Use the jet flow system of Section 12.4 to analyze the ignition of a stagnant combustible of temperature T∞ and reactant mass fractions Yi,∞ by a hot, inert jet of radius ro and initial temperature To and velocity uo. Assume Sc = 1 for simplicity. This problem is somewhat similar to that of the mixing layer treated in Section 12.3.3, except now the ignition source, that is, the jet, is of finite dimension and, hence, during the induction period is continuously cooled down through entrainment of the ambient gas. Just derive the final structure equation for the inner region, with the appropriate boundary conditions. Discuss the issues of similarity and jet cooling.