalysis,the optimal control strategy was put forward,including the determination of high efficiency catalytic air fuel ratio,EGR and ignition timing adjustment.The new control strategy was used to calculate the emissions of WHSC working conditions.Compared with the experimental data of the original control strategy,the NOx emission is effectively reduced,the CO is basically unchanged and kept at very low level,the HC is reduced to a lesser degree.By and large,the emissions of the natural gas engine were effectively controlled.