Use a detonation wave analogy to understand this
To maintain a standing combustion wave in a scramjet, the top air speed would be bounded by the hydrogen-air detonation velocity.
Download this PDF:
www.safetynet.de/Seiten/articles/CMRNov99.pdf
You'll find that the detonation velocity for hydrogen-air at STP is 1968 m/sec. It takes a finite time to break and form chemical bonds even in a detonation.
Gary
