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Semi Truck Engine Hot Air Exhaust Vent Aero I.Q.
Hello All -
I'm not ready to post pics of my whole aero semi project yet. But I would like to solicit input, thoughts, and constructive suggestions regarding the aerodynamics of the hot engine compartment air exhaust vents. Of course, one would normally not have a body panel protruding away from the body with a sharp cut-off at the rear. You would blend this area into the body to maintain undisturbed flow. But in this case, the skirts behind the steering tires are rolled inwards, and hot 200+ degree air will vent from this area. (fan-on temp is 230 degrees F.) We will fiberglass a small flange around the perimeter of the vent openings, and add grills. Do you think the outside body air traveling over the vent will merge successfully with the hot underhood air exiting from the vent? I obviously do, because I built it this way. We have been too busy with other stuff to model it and run it on CFD yet. We could always add an F1 Fence as the Ferrari did, but I am unsure if this would be necessary. Tuft testing will confirm any and all hypothesis. http://i143.photobucket.com/albums/r...DSC_1154-1.jpg http://i143.photobucket.com/albums/r...7/DSC_1158.jpg http://i143.photobucket.com/albums/r...dodgeviper.jpg http://i143.photobucket.com/albums/r...ri-599XX-1.jpg |
Isn't this form of underhood air management being done on the aero Peterbilts and KW trucks, even lowly Freightliners the past 10-years or so?
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interesting idea.
I have a few thoughts - first, I don't think the size is NEARLY big enough. Keep in mind you are taking 1/2 of the waste heat of the entire 450 horsepower engine, and thinking it will go through that little hole, after the air has gotten hot. I think you are a factor of 20 off. Second, I'm worried about air coming back along outside the tire, and "stacking up" on the fender - you might find you need to tip the lower part of the fender "in" below your vent to get a vortex to keep the air outside of the fender. Third, I think a MUCH more interesting thing is to look at the chin spoiler. A chin spoiler in front of or even with the radiator will keep the air out from under the truck giving the air somewhere to go. |
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The Pete 387 below has the little black side vents on each side of the hood by their red Peterbilt badge emblem. Air is also exhausted on the Pete and my truck at the rear top of the hood at the base of the windshield. http://i143.photobucket.com/albums/r...ERBILT-387.jpg Quote:
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Hey, thanks for the great discussion!
On the silver truck you show, the little vents up high are just to let underhood heat out when you shut the truck off - they are up high so the hot air can get out from under the hood. The VAST majority of air goes out underneath the truck. As an example, look at the height of the front bumper. It is MUCH lower then the frame rails - the front bumper pushes air around the truck giving the underhood air a place to exit out under the truck. On the fender. Look at the front fender of the silver truck. Air is going to go around the front tire, and stack up on the inside of the fender just in front of the step. The skirt on the ferriari is for visual mostly, and to let a bit of air out from under the front of the car. On a Ferrari, they are tubbed, so air doesn't have a great way to get out teh front of the car. |
here is an idea to lower drag on a semi.
Put an adjustable fin on the top of the sleeper. Make it so it pushes air up more or less with electric actuators. Put an automotive barometric pressure electronic sensor on the back of the sleeper. For a given load, for a given trailer, for a given wind condition, you can adjust the fin up or down to minimize air pressure between the truck and the trailer. Then put fins on each side of the sleeper up and down the sides - again adjustable. |
Yes, but my goal is not as much underhood air management, as it is reducing drag and saving fuel. Afterall, this IS the Ecomodder site.
I should have been more specific: faster ariflow through the radiator inlet would seem to be conducive to aero as one can make smaller the inlet, overall, if op-temps are good throughout the work range. This worked on our Jeep Cherokee for flow, and work by others on this site shows the range of "closure" possible. Now that bs is aside, man, that is one cool fan! Any more pictures or description available? I'm gonna head over to a truck specific site and link this up. There are a few users there who I know will be quite interested in this thread. . |
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If by the word "skirt" you are referring to the F1 fence, I disagree. The F1 fence is there to maintain the flow around the bumper and air dam and some air traveling over the wheel and tire. The rolled-in door panel is used to let a bit of air out from under the front of the car. |
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Now that bs is aside, man, that is one cool fan! Any more pictures or description available? That fan is a product of one of our major sponsors, Horton Cooling. Fans and Fan Drives | Horton I can't say enough good things about them. Great folks to work with. Smart and savvy. Been in business over 60 years. They flew their engineers on their company BeechJet from Minnesota to my shop in Connecticut twice, to help me engineer it and set it up. I designed and fabbed all the aluminum tube and bracket frame-work you see in the pics. By the way, you are looking at probably the only Class 8 rig in North America with a crankshaft-driven fan. Horton's computer-controlled Stratis viscous drive is sandwiched in between the two. And they built me a beautiful, billet, CNC piece that bolts to the crank and ties everything else together. http://www.hortonww.com/products/products.asp?/en/11/ Fans and Fan Drives - WindMaster® Revolution / High-efficiency, Hybrid-flow Fans | Horton http://i143.photobucket.com/albums/r...7/dsc_0684.jpg http://i143.photobucket.com/albums/r.../dsc_0746b.jpg |
it looks like an old school radial fan from a VW bug from the 60's. Is that correct?
Those radial fans make surprising amount of pressure. What diameter is the fan? |
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. |
Internal Ductwork
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. |
vents
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. |
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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. http://caringarage.com/wp-content/up...o-ZL1-hood.jpg |
Camaro
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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. |
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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. |
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. |
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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. |
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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. |
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Horton made me sign a waiver not to operate the fan higher than 2200 rpm's. So I know it is good for at least that. But that high an rpm in this truck is a moot point. We will be operating the 450hp Cummins diesel in this truck just like an electric motor. That is, at almost a constant speed, in the most optimal range of 1100-1300 rpm. Procedure: go up a hill, drop to 1800ft. lb. torque peak @ 1100 rpm, split the 13 speed transmission to the next lowest gear, rpm's will climb to only 1300, go up the hill some more. Rinse & repeat. No grade rpm @ 55mph will be 1150, if I remember the math correctly. Horton has supplied the hardware and software for a viscous unit. The WindMaster Revolution fan is controlled by Horton's wonderful Stratis viscous device. And the Stratis is also a very intelligent fan clutch. Fans and Fan Drives - Stratis® / Viscous Fan Drives | Horton It constantly monitors the engine computer (ECM) and if the engine only needs 5% cooling from the fan, that's all the fan puts out. Why use that other 95%, and waste all that fuel, if you don't have to? |
holy crap.
that thing is neat! From the peanut gallery, they need to sell it to the heavy equipment and farm equipment market. Those markets have MASSIVELY oversized fans for extreme conditions, which suck a lot of fuel when they are not needed. Horton has a homerun with that product. Simple, elegant, and effective. |
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That Stratis viscous drive sits in between the beautiful billet adapter they made for me that bolts onto the crankshaft, and the rear of the fan. |
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Jim. |
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We will have that small wheel well and the duct I spoke of earlier to hopefully mitigate any effect of the tire air going forward. If a tremendous amount of air went forward off that tire and under the hood, I agree it would fight with the engine cooling air coming rearward from the radiator and the engine cooling fan. It reminds me of the old line by comedian Steven Wright where he put a humidifier and a dehumidifier in the same room to fight it out. But think of a steering tire in the rain. The vast majority of the splash and spray is going rearward, not forward. Please refer to the last image below. I always thought this splash & spray was most attributable to the speed of the vehicle through the air, and the tires picking up water from the pavement. Not as much due to centrifugal force slinging the water droplets off of the tire itself. I understand the centrifugal force is a contributor to the splash and spray. Just not as much as the water splashing off of the pavement, combined with the slipstream traveling rearward. Fortunately we have XZA2 Anti Splash Steering Tires from our major sponsor, Michelin Truck Tires. The XZA2's have a circular protrusion that extends outward about an inch on each sidewall, to vastly reduce splash & spray. http://staging.michelintruck.com/img...antisplash.png http://www.tyres-online.co.uk/images...ntisplash1.jpg http://www.tyres-online.co.uk/images...ntisplash2.jpg |
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Now the question is: 1) Is the majority of the spray really going "backwards" off the tire from centrifugal force? 2) Is the spray really going forward on top of the tire in the wheel well, hitting objects inside the inner fender, dropping toward the road surface, and the wind catching it and "pushing" it backwards? (this is my choice). One way to find out would be to utilize a tire testing circular drum and test water spray on that, and measure water droplet propagation with a stroboscope. However, the rotating drum itself has air moving across the top of that, and compounding the research..... I doubt anyone has that apparatus available, so onward with speculation on what is really happening. If it was my truck, and I'm looking for aero gains, I would certainly make a specialized duct from the radiator back to the exhaust opening, and keep it separate from the tire well area if possible. Jim. |
Are those MICHELIN tires only for the Steer Axle, or is this also a feature of their single-wides (which I assume this truck is using)? A long overdue and welcomed bit of tech!
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1) Is the majority of the spray really going "backwards" off the tire from centrifugal force? 2) Is the spray really going forward on top of the tire in the wheel well, hitting objects inside the inner fender, dropping toward the road surface, and the wind catching it and "pushing" it backwards? (this is my choice). I can ask the engineers at Michelin. I'm sure they know. But the tire is basically smooth on the footprint surface. If I spin my Dremel tool at 10,000 rpm with even a rough sanding wheel on it, I can't feel any air spinning off of it. And if I recall the math correctly again, truck tires spin at like 500-600 rpm. If truck tires were built like water wheels on Mississippi steamboats, I could see a lot of water spinning off it due to centrifugal force. But again, tires are smooth. I think the tires are picking up the water from the road only, and then slinging it out. http://www.nolanfocus.com/wp-content...hezBoat-07.jpg Quote:
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We do have 8 (four on the tractor and four on the trailer) of Michelin's wonderful X-One Super Singles on the truck. They are completely covered by skirts on both units, so road-side rain splashing of automobiles or other vehicles will not be an issue. We even have aerodynamic mud flaps on both units as well to reduce splash & spray, and of course, to save fuel. |
Wow! nice car.. i love the red one :)
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