空气污染组分H2O和CO2对乙烯点火特性的影响

Effects of H2O and CO2in vitiated Air on Ignition Characteristic of Ethylene

关键词:  污染效应  点火延时  乙烯  激波管 

Key words:  Vitiation effect  Ignition delay time  Ethylene  Shock tube

摘要:

超燃研究地面实验中通过燃烧加热方式获得的高焓气体中通常含有H₂O和CO₂等污染组分,污染组分可能造成地面实验与天空飞行中燃料的点火特性出现差异。为了正确评估这两种污染组分对碳氢燃料点火特性的影响,在预加热激波管上研究了H₂O和CO₂对乙烯点火特性的影响效应。以压力0.2MPa,化学当量比1和0.5乙烯在纯净气体中点火特性为基础,分别进行了单独加入 7.5%,15%和25%的H₂O,单独加入10%的CO₂,以及同时加入25%H₂O＋10％CO₂条件下,污染组分对乙烯点火特性影响的对比实验研究。结果表明:在贫油条件下(Φ＝0.5),单独污染组分H₂O和CO₂对乙烯的点火基本没有影响；在化学当量比条件下(Φ＝1)时,H₂O和CO₂分别对乙烯的点火具有一定的阻滞作用；当H₂O和CO₂同时存在时,污染组分在较大温度范围内表现出对乙烯点火的阻滞作用。从燃烧反应机理和热物理性质的角度对实验结果进行了初步分析。 

Abstract:

In the ground tests of hypersonic scramjet, the high-enthalpy airstream produced by burning hydrocarbon fuels often contains contaminants H₂O and CO₂. The contaminants may cause the ignition characteristics of the fuel to become discrepant between ground tests and real flights. In order to properly assess the effects of the contaminants on ignition characteristics of hydrocarbon fuels, the effects of H₂O and CO_2on ignition charateristics of ethylene were investigated in a preheated shock tube. Based on the ignition delay time of ethylene in clean gas, comparative experiments with clean and vitiated gases were conducted. At pressure of 0.2MPa, equivalence ratios of 1and 0.5, ignition delay time of ethylene were measured for four cases:(1) clean gas, (2) gas vitiated with 7.5%, 15% and 25% H₂O by mole, (3) gas vitiated with 10% CO_2by mole, and (4) gas vitiated with 25% H₂O and 10% CO_2by mole. The experimental results show that water vapor and carbon dioxide have almost no effects at equivalence ratio of 0.5, but an inhibiting effect appears at equivalence ratio of 1. An obviously inhibiting effect appears over a wide temperature range when water vapor and carbon dioxide exist together. The results were also discussed preliminarily by considering both the combustion reaction mechanism and the thermophysics properties of the test mixtures. 