Quote:
Originally Posted by Frank Lee
Nobody has throttled an engine with a tc/sc have they?
I wonder if there is enough energy in the intake airstream to be worth harvesting.
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Apparently, one of my posts didn't post...
The way to throttle an engine with a fan would be to run it at a high speed for low throttle, and run it at zero speed for max throttle... the problem with this, is that it wouldn't be anything close to instant throttle response, and the amount of energy scavenged would directly affect the VE of the engine - according to the laws of conservation of energy, when you extract energy from a mass, the mass would then have that much less energy to give.
Since you're extracting energy from air flow, any energy extracted would cause that flow to slow down, negatively impacting the engine's intake charge.
Per this site:
We can substitute the intake fan for a wind turbine here, and substitute the influx of air for wind.
We can determine the power that can be extracted from the intake air by using the following formula:
P = 0.5 x rho x A x Cp x V3 x Ng x Nb
We'll replace the variables with nominal figures, assuming we're at sea level, and the fan has a 4" diameter, using the Betz limit, which is considered universally unreachable, as our coefficient of performance Cp, assuming our generator is 80% efficient (Ng), and assuming there is no gear or drive losses (Nb):
P = 0.5 x 1.225 kg/m3 x .008 m2 x .59 x V3 x .8 x 1
The only plug left to make is the actual volume of air in M/S.
50 CFM works out to 0.0235973722 m/s3, which replaces V3 in the equation:
P = 0.5 x 1.225 kg/m3 x .008 m2 x .59 x 0.024 m/s3 x .8 x 1
So, given the best know circumstances, the power generation capability would be: 0.0000555072watts at idle speed using 50 CFM of airflow.
Yep - Five one-hundred-thousandths of one watt, under nearly perfect circumstances.
And that's extracting an enormous amount of the energy from the airflow, so much so that the engine couldn't idle any more, with perhaps the most efficient equipment currently known to exist.
Anyone care to check my math? I think I messed up somewhere.