Optical Researches On Combustion Process For Diesel Engines Under The Condition Of O₂/Ar Intake

Diesel engines have the advantages of high thermal efficiency and low fuel consumption, but the large scale applications have brought the serious problems of air pollutions. Because of the trade-off law for PM and NOx in emission products of diesel engines, they bring difficulties to control the emissions. In this thesis, we use the combustion technology of 02/Ar mixture intake. Through the visualization of engine experiments, we research the combustion process of diesel engines under the regular air intake condition and 02/Ar intake condition.We build the model for working process of in-cylinder to the optical engine ZS195 in the ESE Diesel module of software FIRE. Based on reduced reaction mechanism of n-heptane, the numerical simulations of diesel engines working process have been done under the different proportions of 02/Ar intake. The simulation results show that when the argon ratio is 79% the mean pressure of engine is higher than that of argon ratio are 85%、60% and air intake conditions, and the maximum explosion pressure is 78.40bar; the mean temperature is close to that the argon ratio is 60% but higher than that of 85% argon and air intake conditions; the maximum increase rate of pressure and the maximum mean rate of heat release are nearly to those of 85% argon, but lower than those of 60% argon and air intake, namely the engine works smoothly.In this paper, a set of intake system which can be switched freely between air intake and 02/Ar intake is designed on the basis of original optical engine ZS195. According to simulation results, we select 21%O2+79%Ar as the mixed gases intake ratio, then the optical experiments are taken for 16℃A advance angle of fuel supply under the condition of air intake and 02/Ar intake, for 11℃A advance angle of fuel supply under the condition of 02/Ar intake. After experiments the cylinder pressure, rotating speed and combustion flame images are obtained. The experiment results show that under the condition of 02/Ar intake the maximum mean pressure is 52.1% larger than regular air intake, and the pressure can be reduced due to the fuel supply delay but still 24.4 larger than air intake; the time at the maximum pressure rise rate and the maximum heat release under the condition of O2/Ar intake is earlier than air intake condition; the highest temperature and lowest temperature at maximum pressure rise rate and maximum heat release under the condition of 02/Ar intake are the same to the air intake condition, but the average temperature is lower than that of air intake, and the flame spread speed is 2.2 times that of air intake.