Effect of EGR, injection pressure and swirl ratio on engine-out emissions for a HSDI diesel engine at low load and medium speed condition

Combustion and emission formation in LTC regimes using high EGR ratios differs greatly from conventional diesel combustion. Also small bore diesel engines are characterized by their complex spray-wall interactions, influenced by high injection pressures and swirl ratios. Hence the three parameters of EGR, Pinj and SR are chosen for this study. In earlier work done on this engine, EGR ratios up to 50%, Pinj up to 1300 bar and SR up to 3.5 Rs were studied.; Recent studies have shown very high EGR ratios could actually reduce smoke [18]. Swirl ratios up to 3.5 Rs have shown to promote late cycle combustion and reduce soot. Effect of swirl ratios above 3.5 Rs on soot and fuel consumption needed to be investigated. The higher health risk and increased formation of nano particles with current injection technologies is prompting a lot of interest in the size distribution analysis of exhaust soot. All of the above prompted a revisit of the earlier work. In this study, 3bar IMEP, 1500 rpm and LPPC 5° aTDC are chosen to represent the low load and medium speed operating condition. EGR ratios up to mis-firing limit (64%) and swirl ratios up to 7.12 Rs are studied. Particle size distribution at these conditions is also studied using SMPS.; Following observations are made. EGR is found to reduce NOx even up to 64% EGR. At EGR ratios above ∼58%, combustion temperatures are lowered beyond soot formation region and result in decrease in smoke and soot, but are accompanied by an increase in fuel consumption. Fuel consumption increases with EGR, but at an escalating rate after ∼54%. Pinj does not affect NOx emissions at EGR ratios studied (above 48% EGR). Soot is reduced with increasing Pinj, but with diminishing returns beyond 1000 bar. Pinj does not affect fuel consumption significantly, but the fuel pump would add to engine power losses. Increased fuel impingement on piston walls with increasing Pinj is evident from HC and CO emission imprint. SR increases NOx emissions at low EGR ratios (< 30%). At high EGR ratios (above 48%) and high Pinj (1000 bar and above), increase in SR decreases NO x emissions, due to effects of heat losses overshadowing increase in fuel-air mixing with SR. Increasing SR decreases soot, but with diminishing returns beyond 3.77 Rs. SR increases fuel consumption due to higher heat losses to combustion chamber walls. HC and CO emission trends suggest, SR helps in evaporating fuel deposited on combustion chamber walls. Incidence of nano particles greatly increased at injection pressures and swirl ratios above 1000 bar and 3.77 Rs respectively. 58% EGR showed the least tendency to form nano particles, but it could not be confirmed if this was due to EGR or fuel change.; The low concentration of nano particles noticed at 58% EGR needs to be confirmed whether caused due to EGR of fuel change. Nano particle formation at these same injection pressures and swirl ratios at higher loads needs to be investigated. Nano particle formation under dilution conditions more representative of actual exhaust dilution with ambient air needs to be studied.