甲烷机理的简化及其在Flame D火焰数值模拟中的应用

Reduction of methane mechanism and its application in the numerical simulation of flame D

为了获得适用于燃烧数值模拟的简化机理,本文进行了甲烷(CH_(4))燃烧机理的系统简化,并将其用于Flame D火焰的数值模拟。基于C_(0)-C_(4)的149s/925r框架机理(s代表物种、r代表反应),本文采用直接关系图法以CH_(4)为燃料、以点火延迟时间为指标进行简化,获得了三个小尺寸的CH_(4)简化机理(42s/273r、26s/151r、21s/88r),点火延迟时间的最大误差均在13%以内。层流火焰速度的模拟结果表明,只有21s/88r机理与实验结果差别较大,最大误差为45.94%。将这三个简化机理用于Flame D火焰数值模拟,结果表明基于42s/273r和26s/151r机理的数值模拟可以成功实现燃烧,而基于21s/88r的燃烧模拟中没有形成明显的高温燃烧区。26s/151r机理的点火延迟的敏感度分析结果表明,过度简化的21s/88r机理中缺少的组分CH_(2)OH、CH_(2)(S)和CH_(2)及相关反应对点火有促进作用。在21s/88r机理中分别添加组分CH_(2)OH、CH_(2)(S)和CH_(2)的相关反应,形成的改进机理21s+CH_(2)OH、21s+CH_(2)(S)和21s+CH_(2)加快了点火延迟时间,提高了层流火焰速度。Flame D火焰模拟结果表明,这些改进的简化机理可以用于燃烧数值模拟,并且对温度和主要物种浓度的预测结果接近实验值。本文以CH_(4)燃烧模拟为例,探讨了适用于燃烧数值模拟的机理简化的准则,对大分子碳氢燃料的机理简化具有一定的指导意义。

In order to obtain a reduced mechanism suitable for numerical simulation of combustion,a systematic reduction and numerical simulation of Flame D for methane(CH_(4))mechanism are carried out.Based on the 149s/925r(‘s’means species,‘r’means reaction)skeletal mechanism of C_(0)-C_(4),three small-scale reduced mechanisms of 42s/273r,26s/151r and 21s/88r are obtained through directed relation graph method with CH_(4) as fuel and ignition delay time as target,whose maximum errors are within 13%. The simulation results of laminar flame speed for the 21s/88r mechanism vary greatly from the experimental results with a maximum error of 45.94%.Using the three reduced mechanisms for numerical simulations of Flame D,the 42s/273r and 26s/151r mechanisms can successfully achieve combustion,while no significant high-temperature combustion zones are formed for the 21s/88r mechanism.The results of the sensitivity analysis of ignition for the 26s/151r mechanism show that the missing species of CH_(2)OH,CH_(2)(S)and CH_(2) in the over-reduced mechanism of 21s/88r promote ignition.With CH_(2)OH,CH_(2)(S)and CH_(2) added to the 21s/88r mechanism respectively,the newly formed mechanisms of 21s+CH_(2)OH,21s+CH_(2)(S)and 21s+CH_(2) accelerate the ignition delay time and improve the simulation results of the laminar flame speed.The simulation results of Flame D show that the improved reduced mechanisms can be used for combustion numerical simulations.The simulation results on temperature and species concentration are very similar to the experimental data.This work shows that there is a boundary during the process of mechanism reduction.Taking the combustion simulation of CH_(4) as an example,this paper discusses the principle of reduced mechanism suitable for combustion numerical simulation,which has certain guiding significance for the mechanism reduction of hydrocarbon fuels.