engine room pressure/vaccuum

[EricatNordic]

In thread321-181668 someone commented that they believed an engine room should be slightly pressurized.

I wondered everyones consensous is.

I've always believed engine rooms shoulg be slightly below 1 atm because a pressure differential greater then 1 ATM would:

raise engine room temps slightly
allow a denser media for airborn noise trasmit through
pump anything leaking, burning off etc into adjacent compartments when ever a door is open or otherwise less then air tight.

 

[pauljohn]

Eric
The reason I believe the engine room should be slightly pressurized is for correct engine operation. In my opinion many engine power loss problems come from a lack of air available for combustion, it surprises many people how much air is actually needed for correct combustion and it is easy to starve engines of air in tight engine rooms. Ideally I think the engine room should be neutral at all engine revs. But that would be difficult that’s why I aim for slightly more at cruising.

I remember one boat I worked on I could feel resistance when opening the door when the yacht was cruising and you could hear the engine note change as soon as the door or hatch was opened. Another fan remedied the power loss problems it was having.

As for your reasons on lower pressure, I think proper engine operation is more important, also you can approach those issues separately.
High temp? You have other problems. Lack of air for the engines would more likely cause high temp.
Noise? Insulate more.
Fumes? Shouldn’t be any, apart from the air being changed frequently nothing should be burning for any length of time or leaking.

But this is just my opinion I would be interested in hearing others.

 

[JLSeagull]

On larger vessels aren't the engine air intakes external - not from the room air?

One of the HVAC balance issues pertains to accommodating opening and closing doors; and to select the zones where to close dampers upon fire or smoke detected. Closing HVAC dampers and stopping the intake and exhaust fans greatly affects the room air pressure differences.

 

[pauljohn]

I probably should of stated that this applies only to engines that take their air from inside the engine-room.

 

[catserveng]

I spent over 20 years commissioning engine systems, many in marine applications, and found that inadequate ventilation was the #1 cause of performance and fuel consumption complaints in marine engine rooms. Yachts typically the worst, offshore oil platform engine spaces usually the best, everything else usually somewhere in between.

CAT, Cummins, MTU, Mak, and just about all the others I know of publish guidelines for engine room ventilation, almost all universally ignored by builders and installers in my experience.

In general full load intake air restriction (with clean filter/silencer) should be less than 5" H2O, compared to atmospheric pressure. Best practises I have seen try to limit ventilation air temp rise across engine space to less than 10 degrees F, and try to keep air temperature to air inlet within 5 degrees F of outside air temp at full rated load.

Hope that helps

 

[itsmoked]

Nice info cat.

I saw engine room hatches on a large yacht,(60ft Hatteras), that were sucked out of hands to slam shut. (Terrifyingly!) You could hear the two 8V53's change note simultaneously.

It can be pretty tough to get enough air into an engine room when breaking waves and a lot of water surround the problem.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rovineye]

JLSeagull,
Most ships take combustion air from the space.

I have 4 ea 11mW diesel generators. We were originally going to use some sort of logic or VFD to control fans as generators started and stopped. We didn't and I was worried. Turned out the space and supply ducts were large enough that there was no issue. The door closers worked in all combinations, but are trickiest to set with all 4 engines running at full load, which I can't simulate in port.

 

[itsmoked]

11 milliwatts huh? Tweezers?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rovineye]

And you ought to see those tiny little pistons pumping!

OK, OK. MW.

 

[chief]

A diesel engine burns 14 times as much air as fuel. You can never get enough air into an engine room.

Offshore Engineering&Design

 

[ssreese1500]

I have never actually measured the pressure, but I have seen a significant change in exhaust temps in diesel engines merely by changing the direction of air so that it goes to another part of the engine room as opposed to right by the air intakes. This is of course on a system where the engines take their air from the engine room.

The more air the better, the density of the air having an effect on heat of the engine room is a minor player.

 

[KoZot]

I am an offshore-rig mechanical design engineer and we are always having dramatically numbers of air changes per hour in our Engine Rooms, over 60 AC/hr, with preferably 50 Pa pressurized compartment or up to 20% more supply than room exhaust air. That is to be sure no air from surrounding compartments will come in to the Engine Room. All this related to hazardous areas classification and Engine Room is classified and must be a Safe Area.

 

[aungkyawtun]

Pls find attached that we usually calculate