Experimental study on axial stratification process and its effects (I) - Stratification in engine

This paper is the first of several companion papers, which investigate axial stratification process and its effects in an SI engine. The axial stratification is very sophisticate phenomenon, which results from combination of fuel injection, port and in-cylinder flow and mixing. Because of the inherent unsteady condition in the reciprocating engine, it is impossible to understand the mechanism through the analytical method. In this paper, the ports were characterized by swirl and tumble number in steady flow bench test. After this, lean misfire limit of the engines, which had different port characteristic, were investigated as a function of swirl ratio and injection timing for confirming the existence of stratification. In addition, gas fuel was used for verifying whether this phenomenon depends on bulk air motion of cylinder or on evaporation of fuel. High-speed gas sampling and analysis was also performed to estimate stratification charging effect. The results show that the APR at the spark plug and LML are very closely related and the APR is the results of bulk air motion.