Feasibility study of novel DME fuel injection equipment: Part 2- performance, combustion, regulated and unregulated emissions

Abstract

Dimethyl Ether (DME) has emerged as a suitable alternative fuel for compression ignition (CI) engines. It is expected to be substitute fossil diesel on a large scale due to its favourable combustion characteristics and sustainable production. This study evaluates the combustion and emission characteristics of a 3-cylinder, water-cooled CI engine fuelled by DME for off-road vehicles, typically used in the agriculture sector. A detailed-chemistry based 3D CFD software is used for simulations in this study. The findings indicate that the baseline diesel fuel injection equipment (FIE), when used for DME injection, is inadequate to match the reference diesel engine performance. Therefore several modified configurations are evaluated in this study using a simulation approach. Modified fuel injection equipment (FIE) significantly reduced the emissions of NOx, soot, UHC, CO and VOC without compromising the base engine power generation. Due to the lower ignition delay of DME, the observed start of ignition advanced. It led to a lower peak firing temperature than its diesel counterpart. The lower cooling loss ratio of the DME engine established its potential as a low-heat-rejection engine. The lower calorific value of DME leads to a 50% increase in the specific fuel consumption than diesel. However, these two fuels seem to be similar on a specific energy consumption basis. A comprehensive study of the un-regulated emission species such as formaldehyde (CH2O), hydrogen peroxide (H2O2), methane (CH4), ethylene (C2H4), and acetylene (C2H2) indicate that DME combustion results in lower unregulated emissions than baseline diesel. A higher number of nozzle holes and an increased mean effective injection pressure (MEIP) of the FIE generate a conducive environment exhibiting superior engine performance and reduced emissions. However, the study identifies a few aberrations in the operating conditions, which show deteriorated emission trends, which should be avoided during the physical engine testing on DME. This study showcases the tremendous potential of an oxygenated fuel such as DME to facilitate the emergence of thermally efficient and cleaner engines, with very low regulated and unregulated emissions, indicating their future for off-highway vehicles.