Study On The Influence Of Mixed Fuel On Operating Range And Performance Of HCCI Engine

At present,the situation of the scarcity of non-renewable energy and environmental pollution is becoming more and more serious.As the main source of oil consumption and air pollution,the combustion efficiency and emission technology of internal combustion engines need to be further improved to save resources and avoid environmental pollution.Therefore,the Homogeneous Charge Compression Ignition(HCCI)combustion method has emerged in new engines with its advantages of low polluting gas emissions and high efficiency.However,due to the narrow operating conditions of the HCCI engine,its application in the automotive industry is limited.Therefore,it is particularly necessary to expand the range of HCCI engine operating conditions.Studies have shown that the use of mixed fuels with different octane numbers is an effective way to expand the operating range of HCCI engines.However,the use of mixed fuels will affect the combustion timing of the HCCI engine.Research in this area is still relatively weak;in addition,how to adapt to the optimal octane number of various speed conditions has not been studied in depth.Related research on the above-mentioned problems was carried out,and the main work is summarized as follows:1.Different octane fuels to expand the range of HCCI engine operating conditionsGT-Power engine simulation software is used to build a HCCI engine simulation model.Under different speed conditions,simulation tests were carried out on HCCI engines using different octane number fuels,and the operating conditions range of HCCI engines running stably when using different octane number fuels was obtained.It is compared with the operating range of HCCI engine using gasoline fuel.The results show that the use of fuels with different octane numbers can make the HCCI engine run stably in the range of 1000RPM-6000 RPM.Compared with gasoline HCCI engines,mixed-fuel HCCI engines have achieved a certain degree of expansion in both high and low speed operating conditions.2.The optimal fuel octane number should be matched within the range of different speedsBecause fuels with different octane numbers have different effects on the combustion performance of HCCI under the same speed conditions,the corresponding optimal fuel octane number matching strategies under different speed conditions is proposed;and a variable fuel octane number HCCI engine Simulation model was built to improve the power of HCCI engine.3.Research on the influence law of HCCI engine related parameters on its combustion performance and operating condition rangeThe influence of EGR,intake air temperature,compression ratio and four groups of combined variables on the combustion performance and operating range of HCCI engines were studied in this thesis.The test results show that when EGR<0.4,the HCCI engine can run stably under various speed conditions,and the in-cylinder mixture is completely burned.When EGR>0.4,incomplete combustion such as misfire occurs in the cylinder,and exhaust gas emissions increase.As the intake air temperature increases,the power of the HCCI engine decreases,the combustion timing advances,and the combustion duration decreases.When the compression ratio is CR<6,the HCCI engine cannot be compression-ignited normally,and when CR>20,rough combustion such as knocking occurs in the cylinder.4.Research on parameter adjustment strategy when switching between SI-HCCI dual combustion modesAiming at the problem of the engine power output and the large sudden change of CA50 during the switching process of the two combustion modes,a parameter adjustment strategy at the switching time is proposed to improve the stability of the engine performance during the combustion mode switching process.It is verified by experiments that the IMEP mutation range during the combustion mode switching process after adjustment is reduced to 0.02bar-0.33bar;and after switching to the HCCI combustion mode,the CA50 is always stable at about 8deg behind top dead center.