Effect of EGR on spray development, combustion and emissions in a 1.9L direct-injection diesel engine

摘要

The spray development, combustion and emissions in a 1.9L optical, four-cylinder, direct-injection diesel engine were investigated by means of pressure analysis, high-speed cinematography, the two-color method and exhaust gas analysis for various levels of exhaust gas recirculation (EGR), three EGR temperatures (uncontrolled, hot and cold) and three fuels (diesel, n-heptane and a two-component fuel 7D3N). Engine operating conditions included 1000rpm/idle and 2000rpm/2bar with EGR-rates ranging from 0 to 70%. Independent of rate, EGR was found to have a very small effect on spray angle and spray tip penetration but the auto-ignition sites seemed to increase in size and number at higher EGR-rates with associated reduction in the flame luminosity and flame temperature, by, say, 100K at 50% EGR. The emission tests confirmed that for different intake temperatures and three fuels, increasing the EGR-rate leads to reduced NO{sub}x and O{sub}2 levels but increased soot, CO, CO{sub}2 and HC concentrations. Cold EGR resulted in lower NO{sub}x emissions at EGR-rates below 30% but at higher rates hot EGR seems to offer marginal improvements relative to cold EGR and significant NO{sub}x reduction compared to the uncontrolled EGR case.