Industrial gas engine exhaust backpressure minimum?
Industrial gas engine exhaust backpressure minimum?
(OP)
Any idea why an engine manufacturer would specify a minimum exhaust backpressure on both NA and turbo'd models?
I need an exhaust system that will work for a wide variety of engines and outputs. The system needs to be large to keep the pressure below the maximum spec for the biggest engines but results in little backpressure (below manufacturer's specs) for the smallest engines.
I need an exhaust system that will work for a wide variety of engines and outputs. The system needs to be large to keep the pressure below the maximum spec for the biggest engines but results in little backpressure (below manufacturer's specs) for the smallest engines.





RE: Industrial gas engine exhaust backpressure minimum?
I speculate it's because somebody mis-read or otherwise misinterpreted a normalized graph, and nobody else has enough juice to question the edict.
Make the system big, and insert an orifice plate somewhere to restrict the engines that require a minimum.
Mike Halloran
Pembroke Pines, FL, USA
RE: Industrial gas engine exhaust backpressure minimum?
I've asked the manufacturer's applications engineering department about the minimum backpressure requirement and am awaiting a response.
Competing manufacturer's explicitly state there is NO minimum backpressure in their applications guides.
I've heard the burnt valve folklore but haven't seen anything to back this up. I could see how running without headers could burn a valve but I would think it has more to do with temperature fluctuations and has zero relation to backpressure.
RE: Industrial gas engine exhaust backpressure minimum?
I could not find any technical reasoning for that statement...
cheers,
gr2vessels
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
My Caterpillar manual is "Engine Installation & Service Handbook" and is obviously in contradiction with your book, because on page 25, under chapter "Exhaust Systems Formulas", it says:-
"The limits for a given engine's exhaust backpressure can be located in the TMI system. In general terms the backpressure limit is 27 inches of water for all Caterpillar turbocharged engines. 34 inches of water for naturally aspired engines. The 3600 series of engines have a limit of 10 inches of water.......Remember that the closer you get to the limit the more affect the exhaust backpressure will have on the performance of the engine."
I am however, surprised that Caterpillar has published apparently contradicting information on their handbooks.
cheers,
gr2vessels
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
Mike Halloran
Pembroke Pines, FL, USA
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
The turbos are also wastegated based on MAP (mechanically or electronically) so they shouldn't overspeed.
RE: Industrial gas engine exhaust backpressure minimum?
I don't see how creating a restriction makes it easier for the exhaust to escape and my calculations show the temps to remain above the dewpoint.
However, heat transfer requires a lot of assumptions and they've been doing this for a very long time.
RE: Industrial gas engine exhaust backpressure minimum?
As for back pressure, the engine was designed to work with a certain level of back pressure. If you change the back pressure, you need to change other variables, cam timing, fuel flow rate, etc., for the engine to run properly.
RE: Industrial gas engine exhaust backpressure minimum?
For example: Top Fuel Dragsters. They run 8 open individual exhaust stacks with no backpressure. 4 to 6 thousand horsepower from 500 cubic inches. All modern high performance exhaust systems tout "reduced backpressure" or claims to that effect.
Just IMHO.
Franz
eng-tips, by professional engineers for professional engineers
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RE: Industrial gas engine exhaust backpressure minimum?
A lot of turbo-diesel test cells run zero backpressure because they use a fumehood-type exhaust extractor. Natural gas is too hot and NA is too loud though (and a hood interferes with the overhead crane).
Chevrolet's NASCAR engine program runs a blower to reduce backpressure below on-car levels to increase the test sensitivity when making cam/valvetrain changes.
Top fuel engines only have to last 3 minutes or so :) but I haven't seen anything substantiating that backpressure is good, either.
RE: Industrial gas engine exhaust backpressure minimum?
Nothing wrong with a butterfly valve in the exhaust for an engine dyno.
Cheers
Greg Locock
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RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?
RE: Industrial gas engine exhaust backpressure minimum?