The Effect of Fuel Composition on Performance and Emissions of a Variety of Natural Gas Engines

Work was performed to determine the feasibility of operating heavy-duty natural gas engines over a wide range of fuel compositions by evaluating engine performance and emission levels. Heavy-duty compressed natural gas engines from various engine manufacturers, spanning a range of model years and technologies, were evaluated using a diversity of fuel blends. Performance and regulated emission levels from these engines were evaluated using natural gas fuel blends with varying methane number (MN) and Wobbe Index in a dynamometer test cell. Eight natural gas blends were tested with each engine, and ranged from MN 75 to MN 100. Test engines included a 2007 model year Cummins ISL G, a 2006 model year Cummins C Gas Plus, a 2005 model year John Deere 6081H, a 1998 model year Cummins C Gas, and a 1999 model year Detroit Diesel Series 50G TK. All engines used lean-burn technology, except for the ISL G, which was a stoichiometric engine. Performance testing consisted of monitoring engine knock or auto-ignition, as well as engine power levels and overall engine operability. Emissions of total hydrocarbons (HC), non-methane hydrocarbons (NMHC), carbon monoxide (CO), oxides of nitrogen (NO (x)), nitrogen dioxide (NO (2)), particulate matter (PM), and carbon dioxide (CO (2)) were measured using procedures developed by the United States Environmental Protection Agency (EPA) for heavy-duty, on-highway engines. The engines showed no sign of auto ignition throughout the program, with slight differences in power levels with the various test fuels. All lean burn engines showed increased NO x and HC emission levels with decreased MN and increased Wobbe level, while the stoichiometric ISL G showed no clear trend in NO x or HC levels with the various fuels.