Product: Engine: Jet
Piston Pulse-Jet Engine   (+3, -1)  [vote for, against]
A pulse-jet engine powdered by pistons

This may be a test of creative visualisation but here goes . . .

Imagine for a moment a piston in a cylinder, much the same as the cylinder in a car engine. In this case however the ‘bottom’ of the piston (which would normally be attached to the drive shaft), is another smaller piston itself in a cylinder, such that both cylinders form one continuous shaft.

The ‘top’ part of the cylinder is coupled to an adjacent combustion chamber through a valve and also has an intake valve to allow a fuel / air mixture to be sucked into the cylinder from outside the cylinder assembly. The ‘bottom’ part of the cylinder is coupled to another (but different) combustion chamber likewise through a valve assembly.

Some method of initiating movement in the piston – much like a car starter motor would be needed, however given this the combustion cycle would then be: a) The piston moves down sucking fuel / air into the ‘top’ part of the cylinder and into the combustion chamber; b) The piston then moves up compressing the fuel / air mixture; c) The mixture is ignited in the combustion chamber – at the same time the valve between the top of the cylinder is closed and the valves at the bottom of the cylinder and the exhaust valve are opened. d) Expanding gases are simultaneously expelled out of the exhaust valve of he combustion chamber (ie for propulsion) and also into the bottom part of the adjacent cylinder – pushing the cylinder up and starting the cycle over again (refer point b).

The geometry of the various valves and vents means that only a portion of the expanding combustion gases are vented into the bottom of the adjacent cylinder.

You have to also picture cylinders and combustion chambers lined up one next to the other, such that the exhaust (combustion) of one, powers compression of the next. You would probably have to arrange them in a barrel shape or the process would end after one cycle.
-- Brett-Blob, Oct 12 2007

Improved compression ratio <he said hopefully>. More seriously there may be advantages over a regular pulse-jet engine however, from my understanding these types of engine are unreliable and inefficient as compared with a turbo-jet engine. So there is probably no advantage.
-- Brett-Blob, Oct 12 2007

Like this?

Starter->sprays fuel/air mixture into C-1 & compresses C-1

C-1 ignites -> 70% jet exhaust + 30% C-2 fuel/air intake & compression

C-2 ignites -> 70% jet exhaust + 30% C-3 fuel/air intake & compression

etc, firing in a circle until back to the 1st cylinder again.
-- quantum_flux, Oct 12 2007

Yeah thanks <quantum_flux>, that description is pretty much right. You have to also picture that each piston has an associated combusion chamber.
-- Brett-Blob, Oct 12 2007

me no understand.
-- BJS, Oct 12 2007

[] ( ) [] ( ) . . . etc
-- Brett-Blob, Oct 12 2007

You might even want to go with a configuration with 9 cylinders and having every 3rd cylinder firing simultaneously, so you havd kind of a spinning triangle of explosions, like this:

C-1,4,7 ignite -> 3x jet exhaust + C-2,5,8 fuel/air intake & compression

C-2,5,8 ignite -> 3x .... + C-3,6,9 ..&..

C-3,6,9 ignite -> 3x .... + C-1,4,7 ..&..

C-1,4,7 ignite -> etc, [+]
-- quantum_flux, Oct 12 2007

If the engine's pistons reduce it to powder, what use is it?
-- AbsintheWithoutLeave, Oct 12 2007

I think the problem is the obfuscatory and complicated method of achieving something quite simple. In an otto-cycle engine a proportion of the energy from combustion is used to compress the fuel/air mixture and the rest (mostly) is used to power the drive shaft. If instead of this the combustion products were vented as an exhaust jet and only the bit needed to keep the engine going was retained you would have a simple pulse jet engine, which was more reliable and more efficient than a regular pulse-jet.
-- Brett-Blob, Oct 15 2007

random, halfbakery