Toroidal Aerospike Air-Augmented Rocket?

[JMBuilder]

This is just another one of my random ideas that I'd like to discuss and see if it would be practical.

So an air-augmented rocket is basically a rocket that compresses air to produce additional thrust, and a toroidal aerospike rocket is a rocket designed to be more efficient inside of an atmosphere. So what if these two designs were combined? Would it be more efficient?

Edited November 1, 2014 by JMBuilder

[shynung]

Uh, ramjets are more similar to turbojets than to rockets. They're basically a turbojet minus the turbines. They don't, as a rocket does, carry their own oxidizer.

That said, I don't see much improvements over a traditional ramjet design, as they are already more fuel-efficient than pure rockets.

[K^2]

Aerospike has nothing to do with fuel you're using. It's just a way to get rid of the nozzle bell. You can use the principle with a conventional rocket, an air augmented one, a ram jet, or even a turbojet. Though, you start getting diminishing returns as your exhaust velocity drops.

That said, modern scramjets already have aerospike-like geometry. I don't think one can much improve on that. Now, an air augmented rocket could probably make better use of a proper toroidal aerospike.

[JMBuilder]

Oh, okay. I was getting ramjets and air-augmented rockets mixed up. I'll edit the original post.

[shynung]

Though, you start getting diminishing returns as your exhaust velocity drops.

That's what I was thinking. Airbreathing jet engines have lower actual exhaust velocity than rockets. Their nozzles were not designed for maximum exhaust velocity, but to balance it along with mass flow from the air intakes.

[JMBuilder]

Back on topic, would an air-augmented toroidal aerospike rocket be more efficient than either a regular air-augmented rocket or toroidal aerospike rocket alone?

[Kryten]

Both are dependent on the specific conditions. Improvements from aerospikes depend on the chamber pressure; Pressure-fed engines could see dramatic gains, and something like RD-170 and it's descendants would not benefit at all.