Ultra Low Emissions and High Efficiency from an On-Highway Natural Gas Engine 981394

Results from work focusing on the development of an ultra low emissions, high efficiency, natural gas-fueled heavy- duty engine are discussed in this paper. The engine under development was based on a John Deere 8.1L engine; this engine was significantly modified from its production configuration during the course of an engine optimization program funded by the National Renewable Energy Laboratory.

Previous steady-state testing indicated that the modified engine would provide simultaneous reductions in nonmethane hydrocarbon emissions and fuel consumption while maintaining equivalent or lower NO_x levels. Federal Test Procedure transient tests confirmed these expectations. Very low NO_x emissions, averaging 1.0 g/bhp-hr over hot-start cycles, were attained; at these conditions, reductions in engine-out nonmethane hydro-carbons emissions (NMHC) were approximately 30 percent, and fuel consumption over the cycle was also reduced relative to the baseline. The lowest NO_x results obtained were below 0.77 g/bhp-hr. Composite cold-start/hot-start test results were also very good, with NO_x at approximately 1.0 g/bhp-hr and engine-out NMHC emissions less than 0.5 g/bhp-hr.

Overall, the NO_x versus efficiency tradeoff for the engine was improved significantly. Also, in comparison to the California Air Resource Board ultra low-emissions vehicle (ULEV) standards, the composite test results were roughly 60 percent of the ULEV standards for NO_x + NMHC, and the results for the lowest NO_x cycle were below one half of the NO_x + NMHC standard. Carbon monoxide and particulate matter were also well below the ULEV limits, again with no oxidation catalyst being used.