Researches On Premixed Combustion Cyclic Variations In Cylinder For Natural Gas Engine

Compared with traditional fuel engine,the pollutants in exhaust emission of natural gas engine are greatly reduced.The lean combustion technology reduces the combustion temperature in the cylinder,which future reduces the content of pollutants in the exhaust gas.However,lean combustion can lead to combustion instability,which results in the increase of engine combustion cycle.In this paper,the bench test of 12V190 natural gas engine is carried out,and the influence of ignition parameters to the combustion cyclic variations is studied by combining with FIRE software.In this paper,a new type of Venturi mixer is designed,which can get the indicator diagram of 400 cycles under certain conditions.The probability density function of the optimal fitting distribution is obtained by fitting the distribution of the continuous random variable with the maximum explosion pressure and the corresponding crank angle.The best fitting distribution of the maximum explosion pressure is the gamma distribution,and the distribution shape is right,and the probability of the larger explosive pressure is larger.The best fitting distribution of the maximum pressure corresponding crank angle is the normal distribution,which values are more concentrated near the average value.The shape of the probability density function curve is more steep,which shows that the fluctuation of crank angle is less than the maximum explosive pressure.The size and the position of the fire core are changed in the FIRE software to study the influence of ignition parameters to the combustion cyclic variations.The results show that the radius and position of the fire core have a significant effect on the maximum explosion pressure.The larger radius of the fire core and the farther position from the axis of the cylinder will lead to the larger maximum explosion pressure and the smaller crank angle.The optimal regression equation about the size and the position of the fire core is obtained by Taguchi method.Combined with the range of the size and the position of the fire core that is determined by the test,it is concluded that the combustion cyclic variations have been started at the ignition breakdown stage,and will extend to the end of combustion.Ignition parameters are ones of the important factors that cause the combustion cyclic variations.