Multiple combustion modes existing in the engine operating in diesel methanol dual fuel

Abstract

Four typical combustion modes were found in a diesel methanol dual fuel (DMDF) engine, which subverted the traditional viewpoint that the methanol was only ignited by diesel fuel spray. In this manuscript, the results of different combustion modes from constant volume combustion chamber (CVCC), compression ignition (CI) engine and numerical simulations were presented. In DMDF mode 1, diesel and methanol mixture were ignited simultaneously by compression. The role of diesel was the cetane number improver of methanol. In DMDF mode 2, part of diesel formed the mixture of theoretical equivalent ratio and was firstly ignited. Therefore, the role of the firstly ignited diesel in the combustion process was to ignite methanol. In DMDF mode 3, premixed methanol was auto-ignited before diesel injection, which resulted in two obvious heat release rate (HRR) peaks of methanol combustion and diesel combustion in the cylinder. In DMDF mode 4, the combustion process was slow. Therefore, the duration of combustion increased and a large amount of methanol remained unoxidized at the end of the combustion. The role of diesel in this mode was pilot ignition. The thermal efficiency of the first and second combustion modes was higher among the four combustion modes, and the first one was the highest. The results obtained will provide more clean and high thermal efficient combustion mode for dual fuel engines.