First Ever Scramjet Reaches Mach 10

stjobe writes with the news that a group of US and Australian scientists successfully tested a supersonic scramjet engine in the Australian Outback on Friday. The Sydney Morning Herald reports that a rocket carrying the engine reached mach 10, and climbed to an altitude of 330 miles before the apparatus re-entered the Earth's atmosphere. "Australia's Defense Science and Technology Organization (DSTO) said it was believed to be the first time a scramjet had been ignited within the Earth's atmosphere ... Scramjets are supersonic combustion engines that use oxygen from the atmosphere for fuel, making them lighter and faster than fuel carrying rockets. Scientists hope that one day a scramjet aircraft fired into space could cut traveling time from Sydney to London to as little as two hours."

Comments

X-43A?

[Chairboy]

What about the X-43A? It also ignited successfully and flew under power.

http://en.wikipedia.org/wiki/Boeing_X-43

This is cool, yes, but the emphasis on "first" seems a bit off.

Bzzzt. Wrong!

[tritone]

"scramjets are supersonic combustion engines that use oxygen from the atmosphere for fuel"

Scamjets use oxygen from the atmosphere as an oxydizer unlike traditional rocket engines which need to carry their oxydizer. Scramjets still need to carry fuel.

No. I am not a rocket scintist.

HyShot, HyCAUSE and HiFire

[Anonymous Coward]

It was the same fuel as HyShot, plain old hydrogen (plus oxygen gathered from the atmosphere). This scramjet project was named HyCAUSE and the engine was physically a fair bit larger than the successful HyShot flights by the same team a few years back. The team originated from the University of Queensland moved to the Defence Science and Technology Organisation about a year ago. The next flights are a series of ten over five years under the name "HiFire".

Scramjets need an atmosphere

[Moraelin]

Scramjets need an atmosphere anyway, just like ramjets and turbojets. That's the whole idea. The air flows through it, fuel is injected into that air and ignited. Trying to operate a scramjet in a vacuum would make as much sense as trying to operate a turbojet there. Pretty much all 3 are the same jet engine, more or less. A turbojet uses a compressor in the front to push the air into the engine. A ramjet relies on the fact that if you fly fast enough to start with, you get air pushed into the engine anyway. (Plus some clever design of the intake so the flame doesn't go in both directions.) But the air is slowed down to a subsonic speed at the point where the fuel is injected and lit. A scramjet is a ramjet where the air does flow at supersonic speed through the engine, so basically it's choked. You can add the fuel past the choke point and, since waves can't move backwards in a supersonic flow, whatever pressure you generate there by burning fuel can only go towards the back engine. The front of the engine can't "notice" the higher pressure in the back half because a pressure wave would have to travel through that air faster than sound speed, which isn't possible. Another rough description would be that a scramjet is like a turbojet with an afterburner, only without the turbojet. (Sorta like the sound of one hand clapping, I guess;) Instead of having the turbojet push air through a nozzle and add extra fuel to it, the engine _is_ the nozzle and the airplane's existing speed is what pushes air to it. So you just add the fuel and light it. It's an afterburner without a turbojet. But in the end all 3 work by the same basic principle: air comes through the front, fuel is added, hot air comes out the back. No air, no flame, the engine stops. The plans to use a scramjet to get to a highe enough orbit or even leave the planet, involve getting enough speed while still having enough air for the scramjet, or as boosters in addition to the normal rocket engines, or both.

Re:Scramjets need an atmosphere

[dyslexicbunny]

A ramjet relies on the fact that if you fly fast enough to start with, you get air pushed into the engine anyway. (Plus some clever design of the intake so the flame doesn't go in both directions.) Not necessarily. The ramjet inlet's design is such that the air is compressed through ram compression, essentially the air is compressed as it is slowed down. There really isn't any clever design on the inlet. The pressure in the inlet area is greater than the that of the combustor and so long as that is true, no flame will come out. You're essentially correct but I just wanted to nitpick.

Explaining the turbojet is easier after explaining the ramjet. Ramjet performance suffers below Mach 1 because you can't get enough compression for efficient combustion. The turbojet adds a compressor to add work to the flow so you can get the desired pressure ratio coming into the burner. Then you have to go through the turbine such that you can power the compressor.

Engines with compressors are far more interesting as they can be pushed to the point (whether by power setting or flight condition) such that the compressor can stall and flame will shoot out the front of the engine. It's something pretty important in compressor design since they operate with an adverse pressure gradient (pressure out > pressure in). This is why you see compressors with 10+ stages powered by only 1-2 turbine stages. It's really quite interesting.

You basic principle explanation isn't great for non-engineers. Try using "Suck, squeeze, bang, blow." I explained that to some friends of mine and they were way more interested. They not only laughed but they then wanted to hear more detail. But solid explanations on your part, I just wanted to nitpick a couple things since I'm a propulsion guy.

Gah. Once more, with formatting

[Moraelin]

Scramjets need an atmosphere anyway, just like ramjets and turbojets. That's the whole idea. The air flows through it, fuel is injected into that air and ignited. Trying to operate a scramjet in a vacuum would make as much sense as trying to operate a turbojet there.

Pretty much all 3 are the same jet engine, more or less. A turbojet uses a compressor in the front to push the air into the engine. A ramjet relies on the fact that if you fly fast enough to start with, you get air pushed into the engine anyway. (Plus some clever design of the intake so the flame doesn't go in both directions.) But the air is slowed down to a subsonic speed at the point where the fuel is injected and lit. A scramjet is a ramjet where the air does flow at supersonic speed through the engine, so basically it's choked. You can add the fuel past the choke point and, since waves can't move backwards in a supersonic flow, whatever pressure you generate there by burning fuel can only go towards the back engine. The front of the engine can't "notice" the higher pressure in the back half because a pressure wave would have to travel through that air faster than sound speed, which isn't possible.

Another rough description would be that a scramjet is like a turbojet with an afterburner, only without the turbojet. (Sorta like the sound of one hand clapping, I guess;) Instead of having the turbojet push air through a nozzle and add extra fuel to it, the engine _is_ the nozzle and the airplane's existing speed is what pushes air to it. So you just add the fuel and light it. It's an afterburner without a turbojet.

Downside: a turbojet can start at zero speed, ramjets and scramjets need enough airspeed to start. Hence all these experiments involve booster rockets.

But in the end all 3 engines work by the same basic principle: air comes through the front, fuel is added, hot air comes out the back. No air, no flame, the engine stops.

The plans to use a scramjet to get to a highe enough orbit or even leave the planet, involve getting enough speed while still having enough air for the scramjet, or as boosters in addition to the normal rocket engines, or both.