Fuel composition effects on emissions from a spark-ignited engine operatedon simulated biogases

Measurements are reported for a spark-ignited (SI) engine burning natural g as and three simulated biogas fuels (natural gas, CO2, and N-2 mixtures). E xhaust concentrations of CO, CO2, O-2,O- 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,N-2) yield ed reduced NOx emissions. NOx reductions lip to 50 percent were achieved at MBT timing through diluent addition. Reduced peak temperatures caused by d iluent addition, lean conditions, and retarded spark timing reduced combust ion quality slightly, as evidenced by small increases in CO and unburned hy drocarbons emissions.