UNDERSTANDING DIESEL-PILOT ASSISTED METHANE COMBUSTION IN A COMPRESSION IGNITION ENGINE

Developing a sustainable alternative to diesel and gasoline is critical to mitigating climate change effects. Methane, the primary component of natural gas, presents itself as a successor to petroleum-based fuels. Compared to other hydrocarbons, methane (CH₄) has the highest hydrogen to carbon ratio which means when combusted in an engine, fewer carbon-based emissions occur. Natural gas currently has an extensive distribution infrastructure. This makes it a realistic intermediary option as a fuel source until the zero carbon alternatives are understood. This work explores combustion of methane in a single cylinder compression ignition (CI) research engine. A small amount of diesel was used to promote ignition of the methane charge. An exploration of equivalence ratios and injection timings was conducted to seek stable operation and maximum brake torque (MBT). Trends of engine performance metrics, a heat release analysis, and an emission characterization are presented in this manuscript. Performance of methane with diesel pilot injection with blend ratios between 47-51% methane by energy content and 88-90% by volume are compared to a baseline single injection diesel case and a split injection (pilot and main) diesel case. The purpose of the diesel pilot in the methane case is to function as a “spark” for the methane, due to methane’s longer ignition delay time. Key findings include that a dual fuel (diesel pilot + methane), dual injection strategy with a pilot injection event 5 degrees before top dead center (bTDC) maintained the most favorable balance between combustion performance and engine-out emissions. The implications of this study will help to better understand optimal strategies for maximizing the usefulness of methane as a primary fuel source in future dual fuel engines.