The plug fires several degrees BTDC, and as the combustion begins in the cylinder, the piston completes its compression stroke and begins the power stroke downward to absorb the energy from combustion.
The combustion process is not instantaneous- if it were, you would be experiencing Detonation, and that's why smacking the piston as it's still on the way up causes bent rods, cracked rings, broken pistons, etc.
The combustion process is not instantaneous- if it were, you would be experiencing Detonation, and that's why smacking the piston as it's still on the way up causes bent rods, cracked rings, broken pistons, etc.
Neat idea.
Almost like 2 pistons facing each other.
You wouldn't want to fire the plug when the crank is at 90* tho... more like about 45*. So that peak pressure is exerted when the crank is indeed at 90*.
Also I don't know what the heck you guys are talking about the plug firing a "couple of degrees BTDC". Maybe when your doing your timing at idle with the vacum advance disconnected. Most ford V8's run in the neighbourhood of 36* total timing advance. They only run 10* or so when at full throttle during low engine RPM (below 1500). This is of course assuming your running the standard VAC adance/mechanical adv setup.
Almost like 2 pistons facing each other.
You wouldn't want to fire the plug when the crank is at 90* tho... more like about 45*. So that peak pressure is exerted when the crank is indeed at 90*.
Also I don't know what the heck you guys are talking about the plug firing a "couple of degrees BTDC". Maybe when your doing your timing at idle with the vacum advance disconnected. Most ford V8's run in the neighbourhood of 36* total timing advance. They only run 10* or so when at full throttle during low engine RPM (below 1500). This is of course assuming your running the standard VAC adance/mechanical adv setup.
I only just saw this thread. OMG that's not too bad of an idea.
Having two pistons facing each other, with their crankshafts out of phase, say the top one, where the head used to be, should be at TDC when the bottom one is at 90 ATDC when the fuel starts really burning.
Or yeh, I get it now, have the top piston on a cam, so it doesn't move until after the exhaust stroke is under way.
Problems I can see are: You'd need a darn strong cam and lever to cope with the forces, you have to mount the spark plug and inlets somewhere, perhaps a two-stroke would be the key. Perhaps a diesel setup, no spark plug. Also there is extra mass and friction in the engine. Which again may be reduced because no valvetrain, etc.
One really bad thing I just thought of is you'd need ENORMOUS spring pressure to hold the top piston in position against the cam at 6000rpm or so, because it will weigh a LOT more than a valve. It would still operate at the 1/2 speed though, like a valve. This would a great design for a 4000rpm diesel. No spark plug, the fuel lubricates both sets of rings, and lower spring pressure because of low rpm. The max torque firing chamber design too lends itself to this.
You could use the top piston to open and close the intake and exhaust ports though, that would be a good thing, plus it's on a cam anyway.
I'm really starting to think this isn't as crazy of an idea as I first thought.
Having two pistons facing each other, with their crankshafts out of phase, say the top one, where the head used to be, should be at TDC when the bottom one is at 90 ATDC when the fuel starts really burning.
Or yeh, I get it now, have the top piston on a cam, so it doesn't move until after the exhaust stroke is under way.
Problems I can see are: You'd need a darn strong cam and lever to cope with the forces, you have to mount the spark plug and inlets somewhere, perhaps a two-stroke would be the key. Perhaps a diesel setup, no spark plug. Also there is extra mass and friction in the engine. Which again may be reduced because no valvetrain, etc.
One really bad thing I just thought of is you'd need ENORMOUS spring pressure to hold the top piston in position against the cam at 6000rpm or so, because it will weigh a LOT more than a valve. It would still operate at the 1/2 speed though, like a valve. This would a great design for a 4000rpm diesel. No spark plug, the fuel lubricates both sets of rings, and lower spring pressure because of low rpm. The max torque firing chamber design too lends itself to this.
You could use the top piston to open and close the intake and exhaust ports though, that would be a good thing, plus it's on a cam anyway.
I'm really starting to think this isn't as crazy of an idea as I first thought.
WORTH said:
Agreed!
Also.. think of how this would effect compression "leak". Since the engine will spend more time with the fuel under full compression, I would expect to see more loss caused by fuel leaking past the cylinder rings. Especially since now we'd technicaly have 2 sets to piston rings to leak through.
Also the "follower camshaft" would have to be pretty beefy. Almost like another crankshaft.
There already has been an engine in which there was a common cylinder with two cranks, and the pistons opposed to each other. This was the Fairbanks-Morse diesel engine, used in most of the WWII subs and later after the war in railroad locomotives. It was a very successful sub power plant due to it's compact design, but the railroads didn't like it, due to the difficulty in overhauling one. In a sub, the top and bottom cranks were accessible, but in a locomotive, the whole thing needed to be pulled to access the bottom crank. It was an extremely powerful engine for it's size, which was the main reason it was so well liked in subs. The crews called em "rock crushers" .