Posted on 04/08/2019 7:06:11 PM PDT by BenLurkin
Fans of supersonic flight have been yearning for a new way to break the sound barrier ever since Concorde stopped flying in 2003.
Now successful tests of a key part of an air-breathing rocket engine may have brought that dream a step closer to reality.
UK company Reaction Engines announced successful tests of a precooler on Monday, simulating conditions at Mach 3.3, or more than three times the speed of sound.
That's more than 50% faster than the cruising speed of Concorde -- which used to make the journey between New York and Paris in around 3.5 hours -- and matches the speed record of the fastest jet aircraft ever made, the Lockheed SR-71 Blackbird.
The precooler tests were part of the company's plans to develop the Synergetic Air-Breathing Rocket Engine (SABRE) engine and took place at a testing facility at the Colorado Air and Space Port in the United States.
At such high speeds, air flowing through the engine can reach incredibly high temperatures, which can potentially cause damage.
A precooler reduces the temperature of gases before they enter the core engine itself.
(Excerpt) Read more at cnn.com ...
Cant wait to see this hit the market ... oh wait, the gubmint will appropriate it in the interest of “National Security “.
SABRE design is neither a conventional rocket engine nor jet engine, but a hybrid that uses air from the environment at low speeds/altitudes, and stored liquid oxygen (LOX) at higher altitude. The SABRE engine "relies on a heat exchanger capable of cooling incoming air to −150 °C (−238 °F), to provide oxygen for mixing with hydrogen and provide jet thrust during atmospheric flight before switching to tanked liquid oxygen when in space."
In air-breathing mode, air enters the engine through an inlet. A bypass system directs some of the air through a precooler into a compressor, which injects it into a combustion chamber where it is burnt with fuel, the exhaust products are accelerated through nozzles to provide thrust. The remainder of the intake air continues through the bypass system to a ring on flame holders which act as a ramjet for part of the air breathing flight regime. A helium loop is used to transfer the heat from the precooler to the fuel and drive the engine pumps and compressors.
Due to the static thrust capability of the hybrid rocket engine, the vehicle can take off under air-breathing mode, much like a conventional turbojet.[3] As the craft ascends and the outside air pressure drops, more and more air is passed into the compressor as the effectiveness of the ram compression drops. In this fashion the jets are able to operate to a much higher altitude than would normally be possible.
At Mach 5.5 the air-breathing system becomes inefficient and is powered down, replaced by the on-board stored oxygen which allows the engine to accelerate to orbital velocities (around Mach 25).
https://en.wikipedia.org/wiki/SABRE_(rocket_engine)#Engine
Doesn’t the aircraft distort at these speeds because of the friction?
The SR 71 increased about a foot in length at top speed, which created many problems.
“which allows the engine to accelerate to orbital velocities (around Mach 25).”
The heat from friction at that speed will be a problem.
L
That`s how my air conditioner works- suck in hot air and blasts out cool air- no wonder my AC unit keeps flying out the window.
Very cool! ;-)
Thanks for posting!
Note: Mach 25 is orbital, thus not reacting with atmospheric friction in the same way.
"Interest in precooled engines saw an emergence in the UK in 1982, when Alan Bond created a precooled air breathing rocket engine design he called SATAN. The idea was developed as part of the HOTOL SSTO spaceplane project, and became the Rolls-Royce RB545. In 1989, after the HOTOL project was discontinued, some of the RB545 engineers created a company, Reaction Engines Ltd, to develop the idea into the SABRE engine, and the associated Skylon spaceplane.So these guys have been working on this for THIRTY YEARS now!
You cannot have an air-air precooler because there is no air stream to which you can dump the heat. Therefore, all precooled jet engines use cryogenic liquid hydrogen fuel to cool the incoming air. Using liquid hydrogen means major changes to the entire airframe including making it a lot larger to store the fuel.
SABRE is a hypersonic hybrid engine. It draws in air to act like a conventional jet while accelerating to speeds of up to Mach 5 (3,704 mph, 5,961 km/h), then converts to a pure rocket engine burning hydrogen and liquid oxygen, making speeds of up to Mach 25 (17,521 mph, 29,808 km/h) possible.Key to this is a revolutionary heat exchanger that protects the engine as it approaches hypersonic velocity. At high supersonic speeds, the air is coming into the engine with the force 25 times that of a category 5 hurricane, generating temperatures that would melt any material that the engine might be made of. To prevent this, SABRE has a precooler that uses recirculated cryogenic hydrogen fuel to cool incoming air down from 1,000° C to -150° C in 1/100th of a second.
For comparison, the SR-71 engines were each gulping 200 lbm/second of air! that is a huge airflow to cool.
Below is the precooler they just tested in Colorado. They say this about their precooler:
Our pre-coolers are made from thousands of thin-walled tubes to provide high surface area to low weight. Each tube is joined to an inlet and outlet manifold, which allows coolant to be injected and removed for the cooling process. We're the only people in the world with the heat exchanger manufacturing experience to bond thousands of joints in a single operation, and achieve zero leakage. The joints in our pre-cooler modules are hermetically sealed, meaning that the gas which escapes can be measured by the molecule.That is quite an accomplishment (if true).
It will be interesting to see how they deal with all the shock issues and stay within size and weight constraints of a commercial aircraft. The story of the design of the SR-71 engine inlets is an amazing bit of engineering history. It was one of the toughest design challenges on the SR-71. Here's a good presentation on the SR-71 engine inlet design...
That’s only a part of the “whole rocket” problem: Yes, the spacecraft fuselage and coverings expand with heat. Changes CG, dynamic air pressure location (delta wings had that problem as speed increased too), control surfaces, linkages, sensors .... The expansion caused never-solved fuel leaks in the SR71. At best, the fuel leaks were “tolerated” because the fuel was so hard to burn they did not consider it a threat of explosions on the ground.
The SR72 variable length inlet spikes were a long-running problem too. Here, apparently they are testing only a the inlet cooler subsystem.
‘Recent tests prove that the component can cool gases from over 1,000 Celsius to ambient temperature in less than 1/20th of a second, according to a statement from Reaction Engines.”
While 1/20 of a second is a very small amount of time, at Mach 3 it is still 150 or so feet...which is still quite a bit longer than the engine. On the other hand, maybe the gasses are slowed enough in the engine so that 1/20 of a second is fast enough.
But it does sound promising!
SpaceX new rocket more likely than this to succeed in earth to earth long distance travel. Boost to parabolic flight, re-enter and land.
Depending on the curve, they may not need it to be ambient temperature... it may just need to be below the melting point of say aluminum - 660.3°C.
I’m curious how this single device handles that kind of temperature differential. Granted it’s not a glass dish that cracks under boiling water, but wow.
Reading about this, it brought to mind the engines on the SR-71. Another tribute to the thinking of the Skunk Works guys.
It seems that CNN is running an occasional news story now. Apparently non-stop Trump bashing has not paid off.
It will be interesting to see if this precooler can withstand 180 decibels at mach 25. Those are the numbers that I remember from 1991. 3000 degrees f and 180 decibels.
180 dB — that’s a lot of vibration. I didn’t know it was that high, but it’s not surprising at the front of those compressors, the shock waves at the inlet, and the air deceleration and compression.
200 lbm/sec, 1,000° C to -150° C in 10 milliseconds, 180 dB. Hard to believe all the tubes in that heat exchanger lasting under that vibration load and remaining leak free. Hydrogen leaks in the HX would not be good.
My Dad built satellites at GE and took me in to witness a shake table test simulating rocket lift off. It was the most incredible thing to see.
Yes it is. I can’t remember the numbers, but I think a jet engine is around 120 decibels and the sound pressure doubles every 10 decibels. That’s the way I remember picturing what is actually happening.
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