How much ventilation for diesel?

[Uncle Bob]

Originally Posted by Uncle Bob

I guess that technically, yes, however the simple reality is that an engine running at x rpm will consume y cfm of free air.

Originally Posted by Tonali99

Okay ... just what does RPM have to do with volume?
So it moves more cfm in a given time frame, NOT more cfm per stroke.

Ah, do you really need to have my quote explained? Hint, nowhere do I mention cfm/stroke, merely that an engine running at x rpm will consume y cfm of free air, or put another way, the faster it goes the more air it moves.

[hpeer]

Funny this thread.

Just this morning I decided to remove the ducting to the engine room.

72hp YANMAR 4JH4, original was a Perkins (4-236???). Anyway the engine compartment has a 5” diameter duct which runs through a closet and the opens inside a cockpit locker. That locker has a plastic cover. I always try to remember to olen the cover but sometimes that doesn't happen or it blows closed. Opening and closing the cover has no effect in the engine. There is no noticeable suction in the plastic cover.

That tells menthe effective air moving through this gizmo is about zero. Perhaps a practical test on a vent would be to generate some smoke (mosquito coil??) and see if the vent move it.

Anyway I am going to remove the vent tube. The engine room will still have a hole for the air to come in, just from the closet. For what ever reason the vent tube terminates into a box on the side of the engine box. It almost looks like it was intended to house a fan but there are no wires to it and no other holes in it.

Anyway, thinking this through, I see no downside of removing this vent tube and covering the opening with a screen.

Now that I think of it , this would make the perfect place to spray an extinguisher into the engine room in case of fire.

[Jimmyhenry]

4 stroke engines, petrol or diesel, operate on the old method of SUCK, SQUEEZE, BANG, PHEWEY.
That is the 4 strokes, 2 up and 2 down.

If the engine is 2000cc capacity, then every 2 revolutions it inhales, and exhales the 2000cc, albeit the exhaust being hot will be more volume (That's how a turbo works so well.)

Give or take, for a 2 litre engine, the air going in will be for say 2000 RPM, 1000 times the capacity, (i.e.: 1000 X 2000cc) So about 2 cubic metres of air per minute.

So if the engine is running, it will suck all the air in the engine area quite nicely, and then suck in air from outside the room. Conveniently removing engine smells out eh exhaust.

Remember, diesels like to have plenty of air, so if the engine room is tightly sealed you will end up with negative pressure inside that room, not a good thing.

Pete

[Compass790]

Originally Posted by Nineteen

Not true. A petrol and a duesel of the same displacement will use the same amount of air per cycle. The diesel will just compress it much more.
Cheers

Not quite right but yes I was wrong. See post #12, I've already taken my punishment.
Need to read the whole thread to get the whole story.

[Icarus]

Originally Posted by Compass790

Depends if his car is petrol or diesel.
Diesels require roughly twice as much air as the same cc petrol engine, the clue is in the compression ratio.

The amount of air sucked into the combustion chamber is the same regardless if it is a diesel or petrol engine if both are of the same displacement.
Compression has nothing to do with it.

[Uncle Bob]

Originally Posted by Icarus

The amount of air sucked into the combustion chamber is the same regardless if it is a diesel or petrol engine if both are of the same displacement.
Compression has nothing to do with it.

Hi, he has already admitted his confusion, been whipped and beaten, (and loved it ) and as he has said, reading the whole thread would have revealed this.

[mikesu2016]

To answer the OP's question, I would say, that I have a Volvo 3cyl 29hp diesel (about same size/output as the Yanmar) driving my 13.5t gaffer and it is under the cabin steps - a fairly closely fitted sound-proofed box (not very efficient for sound, as there is no bottom to it!) All the combustion air is therefore sucked from the space under the floor. This under floor space runs almost from end to end of the boat and contains 6-7 tons of lead, iron sash weights and some pig iron (all the Ballast in fact) held on cradles between the frames clear of the hull planking. So no restrictions on air flow at all.

Most days it gets used twice for 20mins or so to get out of the marina, down the river to where we can sail as the point is to sail as much as possible.

Unless the OP's engine space is an airtight box, I would guess that he doesn't need to worry about air vents at all.



Here's hoping we all get to sail again this year !


Mike

[Nineteen]

All good - I was speaking generally and on the fly. I wasn't trying to factor in density, dew point and mixture strength[emoji6]

Originally Posted by Compass790

Not quite right but yes I was wrong. See post #12, I've already taken my punishment.
Need to read the whole thread to get the whole story.

[Compass790]

Originally Posted by Nineteen

All good - I was speaking generally and on the fly. I wasn't trying to factor in density, dew point and mixture strength[emoji6]

Hell, I was only on the beer when I got into trouble, dont wanna start on the fly!

[Nineteen]

[emoji1360][emoji23][emoji23][emoji23][emoji23][emoji23]

Originally Posted by Compass790

Hell, I was only on the beer when I got into trouble, dont wanna start on the fly! [emoji3]

[FPNC]

With a small engine on a sailboat, combustion ventilation is usually not a problem. You need to worry about ventilation for removing heat. Both engine heat and alternator heat. As far as the engine is concerned, if your 155° F or less, your fine. Cooler is always better with diesel. Get a thermometer.

[Jdege]

Originally Posted by FPNC

With a small engine on a sailboat, combustion ventilation is usually not a problem. You need to worry about ventilation for removing heat. Both engine heat and alternator heat. As far as the engine is concerned, if your 155° F or less, your fine. Cooler is always better with diesel. Get a thermometer.

Another helpful tip.

I'd planned on covering the vents, closing the hatches, and seeing how the engine ran. Adding a thermometer to the mix should be simple enough. It's the engine getting enough oxygen? Is it getting too hot?

It's something I need to understand, as I determine what needs to be done to this boat.

Of course, it will have to wait. Temps here, this week, are below zero fahrenheit.

[FPNC]

If the engine has the ability to reach and maintain wide open throttle underway without overheating and the engine compartment is not too hot, then the engine installation should be fine. Keeping the engine compartment as cool as possible so as not to heat soak the living quarters is another matter.