Numerical Study of the Effect of Direct-Injection Timing of Methanol and Excess Air Ratio on the Combustion Characteristics of a Marine Diesel-Methanol Dual-Fuel Engine

Abstract

<div class="section abstract"><div class="htmlview paragraph">Methanol is a suitable alternative fuel to relieve the problem of energy shortage and decrease the emission of greenhouse gases. The effect of direct-injection timing of methanol and diesel on the combustion characteristics of a marine diesel engine with bore of 210 mm was simulated with a 3-dimentional computational fluid dynamic (CFD) software AVL-FIRE. The combustion model was set-up and validated by the experimental data from the marine diesel engine. Results show that there are two peaks on the heat release rate (HRR) curves with the normal diesel-methanol combustion process. The first HRR peak is caused by the combustion of diesel. The second HRR peak is resulted from the hybrid combustion process of diesel and methanol. The injection timing of diesel influences the peak pressure rise rate (PPRR) and ignition timing. The indicated mean effective pressure (IMEP), the maximum in-cylinder pressure and combustion duration are influenced by the direct-injection timing of methanol. With direct-injection of diesel and methanol, the nitrogen oxide (NOx) and soot can be reduced simultaneously. The emission of nitrogen oxide is 70% lower than the original diesel engine when the lambda is higher than 2.0. A suitable range of dwell between direct-injection timing of diesel and methanol and excess air ratio can ensure the output of engine power and make emissions under a low level simultaneously.</div></div>