Controlling combustion and exhaust emissions in a direct-injection diesel engine dual-fueled with natural gas

摘要

An experimental study was conducted to determine combustion and exhaust emissions characteristics in an automotive direct-injection diesel engine dual-fueled with natural gas with the objective of improving exhaust emissions and thermal efficiency. Dual-fuel operation can yield a high thermal efficiency almost comparable to the diesel operation and very low smoke at higher loads. However, NO{sub}x cannot be reduced by dual-fueling. On the other hand, at lower loads, a dual-fueled engine inevitably suffers from lower thermal efficiency and higher unburned fuel. To resolve these problems, the effects of exhaust gas recirculation (EGR) were investigated. The results show that in a dual-fuel operation, hot EGR can improve thermal efficiency and reduce unburned fuel emission at lower loads while cooled EGR can considerably reduce NO{sub}x at higher loads. A Pt oxidation catalyst can be used for additional reduction in unburned fuel emitted due to dual-fueling.