轻型直喷柴油机燃用二甲醚性能和燃烧特性研究

Performances and Combustion Characteristics of Dimethyl Ether Fueled Light Duty Direct Injection Diesel Engine

研究了柱塞直径、喷嘴形式、供油提前角、喷嘴伸入汽缸长度、喷油压力、进气涡流比等燃烧系统主要参数对发动机性能的影响，测录了示功图和喷油器针阀升程以及污染物排放，计算了发动机的燃烧特性，并与发动机燃用柴油时进行了对比．发动机性能研究表明：与柴油相比，二甲醚能够提高发动机的热效率，降低ＮＯｘ 排放，实现无烟燃烧．燃烧特性分析结果表明：二甲醚的喷油延迟角大于柴油的喷油延迟角；二甲醚的滞燃期比柴油短，预混燃烧量少，扩散燃烧速度比柴油快．

This paper is concerned with an experimental study of a light duty direct injection diesel engine operating on dimethyl ether (DME). Investigatigated are the effects of plunger diameter, nozzle type, fuel delivery advance angle, vertical distance of nozzle tip into cylinder, injection pressure and swirl ratio on performances and emissions of DME engine. The indicator diagrams and needle valve lifts are recorded. The combustion and emission characteristics are evaluated and compared with those for an engine operating on diesel fuel. The results show that the thermal efficiency improves for larger diameter injection plunger and total orifice flow area injector. The average thermal efficiency of DME engine is about 2%～3% higher than that of diesel engine. The former can reduce NO x emission significantly and achieve smokeless combustion. Combustion characteristics include injection and ignition delays, the rate of pressure rise and the maximum cylinder pressure and the heat release for DME engine are compared with diesel engine. The experimental and calculating results show that the injection delay (in crank angle) is longer because of the lower acoustic velocity in liquid DME. The ignition delay is much shorter and the peak pressure is far lower due to less premixing combustion. Morever, the diffusion combustion of DME operation is much faster and this leads to the reduction of smoke, PM, hydrocarbon and monoxide emissions. The study demonstrates that DME is an excellent alternative fuel for compression ignition engine.