Effects of EGR on Rapid Lean-burning and NOX emission of Spark Ignition LPG Engine

Exhaust Gas Recirculation (EGR) is an extensively applied approach for the engine emission control, which is the most effective for reducing NO_X emissions. However, as increasing EGR rate, the burning velocity of LPG mixture will be slow that it impacts the complete combustion and combustion stability. The effects of EGR on the rapid lean-burning and NO_X emissions of the LPG engine with EFI is introduced in this paper. Test data showed that the dual-spark plug ignition-based rapid burning system could increase the combustion rate of LPG mixture, and improve the rapid burning process of the LPG engine with EGR. Meanwhile, the excess air rate Φa limits of LPG lean-burning will be largely extended within the whole effective range of EGR rate. At the equivalent running conditions of LPG engine, largely extended EGR rate could restrain the formation of NO_X emissions by the high combustion temperature. As a result, due to the increases in burning velocity and heat efficiency, the LPG engine could realize the Φa limits in lean-burning process with a higher EGR rate. The highest R_EGR in the rapid burning process increased from 5% of the normal combustion process to 8.11%. Additionally, Coefficient of Variation (CoV) in the LPG combustion process was under control effectively.