Gaseous Fuels Variation Effects on Combustion and Emissions of a Small Direct Injection Natural Gas Engine 2019-01-0560

Our research focused on the assessment of fuel variation effects on performance of a 34 cc two-stroke, natural gas combustion engine designed for use as the prime mover in either slider-crank or novel linear generator applications. Nearly two-thirds of US homes have either natural gas or liquefied petroleum gas available at low pressures. We tested the engine with three different natural gas blends, pure methane, and pure propane. In order to reduce fuel compression power, we modified the engine to use low-pressure direct injection (LPDI) of gaseous fuels. We examined regulated gaseous emissions, greenhouse gas emissions, and combustion trends over a range of delivered air fuel ratios. Start of Injection (SOI) occurred at either 180 or 190 CA BTDC and efficiency improved by reducing fuel slip. However, for natural gas blends, the predominant emissions were methane - a potent greenhouse gas. We showed that while propane had the highest CO₂ emissions, it also produced the lowest CO₂ equivalent emissions. However, propane also tended to have the highest NO_x, NMHC+NO_x, and CO emissions. As expected, propane and the natural gas blends with high ethane content tended to produce the highest peak cylinder pressure while methane produced the lowest. Denser (higher C2+ content) fuels yielded the lowest COV of IMEP over the broadest range of delivered air fuel ratios, while pure methane yielded the highest. For all fuel blends, LPDI operation showed the capability to meet all current regulated gaseous emissions standards while providing improved efficiency.