Power that a compressor takes 1

[GMath]

Hello,

I have one small problem,

I'm working on an project where a gas engine drives an electric generator and a compressor on the same axis.
To determine the total load of the gas engine we need to know how much power the compressor absorbs.

For technical reasone we can't build a torque measurement between the generator and the piston compressor.

Any ideas how we can solve this?

Tanks,

Gert

 

[crjones]

Try the differential pressure times the flowrate times a unit correction factor and you have adiabatic work. Divide this by an estimated efficiency and you will have a starting point

 

[zdas04]

Every industrial engine has a way to calculate generated hp from manifold pressure. I'd start there, then do an adiabatic hp calc on the compressor and get the output of the generator and compare them that way.

David

 

[j2bprometheus]

GMATH-

As zdas04 says, the manufacturer of the gas engine should be able to tell you approximately how much power the engine is putting out given the engine speed, intake manifold pressure, and, perferably, intake manifold temperature.

The engine manufacturer may want to know what accessories are installed on the engine for better accuracy (examples: the engine has an extra large cooling fan or an extra large alternator installed).

If the gas engine is an electronic engine, it might also have a fuel flow sensor, or an air mass flow sensor, and a estimated power in the engine control module.

A dealer or distributor should be able to access the info from the engine control module.

j2bprometheus

 

[dcasto]

realize that intake manifold pressure would mean downstream of any turbocharger or blower (love those MEPs, not)

 

[j2bprometheus]

Dcasto-

Yes, intake manifold pressure is downstream of the turbo or blower.

The intake manifold is also downstream of the charge air cooler or after-cooler. There is a significant pressure drop from the compressor outlet to the intake manifold.

The intake manifold is near the intake ports of the engine and is downstream of the intake throttle.

If the engine is an electronic engine, then it probably has an intake manifold pressure sensor on it. The sensor might be a combination temperature and pressure sensor.


j2bprometheus

 

[GMath]

Thanks for the help!

It is an electronic engine equipped with a fuel flow sensor.
I will contact the manufacturer for information.
When working with these data, we get estimates ... but how accurate?
I'm still looking for a more accurate method. (if it exists)

The flow of the compressor, we can't measure because the refrigerant is ammonia. (probably to expensive)

I've found a few formulas:
Wt = m / (m-1) Pa Va (((Pu / Pa) ^ (m-1) / m) -1)
with
Va = Ve + Vs-Vr
Vr = Ve (Pu / Pa) ^ (1/mr)

Wt / stroke -> power

This formula gives the adiabatic work. Will the outcome of this approach to reality?

Another option, by simultaneously measuring the pressures in the compression chambers, we can calculate the force of the piston. Is it then possible to calculate the torque?

Tanks,

Gert

 

[dcasto]

I'd recommend going to the compressor manufacturer and see if they can tell you what mass of the ammonia that is going through the unit.

But tell us why you can't measure ammonia again? a clamp on ultra sonic is available. Meaure the liquid phase coming out of the condensor. Unless there is a flash economizer then you'll need to measure the liquid coming out of that stream too.

 

[rjs286]

From a reciprocating compressor standpoint:

B.H.P.= Adiabatic HP/(Adiabatic Eff. * Mech. Eff.)

Adiabatic HP= 3.03 * 14.4 psia * (N/(N-1)) * (R^((N-1)/N)-1)

3.03 = constant
N = ratio of specific heats of gas compressed
R = ratio of compression

Try .95 for mech. eff. or verify with comp. manufacturer.

Hope this helps!