A shock-induced combustion ramjet engine (abbreviated as shcramjet; also called oblique detonation wave engine; also called standing oblique detonation ramjet (sodramjet); or simply referred to as shock-ramjet engine) is a concept of air-breathing

ramjet A ramjet, or athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary (no ram air) ramjet-powered vehicles require an a ...

engine, proposed to be used for

hypersonic In aerodynamics, a hypersonic speed is one that exceeds 5 times the speed of sound, often stated as starting at speeds of Mach 5 and above. The precise Mach number at which a craft can be said to be flying at hypersonic speed varies, since i ...

and/or single-stage-to-orbit propulsion applications.

Design

The shcramjet engine geometry is simple and similar to

scramjet A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to compress the incoming air forceful ...

, varying only in the

combustor A combustor is a component or area of a gas turbine, ramjet, or scramjet engine where combustion takes place. It is also known as a burner, combustion chamber or flame holder. In a gas turbine engine, the ''combustor'' or combustion chamber is fed ...

design. The engine includes a supersonic

inlet An inlet is a (usually long and narrow) indentation of a shoreline, such as a small arm, bay, sound, fjord, lagoon or marsh, that leads to an enclosed larger body of water such as a lake, estuary, gulf or marginal sea. Overview In ma ...

followed by a

combustion chamber A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process. Intern ...

and a

nozzle A nozzle is a device designed to control the direction or characteristics of a fluid flow (specially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. A nozzle is often a pipe or tube of varying cross sectional area, ...

, respectively. The inlet design is similar to a scramjet, in which the whole nose structure is used as inlet. Combustion in a shcramjet can occur in shock-induced combustion or detonation combustion, depending on the strength of the inducing shock. If ignition occurs far enough downstream that the ensuing combustion process does not influence the preceding shock, the combustion is said to be shock-induced. However, for extremely fast reactions, ignition occurs close to the preceding shock wave and the combustion couples with the

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

and forms a detonation wave. Therefore, detonation wave ramjet, or oblique detonation wave engine, is a particular case of shcramjet. Though shock and detonation waves are related to high pressure loss during combustion, the theoretical total pressure loss associated with shcramjet combustor approaches that of the scramjet engine at increasing mach numbers. This fact, together with the simpler engine geometry with concomitant increase in component efficiencies, results in superior predicted performance at flight Mach numbers beyond 12.

Oblique detonation wave engine

This engine funnels a mixture of air and fuel at

speeds (more than five times the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as ...

) toward a ramp, which creates a shock wave. This shock wave heats the mixture and causes it to detonate, ejecting exhaust gasses from the engine. Such an approach burns nearly 100% of the fuel. In theory, vehicle speeds could reach 17 times the speed of sound. A critical challenge is to confine the detonation in a small area, without allowing it to direct energy upstream towards the fuel source or downstream where it will lose force. In 2021 an experimental device maintained a detonation in a fixed location for 3 seconds, far longer than earlier attempts.

Scramjet

A shcramjet engine is similar to a

engine; however, unlike the diffusive mode of combustion in a scramjet engine, shcramjet engine combustion takes place across a thin region of standing

oblique shock An oblique shock wave is a shock wave that, unlike a normal shock, is inclined with respect to the incident upstream flow direction. It will occur when a supersonic flow encounters a corner that effectively turns the flow into itself and comp ...

and/or

detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...

waves stabilized over a wedge, blunt body, etc. Since combustion is confined to a narrow region across the igniting wave, the

length in a shcramjet can be significantly shorter than the scramjet, which requires a lengthy combustor for complete fuel-air mixing and combustion. Also, the shcramjet is believed to have a better overall propulsive performance than the scramjet at higher

Mach number Mach number (M or Ma) (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. It is named after the Moravian physicist and philosopher Ernst Mach. : \mathrm = \ ...

s, especially above Mach 12. Recent researches have stipulated that shcramjet, alongside its other airbreathing variants, can act as an efficient high-speed vehicle propulsion system for SSTO flights. These potential advantages have attracted substantial research on propulsive applications, as well as on the fundamental physical phenomena.

References

{{reflist Aircraft propulsion components Single-stage-to-orbit