直喷天然气发动机燃烧效率分析

利用快速压缩装置对直喷天然气发动机的效率进行了分析。在宽广的当量比范围内，分析了三种燃料喷射方式下和均匀混合气燃烧时的燃烧效率。结果表明，燃油喷射方式下的燃烧效率在0．2－0．9当量比范围内均具有较高的数值并与喷射方式无关；在当量比小于0．2和大于0．9时，由于CO的原因，使燃烧效率降低。均匀混合气燃烧时，燃烧效率在当量比大于0．7时较高，而当量比小于0．7时，由于很高的未燃甲烷的生成使燃烧效率损失较大。燃料喷射燃烧与均匀混合气燃烧相比，维持高燃烧的比范围宽。因未燃甲烷的生成造成的燃烧效率的损失与喷油时刻无关，因CO造成的燃烧效率的损失随喷油滞后而增加。

Analysis of Combustion Efficiency in Direct Injection Natural Gas Engine

Investigation of combustion efficiency of direct injection natural gas engine is carried out using a rapid compression machine. Combustion efficiency of three types of injection modes and homogeneous mixture combustion are analyzed over the wide range of equivalence ratio. The results show that in the case of fuel injection modes,high combustion efficiency is observed when the equivalence ratio is in the range from 0.2 to 0.9 regardless of fuel injection modes.Obvious loss of combustion efficiency occurs when φ＜0.2 and φ＞0.9.For homogeneous mixture combustion,high combustion efficiency is found when φ＞0.7 and large reduction of combustion efficiency occurs when φ＜0.7 due to the higher unburned methane caused by bulk quenching. Fuel injection maintains high combustion efficiency over the wide range of equivalence ratio compared with that of homogeneous mixture combustion.The study also shows that little influence of unburned methane on the loss of combustion efficiency is observed with fuel injection timing but the reduction of combustion efficiency is found in the case of late injection timing.