1995-10-01

Effect of EGR on Spray Development, Combustion and Emissions in a 1.9L Direct-Injection Diesel Engine 952356

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-colour 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 1000 rpm/idle and 2000 rpm/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 NOx and O2 levels but increased soot, CO, CO2, and HC concentrations. Cold EGR resulted in lower NOx emissions at EGR-rates below 30% but at higher rates hot EGR seems to offer marginal improvements relative to cold EGR and significant NOx reduction compared to the uncontrolled EGR case.

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