A shock wave, like any other wave, contains energy and may travel through a medium, but it is distinguished by a sudden, almost discontinuous change in the medium’s pressure, temperature, and density. A shock wave is a powerful pressure wave generated from supersonic aircraft, explosions, lightning, and other events that cause rapid pressure changes in any elastic media such as air, water, or solid material. Shock waves are distinguished from sound waves by the fact that wavefront, where compression occurs, is an area of abrupt and severe alteration in stress, concentration, as well as temperature. Shock waves transmit in some kind of a different way than regular acoustic waves as a result of this.

The movement change is permanent and the entropy rises when an item travels faster than sound and the flow area abruptly drops. Shockwaves are produced. The pressure gradient, heat, and gas density rise nearly instantly across a shock wave. Since there is no thermal absorption and no work done by a shock wave, the overall enthalpy and temperature remain unchanged. A normal shock occurs when the shock wave travels perpendicular towards the direction of flow. The equations that explain the modification inflow parameters during flow over a normal shock are given on this slide. The equations given here were obtained by neglecting viscous effects while addressing the conservation of momentum, mass, as well as energy for just a compressible gas. If indeed the flow is reversed by a significant amount as well as the shock cannot stay connected to the body, a regular disruption occurs before a supersonic item. All these wedges & cones experience the disconnected shock. In most supersonic inlets, a conventional shock also is present. The flow shifts from the supersonic into the subsonic throughout the normal shock. Because gas turbine engines run at subsonic speeds, a normal shock must be introduced into the intake compression system. Shock tubes may also produce normal shocks. The temperature jump over the typical shock is used to mimic the high heating conditions during spacecraft re-entry in a shock tube, which is a high-velocity wind tunnel.

The Japan Aerospace Exploration Agency (JAXA) recently developed and tested a more efficient shock wave-powered rocket engine. The rocket took off from Kagoshima Prefecture’s Uchinoura Space Center and climbed to a height of 146 miles (235 kilometers) in four minutes. It was a total 8 minute recorded flight. After landing, the agency recovered a capsule from the water that contained critical information more about the launch, including a picture of such 500N class RDE in orbit.

This is a major step forward in the deployment of various propulsion systems, which aims to reduce the cost of rocket engines while improving their efficacy. The current engine design is expected to be up to the task of the next space era, which may include deep space travel.

Rotating detonation engines and Pulse detonation engine used in JAXA’s rocket

Detonation waves are used in rotating detonation engines to burn the fuel and oxidizer combination. The explosions create gases that are expelled through one side of either the ring-shaped duct to generate thrust in the reverse direction as they travel around in an annular compartment in a loop. The shockwave from the explosion then travels roughly 5 times faster than the speed of sound, whirling and spreading. This produces high-frequency shock & compression waves, which may be utilized to create additional detonations inside a self-sustaining pattern, assisted by tiny quantities of fuel. As a consequence, compared to combustion, this kind of engine produces considerably more energy off considerably reduced fuel mass.

Detonation of a pulse injecting propellants into lengthy cylinders that are open solely on a single end but closed on another is how rocket engines work. An igniter, including a spark plug, is triggered whenever gas fills the cylinder. Fuel starts to burn and quickly converts to a powerful shock or explosion. Because the shock wave moves ten times faster than the speed of sound through the cylinder, combustion occurs before the gas has a chance to expand. The exhaust is pushed out all the opening of the cylinder by the explosive force of the explosion, giving propulsion to the vehicle.

The pulse detonation engine was used as a backup engine in JAXA’s rocket test. In three instances, it functioned for two seconds, while the spinning detonation engine functioned for about 6 seconds during liftoff. Despite this, the test proved how both PDEs, as well as RDEs, are feasible rocket technologies. PDEs were formerly thought to be weaker than RDEs because the waves in RDEs travel cyclically through the chamber, while with PDEs, the chambers must be cleansed between pulses.

Oblique wave detonation engine

It is made up of three parts that are connected by a hollow tube. The first part is a mixing container, in which a jet containing hydrogen fuel is fired as well as accelerated after being pre-mixed with air. The high-pressure air flowing down the tube is mixed with ultra-high-purity hydrogen fuel in the second chamber. The tube subsequently tapers, speeding up a mix into Mach 5.0 before entering the last “test section,” which is where the explosion occurs. The air/fuel mixture is sent up an inclined ramp in the last portion. The pressure wave couplings in the chamber resulted in a steady, continuous explosion that remained almost motionless. An OWDE engine may theoretically enable airplanes to fly around Seventeen times faster than the speed of sound.

Sources:

https://www.japantimes.co.jp/news/2021/07/27/national/science-health/japan-rocket-engine-test/

https://room.eu.com/news/japan-successfully-tests-rocket-engine-propelled-by-shock-waves

http://www.parabolicarc.com/2021/06/13/japan-to-test-pulse-detonation-rocket-engine/

https://thehackposts.com/japans-new-rocket-engine-uses-shock-waves-as-propellant/