Turbulent Diffusion Flames Far from Chemical Equilibrium

这项工作开发、测试并使用了一种湍流燃烧模型，该模型可以解释远非平衡效应，包括局部灭绝。 这项工作的起点是速度和成分的联合概率密度函数 (pdf) 的建模输运方程。 在之前的工作中，该方程已通过蒙特卡罗方法求解，以计算近平衡湍流扩散火焰的属性。 为了能够解释远离平衡的效应，这种 pdf 方法在两个方面进行了扩展。 首先，将开发、测试和合并一个改进的混合模型，该模型考虑了反应对混合的影响。 其次，将纳入甲烷/空气燃烧的四步方案。 柴油发动机燃烧和燃气轮机燃烧室中的一些重要现象与远离平衡效应有关。 例如点火、熄火、重新点燃以及大量二氧化碳和未燃烧碳氢化合物的排放。 尽管这项研究专门针对湍流火焰，但成功将对跨越广泛的湍流流体力学的相关问题产生影响。 改进的湍流模型反过来会对推进系统（内燃机、火箭和涡轮机）、酸雨（物种的形成及其随后在整个环境中的扩散）、有毒废物的处理、半导体和超导体制造技术以及医学科学产生影响，仅举几例。

This work develops, tests, and uses a turbulent combustion model that accounts for far-from-equilibrium effects, including local extinction. The starting point of the work is the modelled transport equation for the joint probability density function (pdf) of velocity and compositions. In previous work this equation has been solved by a Monte Carlo method to calculate the properties of a near-equilibrium turbulent diffusion flame. In order to be able to account for far-from-equilibrium effects, this pdf approach is extended in two respects. First, an improved mixing model, that accounts for the effects of reactions on mixing, will be developed, tested, and incorporated. Second, a four-step scheme for methane/air combustion will be incorporated. Some important phenomena in diesel-engine combustion and in gas-turbine combustors are associated with far-from- equilibrium effects. Examples are ignition, blow-out, relight, and the emission of significant amounts of CO and unburnt hydrocarbons. Although this research deals specifically with turbulent flames, success will have an impact on related problems that span the wide spectrum of turbulent fluid mechanics. Improved turbulence modeling would have, in turn, an impact on propulsion systems (internal combustion engines, rockets, and turbines), on acid rain (both in formation of species and their subsequent dispersion throughout the environment), disposal of toxic wastes, semiconductor and superconductor fabrication techniques, and medical science, to cite a few.