The effects of intake backflow on in-cylinder situation and auto ignition in a gasoline controlled auto ignition engine

The inability to control the auto ignition in CAI combustion is an obstacle against its practical use, and the in-cylinder thermal and component distributions are being investigated in more depth as a way to control auto ignition. A 3D simulation using KIVA code is applied to study the effects of intake backflow on the in-cylinder situation. When the intake backflow is increased, the mean temperature is found to be significantly lower. In addition, the difference in the mean temperature of the cylinder reaches 40 K at 320° CA ATDC for a 73–75.8% residual gas fraction. The in-cylinder temperature distribution becomes concentrative and the highest temperature in the cylinder decreases as the intake backflow increases. In this paper, the characteristics of the hot zone are studied, and the superposition ratio of the hot zone and the high residual gas fraction zone is proposed to represent the temperature and residual gas fraction of the mixture in the cylinder. The hot and relatively low residual gas fraction zone increases as the intake backflow increases. Experiments were performed on a single-cylinder engine with a variable valve system. Results indicated that the autoignition timing first delays and then advances as the intake backflow increases. The autoignition changes 3.7° CA at a 58.1–60.6% residual gas fraction. The intake backflow is a potential means of controlling auto ignition timing for CAI.