Fuel Composition Effects in a CI Engine Converted to SI Natural Gas Operation 2018-01-1137

Low-carbon fuels such as natural gas (NG) have the potential to lower the demand of petroleum-based fuels, reduce engine-out emissions, and increase IC engine thermal efficiency. One of the most rapid and efficient use of NG in the transportation sector would be as a direct replacement of the diesel fuel in compression ignition (CI) engines without any major engine modifications to the combustion chamber such as new pistons and/or engine head. An issue is the large variation in NG composition with the location and age of the gas well across U.S., which would affect engine operation, as well as the technology integration with emissions after treatment systems. This study used a conventional CI engine modified for spark ignition (SI) NG operation to investigate the effects of methane and a C₁-C₄ alkane blend on main combustion parameters like in-cylinder pressure, apparent heat release rate, IMEP, etc. Steady-state engine experiments were conducted at several operating conditions that changed spark timing, engine speed, and equivalence ratio. The study found that NG operation increased peak pressure, IMEP, and indicated thermal efficiency compared to methane, for all the operating conditions investigated in this work. This suggests caution when translating methane-based experimental observations to real world NG operation, even for NG with mostly methane as the one used in this work. As many NG studies in the literature used methane as an NG surrogate, a better understanding of real fuel effects in diesel-like combustion environments could be important for the successful conversion of conventional diesel engines to NG operation.