What is a Scramjet?

Supersonic combustion ram engines, which are referred to as super-combustion ram engines, can obtain oxygen from the atmosphere during the ascent. Giving up carrying oxidants, obtaining oxygen from flight, and saving weight mean that under the condition of consuming the same mass of propellant, a super-combustion stamping engine can produce 4 times the thrust of a rocket.

A super-ignition ram engine is a ram engine in which fuel is burned in a supersonic flow. When using hydrocarbon fuel, the flying Ma number of the supercombustion ram engine is less than 8, and when using liquid hydrogen fuel, its flying Ma number can reach 6 ~ 25. The supersonic or hypersonic airflow is diffused in the inlet to the lower supersonic speed of Mach 4, and then fuel is injected from the wall and / or the protrusions in the airflow, mixed with the air in the supersonic combustion chamber and burned. The gas is discharged through the expanded nozzle.

The use of super-combustion ram engines for propulsion is not a new concept. The development of foreign super-combustion ram engine technology has a history of more than 50 years. In the 1990s, the earliest patents were recorded. In the mid-1960s, some super-combustion ram engines had undergone flight tests, with top speeds reaching Mach 7.3. General Electric, United Technologies, Marquardt, Johns Hopkins APL Labs, and NASA Langley Research Center have developed typical hydrogen-fueled supercombustion ram engines (the same fuel is also used in space shuttles and other Liquid rocket booster).

In the mid-1980s, the U.S. government launched a national air and space plane program powered by superburning ram engines. However, with the end of the Cold War and fiscal austerity, the US government had to cancel the plan in 1994, when they had invested nearly $ 2 billion. In 2004, NASA's HyperX program was completed and two flight tests of a hydrogen-fueled supercombustion ram engine were successfully performed. Both flights lasted a few seconds at a single speed and altitude.

At the end of the same year, the X-43A super-combustion ram engine test aircraft set a record of Mach number 9.6. The U.S. Air Force is trying to use next-generation super-combustion ram engine technology to accelerate the aircraft at a certain speed and altitude range, and use liquid hydrocarbon fuel as the fuel of the engine, and also use it to cool the engine.

The first is that super-combustion ram engines have the advantages of simple structure, light weight, low cost, high unit thrust (thrust generated by unit mass flow propellant) and high speed. Compared to rocket engines, super-combustion ram engines do not need to carry oxidants.

Therefore, the payload is larger, which is suitable for the power of hypersonic cruise missiles, hypersonic aircraft, trans-atmospheric aircraft, reusable space launchers, and single-stage orbiting aerospace aircraft. Because of the important military and aerospace application prospects, super-combustion stamping engines have attracted much attention from countries around the world. Expensive test costs are one of the main factors restricting the development of super-combustion ram engines.

The second is that the disadvantage of super-combustion ram engines is that they cannot start on their own in a static state, and they need to be boosted to a certain speed before they can work effectively, and their low-speed performance is not good.

After years of development, foreign countries have studied and designed a variety of schemes for super-combustion stamping engines. Mainly including ordinary super-combustion ram engines, sub-combustion / super-combustion dual-mode ram engines, sub-combustion / super-combustion dual-combustion ram engines, suction pre-combustion chamber super-combustion ram engines, ejection super-combustion ram engines, monolithic Rocket liquid super-combustion ram engines, solid dual-mode ram engines and super-combustion combined engines. Among them, dual-mode ram engines and dual-combustion chamber ram engines are the two most studied types.

Research on super-combustion ram engines has been conducted since the 1950s. The initial application targets were single-stage orbiting aircraft, long-range high-speed aircraft and long-range hypersonic missiles. Since the 1990s, the focus has shifted to the development of super-combustion ram engines for cruise missiles. The United States, France, Russia, Canada, Germany, India, Italy and other countries are developing super-combustion stamping engines for cruise missiles with M-numbers of 4 to 8 and a range of more than 1000 km. The dual-mode supercombustion ram engine using hydrocarbon fuel and M number 3 ~ 8 has completed the ground test verification and conducted flight tests. It is expected that by 2010, supersonic cruise missiles powered by super-combustion ram engines will be available. By 2025, hypersonic spaceflight aircraft powered by super-combustion ram engines will likely be put into use.

Due to the huge military and economic application prospects of super-combustion stamping engines, as early as the 1960s, the United States carried out large-scale research related to this, and gradually completed the construction of engine prototypes to verify the feasibility of super-combustion design methods. According to the experimental results, the design concept of engine and fuselage integration was proposed, which was widely recognized. By the 1980s, one of the important research results was the so-called Dual-mode scramjet , which is suitable for medium flying Mach numbers (4 ~ 8). The supersonic combustion of the ram engine has broadened the application limit of the super-combustion ram engine. It is a ring-shaped inlet structure, which includes two subsonic and supersonic inlets. Under different flying Mach numbers and fuel equivalent ratios, the engine automatically realizes sub-combustion and super-combustion mode conversion.

Headed by the Moscow Central Aviation Engine Research Institute, Russia has also carried out a lot of research on super-combustion engines. Five flight tests have been carried out, 4 of which have been successful. Other countries have also actively carried out research on super-combustion engines. Domestic research in this field has begun, some basic experiments and numerical simulation studies have been carried out, and preliminary designs for supercombustion stamping engines are being prepared. Drawing on foreign research experience, China first conducted research on super-combustion stamping engines using ordinary aviation kerosene at low Mach numbers. The technical difficulty is relatively small, and it has good feasibility and strong practicability. It is expected that it will be in the near future. In the future, China will successfully develop a super-combustion ramjet engine for China's hypersonic cruise missiles, which will serve the modernization of our national defense. In fact, our country has initially possessed a hypersonic strategic strike capability, which has to be attributed to the successful development of stamping engines.

Super-combustion stamping engine

Judging from China's national conditions, China has achieved manned space flight, the establishment of a space station and the moon landing plan are being carried out in an orderly manner, and optical and radar reconnaissance satellite technology has developed considerably. The Beidou satellite positioning and navigation system has been put into use, and Galileo is being jointly developed with the European Union. Satellite positioning and navigation system, and in the 1990s China developed the C101 and C301 supersonic anti-ship cruise missiles powered by ramjet engines; China's scientific and technological strength is also known as a technological power in the world. China Research and development of super-combustion stamping engines still have certain talents, technical conditions and technical reserves.

The space shuttle's speedy dream will one day send people and cargo into space for less than today's rockets. This dream will build on the success of supersonic combustion ram engines.

In order for super-combustion ram engines to achieve hypersonic flight, many research groups around the world are working to overcome huge technical challenges. The discussion in this article will focus on the US Air Force and Pratt & Whitney 's HyTech Supercombustion Stamping Engine Program, one of the programs I am most familiar with.

In addition, a large number of research and development work has been carried out in the United States Navy, the National Aeronautics and Space Administration (NASA), the United States Department of Defense Advanced Research Projects Agency (DARPA), and Australia, the United Kingdom, Japan and other places. Major domestic research units in this area include Harbin Institute of Technology, Beijing University of Aeronautics and Astronautics, Northwestern Polytechnical University, National University of Defense Technology, etc., and have trained a large number of basic talents in this area for China. I believe that in the near future, as technology matures, Combustion ram engines will have wider applications ^[1] .