Low Load Ignitability of Methanol in a Heavy-Duty Compression Ignition Engine 2022-01-1093

An increasing need to lower greenhouse gas emissions, and so move away from fossil fuels like diesel and gasoline, has greatly increased the interest for methanol. Methanol can be produced from renewable sources and eliminate soot emissions from combustion engines [1]. Since compression ignition (CI) engines are used for the majority of commercial applications, research is intensifying into the use of methanol, as a replacement for diesel fuel, in CI engines. This includes work on dual-fuel set-ups, different fuel blends with methanol, ignition enhancers mixed with methanol, and partially premixed combustion (PPC) strategies with methanol. However, methanol is difficult to ignite, using compression alone, at low load conditions. The problem comes from methanol’s high octane number, low lower heating value and high heat of vaporization, which add up to a lot of heat being needed from the start to combust methanol [2]. This paper investigates methanol combustion at low load and compares it to diesel fuel, using a more classical diesel combustion strategy of diffusion combustion. This paper also investigates how a high compression ratio could aid the low load combustion of methanol. To get the methanol burning, with similar stability as diesel fuel, intake heating was used together with a pilot injection, of about a third of the main injection quantity. The resulting efficiencies were similar between diesel fuel and methanol, and for the emission measurements NOx was much lower for methanol than for diesel fuel. Increasing the compression ratio resulted in stable combustion without the need for intake heating and a pilot injection, at even lower loads. It also yielded higher efficiency without having a major effect on the emissions.