Combined Effects of Cooled EGR and Air Dilution on Butanol-Gasoline TGDI Engine Operation, Efficiency, Gaseous, and PM Emissions

Biobutanol is a promising alternative fuel for spark-ignition engines. Exhaust gas recirculation (EGR) and air dilution were evaluated on a TGDI engine fueled with butanol-gasoline (B20) in view of engine operation, efficiency, gaseous emissions, and PM emissions. For the B20 engine, EGR affected combustion more strongly than excess air dilution; the brake thermal efficiency (BTE) under excess air dilution was much higher than that with EGR. The oxygen concentration in the cylinder was also markedly reduced with EGR relative to air dilution, as the partial fresh charge was substituted with nonreactive gas. A reduced oxygen concentration contributed to differences in combustion between excess air dilution and EGR. Higher BTE was observed during combined EGR and excess air dilution operation, though it was slightly lower than that under excess air dilution alone. NOx was also markedly reduced by the combination of EGR and excess air dilution, but was slightly higher than that with EGR alone. Under combined dilution conditions, the particle number (PN) emissions from the B20 engine were reduced significantly, particle sizes decreased, and the nucleate PN significantly decreased.