Experimental Study On The Effect Of Combustible Components On Pre-Ignition Of End-Mixed Gas

With the increasing shortage of petroleum resources and environmental pollution,gasoline engines are developing to turbocharged direct injection,which also brings a new abnormal combustion phenomenon-"super knock".At present,the understanding of this phenomenon is not sufficient,and no effective control strategy has been found.It has become a problem for the current supercharged direct injection gasoline engine to further increase the power density.This paper focuses on the "pre-ignition" that must occur in the super knock cycle,and tests the effects of combustible components on Pre-ignition of End-mixed Gas.The view on the causes of premature combustion and its influencing factors has not been unified.Based on the visualized constant-volume combustion test platform,this paper studies the combustible components(oil and gasoline)that are likely to be the cause of premature combustion.In order to avoid the mixing of oil and gasoline,the micro-oil and gasoline components were separately introduced into the combustion chamber to observe the effect on the combustion process.Methane gas and propane gas were selected as fuels for comparative.First,build a visualized constant volume bomb test platform and develop a test plan.Then,the oil is separately introduced into the methane mixture and the propane mixture,and the optical technique is used to observe whether the end mixture is pre-ignited.Change the initial pressure,oil injection quantity,fuel-air equivalent ratio,initial temperature of the cylinder wall,and study the influence of the above initial conditions on the early combustion of the oil.The incylinder combustion pressure is collected,and the combustion characteristics are analyzed,and the average temperature of the unburned area when the computer oil is self-ignited.Finally,replace with the gasoline component and repeat the above test.Research indicates:The injection of micro-oil and gasoline into the combustion chamber can induce preignition.The difference is that the oil component only induces the pre-ignition of the methane mixture,and does not cause the pre-ignition of the propane mixture;and the gasoline component induces the pre-ignition at the end of the two mixtures.Under the same initial conditions,the oil component appears to prematurely burn earlier than the gasoline component.The average temperature of the unburned zone at the time of early combustion is calculated,and the temperature at the time of self-ignition of the oil component is about 725 K,and the temperature at the time of self-ignition of the gasoline component is about 830 K.The study on the influence of oil on the premature combustion law of methane mixture shows that with the increase of initial pressure,the combustion rate of methane mixture is slower,the oil burns earlier,but it is easier to reach the spontaneous combustion state.The corresponding flame radius changes when pre-ignition occurs.Small,the ignition area ignited by pre-ignition increases;the amount of random oil injection increases,the time of early combustion of methane mixture is advanced,when the amount of oil exceeds a certain value,the influence on the pre-ignition time is small;When the methane/air mixture equivalent ratio is 1,the time of occurrence of pre-ignition is the earliest.When the equivalence ratio is 1.1,the pre-ignition time is the closest to the stoichiometric ratio.If the mixture is too rich or too lean,the pre-ignition can be suppressed.The time of pre-ignition is the most late;as the temperature of the cylinder wall increases,the number of oil droplets suspended in the cylinder is larger,the particle size is smaller,and the timing of premixing of the mixture is advanced.The study on the effects of gasoline components on the pre-ignition law of methane and propane mixed gas shows that with the increase of initial pressure,the pre-ignition time is delayed,and the methane mixture with initial pressure of 0.4MPa-0.8MPa has premature combustion.Pre-ignition began to occur when the initial pressure of the propane mixture reached 0.8 MPa.When the gasoline injection amount is increased from 1.0 mg to 2.0 mg,the difference in the pre-combustion timing of the methane mixture is small;when the gasoline injection amount is less than 1.0 mg,the propane mixture is less prone to premature combustion,and the propane mixture is increased as the gasoline injection amount is increased.The gas pre-ignition time is advanced.When the gasoline injection amount reaches 2.0 mg,the laminar combustion of the propane mixture gas is destroyed,and more than one early ignition point appears at the end.Under the conditions of this test,due to the large difference between the initial temperature in the combustion bomb and the top dead center of the engine,the pre-ignition of the combustible component did not cause significant pressure fluctuations and knocking.However,the combustion process is shortened and the combustion pressure are increased.