The method of fuel injection highly affects the efficiency of scramject engines. This book presents a numerical study to investigate the mixing, combustion, and flow characteristics of different scramjet-combustor configurations. In the first part of the book, the effects of the side angle of the fuel injectors in both mixing and combustion processes are investigated. Raised (compression) and relieved (expansion) wall-mounted ramps are used with side angles of 0 (unswept), 5, and 10 degrees. Results are presented for nonreacting flows as well as for reacting flows. Hydrogen is used as the fuel in all reacting cases. In the second part, two dual- mode scramjet-combustor models are investigated. In the first model, fuel is injected through a single unswept wall-mounted ramp parallel to the airstream. In the second model, fuel is injected behind a rearward facing step normal to the airstream. The effects of the combustor length, the equivalence ratio, the number, and the arrangements of the fuel injectors are investigated. Also, the effect of the initial boundary layer thickness is studied.