Volumetric efficiency and torque output.
Volumetric efficiency and torque output.
(OP)
This post relates to a similar discussion I've had on another board.
I have been under the impression that the Volumetric efficiency of an IC engine would very closely follow the torque curve of the engine and that generally speaking the torque peak of the engine would represent the point of maximum VE.
Am I mistaken?
If so please explain.
Also what would be the proper way to determine accurately the VE of an engine?
I have been under the impression that the Volumetric efficiency of an IC engine would very closely follow the torque curve of the engine and that generally speaking the torque peak of the engine would represent the point of maximum VE.
Am I mistaken?
If so please explain.
Also what would be the proper way to determine accurately the VE of an engine?





RE: Volumetric efficiency and torque output.
RE: Volumetric efficiency and torque output.
"Also what would be the proper way to determine accurately the VE of an engine? "
measure the flow rate in the intake.
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: Volumetric efficiency and torque output.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.
RE: Volumetric efficiency and torque output.
RE: Volumetric efficiency and torque output.
A) HP = (T*RPM)/(5252) ...from: T = (5252*HP)/(RPM)
B) HP = (AP*CR*VE)*(CID*RPM)/(5252*150.8)
C) (T*RPM)/(5252) = (AP*CR*VE)*(CID*RPM)/(5252*150.8)
where:
T = Engine Torque, ft-lbs(f)
HP = Horspower
AP = Air Pressure, 14.7 psi
CR = Compression Ratio, ie: 8=9:1, 10=10:1
VE = Volumetric Efficiency; ie: stock ~ 0.90; high-performance ~ 1.00; race ~ 1.10
CID = Cubic-Inch-Displacement
RPM = Engine Revolutions-per-Minute
RE: Volumetric efficiency and torque output.
In that case in any engine the "real" torque peak is higher than the dyno reports simply because adding a few hundred rpm "costs" available torque despite the cylinder filling, etc still being good.
RE: Volumetric efficiency and torque output.
RE: Volumetric efficiency and torque output.
Not entirely true. Torque will peak when BMEP peaks. Which may, or may not, be when VE peaks. BMEP is IMEP minus FMEP. FMEP losses include pumping losses, accessory losses and also mechanical friction losses.
RE: Volumetric efficiency and torque output.
A) HP = (T*RPM)/(5252) ...from: T = (5252*HP)/(RPM)
B) HP = (AP*CR*VE)*(CID*RPM)/(5252*150.8)
C) (T*RPM)/(5252) = (AP*CR*VE)*(CID*RPM)/(5252*150.8)"
I sure may be wrong again, but don't see any terms I recognize to capture the influence of things like windage trays, roller rockers, air density (depends on temp and pressure), if its an air-cooled engine spinning a huge cooling fan (that I don't think is part of VE) or even "correct" A/F ratio or ignition timing
RE: Volumetric efficiency and torque output.
2) true, the final BMEP = IMEP-FMEP value will change in magnitude, but typically without (cavet wording) much change to RPM.
RE: Volumetric efficiency and torque output.