Research On The Influence Of High Energy Ignition Coupled EGR On The Performance Of Natural Gas Engine

Natural gas engines have attracted much attention due to their abundant fuel reserves and low prices.In order to meet the increasingly stringent requirements of the CHINA 6 emission regulations,the stoichiometric natural gas engine that can use the three-way catalytic converter has become the mainstream product of the current natural gas engine,but the stoichiometric natural gas engine has the disadvantages of high heat load and poor fuel economy.In order to improve the above shortcomings,this paper takes the 6-cylinder four-stroke turbocharged stoichiometric spark-ignite natural gas engine as the research object,takes the engine test bench and simulation calculation as the research method,adopts the research strategy of coupling EGR and ignition energy,and discusses the performance change of stoichiometric natural gas engine when adjust ignition energy and ignition energy are coupled with EGR.In addition,the influence of ignition energy on the EGR tolerance of stoichiometric natural gas engine is studied.First,the research on the effect of ignition energy on the performance of stoichiometric natural gas engines has been carried out.The research shows that the effect degree of ignition energy is related to engine operating conditions and ignition energy range.The positive effect of ignition energy under small load conditions is limited,and the effect of ignition energy under medium-high load and full load conditions is significant.When the ignition energy is higher than 96 m J,the improvement effect is obvious,and the effect is limited when the ignition energy is below 96 m J.Under test conditions,increasing the ignition energy can optimize the combustion process in the cylinder under stoichiometric,accelerate the flame propagation rate,shorten the flame retardation period and duration of combustion,improve combustion stability,and increase engine power and economy.At the same time,increase ignition energy cause the temperature in the cylinder increase will cause the increase of NOx emissions and the decrease of exhaust temperature,but the ignition energy has little effect on THC emissions.Based on the analysis of the micro-field in the cylinder,the influence mechanism of ignition energy is discussed.Research shows that increasing the ignition energy can promote the flame propagation at the initial stage of the growth of the flame kernel,but as the combustion progresses,the influence of the ignition energy on the flame propagation rate gradually weakens,which is reflected on the advance margin of the start of combustion,the center of gravity of combustion,and the end of combustion gradually decreases in general.Through the research on the effect of ignition energy coupled EGR on the performance of stoichiometric natural gas engines,it can be found that increasing the EGR rate reduces both the peak cylinder temperature and NOx emissions,and also inhibits the combustion in the cylinder,which makes the combustion stability worse,the power and economical reduced,and the THC emission and exhaust temperature are increased.According to the analysis of the combustion process in the cylinder when the ignition energy is coupled with EGR,the increase in ignition energy can effectively compensate for the degradation effect of EGR on combustion,so that the combustion conditions in the cylinder under high EGR rate can reach or even exceed the lower EGR rate.At the same time,the combustion stability under high EGR rate is improved.From the microscopic field,it can be seen that high ignition energy can optimize the flame propagation in the early stage of flame kernel growth at high EGR rate,and the optimization effect on the initial stage of flame kernel growth will affect the combustion phase supported by the exotherm of the chemical reaction.The optimization effect of ignition energy on the combustion process at high EGR rate results in that the engine can still achieve the same or higher torque output and fuel economy as the original engine at high EGR rate.In addition,since EGR has a higher impact on THC and NOx emissions than ignition energy,while using high ignition energy to improve combustion at high EGR rates,it can still achieve lower NOx emissions than the original engine,but ignition energy cannot solve the problem of high THC emissions under high EGR rate.And increasing the ignition energy under high EGR rate can achieve a lower exhaust temperature than the original engine state.Finally,using the cycle variation coefficient as an index to judge the stability of the engine,it is found that the EGR tolerance of the engine can be improved by coupling the ignition energy and EGR,and at the same time,it is better than the original engine in all aspects under the high EGR rate couple with high ignition energy.Not only improves the engine’s power,economy and combustion stability,but also greatly reduces the NOx emissions and exhaust temperature under the premise of little impact on the engine’s thermal load.