Close to stoichiometric partially premixed combustion -the benefit of ethanol in comparison to conventional fuels

Partially Premixed Combustion, PPC, with 50% Exhaust Gas Recirculation (EGR) at lean combustion conditions =1.5, has shown good efficiency and low emissions in a heavy duty single cylinder engine. To meet emission requirements in all loads and transient operation, aftertreatment devices are likely needed. Reducing to unity, when a three-way catalyst can be applied, extremely low emissions possibility exists for stoichiometric PPC. In this study, the possibility to operate clean PPC from lean condition to stoichiometric equivalence ratio with reasonable efficiency and non-excessive soot emission was investigated. Two EGR rates, 48% and 38% with two fuel rates were determined for 99.5 vol% ethanol in comparison with one gasoline fuel and Swedish diesel fuel (MK1). Engine was operated at 1250 rpm and 1600 bar injection pressure with single injection. Results revealed that efficiency was reduced and soot emission increased from lean PPC to stoichiometric PPC operation. Significant increase in soot emission and pronounced efficiency reduction makes stoichiometric diesel PPC impossible. Gasoline PPC showed the same trends but with less efficiency reduction as well as less soot emission. In contrast, ethanol PPC had the advantage with very low soot emission (below 0.1 Filter Smoke Number) and higher efficiency in close to stoichiometric operation. This implies that ethanol can be a viable alternative fuel to produce clean stoichiometric PPC associated with three-way catalyst.