基于详细化学动力学正丁醇定容燃烧过程的损失

Exergy Losses of n-Butanol Constant Volume Combustion by Simulation with Detailed Chemical Kinetics

利用详细化学动力学在绝热均质定容条件下对正丁醇燃烧过程进行了数值模拟,并通过非平衡态热力学熵平衡方程计算了燃烧过程的损失.结果表明:损失率曲线主要有两个峰值,第1个峰值由正丁醇转变为小分子燃料的反应(阶段1)和H_2O_2,loop及支撑反应(阶段2)构成;第2个峰值由CO、H氧化为最终产物反应(阶段3)构成.提高燃烧初始温度或当量比,反应温度上升,阶段1中高温反应路径取代低温反应路径,使损失降低,阶段2和阶段3中主要反应损失持续时间缩短,使损失降低;然而燃烧温度过高致使离解反应发生,导致不完全燃烧.增加燃烧初始压力或降低氧体积分数都可抑制离解反应,减少不完全燃烧.若使用进气加热、增压、稀燃、提高压缩比和废气再循环等发动机技术,可改变燃烧初始条件,使总损失从30.7%,减少至18.7%,.

Combustion of n-butanol was simulated using detailed chemical kinetics under adiabatic premixed constant volume conditions.The exergy losses during n-butanol combustion were studied by calculating the changes in chemical potentials during all chemical reactions.Results show that the history of overall exergy loss rate has two peaks.The first peak is caused by the reactions of n-butanol decomposition into the small molecules(named as stage1)together with the reactions related to the H_2O_2 loop(named as stage 2).The second peak involves the oxidation reactions of CO,H,and O to CO_2 and H_2O(named as stage 3).Increasing the initial temperature or equivalence ratio rises temperature rapidly.In stage 1,the low temperature reactions with high exergy losses are replaced by high temperature reactions with low exergy losses.In stages 2 and 3,significant shorter duration of exergy loss plays a decisive role,resulting in the reduction of exergy loss to the main exergy loss sources.However,higher initial temperature and equivalence ratio increase the dissociation reaction rates,leading to the increase of incomplete combustion.Increasing initial pressure or decreasing oxygen concentration can inhibit the dissociation and decrease the incomplete combustion.Total losses are decreased from 30.7%, to 18.7%, by the combined effects of combustion initial conditions with advanced engine technologies by preheating and boosting the inlet charge,lean combustion,exhaust gas recirculation,higher compression ratio.