Author Topic: Ideal fuel mixture for air augmentation  (Read 901 times)

Offline sevenperforce

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Ideal fuel mixture for air augmentation
« on: 02/13/2016 01:27 pm »
Chrysler's SERV design for a fully reusable SSTO was probably the most unique contender for the Space Shuttle, even if it wasn't ever seriously considered. In the years since it was proposed, there have been quite a few engineering analyses that looked quite promising. Most of the challenges of the SERV design, like engine restart, have been well-handled by more recent advances.

It's likely that the margins would still be fairly close...which is why it's a concept that would benefit greatly from an integral air-augmented design. Unlike a ramjet or its more troublesome brother the scramjet, air augmentation does not rely on atmospheric combustion and thus augments thrust all the way from launch to the start of the orbital insertion burn.

What would the best fuel combinations for an air-augmented SSTO? Specific impulse is still important, because actual exhaust velocity defines the upper speed boundary at which air augmentation is no longer possible, but there are other considerations as well, like specific energy and exhaust mixing. The effectiveness of air augmentation depends on how rapidly and efficiently thermal energy can be added to the airstream. Would a triprop arrangement be best? The possibility of running temporarily fuel-rich to gain slight efficiency boosts from ramjet combustion is a nice advantage, but other factors might outweigh it.

Thoughts?

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