Say you have a normal pneumatic launcher, lets assume a barrel sealing piston valve for now and pressurize it with a propane-air mixture instead of just air.
Then, between the sealing face of the piston and the projectile (the dead space), put another fuel mixture, preferably something like acetylene or hydrogen (propane may work too, I dont know).
When the piston valve opens, the air smacks into the dead space fuel mixture, rapidly compressing it. Shock heating -> ignition. As air goes into the barrel, the flamefront goes into the chamber.
To contain the fuel mixture between the projectile and the piston, you could use a balloon to contain it. Simply load the balloon behind the projectile, and you're done.
The main reason of this is not to create extra pressure (which also happens), but to heat up the air, effectively raising the speed of sound.
The SOS of air is the largest barrier in most high pressure, high velocity launchers. Raising it, using either a lighter gas or higher temperatures, will allow the projectile to be accelerated above the SOS without having a ridiculously large launcher.
Your opinions!
Does anyone know the auto ignition point and the pressure rise needed to reliably exceed it?
) , one could build a pretty good picture of precisely what happens in the dead space, but short of that, such a design would rely, at least to some degree, on trial and error.
