Approaches to extremely low emissions and efficient diesel combustion with oxygenated fuels

Abstract

Significant improvements in smoke, particulate matter, NOx, THC, engine output and thermal efficiency were simultaneously achieved with highly oxygenated liquid fuels. Engine noise was also remarkably reduced for oxygenates with higher ignitability. The improvements in exhaust emissions and thermal efficiency depended almost entirely on the oxygen content in the fuels regardless of the oxygenate-diesel fuel blending ratio or type of oxygenate. Smoke emission decreased sharply and linearly with an increase in oxygen content and disappeared entirely at an oxygen content above 38 wt %, even at stoichiometric conditions. Smoke-free, low NOx diesel combustion with oxygenated fuels was achieved at stoichiometric conditions with the adoption of very high exhaust gas recirculation (EGR). NOx, THC and CO emissions were almost completely removed with a combination of high EGR and a three-way catalyst over a wide range of brake mean effective pressure (b.m.e.p.). The maximum b.m.e.p. with the highly oxygenated fuels was significantly higher than that with the conventional diesel fuel because b.m.e.p. was released from the smoke limits.