BEV mass and Regeneration efficiency

[aerohead]

Originally Posted by aerostealth

I was watching TFL Trucks last night and they were testing a Rivian electric truck towing a flat bed trailer with a large pickup truck on the carrier up to the Ike Gap (from Boulder, CO) and back. I won't post a link here because these guys are seriously aero-ignorant but they had a result I found interesting.

Going downgrade and setting their cruise control to 60 mph they only gained a couple kWh and a few miles of range from the regenerative braking. They were very puzzled by this result. The following occurred to me.

1: Regenerative braking energy returns at speed is a function of aerodynamic drag and rolling resistance.

2: A lower drag shape with all the same parameters (frontal area and mass) would allow more regenerative braking energy returns.

3: That it should be possible to map and graph the potential for regenerative braking energy returns as a function of CDA, mass, and speed.

A) And they're apt to do 75-mph 'climbing' while not allowing the downhill at 75-mph, cutting the kinetic energy in so doing, and skewing the regeneration quanta downwards.
B) To the the point, the aerodynamic abominations rob extremely valuable available wheel power, which could otherwise be harvested, returning 81% back to the battery ( please see Dave Hermance, Executive Engineer, Hybrids, Toyota Motor Company ).
C) When the object is to present a derisive presentation about BEVs, it's incumbent upon the practitioner to construct an 'experiment' designed to amplify the shortcomings of their target, while hoping that no one in the audience is astute enough to see past the deception.

[aerohead]

This thread started because of:
#21 ( permalink ) and #25 ( permalink ), at the RIVIAN R1T 'Truck of the Year' thread.

[redpoint5]

Originally Posted by aerostealth

I was watching TFL Trucks last night and they were testing a Rivian electric truck towing a flat bed trailer with a large pickup truck on the carrier up to the Ike Gap (from Boulder, CO) and back. I won't post a link here because these guys are seriously aero-ignorant but they had a result I found interesting.

Going downgrade and setting their cruise control to 60 mph they only gained a couple kWh and a few miles of range from the regenerative braking. They were very puzzled by this result. The following occurred to me.

1: Regenerative braking energy returns at speed is a function of aerodynamic drag and rolling resistance.

2: A lower drag shape with all the same parameters (frontal area and mass) would allow more regenerative braking energy returns.

3: That it should be possible to map and graph the potential for regenerative braking energy returns as a function of CDA, mass, and speed.

Slope and distance are relevant factors as well, and wind speed and direction an additional variable.

As has been pointed out elsewhere, a trailer could potentially increase efficiency if it improves the overall shape to reduce turbulent air.

Obviously, the faster one travels, the more energy is expended overcoming drag forces. Whatever potential energy is available given the weight and slope of the hill can be used to overcome that drag and regen into the battery. Go faster, and you get less back. Set the car to neutral, and 100% of that energy goes into overcoming drag.

The most I've ever regenerated was about 3 kWh, which brought my Prius from empty to full charge while descending from Yosemite.

[Piotrsko]

Regen is a wattage over time process. If your recovery is watts limited it's gonna take longer than what you have for downhill.

[aerohead]

Originally Posted by redpoint5

Slope and distance are relevant factors as well, and wind speed and direction an additional variable.

As has been pointed out elsewhere, a trailer could potentially increase efficiency if it improves the overall shape to reduce turbulent air.

Obviously, the faster one travels, the more energy is expended overcoming drag forces. Whatever potential energy is available given the weight and slope of the hill can be used to overcome that drag and regen into the battery. Go faster, and you get less back. Set the car to neutral, and 100% of that energy goes into overcoming drag.

The most I've ever regenerated was about 3 kWh, which brought my Prius from empty to full charge while descending from Yosemite.

1) Power to overcome climbing resistance on a 2% grade @ 80-mph
2) Equals that at about 52-mph on a 3% grade
3) 40-mph on a 4% grade
4) 36-mph on a 5% grade
5) 27-mph on a 6% grade
6) 22-mph on a 7% grade
7) 20-mph on a 8% grade
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Wind data and air density at 20-F, 30-F, and 40F would be welcome.
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EPA considers 70-F as 'Cold' as far as tire rolling resistance goes.
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Full-potentiometer acceleration pulling an 8,100-pound load is a sure way to drain a pack.
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Wet roads were mentioned. That's 1-mpg loss @ 55-mph. More at 60.
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7-8-foot gap between load and tailgate.
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The F-100 is Af 31.6 sq-ft, and Cd 0.50 with the tailgate closed, which didn't happen ( mounted a couple feet off the ground).
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Spare trailer tire mounted 'flat' to the airstream makes a fine parachute.
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Narrow pickup pulling very wide flatbed.
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No topper to increase width or height of wake area in which trailer might have drafted.
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I'll look forward to the RAM test, with a 4.485-gallon gas tank, and we'll see all about range anxiety.

[aerohead]

Originally Posted by freebeard

The delta will be down in the noise. Is this the best we can do for argumentation?

The weak link in the chain is PV cell efficiency. Exceed the Shockley-Quiesser limit and the equations all stand on their heads.

1) The 'delta' is ' available wheel power and mass.'
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Here's a truth table:
a) City cycle speeds are prescribed.
b) Wheel rpms are dependent on road speeds of the cycle.
c) Available wheel power at a specified wheel rpm is dependent upon torque.
d) To increase wheel power, available torque must be increased, as rpms are inflexibly prescribed and cannot be increased ( power is a function of torque and rpm ).
e) Torque is dependent upon momentum.
f) Momentum is dependent upon inertia.
g) Inertia is dependent upon mass.
h) If a specified small BEV is to become more efficient in the prescribed urban test cycle, it must experience a mass increase of unspecified magnitude, as per the authors comments, sentence #1, page 26 of the thesis.

[Isaac Zachary]

I think everything should be taken into account, aerodynamics and all.

As stated earlier, just because you get better efficiency in one aspect doesn't mean the overall efficiency will increase or distance per fuel unit spent per person/unit-of-mass will increase either.

• If your vehicle were a solid lead mass, then the amount of energy that could be lost to braking would be much greater than the amount of energy lost to aerodynamic drag. Say the difference is about 90% of inertial energy would be lost during braking and the other 10% to air drag and rolling resistance. If regen is 90% efficient then the total amount of inertial energy that could be recuperated during braking is 81%.
• If your vehicle has the total mass of a feather, then the amount of energy that could be lost to braking is hardly anything and nearly all of it will be lost to aerodynamic drag. If the difference is 50% of your inertial energy is lost to aerodynamic drag and rolling resistance, then it doesn't matter if regen is 100% efficient. You will never recuperate more than the remaining 50%.
• Mind you both vehicles will need to eventually accelerate. The one withe the mass of solid lead will need a whole lot more energy to accelerate. The one mass of a feather will need a whole lot less.
• As aerodynamics and rolling resistance are improved the more all the inertial energy will need a braking effect in order to change it. If a car has 0 aerodynamic drag and 0 rolling resistance, all the inertial energy will have to be either lost or recuperated by some form of braking.
• Something else to take into account is electric motor and controller efficiency curves. A high performance system may be less efficient at low regen currents than higher ones. As a result, it becomes more efficient when there's more mass to slow down. But the same result could be achieved by lowering mass and the performance of the motor and controller. Acceleration would be essencially the same since the power to weight ration would be essencially the same.

[redpoint5]

Nothing was ever explained. We just get footnote non-responses like we didn't even formulate a question. Totally unreadable and non-sequitur to the question.

[freebeard]

I wasn't going to say anything.

duckduckgo.com/?q=truth+table&ia=web

https://open.library.okstate.edu › criticalthinking › chapter › chapter-5-truth-tables
A complete truth table for a sentence that contains four different sentence letters requires 16 lines. Five letters, 32 lines. Six letters, 64 lines. And so on. To be perfectly general: If a complete truth table has n different sentence letters, then it must have 2 n rows.

[aerohead]

Originally Posted by Isaac Zachary

I think everything should be taken into account, aerodynamics and all.

As stated earlier, just because you get better efficiency in one aspect doesn't mean the overall efficiency will increase or distance per fuel unit spent per person/unit-of-mass will increase either.

• If your vehicle were a solid lead mass, then the amount of energy that could be lost to braking would be much greater than the amount of energy lost to aerodynamic drag. Say the difference is about 90% of inertial energy would be lost during braking and the other 10% to air drag and rolling resistance. If regen is 90% efficient then the total amount of inertial energy that could be recuperated during braking is 81%.
• If your vehicle has the total mass of a feather, then the amount of energy that could be lost to braking is hardly anything and nearly all of it will be lost to aerodynamic drag. If the difference is 50% of your inertial energy is lost to aerodynamic drag and rolling resistance, then it doesn't matter if regen is 100% efficient. You will never recuperate more than the remaining 50%.
• Mind you both vehicles will need to eventually accelerate. The one withe the mass of solid lead will need a whole lot more energy to accelerate. The one mass of a feather will need a whole lot less.
• As aerodynamics and rolling resistance are improved the more all the inertial energy will need a braking effect in order to change it. If a car has 0 aerodynamic drag and 0 rolling resistance, all the inertial energy will have to be either lost or recuperated by some form of braking.
• Something else to take into account is electric motor and controller efficiency curves. A high performance system may be less efficient at low regen currents than higher ones. As a result, it becomes more efficient when there's more mass to slow down. But the same result could be achieved by lowering mass and the performance of the motor and controller. Acceleration would be essencially the same since the power to weight ration would be essencially the same.

1) The aerodynamics hasn't changed.
2) Between all three driving cycles, aerodynamics plays a subservient role.
3) Overall efficiency is weighted towards urban driving. It's biased.
4) The BSFC-e of the BEV is 311% more efficient than the ICE stablemate. The inertia loss associated with accelerating the increased mass is meaningless with this 311% advantage compared to the ICE variant. The electric motor just laughs at it.
5) 81.1% of braking energy is recovered by regeneration. There is no energy lost to braking. Mass is your friend.
6) A 10% increase in mass costs only a 1-2 % penalty in rolling resistance.
7) Even with a 20% mass increase, the energy gain from regen is 14.6% net overall, after allowing for the increase in inertia and R-R losses.
8) Again, aerodynamics remains the same.
9) It's a net OVERALL efficiency gain for the small Volvo.
10) Your zero-mass analogy is not germane to the Thesis.
11) I agree completely with your premise about reduced drag and R-R, however they're not germane to the Thesis.
12) Electric motors with powertrain are typically rated at 95% efficiency, with no stipulation as to 'curves.'
13) 'Power' to weight is not germane with BEVs, as 100% torque is always available from zero-to- full rpm.
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The 2021 VOLVO XC40 P8 AWD Recharge ( R-Design ) is still ' such a small vehicle.' ( Mark Rechtin, MOTOR TREND ), but now has ' Strong regenerative braking.' ( Duncan Brady, MOTOR TREND ).
Volvo increased it's weight from, 1572-kg, to 2165-kg.
It out-accelerates the ICE version. It's faster in the quarter-mile. It's 'fuel economy' is 311% higher. I has 1,109 miles range on the ICE's 'tank', compared to 355-miles, 93.4-mpg-e, to 25-mpg.