The principle of determining the optimized operating parameters based on the adopted fuel property in RCCI engines

摘要

Both the gasoline/diesel (G/D) and methanol/diesel (M/D) reactivity controlled compression ignition (RCCI) engines are optimized at low-to-medium load. The results indicated that the impact of fuel property on the determination of the optimal parameters is significant. It is found that homogeneous fuel/air distribution with high premixed ratio and advanced start of injection (SOI) is beneficial for the improvement of engine performance for both G/D and M/D RCCI. Meanwhile, the high initial temperature is indispensable to avoid the excessively late CA50 and the deteriorated combustion efficiency. Fuel reactivity and combustion rate are two important parameters for the fuel in RCCI engines. Due to the lower reactivity and the faster combustion rate of methanol than those of gasoline, lower premixed ratio and more retarded SOI are adopted in M/D RCCI than G/D RCCI to advance the CA50 and alleviate the fast combustion rate. Moreover, higher exhaust gas recirculation (EGR) rate is required for M/D RCCI to reduce its fast combustion rate. Boosting the in-cylinder pressure (P_(IVC)) has two contradictory effects on the combustion temperature and fuel efficiency. Owing to the later CA50 in M/D RCCI, the higher P_(IVC) is favorable for M/D RCCI, while lower P_(IVC) is preferable for G/D RCCI.