Reciprocating Engines

[joan271273]

I know that when you are using gas turbine generators turbines the standard output is rated ( qualified ) against certain rated conditions ( 70F, 60% RH, etc ) and when for example my ambient temperature goes up I will have a reduction on output capability.

Now in the case of reciprocating engines have some co workers telling me this is not the same or is basically negligible.

Can some one shed some light.

 

[redtrumpet]

(From Caterpillar Generator Sets Application and Installation Guide Sept. 1995)
Derating factors are given in NEMA MG1-22.40. Ratings are based on 40 C ambient air temp. For higher ambients the allowable temperature rise of the unit is reduced. Permissible temperature rise is higher for standby duty than continuous duty.

 

[BJC]

The generators are derated due to thinner air and don't cool as well.
The engines are derated based on thinner air as altitude increases. Turbo-charged engines are capable of operating at rated conditions over a wider range of altitude. I believe it's because there is more reserve capacity in the turbochargers.

 

[TheBlacksmith]

BJC,

You are correct, most turbo charged engines have some excess turbo boost, which is controlled or limited based on intake manifold pressure. With hotter/thinner air, the turbo is allowed to increase the pressure more before being limited, which tends to keep manifold pressure and power output more constant.

Also, all reputable manufacturers will publish derating guides. Please also note that recip engines, especially turbocharged ones, are susceptible to back pressure restrictions. You have to follow the manufacturer's guidelines. I could go on forever with the complaints of poor engine performance that "cleared" up right after the intake and exhaust was brought to spec. Also beware of the esthetics folks that plant a shrubbery to hide the ugly radiator, that will dramatically affect your cooling air supply!


Blacksmith