[Air Breathing Junk] How about TurboScramjet?

[RandomRyan]

Scramjets are mechanically very similar to ramjets. Like a ramjet, they consist of an inlet, a combustor, and a nozzle. The primary difference between ramjets and scramjets is that scramjets do not slow the oncoming airflow to subsonic speeds for combustion, they use supersonic combustion instead. The name "scramjet" comes from "supersonic combusting ramjet."

well, we already "have" a turbo ramjet engine*, why not a turbo scramjet**?

it runs at MACH 6, so must be really fast eh? of course! it goes hypersonic!

anyway, its just like a turbo ramjet. put a scramjet in front of (an after-burning) turbojet and you're done.

my question is, will it work?

(yeah, about the * and **)

*Pratt and Whitney J-58

**Boeing X-51

[Porkjet]

Lockheed's trying to built something like that

Noone can say if it'll ever work

[cantab]

Well I think the only IRL "turboramjet" engine is the Pratt & Whitney J58 that powered the SR-71 spyplane. And that adopts a relatively simple approach where the "ramjet" is just the turbojet's afterburner. That's not I think something that would translate to scramjet operation.

Another challenge is there's a gap between the upper end of turbojet and the lower end of scramjet ability. That means you need to support (subsonic) ramjet as well as scramjet propulsion, making things even more difficult.

And however you lay things out - as one engine like the J58, as two separate engines, or partly combined like the picture above, you've still got the weight and complexity of turbojet machinery to lug about. Depending on the application other propulsion might be better used to get up to speed.

[Streetwind]

The air driven by a turbine is not nearly moving fast enough to drive a scramjet.

As it is, it already struggles to make the ramjet work from standstill, getting fairly low thrust on the runway and not allowing the plane to speed up much. But it's enough to get the ram effect going, upon which the engine develops its true potential.

A scramjet however doesn't get going until mach 3 or so. You can't accelerate to mach 3 with nothing but a full bypass turbine blowing air through an inert combustion chamber.

What would work though is taking a turboramjet to accelerate beyond mach 3, and also carrying a scramjet which takes over at that point.

[Kryten]

What would work though is taking a turboramjet to accelerate beyond mach 3, and also carrying a scramjet which takes over at that point.

For most applications it would be easier to just use a rocket booster, probably solid. You don't have to lug all the extra weight around and the overall vehicle is very likely to be disposable anyway.

[Streetwind]

Depends on the application and the location, too. You might have to cruise subsonic for a fair amount of distance after taking off and before landing, due to regulations. Hypersonic booms are even louder than supersonic ones and can actually damage stuff on the ground in low overflights (and I'm not saying eardrums).

[Nothalogh]

As the gentleman pointed out above, the Lockheed design is the most sensible, but would still need rocket for the final kick to orbital velocity.

Though boron zip fuels in the afterburner and the scramjet would probably help squeeze out a little more dv

Edited October 31, 2015 by Nothalogh

[Mithravarun]

I have an idea where I have put the turboramjet( j-58) in the front of the engine including the six bypass tubes. Behind that engine, I have put a scramjet. I know the scramjet won't get enough o2 for combustion. For that, I have given the scramjet two additional air inlets above and below the engine nacelle which will open up only after Mach 3.5. The main air inlet for the j-58 will close at that speed the engine will shut down and the scramjet will turn on only after that speed is reached. In order to cool the j-58, the two air inlets will let some air pass through around the engine nacelle. Thus, it is an air-cooled turboscramjet engine.

I don't know if it will work. Please excuse me, I am only thirteen and I have no experience in these fields.

[magnemoe]

 

2 hours ago, Mithravarun said:

I have an idea where I have put the turboramjet( j-58) in the front of the engine including the six bypass tubes. Behind that engine, I have put a scramjet. I know the scramjet won't get enough o2 for combustion. For that, I have given the scramjet two additional air inlets above and below the engine nacelle which will open up only after Mach 3.5. The main air inlet for the j-58 will close at that speed the engine will shut down and the scramjet will turn on only after that speed is reached. In order to cool the j-58, the two air inlets will let some air pass through around the engine nacelle. Thus, it is an air-cooled turboscramjet engine.

I don't know if it will work. Please excuse me, I am only thirteen and I have no experience in these fields.

This work for an simple ramjet like the sr-71 used, its not optimal but work. 
For an scramjet the geometry of the intake and engine is critical as air is supersonic trough the engine.
You might be able to get an scamjet to work as an bad ramjet taking you from mach 3 to 5 as is porkjets image.
Or you could go full out with an skylon engine followed by an scramjet at mach 5, you are likely to have to run the scram on hydrogen anyway. 
at mach 20 you switch back to skylon in rocket mode
you can use the liquid hydrogen to cool the edges during ramjet mode too.
Want it for KSP, you do the Jool intercept burn in the atmosphere