Asymptotic and numerical analyses of ignition of a fuel jet in a supersonic airstream

Ignition of a cold fuel injection into a supersonic hot airstream is analyzed both asymptotically and numerically. The present study extends the Linan and Crespo's analysis of ignition in a mixing layer of parallel streams to the analysis of ignition in a jet flow. The ignition distance is related explicitly to the thermodynamic parameters and the width of jet. The asymptotic analysis not only correlates the ignition distance in a fuel jet with that in a mixing layer of parallel streams, but also reveals the difference between them. It is shown that ignition mechanism of a fuel jet in an infinite air stream can be divided into three regimes, ignition regime in a mixing layer of parallel streams, ignition regime determined by jet scale and chemical scale, and ignition regime controlled by chemical scale only, according to the width of jet. The present analysis theoretically exhibits the linear dependence of ignition distance on the logarithmic function of jet width. A good agreement is established between the results obtained from the asymptotic analysis and those obtained by numerical simulations.