INTEGRAL METHOD SOLUTION OF TIME-DEPENDENT STRAINED DIFFUSION-REACTION LAYERS WITH MULTISTEP KINETICS

Multiple coupled chemical reactions occurring within strained diffusio n layers are key to a wide range of reactive flow problems. An integra l approach is presented here to allow calculations of global propertie s of such reactive layers for complex multistep chemical kinetics and time-varying strain rates. The infinite-degree-of-freedom partial diff erential equations (PDEs) governing the dynamics of the species concen tration profiles for reactants, intermediates, and products as well as the temperature are projected onto a set of ordinary differential equ ations having just a few degrees of freedom for the evolution of integ ral moments of these profiles. The presence of multistep reaction kine tics leads to a set of highly coupled nonlinear moment equations. Nume rical solutions are presented for four-step methane-air kinetics coupl ed with thermal nitric oxide kinetics and are compared with direct sol utions of the original PDEs. Some properties and numerical illustratio ns of key features of the internal layer structure and global flame pr operties, including the extinction phenomenon characteristic of large Zel'dovich number reaction kinetics, are discussed. The method present ed brings comparatively detailed parametric studies of such problems w ithin reach of rather modest computational requirements.