Quote:
Originally Posted by pgfpro
I do understand your VE statement and somewhat agree. VE is higher then people think at light load especially at lower rpm.
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To help the reader understand, I will simply say, the gasoline engine is designed to operate at or near lambda in most cases - lambda being the air/fuel mixture where all the oxygen in the air is consumed. Power output is directly proportional to the air mass flow. The higher VE at lower RPM is why the throttle is implemented to balance power output with power needs. It is easy to visualize the cylinder of an engine becoming filled 100% with air at zero RPM (at rest). At 120 RPM, it leaves you only 1/4 second to fill the cylinder, but the filling can still be high ( on the order of 95% of filled mass and above ). At 1200 RPM, you only have 1/40th of a second to fill the same cylinder. You can see that the short time period to fill results in a lower total air mass being passed into the cylinder. With all else being equal, as RPM increases, the time to fill is proportionally decreased resulting in decreasing air mass moved into the cylinder and as such, lower VE.
However, the use of a throttle plate changes all of the above by varying the restriction and the effective VE.
The problem George is having is realizing the mass of air at part throttle is very different than at full open throttle no matter what the RPM.