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Am trying to find some information on air requirements for 250 HP 6BTA JWAC engines.
Current air intake uses 2 off 6 slot aftermarket stainless vents on the port and starboard sides.
Each slot has 3″ x 1/2″ opening = 1.5″sq x 6 = 9″sq for each vent.
2 off vents provide 18″ open area for each engine.Will be adding another vent to give a total of 27″sq open area for each engine.
Also, have 2 off 6″ centrifugal blower exhausting hot air from the engine room.Note that the boat has never run at WOT since I purchased it so haven’t been able to check if the engines are getting enough air by opening engine hatches while underway.
After reading this incredibly informative forum I figured that the aftercoolers were blocked, local Cummins wanted to cut open JWAC to clean them !!!!!
Couldn’t find a big enough ultrasonic cleaner and don’t have the time to build a unit so purchased new aftercoolers (Yes, they were new, boxed, bagged and covered in protective grease).What I would like some help with is working out how much air is required at 100% load and WOT.
Cheers
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Engine room Air Ventilation thoughts
Do your best———————————————-Get what you can get “sq inches wise”, but balance water spray as a major thing you MUST deal with..
Next, so you can think “the field” and not just what is in a book…………I want to be sure your understand it all so you do not just add more sq inches and not think think about other ramifications that can bring..
If you were to interpolate air intake specs from various engine manufactures, you would probably come up w/ what I did years ago…
The average air consumption of a diesel engine(4 cycle) is ABOUT 200 CFM per 100 H.P. produced. Although this is a rough average, youĀ“ll find that by looking through engine literature/air cleaner literature, etc., this is a reasonable # that you can use for planning purposes…
Next if you do the same thing with “recommended ventilation requirements” printed by the various manufactures in their installation guidelines, youĀ“ll be able to average out that the typical “square inches” needed or “recommended” is about 50 sq. inches per 100 H.P… Sounds like a lot, but one of the things besides restriction that the engineers want to accomplish is to slow down the velocity of the air movement in the engine room (at least this is a consideration that needs to be considered, especially in smaller engine rooms). This allows moisture/dirt, etc. to drop out of the air before making it to the air inlet. Eng. room temp. also plays a major part is the overall equation and besides keeping the max temp below about 120 F., it would be common to see a manufacturer recommend a maximum delta of 30 F. between outside ambient and the eng room… From my past experience, in many cases one can reduce this “recommendation” to about 25 -30 sq.-30 per 100 H.P. and still meet the ventilation needs.
Another simple # I’ve been using for years that works for planning purposes is to do w/ the other end of the engine; exhaust flow is typically about 2 1/2 times the intake flow (about 500 CFM per 100 H.P. produced)
Tony
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A good rule of thumb is 50 sq. inches per 100 HP… This sounds like a lot but itĀ“s about the average recommendation from interpolating various manufacturers specs I looked (all the big names)..
On a Yanmar “Quick Reference” sheet, the required ventilation is listed as 1218.19 (sq.centimeters, I think ??)(4LH-STE) and if this indeed is correct, then thatĀ“s about 189 sq. inches per engine.. ThatĀ“s even more than my rule of thumb..
From 20+ yrs of experience, I’ve found that one can get by with 30 sq. inches per 100 hp in most cases …Hope this helps………………………………………………………………..Tony
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