碳氢燃料预混火焰中苯的生成规律

Emission of Benzene from Premixed Hydrocarbon Combustion Flame in Constant-Volume Bomb

为了研究碳氢燃料预混火焰中苯的生成规律,首先在定容燃烧弹上进行了实验,对不同工况下,90号汽油和模拟汽油(由异辛烷和正庚烷按9∶1的质量比例配制)燃烧产物中的苯进行了采集和定量分析;随后利用高速摄像机对这两种燃料在定容燃烧弹中的燃烧图像进行了拍摄,将定容燃烧弹中的预混燃烧火焰划分热焰区、蓝焰区和冷焰区;最后,利用CHEMKIN软件对不同火焰结构区域中模拟汽油的燃烧过程进行了化学动力学分析.结果表明,苯在预混火焰中的冷焰、蓝焰区域内形成,并在热焰中完全氧化;苯来源于未完全燃烧的碳氢,其排放量取决于未完全燃烧区中苯的质量分数和未完全燃烧区的容积;汽油燃烧过程中形成的碳粒在一定程度上能减少苯的排放量;汽油机冷起动时,燃烧室壁面吸附作用将对苯的排放量有重要影响.

To study the emission characteristics of benzene in premixed hydrocarbon combustion flames, an experi- ment was carried out on a constant-volume bomb under different experimental conditions. Benzene in exhaust gas was collected and quantified. Photographs of the combustion process of hydrocarbon in bomb were taken by a high speed camera. The space in bomb was divided into complete combustion zone, incomplete combustion zone and unburned zone based on the definition of different flame stages （hot flame stage, blue flame stage and cool flame stage）. After that, a numerical simulation of the chemical kinetics of quasi-gasoline which is composed of iso-octane and n- heptane in a mass ratio of 9 ： 1 was carried out by CHEMKIN under different thermal boundary conditions. Results indicate that benzene forms in cool flame and blue flame and is oxidized in hot flame. The amount of benzene in ex- haust gas is determined by the mass of benzene in the incomplete combustion zone, i. e. the concentration of benzene in incomplete combustion zone and the volume of incomplete combustion zone. Soot generated in combustion can reduce benzene formation to a certain extent. The absorption effect of cylinder wall to air-fuel mixture may result in higher benzene emission in engine cold start condition.