Air inlet temperature for 4-stroke diesel engine

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Pengze
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Air inlet temperature for 4-stroke diesel engine

Postby Pengze » Mon Sep 26, 2011 8:38 pm

Would appreciate if someone could tell us what is the optimum air inlet temperature to be maintain for a 4-stroke diesel combustion engine ? Usually, what should be the optimum air temperature above the ambient (engine room) temperature before going into the engine cylinders for combustion? Thanks.

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JollyJack
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JollyJack » Tue Sep 27, 2011 3:55 am

As low as possible, to maximize air density, but above the dew point, so the entrained water doesn't drop out. So it depends where you are and what you're doing. A supply boat or tanker in the Persian Gulf in August, (ambient temperature 45 C, engine room temp 55 C +, humidity 85%) would be completely different to a bulker or shrimp boat in the Davis Strait in January, (ambient temp -20 C, engine room barely above freezing, humidity 0%.)
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JK
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JK » Tue Sep 27, 2011 5:44 am

Is it not in the operating parameters of the engine? Or in the test data? If you are lucky enough to have that page in your manual.

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Re: Air inlet temperature for 4-stroke diesel engine

Postby Pengze » Wed Sep 28, 2011 12:24 am

To be more precise, my engine is 2574KW, BORE:330mm, STROKE: 440mm, RPM:620, Compression ratio: 13.5, 6 cylinders ,4-stroke, direct injection using MFO 180cst at 120degC and operating in South East Asia waters with average sea water temperature of 31 degC. Normally the engine room temperature is 40degC at engine RPM of 580.
So what should be the optimum temperature for cylinder air inlet temperature in order to get good combustion & satisfactory exhaust temperature.?

Since my engine shop test datas were carried out in Northern China during winter season, I could not compare with it as my environment is different.

Appreciate your kind feedback & valuable comments.

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JK
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JK » Wed Sep 28, 2011 12:59 am

Sorry, if you asked about really cold operations I could stir the brain fuzz a little harder, 32*C SW operating condition is something I never had to deal with (unless the system was going down).

Good luck.

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JollyJack
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JollyJack » Wed Sep 28, 2011 3:31 am

Local, coastal sailors never see warm water around here, unless they lose sight of land (OH! HORROR!) in August when the Gulf Stream changes, then it gets up to 20 C! :)

For the small, medium speed engine you describe, (sounds like a B&W Alpha) find out the ambient air dew point (the wave watchers can help you out there) and keep the turbo aftercooler outlet temperature just above that. Maximise the air density, but keep the water as a vapour so it goes through the engine, don't condense it out. Liquid water in a cylinder does funny things.
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JK
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JK » Thu Sep 29, 2011 3:12 am

JJ, you'd changed that attitude pretty quick, in the ice when the seabays have slushed solid, the pumps are airlocked and you are having cascading failures of machinery on overheat. When you have to take the covers of the strainers and shovel the ice into the bilge and the vents are pumping slush 6 feet over the side. The SW temperature may be just above freezing but you are running the seabay at 25*C to keep it from freezing up.
I have worked with many engineers who you seem to look down on as coastal sailors, I would sail with them before a lot of guys that only worked deep sea. The temperature of the water doesn't make a good engineer.

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JollyJack
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JollyJack » Thu Sep 29, 2011 3:28 am

two years at 71N (120 miles north of Tuk) taught me to recirc SW cooling to the sea bays, so I never had the problem of slush ice in the strainers. :)
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The Dieselduck
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Re: Air inlet temperature for 4-stroke diesel engine

Postby The Dieselduck » Thu Sep 29, 2011 4:57 am

I worked in similar environmental conditions, on a slightly larger power plant, 10mW Wartsila 46. I was going over our past actual running parameters, and at full load, we were running with charge air temperature (air manifold after the aftercooler) of between 55-60 degree celsius.

On the Wartsila 32, similar to your engine, the manual calls for a mid-range reading of 50 Celsius (max and mins for this particular specs, are not listed in manual), in 35 degrees ambient. There is calculations for humidity and various de-rating calculations, but I believe 50C is a good reference point.

Hope that helps.
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JK
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JK » Thu Sep 29, 2011 7:22 am

JollyJack wrote:two years at 71N (120 miles north of Tuk) taught me to recirc SW cooling to the sea bays, so I never had the problem of slush ice in the strainers. :)

condescending aren't we?

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JollyJack
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Re: Air inlet temperature for 4-stroke diesel engine

Postby JollyJack » Thu Sep 29, 2011 7:24 am

It's one of my many charms :)
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Big Pete
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Re: Air inlet temperature for 4-stroke diesel engine

Postby Big Pete » Sat Oct 22, 2011 11:39 pm

I agree that if running at full load you want the charge air temperature as low as possible,to increase the air density and hence themass of air in each charge, BUT if it is too cold you can have problems with thermal stress as the cold air hits the hot combustion chamber, and if you reach the dew point the condensing water will wash all the lube of your cylinders and have to fit all new liners and pistons soon, you certainly have to check your scavenge drains regularly in that humidity.
If you are running at part load then it is a better idea to keep the charge air temperature as hot as possible to improve combustion and overall efficiency as Martin says some engines run with very hot scavenge temps, 40 C used to be normal, but many engines use HT Jacket water for the first stage cooling of the charge air to provide preheating at start up and low load, with LT water used to provide second stage cooling at high loads.
In order to minimise condensation it is better to recirculate SW cooling to raise its temperature rather than throttling the flow of SW, because the SW will still be cold enough to cause condensation. If you have to throttle the sea water it is usual better to throttle the outlet from the cooler rather than the inlet.

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