Upper Bounds on the Flight Speed of Hydrocarbon-Fueled Scramjet-Powered Vehicles

Introduction F ROM the inception of the supersonic combustion ramjet (scramjet) engine cycle (see Fig. 1) in the late 1950s through the present time, there has been much speculation about what the upper bound on  ight Mach number is when using either a gaseous fuel such as hydrogen or a storable liquid hydrocarbon fuel such as kerosene. Some initial studies claimed orbital speeds (Mach 26) and beyond for hydrogen-fueledsystems andMach 14–16  ight for hydrocarbon-fueled systems.1i3 Subsequent studies in the 1960s and early 1970s revised these estimates downward somewhat to Mach 15–20 and Mach 12–14,4i7 respectively. However, most of these studies are not conŽ guration speciŽ c, and none incorporate what has been learned about the operation and performance of scramjet-poweredvehicles since their printing. Subsequent to these early studies, several modern studies have been done for hydrogen-fueled concepts, primarily for Earth-toorbit space transport systems,8i11 in which the upper speed bound is somewhat lower, primarily in the Mach 12–16 range. There have also been a number of studies on hydrocarbon-fueledmissile concepts,12i16 but none of these addressed the upperMach number