Quote:
Originally Posted by The Toecutter
The numbers seem off.
Any in-depth writings on the subject that include the math? I've done all sorts of energy consumption calculations on hypothetical builds, and a change in Cd from 0.23 to 0.18 with nothing else altered, seems far too minor a change to go from 247 to 441 miles range. This is showing a 22% reduction in drag coefficient(and nothing else) yielding a 78% increase in range at 75 mph.
The 0.13 Cd mentioned earlier in this topic would get you much closer to it, but even that would fall a little short(a few percentage points).
I'm guessing the comparisons made between the existing and hypothetical aren't like for like and/or there's a computational error somewhere or perhaps I didn't see some additional mods proposed that would get the efficiency where it is shown in the chart in John Gilikson's video. Or maybe John Gilikson meant to say a 0.13 Cd, and not a 0.18 Cd.
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I'll try and muddy the waters.
*The drag table I constructed for John used a mass-adjusted Rolling -Resistance 'curve' adapted from a HONDA R&D research paper published in the mid-nineties.The values are conservative,and modern LLR tires would most likely reflect a lower power absorption than indicated on the chart.
*Since we know the mechanical efficiency of a single planetary gearset (98%)
we reflected that along the bottom of the power plot,as the electric motor would 'see' this load.
*Targeting 100 mpg-e @ 100 mph,I reverse-engineered a drag coefficient,at at an estimated 84% of gross frontal area,which would satisfy the remainder of the road load associated with 100-mpg-e.
*Using standard SAE air density, Cd 0.179 fell out of the equation,allowing that the single alteration of lowering the Cd, from 0.23,to 0.179 would allow 100-mpg'e @ 100 mph,based upon the reported empirical baseline Watts/per mile of the Long Range Model-3.
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*The now,5-test, EPA Mobile Sources protocol for CAFE HWY mpg makes it virtually impossible to pin down a constant velocity at which a consumer might expect to 'see' the EPA HWY mpg in the real world.
*For the purpose of our thought experiment,we selected 100-km/h as our representative HWY velocity at which we'd see the EPA HWY rating.
*We road tested John's F-150 EcoBoost and discovered it's EPA rated HWY mpg occurred at 100-km/h.So ,at least in one case,this velocity did represent a velocity at which a consumer COULD achieve the rated EPA rating.
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*If you look at the road load on the graph,for 100 km/h you can pick off the Watt/hours,which reflects the power/fuel consumption.
*This value allows a direct conversion to mpg-e.
*A critical consideration with EVs,is that their BSFC is 1/3rd that of an ICE vehicle.
*They don't have much of a fuel tank,but they're 300% more efficient with the 'fuel' they use.Or,you could think in terms of an ICE vehicle who's fuel tank always leaks 66% of it's contents onto the road,thermodynamically.
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*We we're flabbergasted at the implications of the drag table.And I know that John has sweated over all the numbers.
*I think Cd 0.13 indicated 170 mpg-e @ 100-km/h.
*These are all estimations,as we don't have the actual car (yet) to modify and test.The T-100 has registered as low as Cd 0.13 already and hwy mpg close to 40-mpg,on gasoline,so we think we're barking up the right tree.
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