Combustion and emissions behaviors of a stoichiometric GDI engine with simulated EGR (CO_2) at low load and different spark timings

摘要

Exhaust gas recirculation (EGR) is one of the most effective measure to control NOX emissions in the engines. CO2 was introduced to intake as simulated EGR (CO2), the combustion and emissions behaviors of a stoichiometric GDI engine with simulated EGR (CO2) at engine speed of 1500 rpm, engine load of 25% and different spark timings were studied experimentally. Experimental results show that EGR and retarded spark timing would slow the combustion. At the same EGR rate, the effect of actual EGR on combustion parameters is much greater than that of simulated EGR (CO2). A large amount of inert gas in EGR will greatly aggravate combustion, leading to increase COVimep. The order of COVimep is actual EGR rate = 15% ? simulated EGR (CO2) rate = 15% EGR rate = 0%. Spark timing has little effect on BSCO and BSHC for with/without EGR at low load. At any constant spark timing, BSCO actural EGR rate = 15% ? BSCO simulated EGR (CO2) rate = 15% BSCO EGR rate = 0%. BSNOX and soot emissions decrease significantly with retarding spark timing for with/without EGR. BSNOX and soot emissions show same tendencies with retarding spark timing and increasing EGR rate. BSNOX emissions is actual EGR simulated EGR (CO2) ?retarded spark timing. At a constant spark timing, soot actual EGR rate = 15% soot simulated EGR (CO2) rate = 15% soot EGR rate = 0%. EGR reduces reaction rate of soot formation and rises the oxidation rate of soot.