缸内直喷醇类燃料发动机的燃烧与排放特性

根据所测的示功图和排放,分析了一台采用火花点火、缸内直喷周向分层燃烧系统的发动机在燃用甲醇和乙醇时的性能和燃烧特性。研究表明,醇类燃料发动机的燃烧由预混燃烧与扩散燃烧组成,具有非常快的燃烧速率,而且非常稳定,ATDC(3°CA～6°CA)就燃烧完50%燃料,循环变动小于6%。与燃用乙醇相比,燃用甲醇时滞燃期较短,燃烧速率较快。由于采用分层燃烧,醇类燃料发动机具有与直喷柴油机相当的热效率,在负荷特性上,燃用醇类燃料时的NOx排放仅为柴油机的10%～40%,且能实现无烟燃烧,CO排放的增加低于1%,HC排放高于柴油机。

Study on Combustion and Emissions Characteristics of a Spark-Ignited Direct-Injection Alcohol Engine

Analyzed are combustion and emissions characteristics of an alcohol engine with a new type of spark-ignited direct-injection circularly stratified-charge combustion system. The calculated heat release rate of the alcohol engine shows that the combustion process consists of premixing and diffusion stages and the combustion proceeds very stably and rapidly. Its cycle-to-cycle variation is lower than 6%. 50% of fuel burns out while the crank angle is situated at 3-6 degrees after top dead center. The combustion rate is higher and the ignition delay is shorter for methanol operation than that for ethanol operation. The alcohol engine has the advantages of high thermal efficiency equivalent to that of direct injection diesel engine due to adopting the mixture stratification. NO_x emissions for alcohol engine are only 10%-40% of those of diesel engine at load characteristics. In the alcohol engine, CO emission is lower than 1%, and HC emission is slightly higher than that of diesel engine. Smokeless combustion can be realized for alcohol operation at any operating conditions.