高压下燃料低温化学对湍流燃烧影响的机理研究

To achieve high engine efficiency and low emissions, the combustion technologies such as pressure gain combustion, ultra lean, flameless combustion et. al. are often adopted in engine combustors. However, at these near-limit conditions, the role of low temperature fuel chemistry on turbulent combustion becomes more important. Moreover, the low temperature fuel chemistry is closely related to flashback, local flame extinction and re-ignition, combustion instabilities and knock formation. In this study, considering the detailed chemistry and molecular transport, we use the high order direct numerical simulation and large eddy simulation coupled with CHEMKIN and TRANSPORT subroutines. To reduce the computational expense notably, we will develop the efficient parallel multi-time scale and dynamic adaptive chemistry modeling. Based on the above methods, in this study we will focus on the following issues, such as the interaction between low temperature ignition front and pressure wave, and the mechanism of the turbulent flame oscillation driven by low temperature chemistry, as well as the influence of low temperature fuel chemistry on the modes of turbulent combustion for the stratified engine conditions. The aim of this study is to reveal the mechanism of the interaction between turbulence and combustion with the influence of low temperature fuel chemistry, and the effects of low temperature chemistry on combustion instabilities and the transition between the modes of turbulent combustion at near-limit condition. The results of this study will enrich the theory of turbulent combustion in engines, and establish the theoretical base for developing the engines with higher efficiency, more reliability and lower emissions.

为实现高效、低污染燃烧，发动机燃烧室常采用增压、极贫预混燃烧、无焰燃烧等技术。而在这些近极限条件下，燃料低温化学对发动机内湍流燃烧的影响愈加显著，并和发动机中回火、熄火及再燃、燃烧不稳定性以及爆震的形成紧密相关。本课题将采用高精度直接数值模拟及大涡模拟，耦合CHEMKIN及TRANSPORT软件包考虑详细化学及分子输运。为了大幅度减少计算量，本课题将开发高效并行的多时间尺度动态自适应模型简化方法。基于上述方法，课题将对高压下湍流场中低温点火锋面和压力波的相互作用、低温化学驱动的湍流火焰振荡机制，及燃料低温化学对燃料/热分层下的湍流燃烧模式影响的机制等关键科学问题进行研究。以期揭示发动机内燃料低温化学影响下湍流和燃烧的相互作用机制，以及高压、极贫燃等进极限条件下，低温化学对燃烧不稳定性，和对湍流火焰燃烧模式转变的影响机制。研究结果将丰富发动机内湍流燃烧理论，同时为开发先进发动机奠定理论基础。

项目开展了燃料低温化学对湍流燃烧影响的机理研究。基于并行的模型简化方法，项目研究建立了综合的火焰数值诊断方法，在DNS 及 LES 中将模型简化方法及火焰诊断方法的应用和调试，有效地提高了湍流燃烧数值模拟的计算效率，实现了采用详细化学反应机理对实验室级湍流射流火焰的准确模拟。研究开展了低温化学动力学驱动火焰振荡机理研究，通过二甲醚低温反应特性的数值研究发现，存在低温反应的混合气火焰其扰动增长率明显变大，揭示了低温化学影响下，火焰水力学和胞状不稳定性的作用规律。通过低温化学反应对预混火焰热声振荡的影响研究，发现低温化学反应对低频扰动的发展具有明显作用，在这一频段内，低温化学反应速率增加，火焰传递函数的幅值快速上升、幅角显著下降。当火焰锋面处压力-速度脉动的相位差处于一定范围时，低温化学反应速率的变化会导致系统声学稳定性发生转捩，进而引发或抑制热声振荡。低温化学反应显著改变预混火焰的结构和传播规律，对预混燃烧室的多方面工作性能产生影响，研究结果对于燃烧不稳定性基础理论发展以及燃烧室的开发设计指导具有重大意义。