Turbulent Diffusion Flames Far from Chemical Equilibrium

这项工作开发，测试，并使用紊流燃烧模型，该模型解释了远离平衡的影响，包括局部熄灭。本文的出发点是速度和成分的联合概率密度函数（pdf）的输运方程模型。在以前的工作中，用蒙特卡罗方法计算了近平衡湍流扩散火焰的性质，求解了这个方程。为了能够解释远离均衡的影响，这种pdf方法在两个方面得到了扩展。首先，一个改进的混合模型，考虑到反应对混合的影响，将被开发、测试和合并。第二，将纳入甲烷/空气燃烧的四步方案。柴油机燃烧和燃气轮机燃烧中的一些重要现象与远非平衡效应有关。例如点火、爆炸、重燃以及大量CO和未燃烧的碳氢化合物的排放。虽然这项研究专门针对湍流火焰，但成功将对跨越湍流流体力学广泛范围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（包括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，举几个例子。

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.