Improvement in Premixed Diesel Combustion with Intake Port Injection of Methanol(Thermal Engineering)

Abstract

This study discusses exhaust gas emissions and engine performance in premixed diesel combustion with a sufficient premixing period where low temperature oxidation is inhibited with methanol. Diesel fuel was directly injected at around 40℃A BTDC and methanol was introduced with intake port injection. While the inhibitor effect of methanol on low temperature oxidation retards the heat release and suppresses the rapid combustion, the inhibitor effect decreased when reducing uniformity of the premixed diesel fuel. As a result, the ignition timing can be retarded more with earlier injection timings and smaller quantities of diesel fuel. The operating range is limited by both misfiring and knocking, and an optimum quantity of methanol can prevent knocking while excessive methanol results in misfiring. When the injection timing of diesel fuel was set at 40℃A BTDC, without EGR and methanol, the operating range is limited below 0.25MPa BMEP due to knocking, but a combination of methanol port injection and EGR can achieve 0.55MPa BMEP. While ordinary diesel combustion maintaining low NO_x with EGR cannot prevent smoke emissions when BMEP exceeds 0.4MPa, the combination of methanol and EGR can establish ultra low NO_x and smokeless operation with high thermal efficiency even at 0.5MPa BMEP. The THC and CO increased with methanol introduction, but CO could be efficiently removed with an oxidation catalyst. The THC is also reduced with the oxidation catalyst, but remains at around 800ppm.