Simulation Research On The Injection Strategies Of Diesel Ignited Natural Gas Engine

People are actively looking for new alternative fuels and explore new combustion mode in order to improve the severe environmental pollution and energy shortages.With the development of alternative fuels technologies,the natural gas engine has become a hot research topic at home and abroad because of its own advantages.The single natural gas engines have the shortcomings of high-self-ignition temperature,ignition difficult and low volumetric efficiency,higher hydrocarbon emissions,and can't meet the demand;ignition diesel/natural gas dual fuel engine fire during lean mixture combustion will become unstable,fuel consumption and emissions increased;but diesel ignited natural gas engines can improve the combustion process.But how to rationally organize the combustion process and reduce emission is the difficulties of current research,this paper uses the simulation means to explore the influence of combustion process and emissions by pilot diesel injection strategy of natural gas engine.This paper use Pro/E to establish the engine combustion chamber geometry model,build diesel ignited natural gas engine simulation system by using CFD software FIRE,and use the simulation system,firstly research the pilot diesel single injection when different amount of pilot diesel I on the influence of combustion process and emission.The results showed that with the increase of the pilot diesel,the maximum of the peak cylinder pressure and the peak temperature has increased,With respect to I=3%,I=5%of both were increased by about 35.12%,5.3%;the maximum rate of pressure rise with the increase of I;combustion center of gravity CA50 gradually close to the TDC,the ignition delay and combustion duration gradually decreasing;the emissions of NOx,and CO increased,At the same time,get the boundary condition of the pilot diesel I was 1.5%.Secondly,this paper studies the influence of the two ignition diesel injection strategies on combustion process and emissions,Respectively study the three aspects to research the first injection time,the second injection time and first injection ratio,Through the analysis of the cylinder combustion process,emissions and related physical field changes to get the law of influence.The results show that with the first injection timing advanced,the cylinder peak pressure,the peak temperature maximum increased by about 23.3%,2.59%,The maximum pressure rise rate increased with it,CA50 gradually close to the TDC and NOx emissions rise;With the second injection timing delayed,the cylinder peak pressure,peak temperature maximum decreased by about 10.01%,2.33%,The maximum pressure rise rate decrease with it;CA50 gradually away from the TDC as well as CO decreased and NOx increased;with the first injection ratio advanced,the cylinder peak pressure,the peak temperature increased,CA50 gradually close to the TDC and NOx emissions rise.Comparative analysis the maximum pressure rise rate,the ignition timing and emissions of pilot diesel single injection and twice injection,getting that twice injection policy can effectively control the ignition moment,decrease the maximum pressure rise rate and reduce NOx emissions effectively.The results of this paper show that the simulation system is feasible,and the injection strategy can reasonably organize the combustion process and effectively reduce the emission,which provides a basis for further development of the study of the natural gas engine.