Electric cars and cooling drag

[planetaire]

Originally Posted by JulianEdgar

...
When I am talking about 'cooling drag', I am talking about the cooling drag of the radiators. This is the approach taken in all technical aero literature, so I feel pretty relaxed about taking this approach....

Aero is half a good idea.

I came in this forum from 2010. I learned from a lot of guys here several good ideas in order to reduce the drag of my car, aero and tyres. Than'k to all, I can't list here their pseudo each, sorry.
Here I learned that a car is somewhat different from a plane. Mainly because there are 4 $%*§ wheels (or 3 sometimes), and because it is closed the ground. Add some cross wind for exemple for playing more.

So I learn here that aeronautic forget that an ice have exhaust gaz, that are very hot near the engine. So there is a cooling need. Unlike the electric motors.
Maybe they forget this because nobody found a good solution to reduce the drag or because some of the old planes don't have catalyst or mufflers and just a tiny exhaust pipe just to protect the paint.

I would not understand that somebody remove a part of the drag from a device that need it.
For exemple I would not remove the wheels drag because they are moving part from the body of my car or because nobody succeed removing this drag or because first cars have low speeds...

This is because this fu#*$g exhaust that my car have a cd of 0.22 and not less, I have to keep all this #\/*$ system on board.

[JulianEdgar]

There seems to be a lot of confusion - and some excellent points - in this thread.

1. Cooling drag, as defined in all aero textbooks, relates to the drag caused only by the cooling of the engine, ie through water or air cooling. I take the point, though, that in the case of ICE cars, cooling of the exhaust system should be included. As far as I am aware, it is not currently included in any reference or tech paper.

2. Cooling drag, as a proportion of total aerodynamic drag, varies for ICE cars from basically zero (very well designed ICE cars - and very rare) to 6-14 per cent. Jaguar's head of aero told me that, at least for ICE cars, cooling drag percentage was likely to increase as cars got slipperier.

3. It would be logical to expect cooling drag percentage to increase with engine power (more power needing more cooling flow) but this relationship doesn't exist in real production cars. That's because the quality of the cooling system design (quality in terms of aero drag penalty) is a greater variable than engine power.

4. BEV cooling drag, again as a percentage of total aero drag, appears at this stage to be far higher than has been often suggested here (where it was assumed to be zero or very low). That could be because:

- the reduced delta T (ie the reduced temperature difference between the cooling circuits and atmosphere, so requiring larger radiators)

- the fact that BEVs still require an air conditioning condenser - in area at least, these are often as large as the engine cooling radiator in ICE cars

- the currently available data on BEV percentage cooling drag is only for two high power BEVs (but see point #3 above)

5. To suggest that BEVs have zero cooling drag, or ICE cars will always have higher cooling drag than BEVs, is simply wrong.

6. The use of radiator shutters is a red herring: they can be used equally in any car (ICE, BEV, hybrid) to give reduced cooling system drag at lower loads.

7. My prediction is that far more attention will be paid in future car design to cooling system drag reduction, as:

- the proportional drag penalty gets higher as the rest of the car gets slipperier

- without the need for a big ICE engine up front, BEVs have the potential to much better package cooling systems around the car, in turn siting them for lower drag increases.

[AeroMcAeroFace]

I am aware this is an electric car discussion, but seeing as there is more flexibility of cooling in electric cars, why is the radiator always in the front? Is it because the stagnation point is there anyway so there isn't much inlet drag, or is it due to pressure differentials, lift reduction?

It seems to me, from a very limited understanding, that taking cooling air in at the sides and venting into the wake could lower drag compared to a front radiator by allowing a better shaped nose, but I am yet to see a car that does it. (well at least exclusively, many lamborghini have side cooling vents)

[aerohead]

Originally Posted by JulianEdgar

Yes. I am the only person here who has quoted citations from the technical literature that shows percentage cooling drag of BEVs (ie percentage of total aerodynamic drag).

You’ve posted a wide range of irrelevant material, your own theories, and various amounts of typical Aerohead misinformation.

So, situation as normal for your contributions.

I'm ecstatic that uni-dimensional thinking-like posts are, so far, limited to a single member.
And to be fair, I'll attribute the shortcoming to undereducation.
Without immersion in mechanical engineering, you'll remain, sequestered within a one-dimensional universe.
If you'll keep re-reading Dr. Wolf, some patterns may begin to emerge which will provide the needed contrast, necessary to understand the most fundamental underlying functions of a cooling system.
Otherwise, it doesn't matter how many examples from the 'technical literature' you table. They are contextual. Any pretense that they can stand as reported is pure pedantry. SNAFU.

[aerohead]

Originally Posted by JulianEdgar

That information does not tell us what the cooling drag proportion of total Cd is for the listed cars. So basically it’s irrelevant - unless you are suggesting that the change in Cd between the ICE and BEV models is due solely to the change in cooling drag (which it isn’t). The Cruise / Volt comparison is particularly ridiculous - the two cars have completely different shapes.

Again, just sewing the seeds of confusion.

So limit consideration to only KONA / SPARK

[aerohead]

Originally Posted by JulianEdgar

1. Closing off the cooling in low-power electric mode in a Prius tells us nothing relevant to this discussion (which is about BEVs), does it?

2. Cd values (or percentages of total Cd) are used for cooling systems because it is a coefficient. If we used Newtons, we'd need to specify speed. We can easily work out the force for any car for which we have speed, area and cooling drag Cd.

3. Shutters apply equally to all cars these days - ICE, Hybrid, BEV. Cooling drag is with the shutters open ie the cooling system working.

' ... the drag caused by the cooling system can be measured by simply blocking the radiator.'
Julian Edgar, ' Modifying the Aerodynamics of Your Road Car ', page 120- 121

[aerohead]

Originally Posted by JulianEdgar

Sorry, but again I can't see the relevance to the discussion. If they make underfloor changes to the electric version (as you say they do) then obviously the Cd of that version will be lower, and so it doesn't tell us what proportion of total drag is made up by the EV cooling system on the EV car. This can only be found out by testing the cooling drag of each version and telling us what it is.



Nearly all modern prestige cars use cooling shutters - BEV or ICE or Hybrid. It's nothing to do with the car being a BEV.

After a review of the thermodynamic differences between ICE and BEVs you may find your argument impossible to maintain.

'It's hard to reason an idea out of a man, who wasn't reasoned into it.' Swift

[aerohead]

Originally Posted by JulianEdgar

Sorry, but again I can't see the relevance to the discussion. If they make underfloor changes to the electric version (as you say they do) then obviously the Cd of that version will be lower, and so it doesn't tell us what proportion of total drag is made up by the EV cooling system on the EV car. This can only be found out by testing the cooling drag of each version and telling us what it is.



Nearly all modern prestige cars use cooling shutters - BEV or ICE or Hybrid. It's nothing to do with the car being a BEV.

You're rubbing shoulders with ICE / BEV cooling context, and you're completely unaware of it as you witness it. Keep digging.

[aerohead]

Originally Posted by JulianEdgar

I have no idea about the car - I am quoting only what you wrote. And you wrote, "The exhaust tunnel is closed". That will immediately reduce drag, and so the value of overall aero drag we're comparing to has also changed.



I am not sure if you're trying to be misleading but that statement is quite incorrect. The delta Cd between the two cars is that, not their cooling systems. We have no data at all on their cooling systems!



I don't know what that means.

Finally something truthful.

[aerohead]

Originally Posted by JulianEdgar

That is true - but no mainstream BEV will ever be sold with as little power as an electric-only Prius. So it's a bit cute saying you can run with its cooling reduced to zero - and drawing any comparison with a proper BEV.

The cooling drag on my electric bicycle I once made was very low, but it's irrelevant to the discussion.

Every mainstream BEV sold, has as little 'developed' power as the reported Prius, whenever their road load demand encountered, matches that of the said Prius. Every one of them, up to their full rated power.
Cooling requirements will be whatever they are. If each vehicle shared equal mechanical efficiency, they would all experience identical cooling loads.