re: The only design for a scramjet that works in theory
has combustion take place for a short time (perhaps 10 seconds, I forget), and then coasting for at least as long, allowing convection to cool the engine, before restarting. I read the published description of the hypersonic propulsion system in the SAE Aerospace Journal, and it included magnetron ionization of the airflow to allow instant combustion of hydrogen and oxygen. I tossed the journal in the blue box several years ago. They published too often, if I didn't throw them out they'd have created a fire hazard!