[Possible Causes?? of ] Cracks in exhaust system 3

[enginepuppet]

I'm having trouble with our gas engine (recip). It was shutdown because of the following indications:
1st. Engine overspeed
2nd. Turbocharger temp high high
3rd. Exhaust manifold temp high high
4th. Jacket Water surge tank level low
5th. aux water surge tank low

and we found that there are cracks spotted on several areas:
- 3 inside the exhaust manifolds
- wastegate
- and exhaust outlet

what is the possible causes of these cracks?

Ask me question and I'll give you more details.

Thnks
EP

 

[ivymike]

close.. you're thinking of 14.7

 

[ivymike]

not seeing the AFR on there, but 16g/hp-hr NOx means it's a "rich-burn" engine (says @5% O2, so guessing it's about 5% excess O2 in the tailpipe).

 

[gruntguru]

Rich burn? 5% exhaust O2 is about 25% excess air ie lambda = 1.25 or AFR = 21.5:1

Most NG engines will increase exhaust temp if the mixture goes leaner than design, because of slow burn (NG is particularly prone) and late heat release = higher exhaust temp.

Engineering is the art of creating things you need, from things you can get.

 

[MikeHalloran]

So find and fix leaks, or just go ahead and re-seal, the pipe between the carburetor and the turbo compressor inlet.



Mike Halloran
Pembroke Pines, FL, USA

 

[ivymike]

Rich burn? 5% exhaust O2 is about 25% excess air.

yeah, and anything under 5% excess O2 is counted as a "rich burn" engine in the vernacular. Common configurations of "rich burn" engines are "catalyst" settings (~0.5% O2) and "best bsfc" (2%-4% O2). I think I mentioned before that "rich burn" ng engines are typically operated on the lean side of stoich.

so anyway, if exhaust temps are too high, check the following:
- A/F ratio correctly?
- engine load too high?
- exhaust restriction too high?
- wrong ignition timing (for fuel MN used)

 

[ivymike]

...and for clarity, excessive exhaust temperatures on a natural gas engine can occur if air/fuel ratio is richer than specification.