Effect of injection strategy on a diesel/methanol dual-fuel direct-injection engine

Abstract

Methanol direct-injection achieves direct injection of diesel and methanol in the cylinder by using two independent fuel injection systems. This yields an extremely high methanol substitution rate and extremely low pollutant emissions. Due to these advantages, three injection strategies are proposed to investigate this injection method: D/M mode and M/D mode are where methanol injection occurs later and earlier than diesel injection respectively while M/D/M mode is where methanol is injected once before and once after the diesel injection. In this paper, these strategies are investigated, and the optimal settings of each are obtained and compared at low load and high load. The results show that in D/M mode, fuel economy is optimized and knock intensity increases with advancement of fuel injection and decreased injection dwell. This mode also effectively prevents knock but is not conducive to fuel economy. The most suitable methanol injection timings are obtained in M/D mode, namely 20°CA before the top dead center (BTDC) at low load and 30°CA BTDC at high load. Moreover, at low load the higher the first methanol injection ratio is, the better the fuel economy becomes, while at high load continued increases in the first ratio are limited by knock. Ultimately, M/D/M mode is found to be the best injection strategy at low load and high load.