Multidimensional Simulation Study On The Effect Of Diesel Engine Injection System Parameters On Combustion And Emissions At High Altitud

China’s terrain is complex and the plateau area is wide,agricultural equipment and construction machinery with diesel engine as the power source play an irreplaceable role in people’s social production activities.In the context of carbon peaking and carbon neutrality,power recovery and emission control of engines operating at high altitude have become a key concern.In this paper,a 186F off-road direct injection diesel engine is used as the target prototype.The goal is to reduce NOx and soot emissions from diesel engines while improving the deterioration of plateau engine power.The main research contents and conclusions are as follows:First,the combustion,oil and gas formation and emission characteristics of engines at different altitudes are analyzed in this paper.As the altitude increases,the penetration distance of the fuel spray in the combustion chamber gradually becomes longer,the atomization and evaporation process of the fuel beam slows down,the oil-gas mixture gradually accumulates toward the side walls and pits of the combustion chamber,The quality of oil film formation increases,the stagnation period lengthens,and the maximum combustion pressure gradually decreases.Pre-mixed combustion becomes more intense as the altitude rises,the maximum average temperature in the cylinder increases,NOx generation increases,and diffusion combustion is suppressed;the mass distribution gradient of combustion air-equivalent ratio increases,the unevenness of oil-gas mixture increases,the local oxygen deficiency combustion phenomenon intensifies,and carbon smoke and CO emissions increase.At an altitude of 2500 meters,a large amount of combustible mixture in the combustion chamber pit rapid combustion,the average local temperature in the cylinder decreases during the piston downward movement,the probability of flame quenching by cooling increases,and the incomplete combustion products HC emission increases.Secondly,the nozzle extension length,injection timing,injection duration and injection angle were optimized in a secondary orthogonal manner at 2500m altitude.The injection angle at high altitude has an important effect on engine combustion and emission.When increasing the injection angle,the volume under the spray cone increases,part of the fuel enters into the clearance,the accumulation of oil and gas in the crater is relieved,the residual air is effectively used,and the specific fuel consumption of the engine is reduced.Increase the injection angle and take the measure of early injection,which can make full use of the squeezing flow movement of the compression stroke,increase the oil-gas mixing rate,advance the starting point of combustion;After secondary optimization,the engine’s indicated ratio fuel consumption was reduced by 3.3%compared to the original engine.After optimization,the air utilization rate of the clearance and the center of the combustion chamber increased,and the oil-gas mixing condition was improved,NOx increased by 17.9%and 38.8%in primary optimization and secondary optimization,while soot decreased by 55.2%and 62.7%,respectively.Finally,the pre-injection timing,main pre-injection interval and pre-injection quality were optimized in an orthogonal test under the segmental injection strategy at 2500m altitude.With the advancement of pre-injection timing,the fuel-air interaction time increases,the center of gravity of combustion gradually approaches the top dead center.the overall SOOT ratio emission shows a decreasing trend with the increase of pre-injection quality;when the main pre-injection interval increases,the in-cylinder average combustion temperature decreases and NOx emission decreases.Under the orthogonal optimized segmental injection strategy,due to the presence of the main pre-injection interval,the air utilization rate in the center of the combustion chamber and the clearance is significantly improved,the fuel evaporation rate in the center of the combustion chamber is accelerated,and the gathering of the mixture into the crater is improved,and the NOx emission is reduced by 18.6%compared with the case of quadratic optimization,the CO and carbon smoke emissions were reduced by 36.7%and 56.9%,respectively,compared with the original machine.