Scramjet Technology - How A Hypersonic Engine Was Created - Alternative View

Scramjet Technology - How A Hypersonic Engine Was Created - Alternative View
Scramjet Technology - How A Hypersonic Engine Was Created - Alternative View

Video: Scramjet Technology - How A Hypersonic Engine Was Created - Alternative View

Video: Scramjet Technology - How A Hypersonic Engine Was Created - Alternative View
Video: How Do Hypersonic Aircraft (Scramjets) Create Thrust? 2024, March
Anonim

Combat missile "surface-to-air" looked somewhat unusual - its nose was lengthened by a metal cone. On November 28, 1991, she launched from a test site near the Baikonur cosmodrome and self-destructed high above the ground. Although the missile did not shoot down any aerial object, the launch target was achieved. For the first time in the world, a hypersonic ramjet engine (scramjet engine) was tested in flight.

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The scramjet engine, or, as they say, "hypersonic forward flow" will allow you to fly from Moscow to New York in 2 - 3 hours, leave the winged machine from the atmosphere into space. An aerospace plane will not need a booster plane, as for Zenger (see TM, No. 1, 1991), or a launch vehicle, as for shuttles and Buran (see TM No. 4, 1989), - delivery of cargo to orbit will cost almost ten times cheaper. In the West, such tests will take place no earlier than three years later …

The scramjet engine is capable of accelerating the aircraft up to 15 - 25M (M is the Mach number, in this case, the speed of sound in the air), while the most powerful turbojet engines, which are equipped with modern civilian and military winged aircraft, are only up to 3.5M. It does not work faster - the air temperature, when the flow in the air intake is decelerated, rises so much that the turbocompressor unit is not able to compress it and feed it into the combustion chamber (CC). It is possible, of course, to strengthen the cooling system and the compressor, but then their dimensions and weight will increase so much that hypersonic speeds will be out of the question - to get off the ground.

A ramjet engine works without a compressor - the air in front of the compressor station is compressed due to its velocity head (Fig. 1). The rest, in principle, is the same as for a turbojet - combustion products, escaping through the nozzle, accelerate the apparatus.

The idea of a ramjet, then not yet hypersonic, was put forward in 1907 by the French engineer Rene Laurent. But they built a real "forward flow" much later. Here Soviet specialists were in the lead.

First, in 1929, one of the students of N. E. Zhukovsky, B. S. Stechkin (later an academician), created the theory of an air-jet engine. And then, four years later, under the leadership of designer Yu. A. Pobedonostsev in the GIRD (Group for the Study of Jet Propulsion), after experiments at the stand, the ramjet was first sent flying.

The engine was housed in the shell of a 76 mm cannon and fired from the barrel at a supersonic speed of 588 m / s. The tests went on for two years. Projectiles with a ramjet engine developed more than 2M - no other aircraft in the world flew faster at that time. At the same time, the Girdovites proposed, built and tested a model of a pulsating ramjet engine - its air intake periodically opened and closed, as a result of which the combustion in the combustion chamber pulsed. Similar engines were later used in Germany on FAU-1 rockets.

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The first large ramjet engines were again created by Soviet designers I. A. Merkulov in 1939 (subsonic ramjet engine) and M. M. Bondaryuk in 1944 (supersonic). Since the 40s, work on "direct flow" began at the Central Institute of Aviation Motors (CIAM).

Some types of aircraft, including missiles, were equipped with supersonic ramjet engines. However, back in the 50s it became clear that with M numbers exceeding 6 - 7, the ramjet is ineffective. Again, as in the case of the turbojet engine, the air braked in front of the compressor station got into it too hot. It made no sense to compensate for this by increasing the mass and dimensions of the ramjet engine. In addition, at high temperatures, molecules of combustion products begin to dissociate, absorbing the energy intended to create thrust.

It was then in 1957 that E. S. Shchetinkov, a famous scientist, a participant in the first flight tests of a ramjet engine, invented a hypersonic engine. A year later, publications about similar developments appeared in the West. The scramjet combustion chamber begins almost immediately behind the air intake, then it smoothly passes into an expanding nozzle (Fig. 2). Although the air is slowed down at the entrance to it, unlike previous engines, it moves to the compressor station, or rather, rushes at supersonic speed. Therefore, its pressure on the chamber walls and temperature are much lower than in a ramjet engine.

A little later, a scramjet engine with external combustion was proposed (Fig. 3) In an aircraft with such an engine, the fuel will burn directly under the fuselage, which will serve as part of the open CS. Naturally, the pressure in the combustion zone will be less than in a conventional combustor - the engine thrust will decrease slightly. But you get a weight gain - the engine will get rid of the massive outer wall of the compressor station and part of the cooling system. True, a reliable "open direct flow" has not yet been created - its finest hour will probably come in the middle of the XXI century.

Let's return, however, to the scramjet engine, which was tested on the eve of last winter. It was fueled by liquid hydrogen stored in a tank at a temperature of about 20 K (- 253 ° C). Supersonic combustion was perhaps the most difficult problem. Will hydrogen be evenly distributed over the chamber cross section? Will it have time to completely burn out? How to organize automatic combustion control? - you can't install sensors in the chamber, they will melt.

Neither mathematical modeling on ultra-powerful computers, nor bench tests provided comprehensive answers to many questions. By the way, to simulate an air flow, for example, at 8M, the stand requires a pressure of hundreds of atmospheres and a temperature of about 2500 K - liquid metal in a hot open-hearth furnace is much cooler. At even higher speeds, engine and aircraft performance can only be verified in flight.

It was thought for a long time both here and abroad. Back in the 60s, the United States was preparing tests of a scramjet engine on a high-speed X-15 rocket aircraft, however, apparently, they did not take place.

The domestic experimental scramjet engine was made dual-mode - at a flight speed exceeding 3M, it worked as a normal "direct flow", and after 5 - 6M - as a hypersonic one. For this, the places of fuel supply to the compressor station were changed. The anti-aircraft missile being removed from service became the engine accelerator and carrier of the hypersonic flying laboratory (HLL). The GLL, which includes control systems, measurements and communication with the ground, a hydrogen tank and fuel assemblies, were docked to the compartments of the second stage, where, after the removal of the warhead, the main engine (LRE) with its fuel tanks remained. The first stage - powder boosters, - having dispersed the rocket from the start, separated after a few seconds.

Anti-aircraft missile with scramjet at the launch pad (photo is published for the first time)
Anti-aircraft missile with scramjet at the launch pad (photo is published for the first time)

Anti-aircraft missile with scramjet at the launch pad (photo is published for the first time).

Bench tests and preparation for the flight were carried out at the P. I. Baranov Central Institute of Aviation Motors in cooperation with the Air Force, the Fakel machine-building design bureau, which turned its rocket into a flying laboratory, the Soyuz design bureau in Tuyev and the Temp design bureau in Moscow, which manufactured the engine. and the fuel regulator, and other organizations. The program was supervised by well-known aviation specialists R. I. Kurziner, D. A. Ogorodnikov and V. A. Sosunov.

To support the flight, CIAM created a mobile liquid hydrogen refueling complex and an onboard liquid hydrogen supply system. Now, when liquid hydrogen is considered as one of the most promising fuels, the experience of handling it, accumulated at CIAM, can be useful to many.

… The rocket launched late in the evening, it was already almost dark. In a few moments the carrier of the "cone" disappeared into low clouds. There was a silence that was unexpected compared to the initial rumble. The testers who watched the start even thought: did everything really go wrong? No, the apparatus continued on its intended path. At the 38th second, when the speed reached 3.5M, the engine started, hydrogen began to flow into the CC.

But on the 62nd, the unexpected really happened: the automatic shutdown of the fuel supply worked - the scramjet engine shut down. Then, at about the 195th second, it automatically started up again and worked until the 200th … It was previously determined as the last second of the flight. At this moment, the rocket, while still over the territory of the test site, self-destructed.

The maximum speed was 6200 km / h (just over 5.2M). The engine and its systems were monitored by 250 onboard sensors. The measurements were transmitted to the ground by radio telemetry.

Not all information has been processed yet, and a more detailed story about the flight is premature. But it is already clear now that in a few decades the pilots and cosmonauts will ride the "hypersonic forward flow".

From the editor. Flight tests of scramjet engines on X-30 aircraft in the United States and on Hytex in Germany are planned for 1995 or the next few years. Our specialists, however, could in the near future test the "direct flow" at a speed of more than 10M on powerful missiles, which are now being withdrawn from service. True, they are dominated by an unresolved problem. Not scientific or technical. CIAM has no money. They are not even available for the half-beggarly salaries of employees.

What's next? Now there are only four countries in the world that have a full cycle of aircraft engine building - from fundamental research to serial production. These are the USA, England, France and, for now, Russia. So there would be no more of them in the future - three.

The Americans are now investing hundreds of millions of dollars in the scramjet program …

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Figure: 1. Schematic diagram of a ramjet engine (ramjet): 1 - the central body of the air intake, 2 - the throat of the air intake, 3 - the combustion chamber (CC), 4 - nozzle with a critical section. White arrows indicate fuel delivery. The design of the air intake is such that the air flow that has entered it is inhibited and enters the compressor station under high pressure. Combustion products, leaving the combustion chamber, are accelerated in a narrowed nozzle to the speed of sound. Interestingly, the nozzle must be expanded to further accelerate the gases. The example with a river, when the current accelerates in proportion to the narrowing of the banks, is suitable only for subsonic flows.

Figure: 2. Schematic diagram of a hypersonic ramjet engine (scramjet engine): 1 - CS, 2 - expanding nozzle. The CS begins not behind the diffuser, as in the ramjet engine, but almost immediately behind the throat of the air intake. The fuel-air mixture burns at supersonic speed. The combustion products are accelerated even more in the expanding nozzle.

Figure: 3. Schematic diagram of a scramjet engine with external combustion: 1 - fuel injection point. Combustion takes place on the outside of the engine - the pressure of the combustion products is less than in a closed combustion chamber, but the thrust - the force acting on the walls of the airframe is greater than the frontal resistance, which sets the device in motion.

Authors: Yuri SHIKHMAN, Vyacheslav SEMENOV, researchers of the Central Institute of Aviation Motors