Study Of Low Load Combustion Stability Of GCI Engine Based On Octane Sensitivity

Gasoline compression ignition is an energy efficient combustion technology that achieves higher thermal efficiency while maintaining low NOx and soot emissions.One of the difficulties facing gasoline compression ignition is the difficulty of ignition at low loads and poor combustion stability.Numerous studies have shown that inlet gas conditions play an important role in its low-load combustion,but few studies have used key influencing parameters and active additives to achieve stable low-load combustion of octane-sensitive fuels.In this paper,the influence of octane sensitivity on combustion stability is studied,and the key influencing parameters are adjusted and active additives are added to the inlet gas to optimize its combustion process,which is of reference significance for achieving efficient and stable combustion of octane-sensitive fuels.First,the combustion stability of GCI low load multi-cycle numerical simulation was investigated.The main conclusions are as follows: the combustion stability decreases and then increases as the octane sensitivity increases;the fuel with low sensitivity has a more uniform oil-gas mixture at high temperature ignition,and the combustion is complete and stable;the higher-sensitive fuel has a large gap in the mixing condition between cycles,and the combustion is the most unstable;the mixture of the highest-sensitive fuel is more uneven,and the average pressure indicated by each cycle is low but the gap is reduced,and the combustion stability increases;the low-temperature heat release induced temperature increase,which is good for combustion stability,but the combustion improvement effect of some cycles is not obvious;low-sensitivity fuel is more suitable for achieving GCI low load stable combustion.Secondly,the effects of key influencing parameters on the combustion characteristics of GCI with different octane sensitivities were investigated.The main conclusions are as follows: the injection moment is advanced,the low-temperature heat release rate of the fuel decreases,the indicated thermal efficiency increases and then decreases,the combustion is controlled by chemical kinetics,and the sensitivity has a stronger influence on the combustion phase and the indicated thermal efficiency;the internal EGR rate increases,the combustion chamber temperature increases,the stall combustion period shortens,and the peak heat release rate and the indicated thermal efficiency increase;increasing the compression ratio can effectively promote combustion,but the high compression ratio will Increase the compression ratio can effectively promote the combustion,but high compression ratio will lead to high pressure rise rate of low-sensitive fuel,and the phenomenon of rough combustion.A reasonable choice of injection timing and EGR rate can make the low-sensitive fuel burn efficiently,while increasing the compression ratio is more suitable for the highsensitive fuel.Finally,the effect of active additives on the combustion characteristics of GCI was investigated.The main conclusions are as follows: ozone and nitrogen oxide can effectively optimize the combustion process,and the promotion effect tends to saturate as the concentration increases.Ozone decomposes into oxygen and oxygen atoms,producing OH and other free radicals to promote low temperature exotherm,which in turn enhances the combustion process;nitric oxide is converted into nitrogen dioxide at low temperature to produce OH to promote combustion,and nitrogen dioxide is converted into nitric oxide at high temperature to produce oxygen and OH to promote combustion.