Decarbonization of Off-Road Engines by Methanol Mixing-Controlled Compression Ignition with Ignition Enhancer

Methanol is one of the most promising fuels for the decarbonization of the off-road and transportation sectors. Although methanol is typically considered 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, methanol MCCI combustion was enabled using ignition improvers and the potential benefits of this approach compared to conventional diesel combustion were investigated. Methanol was blended with 7%vol 2-ethylhexyl nitrate (EHN) and experiments were performed in a single-cylinder production-like diesel engine with a displacement volume of 0.83 L and a compression ratio of 16.5: 1. The conditions of the ISO 8178 C1 regulatory cycle for off-road engines were tested, and performance and emissions over the cycle were calculated. Methanol MCCI shows 6.5% lower fuel consumption (in gallons of diesel equivalent) than conventional diesel combustion, resulting in a 21% reduction in operation costs. Smoke emissions are also very low, 98% lower than those of conventional diesel over the cycle, and a diesel particulate filter will not be required with methanol. CO emissions are higher than those of diesel and slightly higher than the legal limit, so an oxidation catalyst will be required with methanol. However, low load operation at rated speed accounts for 44% of the total CO emissions over the regulatory cycle, so optimization of this operating point is key to reduce CO and simplify the required aftertreatment. NOx emissions are higher than the legal limit for both methanol and diesel, so both technologies will require NOx aftertreatment, such as a selective catalyst reduction catalyst. In conclusion, the ultra-low soot, lower fuel consumption, lower operating cost, and retrofit potential of methanol MCCI indicate that this is a promising approach for decarbonization of the off-road sector.