Turbulent Diffusion Flames Far from Chemical Equilibrium

点击翻译按钮获取中文摘要

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.