# Is it possible to create a direct supersonic airflow to a turbofan's afterburner in order to enhance the performance or reduce the fuel consumption?

so I found out that SR-71 Blackbird is using what's called "turboramjet" and I find the idea a bit appealing since they say with such engine, the Blackbird is more fuel efficient at it's top speed. I know that the mechanism for such engine is extremely complicated, but what's on my mind is not making an engine like Blackbird's, more to the point of having a direct supersonic fresh airflow to the afterburner to keep the fuel consumption slightly lower thanks to more oxygen to keep the afterburner effectively burn(because I heard somehwhere afterburners burns 3 times more fuel than dry thrust, I hope this can reduce it to only twice or even 1.5 times original dry thrust fuel consumption and have the same performance). Is it possible to do such thing? what would be the main problem to such engine/design? can it produce more thrust/more efficient in fuel consumption? and for the sake of calculations, let's say the turbofan engine in question is GE F-414-EPE, on afterburner, in supersonic speed.

• Are you asking whether the turbofan you mention could be modified to become a ramjet (or well, ram-fan)? There's a lot of fluff to your question which makes it hard to condense your main point. – Sanchises Oct 8 '16 at 8:45
• not necessarily a ramjet, more on to make a direct fresh airflow to enhance the combustion process in afterburner, the jet engine is still running during that time unlike Blackbird's turboramjet – Albert G. Oct 8 '16 at 9:20
• A turbofan already has bypass air, which could be considered 'fresh' air for the afterburner. So I'm not sure what else you're looking for. – Sanchises Oct 8 '16 at 11:37
• you're right, I might have to edit the question a lot... I'm was looking for a way to put direct supersonic airflow into the afterburner, since turbofan's bypass air is not really supersonic, I'd like to see if I can add more air for that – Albert G. Oct 8 '16 at 12:24
• Burning fuel in super sonic flow is hard. It's in active research but hasn't made into any service aircraft yet. Also your question makes it a much much harder because it implicitly requires the turbine exhaust be super sonic, and potentially also super sonic in the main combustion chamber. Most jet engines, including turbofan, turbo jet, or rocket engine doesn't have any super sonic flow until the nozzle. If you want supwersonic flow from the intake, through compressor, combustion chamber, turbine, into afterburner, plus supersonic bypass. I think 20 years of R&D from now is quite optimistic. – user3528438 Nov 15 '17 at 0:37

This is only possible because the intake would already compress the air by a factor of nearly 40 when flying at Mach 3.2. This precompression scales with $$p_0 = p_{\infty}\cdot\frac{(1.2\cdot Ma^2)^{3.5}}{\left(1+\frac{5}{6}\cdot(Ma^2-1)\right)^{2.5}}$$ so the precompression is much lower (less than 6) for a typical F-414 maximum speed of Mach 1.8.
($Ma$ = Mach number, $p_0$ = ram pressure, $p_{\infty}$ = atmospheric pressure).