Engine Ventilation: Skip it?

[YourOldNemesis]

Hmm, I'm not sure that air is responsible for as much as 10% of the cooling. A water-cooled engine has a heat exchanger to dissipate heat. If it were advantageous to air-cool as well, there'd be fins all over the cylinder head.

According to wikipedia - that well-known font of all knowledge -

Comparing air and water, air has vastly lower heat capacity per gram and per volume (4000) and less than a tenth the conductivity, but also much lower viscosity (about 200 times lower: 17.4 × 10−6 Pa·s for air vs 8.94 × 10−4 Pa·s for water). Continuing the calculation from two paragraphs above, air cooling needs ten times of the surface area, therefore the fins, and air needs 2000 times the flow velocity and thus a recirculating air fan needs ten times the power of a recirculating water pump.

I don't think that the kind of fan you're thinking of installing is going to be able to increase the airflow over your non-finned engine enough to make a difference!

[Boracay]

Is it possible that a 140 degree F (60 degrees Celsius) temperature would be about the maximum heat I could stand if I held my hand against the engine cover, while 115 degrees Fahrenheit (46 degrees Celsius) would be quite noticeably warm ?

[forsailbyowner]

The last time I was boarded and inspected the coast guard officer asked me to turn on bilge blower as part of his inspection. ?required?

[daddle]

Hmmm, inspections, interesting. As for feeling temp by hand around 130F you will not be able to hold something without burning skin. If you are a cook and have already burned out your hands use the inside of your arm for the test. Something like 120F is comfy hot. Like water for yeast or a really hot bath.

[Chief Engineer]

The cooler you can provide air to a diesel...the better....Most blowers I see on boats are inadequate and usually utilize dryer hose.

I have a couple customers that run their blowers all the time (gas or diesel) to evacuate the hot air from the engine comaprtment.

[YourOldNemesis]

Originally Posted by Chief Engineer

The cooler you can provide air to a diesel...the better....

Please explain & quantify - you're an engineer!

Most blowers I see on boats are inadequate and usually utilize dryer hose.

I'd go further and say that they are ALL inadequate for cooling a water-cooled engine, but what's wrong with dryer hose as ducting?

I have a couple customers that run their blowers all the time (gas or diesel) to evacuate the hot air from the engine comaprtment.

Does this mean it's an efficient way to cool their engine compartment, that they don't understand how a water-cooled engine is designed to dissipate heat or that they want a bit of fresh air down there when they're working on the engine?

[YourOldNemesis]

Originally Posted by forsailbyowner

The last time I was boarded and inspected the coast guard officer asked me to turn on bilge blower as part of his inspection. ?required?

Might be required in some countries as a means of ventilating the bilge in the event of an LPG leak or a gasoline spill, however, I'm not sure I'd want to fire up an electrical motor in the presence of LPG or gasoline fumes - spark, spark BANG!

[GordMay]

Colder air is more dense than hot air, so cold air requires more fuel to maintain the same air/fuel ratio, which results in more power. A common rule of thumb holds that decreasing air intake temperature by 10 degrees F will increase horsepower and torque by 1%. Lower inlet manifold temperatures also reduce the production of NOX.


Plastic Dryer Vent is corrugated. Due to it’s higher absolute roughness, there is a performance penalty associated with corrugated ducts, such that at a given volumetric flow rate, the same diameter corrugated duct will have a higher pressure loss than the corresponding non-corrugated duct, and a larger corrugated duct diameter is required to convey the same volumetric flow of air, at the same pressure loss per unit length, relative to conventional non-corrugated duct.

[YourOldNemesis]

I know I'm being a stubborn pedant, so, sorry in advance but...

Realistically, it seems unlikely that the use of dryer hose and its associated roughness is going to offer anything like as much resistance to the engine's air draw as, say the air filter. So I don't think it's worth worrying about. If you're concerned about the induction air temperature and associated density, it would make sense to attach the airbox directly to a large-diameter hose and place the opening of the hose so as to draw air from somewhere outside the engine bay.

NOX is formed in an ICE when nitrogen in the combustion air combines with oxygen in the cylinder at high temp and pressure. Are you suggesting that reducing the air-intake temperature by 10F will reduce the combustion temperature significantly enough to reduce NOX formation?

The original question was about whether or not an engine exhaust blower was necessary, your response makes no mention of the idea of air-cooling a water-cooled engine using 'blowers'. Does that mean we can now safely assume that, as I stated above, they don't contribute significantly to engine cooling?

[GordMay]

Nemesis:
I think you’re (partly) conflating Engine ROOM Ventilation (cooling) air with Engine Combustion Air.

[sigmasailor]

Cooler air not only gives more HP it also improves efficiency.

Efficiency is a formula with the lowest temperature in the process (intake or suck) and the maximum temperature (bang). The bigger the difference between those two the more HP and as a bonus better efficiency.

It's all about thermo dynamics: http://lmgtfy.com/?q=Carnot+cycle+efficiency.

[jkleins]

Originally Posted by YourOldNemesis

The original question was about whether or not an engine exhaust blower was necessary, your response makes no mention of the idea of air-cooling a water-cooled engine using 'blowers'. Does that mean we can now safely assume that, as I stated above, they don't contribute significantly to engine cooling?

While you sarcasm is fun you should at least make some effort to equate the two types of cooling you are making fun of. The "water-cooling" you are referring to is to keep the engine at operating temperature. The manufacturer makes no effort to reduce the heat of the engine to anything but what is "cool enough" to maintain the health of the engine.
The "air-cooling" you are trying to equate to this is to maintain the engine room temperature at a lower level for all the other components that might be housed there. I know there are several threads going on in this one and you might be addressing only those that specifically mention lowering the engine temperature. If so go back to the sarcasm. If you are trying to suggest that you can replace the blowers that lower engine room temp with the water cooled system I would really like to know how.

Jim

[GordMay]

Caterpillar has a good application guide on Diesel Engine Room Ventilation:
☛ http://www.gregorypoole.com/products...ENTILATION.pdf

See also Yanmar Help, for additional information on the subject:
☛ AIR VENTS

[YourOldNemesis]

Gord, ironically, I was trying to dissociate these two things (shows how good I am at communication!). In my earlier posts, I have tried to explain:

1. The engine sucks in air and it sucks more than you're likely to force into the engine room with an electric fan, so from an induction point of view (ie getting enough air to the intake) you're better off with decent ventilation to the engine bay than you are with a 'blower'.

2. If you think that the engine is going to perform better with cooler induction air than you currently find in the engine room you can do 2 things: a) duct the airbox directly to outside or b) reduce the temperature in the engine room, which leads me on to my response to Jim...

Hi Jim,

Yes I am saying that you can keep the engine room temps down with a better heat exchanger. This is because the source of the heat in the engine room is the engine. If your engine room gets so hot that other components are failing then your engine cooling system is either not working properly or is under-spec'd for the job. In either case, the solution is not to add a 'blower'!

Sorry to all for the tone, I have a sarcasm problem!

[YourOldNemesis]

Originally Posted by GordMay

Caterpillar has a good application guide on Diesel Engine Room Ventilation:
☛ http://www.gregorypoole.com/products...ENTILATION.pdf

This includes the text:
"Remote mounted and specially ducted engine-mounted radiators do not require engine room air for cooling"

This is the closest I could find in there to any explanation of how cooling ventilation should be organized for a water-cooled marine installation. If you have a flick through the diagrams you will see that they are basically dealing with air-cooled engines.

See also Yanmar Help, for additional information on the subject:
☛ AIR VENTS

this article makes no mention at all of blowers, only of induction vents