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Homogeneous charge compression ignition (HCCI) is a new combustion concept, which achieves high thermal efficiency and ultra-low emissions. In order to realize the HCCI combustion, a homogenous mixture preparation plays an important role in the HCCI engine concept. However, there are some problems for conventional diesel fuel to achieve a uniform mixture distribution in the cylinder because of its high viscosity and low volatility. This paper describes the effects of the DME addition on the spray behavior and atomization characteristics of diesel fuel. Pure diesel fuel, pure DME fuel and DME/diesel blended fuels with DME mass fraction of 25% and 50% were used to evaluate the effects of the DME concentration on the macroscopic and microscopic structure of the steady spray.

An investigation has been carried out to evaluate the combustion and emission characteristics of dimethyl ether(DME) using a small direct-injection diesel engine. The fraction of the fuel leakage from the fuel pump plunger pinion to the supplied fuel is determined by the fuel injection experiment under engine motored conditions. The effects of engine configuration and operation parameters on engine performance, regulated and unregulated exhaust emissions are investigated. The unregulated pollutants of formaldehyde, methyl formate and formic acid from a DME fueled engine are measured by gas chromatography and FT-IR analyzers. The test results show that the performance and regulated exhaust emission characteristics of DME are superior when compared to the original diesel engine. The formaldehyde is the principal component of unregulated pollutants. The behaviors of formaldehyde, methyl formate and formic acid emissions to engine design parameters and operation conditions are clarified.