Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 11-21-2014, 06:47 AM   #1 (permalink)
EcoModding Lurker
 
Join Date: Nov 2014
Location: UK
Posts: 42
Thanks: 0
Thanked 12 Times in 12 Posts
Question Full Grill Block - Where best to get air for cooling?

With the grill fully blocked and no airflow through the radiator and going up a steep hill the engine will overheat fairly quickly but on the flat with gentle driving it can take 15 minutes (maybe the full journey) before needing any air for cooling. It seems widely accepted that there is an aerodynamic advantage to keeping the grill fully blocked until cooling air is needed.

Question - When the radiator does need some air for cooling, where is the best place to get it?

I could open a flap in the grill but that increases the amount of air flowing under the car and that appears to be bad for fuel economy.

Alternatively I could use the radiator cooling fan to suck air from behind the front splitter through the radiator. That way the air that ends up under the car is air that was already under the car so maybe has no overall effect on fuel consumption, except for the 10-30W (depending on air temperature) of power needed for the fan. A few guesses suggests that keeping the grill blocked might save a KW of engine power so using a few 10s of W for the fan may give a good return...

Has anyone tried sourcing the cooling air from anywhere but the grill? Are there any figures available for the results? Any knowledge if it is a good or bad idea?

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 11-21-2014, 08:25 AM   #2 (permalink)
Master EcoModder
 
Sven7's Avatar
 
Join Date: Aug 2011
Location: Warren, MI
Posts: 2,456

Boo Radley - '65 Ford F100
90 day: 13.28 mpg (US)
Thanks: 782
Thanked 667 Times in 409 Posts
As a general rule, if you're going to block part of the grille, leave the center open. The reason for this is that if you have the sides open, you are spoiling clean airflow coming from the very front of the car. It is instead best to pull from the stagnation point and let anything outside of that flow around cleanly.

I'm almost positive there are threads that discuss this. Look up "bottom breathers" like the Corvette. It uses the high pressure zone in front of the air dam to shove air into the radiator.



Or just punch a 25 square cm hole in the lower middle of your grille block, since it won't affect that much.

Or rig up a flap in the lower middle of the block, with a hinge so it can open when you need it. Actuate by cable or solenoid.
__________________
He gave me a dollar. A blood-soaked dollar.
I cannot get the spot out but it's okay; It still works in the store

Last edited by Sven7; 11-21-2014 at 09:01 AM..
  Reply With Quote
Old 11-21-2014, 09:01 AM   #3 (permalink)
Administrator
 
Daox's Avatar
 
Join Date: Dec 2007
Location: Germantown, WI
Posts: 11,203

CM400E - '81 Honda CM400E
90 day: 51.49 mpg (US)

Daox's Grey Prius - '04 Toyota Prius
Team Toyota
90 day: 49.53 mpg (US)

Daox's Insight - '00 Honda Insight
90 day: 64.33 mpg (US)

Swarthy - '14 Mitsubishi Mirage DE
Mitsubishi
90 day: 56.69 mpg (US)

Daox's Volt - '13 Chevrolet Volt
Thanks: 2,501
Thanked 2,585 Times in 1,553 Posts
The radiator fan can pull some decent power, and alternators aren't that efficient. So, the fan should be avoided. However, if it only comes on 1-2 times on your trip, I'd just leave it.

On my Prius, I run a full grill block all winter unless I'll be going on the highway. Then, I remove one of the pipe insulation strips from the grill. That allows for plenty of cooling.
__________________
Current project: A better alternator delete
  Reply With Quote
The Following User Says Thank You to Daox For This Useful Post:
user removed (11-24-2014)
Old 11-21-2014, 10:03 AM   #4 (permalink)
EcoModding Lurker
 
Join Date: Nov 2014
Location: UK
Posts: 42
Thanks: 0
Thanked 12 Times in 12 Posts
Quote:
Originally Posted by Daox View Post
The radiator fan can pull some decent power, and alternators aren't that efficient. So, the fan should be avoided. However, if it only comes on 1-2 times on your trip, I'd just leave it.

On my Prius, I run a full grill block all winter unless I'll be going on the highway. Then, I remove one of the pipe insulation strips from the grill. That allows for plenty of cooling.
I have a variable speed fan that keeps the coolant returning from the radiator 10 degrees C below the thermostat opening temperature thus allowing the thermostat to mix warm and cool coolant and keep the engine temperature constant.

In normal running the fan stays off for 10-15 minutes and then runs slowly, if I go up a steep hill it speeds up. The amount of power used is typically 15W while the grill block appears to be saving several KW. So even though alternators aren't 100% efficient it doesn't matter as long as I save more than I use...

Quote:
Originally Posted by Sven7 View Post
I'm almost positive there are threads that discuss this. Look up "bottom breathers" like the Corvette. It uses the high pressure zone in front of the air dam to shove air into the radiator.

Or just punch a 25 square cm hole in the lower middle of your grille block, since it won't affect that much.

Or rig up a flap in the lower middle of the block, with a hinge so it can open when you need it. Actuate by cable or solenoid.
Thanks for the search tip, helps to know what to search for.

They still seem to have the intake in the high pressure area though, and in a place my car doesn't have. The obvious places to put a hole and maybe flap on my car are in the lower grill block or in the undertray in front of the radiator which is a low pressure area so would need some extra effort from the fan possibly in return for gains in aerodynamics.
  Reply With Quote
Old 11-21-2014, 10:31 AM   #5 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,513

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 60.16 mpg (US)
Thanks: 4,058
Thanked 6,957 Times in 3,602 Posts
Quote:
Originally Posted by Nigel_S View Post
They still seem to have the intake in the high pressure area though, and in a place my car doesn't have.
Well, the stagnation point is a good high pressure area. You've got one of those.

What car is this? Tip: add a garage entry. Then your vehicle shows up with all your posts, beneath your username. Potentially useful context.
__________________
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
  Reply With Quote
The Following User Says Thank You to MetroMPG For This Useful Post:
Sven7 (11-21-2014)
Old 11-21-2014, 11:13 AM   #6 (permalink)
herp derp Apprentice
 
Join Date: Oct 2008
Location: Lawrence, KS
Posts: 1,049

Saturn-sold - '99 saturn sc1
Team Saturn
90 day: 28.28 mpg (US)

Yukon - '03 GMC Yukon Denali
90 day: 13.74 mpg (US)
Thanks: 43
Thanked 331 Times in 233 Posts
I think you might be reading into the full grill block too hard. I think there are a lot of vehicles on here that might have a "full grill block", where the entire upper or lower grill is blocked, but one of the 2 is left partially open, or there is a gap in the body work, or at the edge of the hood that allows air flow. My grill is completely blocked, but it pulls air like the corvette pictured above. it's not that differnt or special from any other grill opening, it's just not surrounded by body work on all sides, it still uses some amount of frontal area to grab air to direct through the radiator.

Last edited by 2000mc; 11-21-2014 at 11:20 AM..
  Reply With Quote
Old 11-21-2014, 11:17 AM   #7 (permalink)
Rat Racer
 
Fat Charlie's Avatar
 
Join Date: May 2011
Location: Route 16
Posts: 4,150

Al the Third, year four - '13 Honda Fit Base
Team Honda
90 day: 42.9 mpg (US)
Thanks: 1,784
Thanked 1,922 Times in 1,246 Posts
Yeah, grille blocks don't generally make the engine compartment airtight.
__________________

Quote:
Originally Posted by sheepdog44 View Post
Transmission type Efficiency
Manual neutral engine off.100% @MPG <----- Fun Fact.
Manual 1:1 gear ratio .......98%
CVT belt ............................88%
Automatic .........................86%

  Reply With Quote
Old 11-21-2014, 11:34 AM   #8 (permalink)
Master EcoModder
 
Sven7's Avatar
 
Join Date: Aug 2011
Location: Warren, MI
Posts: 2,456

Boo Radley - '65 Ford F100
90 day: 13.28 mpg (US)
Thanks: 782
Thanked 667 Times in 409 Posts
Edit: looks like it's already been stated. I'll just leave it here anyway.

The stagnation point will be a high enough pressure area to get air through your radiator, especially if you duct it. You don't need a big cantilevering front end to make it work; almost all active members here have some form of grille block, so just check the project threads. You can have a reasonable grille opening and still not cause unreasonable drag. It's a balance.

What car is it?
__________________
He gave me a dollar. A blood-soaked dollar.
I cannot get the spot out but it's okay; It still works in the store
  Reply With Quote
Old 11-21-2014, 11:34 AM   #9 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts
Air in at the stagnation point.

Highly evolved cooling systems have a fixed intake and a flap in the exit. (P-51)

Best location for the exit is at the widest part of the body, where the air is moving the fastest. (Edison 2)
  Reply With Quote
Old 11-21-2014, 11:48 AM   #10 (permalink)
EcoModding Lurker
 
Join Date: Nov 2014
Location: UK
Posts: 42
Thanks: 0
Thanked 12 Times in 12 Posts
Quote:
Originally Posted by MetroMPG View Post
Well, the stagnation point is a good high pressure area. You've got one of those.

What car is this? Tip: add a garage entry. Then your vehicle shows up with all your posts, beneath your username. Potentially useful context.
Not quite the right image but it shows the grill area:



Quote:
Originally Posted by 2000mc View Post
I think you might be reading into the full grill block too hard. I think there are a lot of vehicles on here that might have a "full grill block", where the entire upper or lower grill is blocked, but one of the 2 is left partially open, or there is a gap in the body work, or at the edge of the hood that allows air flow. My grill is completely blocked, but it pulls air like the corvette pictured above. it's not that differnt or special from any other grill opening, it's just not surrounded by body work on all sides, it still uses some amount of frontal area to grab air to direct through the radiator.
Yes, I realise that most people don't completely block the grill, and most people try to avoid using the fan, but I have a fan that I am happy to use and which will only use the amount of energy needed so I have a choice of where to draw the air from. The question is, which is the best place to draw the air from? Maybe it is from in front of the grill adding to the amount that ends up under the car, maybe not...

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com