The Simulation Study On The Cold Starting Process Of Spark Ignition Aviation Direct Injection Engine

Presently because of the requirements and technical conditions in aviation industry,as the best technical plan for small aviation motor,ignition type aviation engine powered by kerosene can meet all requirements from fuel storage,transportation,safety of utilization phase and fuel integration.Meanwhile,it can effectively alleviate the shortage of aviation gasoline resources.But,the big kinematic viscosity and the worse evaporation natures of the aviation kerosene make the normal ignition and stable combustion of the engine difficult,especially the low temperature and the low strength of air flow under the cold-start working condition.So,it is important to do the performance optimization research of starting the aviation GDI engine powered by kerosene under the low temperature,which has important engineering instruction significance and academic value.The paper chooses a four-stroke ignition type direct-injection aviation engine with two air valves for the research,fulfills the building of the structural model and calculation network of the air inlet and combustion chamber.Based on the effective configuration to the spray model and combustion model,the paper discusses the liquid drop gathering phenomenon under the pure compressing condition.Meanwhile,the paper analyses the sensibility of the excess air coefficient,injection time,ignition timing on the ignition and combustion process of the aviation kerosene.Finally,the paper compares the improvement effect of the double injections,asynchronous ignition,different preheating methods on the cold-start performance of the engine,the result shows:Under the compressing state ignoring the inlet turbulence,the probability of the drop colliding and gathering for aviation kerosene is higher than gasoline,the enlargement of SMD is faster,the evaporation is more difficult.Lowering the initial particle size of the kerosene and improving evenness of the drop can effectively inhibit the reunion phenomenon.The output power for aviation kerosene is the biggest when the excess air coefficient is 0.8.Enlarging the injection can accelerate the formation and initial spread of the fire core,but when the enlargement is excessive,the wet wall phenomenon of fuel will be bad,making the thermal efficiency lower.Injection time is key factor of affecting evaporation and spread of the kerosene and formation of the mixed gas,different with the injection during the initial intake phase strategy when the engine adopts the gasoline,aviation kerosene is injected during the late compression phase,and its efficiency in evaporation and combustion is higher;The delayed ignition can shorten the ignition delay period,but that will lower the power output.Preparing the stratified mixture by double injections can effectively shorten the ignition delay period.But because of the deviation from the optimum ignition advance angle for the second injection,the total amount of evaporating fuel and the output power decrease.By the concentration difference of the fuel near the double spark plugs,adopting asynchronous ignition strategy can improve combustion efficiency.But this method does nothing in shortening the ignition delay;Preheating the cylinder block has more direct influence on the fuel evaporation phase than preheating the fuel.Considering the optimization effect of cold-start performance and the safety,preheating the cylinder block is more appropriate.