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
(NOX), nitrogen dioxide (NO₂), particulate matter (PM), and
carbon dioxide (CO₂) 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
autoignition throughout the program, with slight differences in
power levels with the various test fuels. All lean burn engines
showed increased NOX and HC emission levels with decreased MN and
increased Wobbe level, while the stoichiometric ISL G showed no
clear trend in NOX or HC levels with the various fuels.
