Visualization Research and Optimization Strategy for Combustion Process and Emission Characteristics of Internal Exhaust Gas Recirculation Small Non-Road Diesel Engine

Abstract

Based on a small non-road diesel engine, internal exhaust gas recirculation (IEGR) was realized by the exhaust valve re-opening (2EVO). The influences of IEGR on combustion and emission performance were analyzed. The results showed that in-cylinder pressure peak decreased, the start of heat release was delayed by 0.5 oCA and the heat release rate peak was reduced after the introduction of IEGR. Furthermore, the average temperature of combustion flame was reduced, centering between 1900 and 2100 K. That was beneficial to curbed nitrogen oxides (NOX) emissions. The average value for KL factor was obviously increased within the entire range of combustion, which resulting in an increase in soot emission. In terms of emission characteristics, NOX emission was significantly reduced under the original injection timing but soot emission was increased slightly. Subsequently, the start of injection (SOI) were adjusted based on IEGR and two fuel injection control strategies were formulated from the perspective of reducing pollutant emissions and fuel consumption: Strategy 1 keeping BSFC consistent with the original engine, the NOX+HC weighted emission was reduced by 17.6 %; Strategy 2 keeping NOX+HC emissions consistent with the original engine, BSFC and CO were reduced by 10 % and 20 % respectively and Soot emission was slightly increased.