Fuel Composition Effects on Emissions From a Spark-Ignited Engine Operated on Simulated Biogases

Measurements are reported for a spark-ignited (SI) engine burning natural gas and three simulated biogas fuels (natural gas, CO2, and N2 mixtures). Exhaust concentrations of CO, CO2,O2,NOx, and unburned hydrocarbons, as well as brake power and brake specific energy consumption, were measured. Leaner mixtures, retarded spark timing and diluent addition CO2,N2 yielded reduced NOx emissions. NOx reductions up to 50 percent were achieved at MBT timing through diluent addition. Reduced peak temperatures caused by diluent addition, lean conditions, and retarded spark timing reduced combustion quality slightly, as evidenced by small increases in CO and unburned hydrocarbons emissions.