Effects Of Natural Gas Injection And Combustion Chamber Geometry On Combustion Characteristics Of Lean-Burn Natural Gas Engine

A large number of energy consumption and the serious environmental pollution energy force people to speed up the pace of development of new energy.Natural gas as a kind of abundant reserve,clean burning energy which has been quickly becoming a major alternative energy for current multiple industries and it also promotes the rapid development of natural gas engine.The combustion characteristic of natural gas energine determines the dynamics,economy and emission performance of natural gas engine,so it is very necessary to be deeply studied.In this paper,the 2135 G diesel engine was transformed into a natural gas engine and basing on it,the effect of the different injection regularity on lean-burn characteristics is studied respectively by the combined method of experiment and CFD simulation technology in its 25% and 75% workloads.Results indicate as following: the effect is different that changes the injection regularity combustion characteristics in the 25% and 75% workloads.At the lower 25% workload,the decreasing injection pressure and increasing injection duration properly can help to improve the energine's dynamics and economy performance,the phenomenon that a larger gradient on the concentration of mixture stratification which is concentrated in upper and dilute in downer is formed in the ignition time at the 3# injection regularity(3.8bar,13.55ms)in studied four injection regularity,what's more,in the combustion process,there is wider distribution of high flame surface density zone in the cylinder,faster combustion rate and the shortest combustion duration.While at the higher 75% workload,the increasing injection pressure and decreasing injection duration properly can conducive to improve the fuel efficiency and thermal efficiency of engine,at 7# injection regularity(7.9bar,12.5ms),the concentration of mixture stratification which is more well-distributed and thicker is formed around the ignition position,it decrease the effect of flame spread rate due to mixture distributes only one side on the ignition position in the ignition time,accelerate the burning rate and effectively shorten the ignition delay period and post-combustion period.In this paper,three new combustion chamber are designed by basing on the original engine combustion chamber and the effect of different combustion chamber geometry on combustion characteristics is sdudied in the 25% load of natural gas engine.The combustion result is better at the 2# combustion chamber by comparing the combustion chamber of 1# flat shape,2# lower ? shape and 3# higher ? shape,so improving the height of the combustion chamber bottom properly can increase the in-cylinder gradient on the concentration of mixture stratification which is concentrated in upper and dilute in downer in the ignition time and effectively shorten the combustion duration,but the exorbitant hump at the bottom of the combustion chamber is able to suppress the rapid propagation of the flame.While compared with the combustion chamber of 2# lower ? shape and 4# round bottom shape,in the 4# combustion chamber,it shows larger the higher flame surface density area,faster flame speed and shorter the combustion duration,so it indicates that increasing the distance between the spark plug and the bottom of combustion chamber can more beneficial to accelerate the burning rate.