China has successfully tested a prototype of a hypersonic engine that provides a speed sufficient to fly around the Earth in two hours
In China, scientists have successfully tested a prototype of a Hypersonic airbreathing propulsion, with which an aircraft can circumnavigate the Earth within two hours. The test report was published by researchers from the Chinese Academy of Sciences (CAS) in the Chinese Journal of Aeronautics.
The authors of the study believe that their development will serve as the basis for the creation of reusable orbital spacecraft and hypersonic aircraft for the future.
The engine runs on pure hydrogen and uses unnamed special alloys. They were created on purpose, since metals used in the rocket and space industry would hardly withstand the temperatures that arise in the new ramjet engine. The device of the tested prototype is strikingly different from the known schemes of hypersonic ramjet engines.
Engineers and scientists from the Chinese Academy of Sciences conducted an experiment in a hypersonic wind tunnel capable of creating an airflow rate of up to Mach 9. This is approximately equal to 11 thousand kilometers per hour. The prototype performance was stable during testing.
During the extrapolation of the measurement results, the scientists concluded that the engine will accelerate steadily and work efficiently at a speed of up to Mach 16. And this is about 19.5 thousand kilometers per hour, that is, the entire equator aircraft with such an engine will fly around in a little more than two hours.
To test the theoretical calculations will have to wait for the construction of a more powerful wind tunnel. Well, the practical application of the engine may never come. It is noted that the materials used in its design withstood only short-term experiments. How it will behave during flights lasting ten minutes – it is difficult to predict yet.
Direct-flow jet engines have attracted aircraft designers and rocket scientists for their simplicity and high theoretical characteristics since their very invention at the beginning of the 20th century. A minimum of moving parts (except that an adjustable air intake is needed), maximum efficiency at high speeds is just a fairy tale. However, they have found practical application in rather narrow areas.
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The principle of operation of such engines is based on the compression of the incoming air not by the compressor, but by the shape of the air intake. Because of this, they are unable to operate at zero speed and have deplorable efficiency up to Mach 1. Supersonic ramjets, where the incoming airflow slows down to subsonic speed, turned out to be almost impossible to accelerate beyond 5 Mach numbers. Faster – and the temperatures in the air intake and in the combustion chamber exceed all reasonable limits. Together with this, fuel efficiency drops sharply. But they have found application in anti-aircraft and anti-ship missiles, which are accelerated to supersonic speed with solid-propellant first stages.
Hypersonic ramjet is arranged in a slightly different way. In these, the airflow is never braked below the speed of sound, thus extending the engine’s operating range. Judging by the data that is in the public domain, modern scramjets reach speeds of 7-8 Mach numbers. Further acceleration is impeded by the fronts of shock waves arising in the air intake, which literally tear off the flame in the combustion chamber. In addition, due to the unstable operation of the engine, the temperature in it also rises like an avalanche.
Theoretically, all these limitations can be circumvented, and sometimes even by implementing some ideas “in metal”. This is exactly what the Chinese experts demonstrated. However, having solved the problem with engine overheating, a similar situation arises with the aircraft. At speeds above Mach 3, the aeroplane or rocket glider begins to heat up to temperatures at which aluminium alloys lose strength. After Mach 5, only disposable constructions can be used. To date, it is not possible to implement a reusable hypersonic aircraft without the use of complex cooling systems or ablation coatings (usually disposable).