Static Compression VS Dynamic compression

[David Redszus]

I found a use for Dynamic Compression Ratio other than to determine temperature and pressure.

DCR is directly related to Thermal Efficiency.

DCR......Thermal Efficiency
7..........54.32%
8..........56.50
9..........58.47
10.........60.26
11.........61.71

As long as compression temperature stays under control, shoot for a higher DCR.

[MadBill]

David, do those numbers take into account the Miller Cycle effect of a shorter effective compression stroke with an unchanging power stroke?

[David Redszus]

David, do those numbers take into account the Miller Cycle effect of a shorter effective compression stroke with an unchanging power stroke?

Bill,
I kept the engine parameters unchanged and only changed the chamber volumes. I could have changed IVC as well.
The change in SCR did not matter since it is not used in the calcs.

[GARY C]

I found a use for Dynamic Compression Ratio other than to determine temperature and pressure.

DCR is directly related to Thermal Efficiency.

DCR......Thermal Efficiency
7..........54.32%
8..........56.50
9..........58.47
10.........60.26
11.........61.71

As long as compression temperature stays under control, shoot for a higher DCR.

Between that and more cylinder pressure wouldn't that give a more complete burn of the fuel. The correct fuel of coarse.

[GARY C]

David, do those numbers take into account the Miller Cycle effect of a shorter effective compression stroke with an unchanging power stroke?

Bill,
I kept the engine parameters unchanged and only changed the chamber volumes. I could have changed IVC as well.
The change in SCR did not matter since it is not used in the calcs.

Wouldn't changing the chamber volume change the SC?

[David Redszus]

I found a use for Dynamic Compression Ratio other than to determine temperature and pressure.

DCR is directly related to Thermal Efficiency.

DCR......Thermal Efficiency
7..........54.32%
8..........56.50
9..........58.47
10.........60.26
11.........61.71

As long as compression temperature stays under control, shoot for a higher DCR.

Between that and more cylinder pressure wouldn't that give a more complete burn of the fuel. The correct fuel of coarse.

Gary, the higher DCR values would produce higher temperatures and pressures, which should cause a faster burn rate, raising combustion peak pressure and advancing the burn angle. Yes, that should result in a more complete fuel burn which is important since we can only actually burn a quantity of fuel predicted by air mass and stoich value. We can't burn more but we certainly can burn less.

[GARY C]

I found a use for Dynamic Compression Ratio other than to determine temperature and pressure.

DCR is directly related to Thermal Efficiency.

DCR......Thermal Efficiency
7..........54.32%
8..........56.50
9..........58.47
10.........60.26
11.........61.71

As long as compression temperature stays under control, shoot for a higher DCR.

Between that and more cylinder pressure wouldn't that give a more complete burn of the fuel. The correct fuel of coarse.

Gary, the higher DCR values would produce higher temperatures and pressures, which should cause a faster burn rate, raising combustion peak pressure and advancing the burn angle. Yes, that should result in a more complete fuel burn which is important since we can only actually burn a quantity of fuel predicted by air mass and stoich value. We can't burn more but we certainly can burn less.

Thanks, that kind of explains why cylinder pressure and DCR are looked at in reference to a pump gas engine that would be operating primarily at low rpm, high heat and on substandard fuel.