Methanol is one of the most promising fuels for the decarbonization of the off-road and transportation sectors. Although methanol is typically seen as an alternative fuel for spark ignition engines, mixing-controlled compression ignition (MCCI) combustion is typically preferred in most off-road and medium-and heavy-duty applications due to its high reliability, durability and high-efficiency. In this paper, the potential of using ignition enhancers to enable methanol MCCI combustion was investigated.
Methanol was blended with 2-ethylhexyl nitrate (EHN) and experiments were performed in a single-cylinder production-like diesel research engine, which has a displacement volume of 0.83 L and compression ratio of 16:1. The effect of EHN has been evaluated with three different levels (3%vol, 5%vol, and 7%vol) under low- and part-load conditions. The injection timing has been swept to find the stable injection window for each EHN level and load. With the highest EHN level, better combustion stability and the widest combustion control window were found due to the higher reactivity of the fuel. However, NOx emissions increased as the EHN level increases mainly due to the contribution of the nitrate group of EHN to engine-out NOx. Stable combustion under low-load condition was achieved only with 7%vol EHN. Due to the absence of carbon-to-carbon bonding and high oxygen content in the fuel, highly improved particle emission characteristics were detected regardless the level of EHN. Finally, comparisons against baseline operation with diesel fuel show that higher thermal efficiency values can be reached with methanol MCCI for a given engine-out NOx level due to much lower heat transfer loses.