Semi Truck Engine Hot Air Exhaust Vent Aero I.Q.

[ALFIERI_78]

Shepherd,

Can't comment on your side vents as I'm still learning air flow dynamics.

But can tell you that the vents on the Peterbilt aren't to exhaust hot air out of the engine compartment; they are the fresh air inlet for the air filter.

[3-Wheeler]

I would think that you would want to separate the air that is escaping from the radiator to the outside world, from the air that going twice the surface speed of the road at the top of the tire! Picture 2 really brings this home.

If your going to vent radiator air at this particular location, then a baffle between the vented air and the top of the tire would be very beneficial.

Without that, you will have one heck of a parasitic load from all the air churning about in that location.

Jim.

[aerohead]

Dr.Alberto Morelli's work in the Pininfarina wind tunnel for the CNR 'banana car',beginning in 1976,probably owns the distinction of the most efficient extractor vent technology I've seen published.
Cooling air off the heat exchanger was divided into four ducted streams which exited the engine bay,blending with the surface flow at exactly the same velocity so as not to trip the flow into turbulence.
If you look for the oil-streaked tunnel photos of the car you will see unperturbed streamlines at these outlet locations.
When the Pontiac Trans Am was undergoing wind tunnel development at the Lockheed Marietta tunnel,the extractor gill slits registered a minor drag increase.
To get a net zero effect or gain may require much tunnel time.Don't know.
If you can snag a July 11,2011 copy of AUTOWEEK,on page 16,there's a small mention of the Iveco 'Glider' tractor-truck with radiator-less flat heat exchangers integrated into the side pods.
Iveco is skipping the cooling system drag altogether.
The Glider also sports photovoltaics on the roof,regenerative braking,beltless engine,and active shutters to maximize exhaust system-generated electricity.
Iveco claims a 40% fuel economy/carbon dioxide improvement for the tractor.

[Shepherd777]

Originally Posted by 3-Wheeler

I would think that you would want to separate the air that is escaping from the radiator to the outside world, from the air that going twice the surface speed of the road at the top of the tire! Picture 2 really brings this home.

If your going to vent radiator air at this particular location, then a baffle between the vented air and the top of the tire would be very beneficial.

Without that, you will have one heck of a parasitic load from all the air churning about in that location.

Jim.

Thanks Jim, but I'm not sure if I agree with your postulate. The air at the top of the tire is going forward, not towards the rear. Only the area of the tire that is below the axle goes rearward, correct? We will have a small wheel-well over the tire to hopefully mitigate the effect you are describing.

Originally Posted by aerohead

Dr.Alberto Morelli's work in the Pininfarina wind tunnel for the CNR 'banana car',beginning in 1976,probably owns the distinction of the most efficient extractor vent technology I've seen published.


If you can snag a July 11,2011 copy of AUTOWEEK,on page 16,there's a small mention of the Iveco 'Glider' tractor-truck with radiator-less flat heat exchangers integrated into the side pods.
Iveco is skipping the cooling system drag altogether.

Thanks for the references aerohead. I have never seen that banana car. Very cool.

I checked out the Iveco. The major problem here is it is a euro truck. So they are limited to the square cabover platform due to length limits. So a euro aero cabover is like being the best ice hockey player in Ecuador, in my opinion.

By the way, my last aero rig was featured in Autoweek Magazine in 1984. I still have the article. It was printed on news-print way back then and was not the high-gloss automotive magazine it is now.

The new Camaro ZL1, which is on my wish list by the way, expells underhood heat differently. Similar to a Ford GT40.

I was thinking about doing a similar underhood air hood vent on this truck, for about 30 seconds or so. Then, while visualizing the flow, I was reminded of the urinate-poor OEM windshield angle of 65 degrees, and summarily dismissed the notion. I thought about an "A" pillar emergency surgery relocation for about 10 seconds, and dismissed that as well. But just wait for the next truck, which will be entirely built from scratch. Assuming we can get several wheel-barrels full of large note $$$$$$$ from investors and or sponsors.

[aerohead]

Originally Posted by Shepherd777

Thanks Jim, but I'm not sure if I agree with your postulate. The air at the top of the tire is going forward, not towards the rear. Only the area of the tire that is below the axle goes rearward, correct? We will have a small wheel-well over the tire to hopefully mitigate the effect you are describing.





Thanks for the references aerohead. I have never seen that banana car. Very cool.

I checked out the Iveco. The major problem here is it is a euro truck. So they are limited to the square cabover platform due to length limits. So a euro aero cabover is like being the best ice hockey player in Ecuador, in my opinion.

By the way, my last aero rig was featured in Autoweek Magazine in 1984. I still have the article. It was printed on news-print way back then and was not the high-gloss automotive magazine it is now.

The new Camaro ZL1, which is on my wish list by the way, expells underhood heat differently. Similar to a Ford GT40.

I was thinking about doing a similar underhood air hood vent on this truck, for about 30 seconds or so. Then, while visualizing the flow, I was reminded of the urinate-poor OEM windshield angle of 65 degrees, and summarily dismissed the notion. I thought about an "A" pillar emergency surgery relocation for about 10 seconds, and dismissed that as well. But just wait for the next truck, which will be entirely built from scratch. Assuming we can get several wheel-barrels full of large note $$$$$$$ from investors and or sponsors.

The thing that spooks me about any sort of 'centerline' hood-top extractor vent is what happens if the radiator explodes,which I have witnessed three times now.
If the glycol hits the windscreen the wipers only smear it around.Depending on your velocity at the time,you can have a very brief event horizon before you plow into something.
I was on the 105 Freeway in Los Angeles when some little f---ing s---------- dropped a rock off an overpass.It was like a shotgun blast shattering the windshield and I had to roll the window down and stick my head out the side to 'see' where I was,as I was completely blinded.
Very dangerous! Glycol would do the same.
On a racing car everyone is going the same direction and it's a closed course.The bits and pieces of a race car may have a life expectancy of one season.And there are medics and air ambulance standing by.
Just thinking safety.You and your venture capitalists don't need a class-action lawsuit if a driver has a bad day.

[Shepherd777]

Originally Posted by aerohead

The thing that spooks me about any sort of 'centerline' hood-top extractor vent is what happens if the radiator explodes,which I have witnessed three times now.
If the glycol hits the windscreen the wipers only smear it around.Depending on your velocity at the time,you can have a very brief event horizon before you plow into something.

That should not be a problem with this truck or the next one. I cannot envision any scenario where the radiator in either truck would "explode".

We use only waterless engine coolant, and the cooling system is not pressurized. So without pressure, it would absolutely not explode. Just leak.

So if the radiator would for some reason spring a leak, and the coolant would somehow vent through that hood vent, I suppose I would just try the wipers. I imagine without the water in the coolant, it would not smear as much, or even at all. Because what is causing the smearing is the wipers trying to mix the glycol with water. And as we all know, you can't mix oil (or glycol) with water.

[instarx]

That is basically a squirrel-cage fan that pulls air from the center and exhausts it around the edge. That is an interesting automotive application. Squirrel-cage fans can pull air across higher resistances than vane-axial fans (typical propeller fans) and move much more air at higher velocities. That means a smaller fan using less horsepower can be used. Or you could use a denser, smaller radiator with this type of fan. Squirrel cage fans are also much quieter.

Here is an idea - if you put an enclosure with an outlet around that fan you could direct all (or any fraction) of radiator air into a duct that could be routed anywhere - eliminating the need for hood and fender extractor vents all together.

[Shepherd777]

Originally Posted by drmiller100

Those radial fans make surprising amount of pressure. What diameter is the fan?

750 mm. I don't know what 750 mm is in inches. I'm American.

[Shepherd777]

Originally Posted by instarx

Here is an idea - if you put an enclosure with an outlet around that fan you could direct all (or any fraction) of radiator air into a duct that could be routed anywhere - eliminating the need for hood and fender extractor vents all together.

One could indeed do that, but it would degrade and hurt engine cooling.

A large portion of engine cooling on this, or any other automotive-type engine, results from the air being directed over and around the engine. This portion of the fan air effectively air-cools the engine, similar to a small aircraft, motorcycle, or old VW. So water-cooled automotive-type engine cooling is predicated upon both water cooling and air cooling, to some extent.

We have an "air channel/duct", for lack of a better term, built inside the hood body that directs some of the exhaust fan air out the skirt vent, after passing over the engine. This will become evident after we paint the rig and I post full pics of the front end of the vehicle.

[drmiller100]

Originally Posted by Shepherd777

750 mm. I don't know what 750 mm is in inches. I'm American.

about 30 inches.

Be VERY careful about the rpm you try to spin it at. Axial flow fans (traditionally a boat's propeller, but a traditional car fan sort of acts like one) the amount of air is a function of the RPM, the diameter, and the pitch of the blades.

Your's looks to be a radial flow, which functions in part as the SQUARE of the RPM. So, as you spin it faster, your horsepower requirements can go up a LOT.

Like Instarx says, the radial fans will build more suction/pressure then axial flow.

An aside. What would be REALLY cool would be to drive the fan with a hydrostatic pump - the logic would be to measure exit temp coolant out of the radiator, and drive the fan faster until the coolant temp drops.

Optionally, the a traditional fan clutch would work also, and is much simpler, and proven and cheap and an example of doing it the easy way.