Abstract
Keywords - Alternative Fuels, Heavy-Duty Low Emission Vehicles, Diesel Engines, Exhaust Emissions, Dimethyl Ether
Abstract - The air pollution situation in Japan is serious, particularly in major metropolitan areas, and the main cause is the nitrogen oxides (NOx) and particulate matter (PM) emitted by diesel trucks. For that reason, the Japanese government has repeatedly strengthened its emission regulations for diesel engines.
At the same time, attempts have been made to popularize low-emission vehicles such as CNG trucks, LPG trucks and hybrid trucks. However, these low-emission trucks have poorer fuel economy and shorter cruising ranges in actual traffic including high speed / high load operation than diesel trucks, and these factors interfere with both their widespread acceptance and low-emission trucks development.
Unlike CNG and LPG, DME can be easily ignited by compression and so can be expected to provide fuel consumption as good as diesel, making it suitable for trucks that travel long distances. The properties of this oxygenated fuel allow it to be burned with no smoke and low PM emissions, raising the possibility that NOx emissions could be reduced significantly through high-EGR.
This paper describes the research and development of a medium-duty DME truck in Japan that was being carried out in order to solve these technical problems of CNG trucks, LPG trucks and hybrid trucks. The performance and exhaust emission targets of the DME engine has been demonstrated and the truck has been converted to accommodate the DME engine and the fuel supply system. The developed DME engine showed engine performance almost same as a diesel engine by combustion improvement due to increase of fuel injection pressure mainly. In addition, the DME engine achieved about 4/5 levels of NOx emission regulation value of 2003 by an application of EGR and optimization of injection timing. However, performance improvement of a fuel supply device, development of combustion technology to be suited for DME and more NOx emission reduction are future subjects.
Through the DME truck development, it was shown that development of the fuel system that could supply stable fuel pressure and fuel flow rate was necessary. The engine startability and acceleration performance of the DME truck was inferior in comparison with a diesel truck, and these causes depend on the problem of a fuel system and lack of the engine tuning. In future, these problems must be solved.