Speed is the key to determining whether an aircraft can break through the interception of air defense systems and successfully complete combat missions. Behind the breakthrough speed of hypersonic missiles represented by "Zircon" at 7 times the speed of sound is the enormous thrust provided by supersonic ramjet engines. The scramjet engine is considered the best power unit for hypersonic flight, capable of producing four times the thrust of a conventional rocket engine while consuming the same amount of propellant. It has unparalleled propulsion capability and strategic value. The source of high-speed power, the supersonic combustion ramjet engine, also known as the supersonic combustion ramjet engine, is a type of ramjet engine that allows fuel to burn in supersonic airflow to generate kinetic thrust. Compared with turbine engines, scramjet engines cleverly utilize the impact effect of the oncoming airflow during high-speed flight, allowing the airflow to be naturally compressed after entering the engine, eliminating the complex compressor turbine components of traditional turbine engines. When the speed of the aircraft reaches more than 5 times the speed of sound, this "compression" effect is extremely significant, providing the necessary high-temperature and high-pressure airflow for supersonic combustion. The scramjet engine is mainly composed of three major components: intake duct, combustion chamber, and exhaust nozzle. The intake duct moderately decelerates and boosts the hypersonic airflow to achieve a state suitable for combustion; The fuel and airflow in the combustion chamber are fully mixed and burned, converting chemical energy into thermal energy. The high-temperature and high-pressure gas after combustion further expands and accelerates inside the tail nozzle, and is ejected backwards from the nozzle, forming a huge thrust. The scramjet engine can support hypersonic flight of aircraft, while ordinary engines have a thrust limit and the aircraft speed is limited to around three times the speed of sound. For example, the S-71 Blackbird and MiG-25 fighter jets developed by the United States and the Soviet Union in the 1960s had a maximum flight speed of no more than 3 Mach. The reason for this is that the faster the aircraft speed, the greater the thrust required by the engine. When the aircraft speed exceeds three times the speed of sound, the turbine engine can no longer meet the demand. In contrast, subsonic ramjet engines can provide sufficient thrust and are suitable for supersonic aircraft. When the speed of the aircraft needs to be further increased to over 5 times the speed of sound, or even up to 7 times the speed of sound, the complex internal structure of the subsonic ramjet engine makes it unable to overcome challenges such as high temperature and thermal barriers. The scramjet engine can effectively overcome these problems by allowing the airflow to maintain supersonic state in the combustion chamber for combustion, making it possible for aircraft to fly at higher speeds. The outstanding advantages of multiple countries competing to develop scramjet engines lie in their simple structure, light weight, and high thrust, especially with a thrust to weight ratio of over 20. This means that the engine has excellent performance and can provide higher maneuverability and stronger acceleration capabilities for aircraft, which has revolutionary significance for achieving military tasks such as rapid strikes, high-altitude reconnaissance, and rapid entry into space. In recent years, major military powers have invested in the research of scramjet engines to compete for this technological high ground. The United States started research in the field of scramjet engines earlier. The X-43, a hypersonic flight test aircraft developed by NASA's Dryden Flight Research Center, once set a speed record of 9.6 times the speed of sound. With the support of the US Air Force Research Laboratory, the high thrust scramjet engine developed by companies such as Lockheed Martin completed a 12-month ground test to verify its performance under different supersonic conditions. At present, the "Zircon" hypersonic missile has been deployed in actual combat. This air breathing hypersonic cruise missile is launched from frigates, cruisers, and submarines, with a maximum range of 1000 kilometers and a warhead weighing 400 kilograms. It can break through air defense system interception at a flight speed of more than 5 times the speed of sound, mainly targeting large ship clusters and high-value time sensitive targets on land. Australia has also made significant progress in the field of scramjet engine technology. A company in the country has completed testing of a hydrogen powered scramjet engine, which has several times the power of a turbine engine. The development trend of scramjet engines in multiple countries highlights the significant value of this engine in the fields of national defense and aerospace. In this competition, whoever first masters this technology and puts it into use may take the initiative in future wars dominated by hypersonic weapons. Although the prospects of scramjet engines are promising, they still face a series of technical challenges as they move from the laboratory to mature applications. The primary challenge lies in the organization and control of supersonic combustion. The fuel of a scramjet engine must complete the processes of injection, evaporation, blending, ignition, and combustion in milliseconds, which is described as the difficulty of "lighting a match in a tornado and maintaining stable combustion". To achieve this, it is necessary to optimize a series of related factors and conditions such as fuel injection method, injector design, and mixing ratio with air to the extreme. Secondly, the issue of thermal management is prominent. The scramjet engine experiences extremely high thermal loads during operation. When the flight speed reaches 6 times the speed of sound, the airflow temperature reaches 1400 degrees Celsius, and the total internal airflow temperature of the engine exceeds 2700 degrees Celsius. This means that engine materials must be able to withstand extreme high temperatures, while also requiring efficient active cooling systems. Usually, fuel is also used as a coolant, flowing through the engine's heating components to cool it before entering the combustion chamber. This requires fuel to not only have good combustion performance, but also excellent heat absorption ability. How to design an efficient cooling structure, balance cooling demand and fuel consumption, and avoid excessive heat accumulation is a complex system engineering challenge. Finally, the integrated design of the body and engine is a major challenge. Under hypersonic flight conditions, the shape of the aircraft's front body affects the quality of the airflow entering the engine inlet, while the shape of the rear body is related to the expansion efficiency of the engine nozzle gas. Therefore, the engine and aircraft must be highly integrated in design, which involves multiple aspects such as aerodynamics, structure, fuel supply, and cooling systems, with extremely high technical complexity. The technology of scramjet engines is a core key technology for controlling near space and gaining rapid strike advantages. Its development level is related to national defense security and strategic advantages, and its mature application will profoundly change the future battlefield form and air and space transportation mode. This competition around 'higher speed' has been ongoing. (New Society)