You don’t typically use them on something that’s starting from a stop. I think ramjets are common on missiles. I think there are ramjet/scramjet planes which would also use a turbojet engine to get the plane off the ground before switching to the ramjet engine.

I’m pretty sure scramjet engines will have a shockwave inside the engine which will change the properties of the airflow through it. It’s been many a year since I studied propulsion and compressible fluid dynamics so I’m probably misremembering a fair amount of this but after the shockwave the air will flow slower through the engine. I think its temperature and pressure increases across a shockwave while velocity of the air decreases.

The thrust from a jet will always come from pretty much throwing the air out of the nozzle. You only have explosions outside of the engine being used for propulsion in a very specific kind of rocket engine.