To achieve high methanol substitution ratio and clean combustion on a diesel/methanol dual fuel engine: A comparison of diesel methanol compound combustion (DMCC) and direct dual fuel stratification (DDFS) strategies

Abstract

Diesel methanol compound combustion (DMCC) suffers from poor fuel economy at low load and knock at high load. A direct dual fuel stratification (DDFS) strategy in which diesel is injected before the top dead center (TDC) and methanol is directly injected after the auto-ignition of diesel has been proposed and investigated in previous research. In this study, a three-dimensional simulation model coupled chemical reaction kinetic mechanism is used to investigate and compare the DMCC and DDFS strategies. In the former strategy, the ratio of methanol energy to total fuel energy (Rm) is limited by inefficient combustion at low load, and although fuel economy can be improved by advancing diesel injection and increasing initial temperature, Rm still cannot exceed 30%. Moreover, Rm is limited by knock at high load; however, knock intensity can be suppressed by delaying diesel injection and increasing exhaust gas recirculation (EGR) rate, allowing Rm to reach values as high as 50%. In contrast, the latter strategy can yield Rm values as large as 90%, stable combustion, good fuel economy, and low emissions without intake air heating and EGR. In short, the DDFS strategy is a promising way of applying methanol to diesel engines.