基于HCCI发动机着火特性的柴油三组分表征燃料详细化学动力学模型

Detailed Kinetic Modeling on a New Three-Component Diesel Surrogate

构建了一个由正庚烷、甲苯和环己烷组成,并加入正庚烷与甲苯的交叉反应,三组分柴油表征燃料的详细化学动力学机理模型,包含1 171种物质、4 580个基元反应.基于着火时刻对于均质充量压燃(HCCI)燃烧的重要性,以着火点为主要衡量标准,采用单区燃烧模型,以不同比例的三组分表征燃料详细化学反应动力学机理模拟HCCI燃烧的燃烧始点,根据HCCI发动机试验数据,确定了三组分机理的最佳组分质量比为8∶1∶1(正庚烷∶甲苯∶环己烷).还对单组分(正庚烷)、最佳比例的双组分(正庚烷、甲苯)和最佳比例的三组分机理进行了比较验证,对3种机理模拟得到的着火滞燃期和放热率的结果进行对比,详细分析了环己烷对表征燃料滞燃期的调整作用,以及交叉反应的加入对表征燃料的影响.结果表明:新的柴油三组分详细机理可以更为准确地描述柴油HCCI着火时刻.

A detailed chemical kinetics model for three-component diesel surrogate fuel was proposed,which consists of 1 171 species and 4 580 reactions,and includes the mechanisms of n-heptane,toluene,cyclohexane and cross-reaction mechanism between n-heptane and toluene. Main reaction paths of the three components and the cross-reaction were discussed in the validation of the surrogate fuel. Ignition timing is used as the judgment to select the best component ratio,as it is the most important factor for HCCI combustion. Ignition delays were simulated for the surrogate fuel with different component ratios by a single-zone combustion model. By comparison of the simulated data with the experiments data,the best mass ratio of 8∶1∶1 for heptane∶toluene∶cyclohexane was determined for the three-component diesel surrogate fuel. Comparing with two-component and single component surrogate fuel model on the apparent heat release and ignition delay,the three components model gives well prediction to the experimental data. Further analysis on the effect of cyclohexane and cross reactions indicates that cyclohexane can change the ignition delay of the surrogate fuel,and the effect of adding cross reactions on the characterized fuel. The three-component model can accurately describe the ignition timing of HCCI combustion.