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The U.S. Environmental Protection Agency has completed a program to demonstrate the feasibility of using integrated catalyst-muffler exhaust systems for nonroad spark ignition gasoline Class I engines (sub-19 kW, less than 225 cc). Integrated catalyst-muffler systems were developed for 4 different Class I engine families. Passive secondary air-injection systems were used with most of the systems to provide an exhaust feed-gas composition that was slightly rich of stoichiometry when used in conjunction with unmodified “Phase 2” carburetor A/F ratio calibrations. Catalyst sizing, PGM loading, and secondary-air venturi design were selected to limit CO oxidation and the typically resultant high heat rejection at high load operating points while still providing good NOx and HC emission control. Infrared thermal imaging was used to assess heat rejection at the EPA A-cycle operational points and during simulated hot soaks for selected configurations.

A series of paired fuel tests were conducted comparing certification-grade highway diesel fuel with 5 to 50 vol% soy-methyl-ester biodiesel blends. Each fuel pair was tested for up to seven transient cycles representing various load conditions, using a 2006 model year Cummins ISB compression ignition engine equipped with exhaust gas recirculation. Except for the most lightly-loaded cycle, the results show statistically significant differences in NOx emission for all fuel pairs. The average NOx emissions due to biodiesel increased over each cycle, ranging from 0.9 to 6.6% and from 2.2 to 17.2% for the B20/B0 and B50/B0 fuel pairs, respectively. Significant reductions in CO and PM were observed over a majority of the cycles tested. The data also reveal that the change in NOx emissions increases linearly with the average cycle load. To complement the transient results, a single modal point was monitored daily to investigate biodiesel effects on engine operating parameters.