Effect of compression ratio and Miller cycle on performance of methanol engine under medium and low loads

Abstract

Listen

Translate article

Considering the excellent anti-knock property of methanol fuel and the fact that passenger car engines typically operate at medium to low loads, this paper increasing the compression ratio and adopting the Miller cycle to improve the engine's efficiency, based on a methanol engine with compression ratio of 9.5:1. Experimental research is conducted to analyze the engine's combustion and emission characteristics under different operating conditions. The research shows that increasing the compression ratio to 12:1 can effectively reduce methanol consumption under medium to low loads, and applying the Miller cycle on the compression ratio of 12:1 can further improve fuel economy at low loads. Increasing the compression ratio raises the engine's cylinder pressure, maximum pressure rise rate, and cycle-to-cycle variation, thereby enhancing the tendency for knocking. However, the Miller cycle can effectively alleviate this situation while reducing engine pumping losses. From the perspective of emissions at medium and low loads, the high compression ratio reduces CO and HC emissions but increases NOx emissions due to high combustion temperature. The Miller cycle's shorter combustion duration and lower combustion temperature result in higher CO and HC emissions compared to an Otto cycle at the same compression ratio, but NOx emissions are improved.