Abstract
Abstract
Among a lot of benefits of Dimethyl Ether (DME) as an alternative fuel, the combustion characteristic for diesel engines, are high cetane number and no soot combustion. The high cetane number of DME enables to operate the low compression ratio engines produced for spark ignition engines designed for a direct gasoline injection. And no soot combustion enables to operate engines at high rate of exhaust gas re-circulation (EGR). Therefore, the DME engines can operate with the stoichiometric working gas combustion (SC) at relatively low compression ratio (LCR). The NOx concentration from low compression ratio stoichiometric combustion (LCR-SC) DME engine is very low as the same level of homogeneous charge compression ignition (HCCI) engines. Naturally, the three-way-catalyst system for S.I. engines can apply to this LCR-SC DME engines. This concept can overcome the weak point of HCCI engines, namely how to extend the operating regions to the high load. The weak point of LCR-SC DME engine is an unstable combustion at very low load because of the increased high EGR rate such as 8-0%. Therefore, the combination of HCCI (PCI-Premixed Compression Ignition Combustion in narrow sense) combustion at low load and the SC at middle and high load can solve the problem of HCCI engines. Furthermore, the engine based on this concept can apply to the engines for not only the heavy duty but also light duty automobiles. Then, DME and this combustion concept can overcome the increasing the demand of crude oil and becoming the tight exhaust gas regulation in the future.