Ramjet is a really great idea that it has no moving parts to have problems with.
(Pulsejet is another similar great idea.)
The problem with ramjet is that it does not work efficiently in low aircraft speeds.
Normal jet engines work efficiently in low speeds, but why?
What is the difference?
I think it must be because normal jet engines create a vortex when they run.
A vortex like the vortex of a tornado.
So how a ramjet could create a vortex?
What if there is a (non-moving) helicoid in the middle (fire chamber) of the ramjet.
It would force the movement of gas into a vortex motion.
If the helicoid designed with more and more turns, it would increase the speed of gas going thru the vortex motion.
I think that means then the ramjet engine could work at lower and lower aircraft speeds.
(Until at some point it would be possible to start the ramjet while aircraft is not moving on the ground.
In the front of the ramjet there maybe an airpump to start it if necessary.
Also there maybe many little gas fuel (LPG/LNG?) outlets around the fire chamber, inside the engine,
located like equal distant points on a helix
to start/help continue the vortex motion.
I think this ideas could also help improve the pulsejet engines.