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Occasionally6 · 10-10-2013, 11:06 PM

I get what you are saying but 4 should be enough. The pressure in the cylinder at the bottom of the expansion stroke is always higher than that at the top of the compression stroke in the next cylinder to fire. (There are more moles of gas and they're hotter.) At WOT it's that simple and the engine will run.

To simplify it further, picture a 2 cylinder engine without valves, each 180 degrees apart on the crankshaft, with each cylinder containing the same mass of air as the other. In one cylinder the air is hot and the other it's cold. Where do the cylinders end up?

Throttled would require subtracting the pressure difference between that in the cylinder that is on the inlet stroke and that in the cylinder on the exhaust stroke, from that in the cylinder that has just fired. As long as the sum of those is still greater than the pressure in the cylinder that is on compression - also at lower pressure than with WOT - and it will be, the engine will run.

Even allowing for the exhaust valve to be opened before BDC and ignition advance in the next cylinder in the firing order, that will be the case.

(jeff88, you ask good questions.)

10-10-2013, 11:06 PM	#46 (permalink)
Occasionally6 Master EcoModder Join Date: Apr 2013 Location: World Posts: 385 Thanks: 82 Thanked 82 Times in 67 Posts	I get what you are saying but 4 should be enough. The pressure in the cylinder at the bottom of the expansion stroke is always higher than that at the top of the compression stroke in the next cylinder to fire. (There are more moles of gas and they're hotter.) At WOT it's that simple and the engine will run. To simplify it further, picture a 2 cylinder engine without valves, each 180 degrees apart on the crankshaft, with each cylinder containing the same mass of air as the other. In one cylinder the air is hot and the other it's cold. Where do the cylinders end up? Throttled would require subtracting the pressure difference between that in the cylinder that is on the inlet stroke and that in the cylinder on the exhaust stroke, from that in the cylinder that has just fired. As long as the sum of those is still greater than the pressure in the cylinder that is on compression - also at lower pressure than with WOT - and it will be, the engine will run. Even allowing for the exhaust valve to be opened before BDC and ignition advance in the next cylinder in the firing order, that will be the case. (jeff88, you ask good questions.) Last edited by Occasionally6; 10-10-2013 at 11:18 PM..