正十二烷高温机理简化及验证

由于详细化学反应机理在模拟燃烧室燃烧时,计算量极大,很难被广泛运用。为了满足工程设计要求,采用替代燃料的简化机理进行计算不失为一种行之有效的方法。本文基于误差传播的直接关系图法和敏感性分析法对正十二烷180组分1962步高温机理(温度大于1100 K)进行简化,获得40组分234步化学反应机理。在温度为1100–1650 K,压力为0.1–4 MPa条件下,采用简化机理及详细机理对不同当量比、压力下着火延迟时间进行模拟,模拟结果与实验数据吻合得较好。通过对不同压力及温度下火焰传播速度进行模拟,验证了简化机理能够正确地反映正十二烷的燃烧特性。利用C_(12)H_(26)/OH/H_2O/CO_2等重要组分随时间变化的数据,验证了简化机理能够准确描述燃烧过程反应物消耗、基团变化、生成物产生的过程,并表明该机理具有较高的模拟精度。利用该简化机理对本生灯进行数值分析,结果表明该机理能够准确地反映火焰区温度和组分浓度的变化。紧凑的正十二烷高温简化机理不仅能够正确体现其物理化学特性,而且能够用于三维数值模拟,具有较高的工程运用价值和应用前景。

Mechanism Reduction and Verification for the High-Temperature Combustion of n-Dodecane

When simulating combustion in a combustion chamber, the associated chemical reaction mechanism is extremely complex and computationally intensive, complicating its widespread use. To meet the requirements of engineering design, simulation is an effective method to determine the combustion mechanism of surrogate fuel. Based on the directed relation graph with error propagation and sensitivity analysis, 40 species and 234 reactions were involved in the mechanism obtained by high-temperature (> 1100 K) simulation with 180 species and 1962 reactions of n-dodecane. Simplified and detailed mechanisms were used to simulate ignition delay times for different equivalence ratios and pressures. At the same pressure and equivalence ratio, the ignition delay times decreased with increasing temperature. At different equivalence ratios, the simulation results agreed with the experimental data, especially at high temperatures. At constant temperature and equivalence ratio, the ignition delay times decreased with increasing pressure, and the simulation results accurately reflect this trend. Because the mechanism was simplified for the high temperature conditions, the calculated data for ignition delay times of the simplified mechanism have a larger error at low temperatures, with a maximum of 23.86%, compared to the detailed mechanism. Between 1100 and 1250 K, the average error was 8.89%. The flame propagation speed at different initial pressures and temperatures was simulated using the simplified and detailed mechanisms. As the initial pressure increased, the flame propagation speed continuously decreased, while the propagation speed increased. These simulation results are in good agreement with the experimental results, verifying that the simplified mechanism can accurately reflect the combustion characteristics of n-dodecane. Using the concentration data of C₁₂H₂₆/OH/H₂O/CO₂ and other important species over time, it was revealed that the simplified mechanism can accurately describe the reactant consumption, radical changes, and product generation during the combustion process. The temperature has a significant influence on the pyrolysis of C₁₂H₂₆. At 1390 K, C₁₂H₂₆ is almost completely consumed within 0.1 ms. At different temperatures, two peaks were observed in the OH radical concentration. The detailed and simplified mechanisms can reflect the variation characteristics of the OH radical concentration and the maximum value of the peaks. Both the simplified and detailed mechanisms accurately reflect the characteristics of H₂O and CO₂ concentration that initially slowly increased and then were generated rapidly. Using the simplified mechanism, a numerical analysis of the Bunsen burner was performed. The simulation results accurately reflected the changes of the temperature and species of the flame in the axial and radial directions and reproduced the combustion process of the Bunsen burner flame. Simulation results of Bunsen burner showed that this mechanism can be applied to numerical calculations and produced good simulation results. Comprehensively, the simplified high-temperature mechanism of n-dodecane correctly reflects the physical and chemical properties and can be used for 3D numerical simulation, which has good engineering and application prospects.