Generator Exhaust Gas Temperature vs. Load 1

[jmbelectrical]

A mechanical engineer presented to me a specification sheet of a 2.5MW, medium-voltage, natural gas generator. The engine appears to be turbocharged and combustion is classified as "low emission." He is interested in the temperature of the exhaust gases as a function of load. The specification sheet states the following:

50% load: 913°F
75% load: 810°F
100% load: 752°F

This is the opposite of what I was expecting. All of the literature that I've read seems to indicate that, both for diesel and natural gas generators, temperature increases with load. What is going on here?

Any assistance would be greatly appreciated.

 

[catserveng]

These are likely the temperature readings at the stack (post turbo), and very common to see in low emission SI engines. The turbo is pulling more energy out of the exhaust at higher loads to supply more air.

To get a better answer more details would help, like maybe a copy of the spec sheet and details about manufacturer and model of the unit.

MikeL.

 

[EdStainless]

This is what I would expect from an engine highly optimized for one load level.
My question is 'does 50% load represent max EGT?'.
You need to know that.


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P.E. Metallurgy, consulting work welcomed

 

[catserveng]

Depends on the engine and its performance mapping. Many of the engines I get around actually have highest stack temp at startup and just after breaker close, fuel air maps get rich to get unit started and online, then lean out as boost comes up and usually target being in emissions compliance as it gets to 50% load.

Most gas engine manufacturers will supply more comprehensive data sheets if requested, about 90% of the time I need to push to get something besides the "spec sheet" given to customers by the sales guy.

If you're looking at a specific manufacturer and model, request a complete engine data sheet and any available application and installation materials that pertain to that unit as well.

Hope that helps, MikeL.

 

[waross]

Which side of the turbo is the temperature measured on?
When highway diesels first went to turbos, a pyrometer was often included.
I assumed that It was installed on the "hot" side of the turbo.
The temperatures would climb when the engine was under heavy load.
On a long grade, at full throttle, there was a concern that the exhaust valves may be damaged by excessive heat.
Drivers watched the pyrometer on long hills and dropped a gear and eased off on the throttle if temperatures went too high.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Hoxton123]

In the case of spark ignition gas engines, the user is interested in the temperature after / downstream of the turbo. Heat is often recovered from the exhaust in cogeneration / combined heat and power applications.

This temperature is not always monitored by the engine management system 'since it is what it is'. It is often monitored by the plant monitoring system to allow evaluation of total plant performance, and exhaust catalyst performance.

Most gas engine applications are to run continuously at rated power. Consideration must be made of the higher exhaust temperature at low load, especially during commissioning.

Most engine manufacturers have a ‘plant design guide’ where these factors are detailed. This is not the engine service manual!

Finally if your exhaust gas heat recovery system has a bypass, remember that the tail pipe after the heat recovery has to be designed for the higher engine exhaust temperatures!

 

[TugboatEng]

Most engine manufacturers will supply their engines with a turbo inlet temperature. Whatever goes on after the turbo is for the end user to determine importance and monitor.

 

[catserveng]

Tug,

With industrial gas engines, especially those used for power generation, turbo outlet or stack temperature (seen it called both ways by different manufacturers) is a pretty important parameter for the installer and end user.

Two primary reasons,
A large number of these engines operate in emissions regulated areas and expected stack temperature is used in the calculations for actual engine emissions output. The parameter is required in many areas when applying for air emissions permits.
Also a lot of these engines utilize heat recovery, and the engine outlet exhaust temperature is a design criterion for the heat recovery equipment.
Another time we saw a large number of requests for this parameter was when gas engines started to get more widely used in standby applications, and many of these applications had requirements for very tall or long exhaust runs, and stack temp was used to help determine length of run, diameter and material selection.

MikeL.