Model 3 Range on Highway at 87mph/h 140km/h

Thomas Mikl

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#21
OK I try to explain within the laws of physics :)

There are 2 factors why you ICE car uses less gas at 75mph per mile than going low speed in town. (However the gas consumption will again rise hugely when you get near the cars top speed or beyond 90mph for most cars).

First is actually thermodynamics of the engine and drivetrain. An ICE car is hugely inefficient. The best combustion engine in the world inside an ICE car is currently the gas engine used in the new Mazda CX series and its best case efficiency is close to 30%. So about 70% of the energy stored in euch gallon of fuel is wasted by the engine itself. Especially friction and access heat. If you factor in losses of the drivetrain your combined efficiency will sink to possibly 20-25% (not an expert on drivetrains so this is a guess).

Now why does this mean I use less gas per mile on higher speed?
Well inside a town going slowly you are more likely to stop and go and drive the motor in "bad gearing" and outside the motors comfort zone of RPMs. Also starting the car from ZERO to say 20mph is hugely inefficient as the engine friction is highest after a standstill, but torque is not good at low revs so you have to actually hit the gas pedal more to rev up and the clutch needs to slowly engange to not kill the engine.
All of that menas high waste, which means high consumption.

On the other hand if you are going 65-75 on a highway for 2 hours, you car will most likely be close to optimal revs, the engine will be well lubricated and there will be no gears switched and the clutch (or with automatics the auto gear lock) will be engaged fully the whole time. Meaning you are driving the whole thing at its most efficient setting. If your car then has at least a decent drag coefficient (aka not a Hummer) then you should use less gas per mile.

This will again get worse at high speeds, since you cannot trick aerodynamic and the more your car looks like a brick, the worse it gets. But also for example (at test we did here) an Audi R8 has an optimal efficiency going straight at 80mph, but will be extremely bad at 120mph.

With EVs this is totally different as the whole engine and drivetrain is hugely more efficient and you have all the torque all the time. Hence it is really only car weight and aerodynamics that come into play. And since aoero drag is exponentially higher at higher speeds a good drag coefficient (like in the model 3) will help but not eliminate the problem. But my guess the 3 will be much more efficient at 75 than a Bolt.

Fun fact if you have a gas car that can get 500 miles on a tank of gas, if you could convert all the stored energy in that fuel into electric energy at 100% efficiency, your Tesla could go prolly close to 3000 miles....
 

KarenRei

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#22
Thomas is closest, but still not completely there. And it's actually quite simple.

Here's your answer:



That's called a "brake specific fuel consumption" graph; google image search for more. It means "fuel consumed divided by power produced", so obviously, low numbers are good. A car engine may have a 35% thermodynamic efficiency at its peak but average only 20% in operation, because that peak efficiency is only available in - as you'll notice - low RPM / high torque situations. Torque in particular is the killer issue - if you're not producing a lot of torque, your efficiency is terrible.

Now, you have a gearbox, whether manual or automatic. So, you can trade off - to some extent - RPM and torque. So you try to keep your engine at low revs / high torque as much as possible. But the simple fact is that at low speed, you simply can't do that very well. The air and rolling resistance are so low there that even at low revs, holding your speed constant just isn't going to require much torque. Cruising even at highway speeds generally requires much less torque than your engine can provide, so that your car doesn't feel sluggish or have trouble climbing hills; at low speeds, cruising power is a tiny fraction of what your engine has the potential to provide. Which means that you're low down on that graph, which means that your efficiency sucks. When you're on the highway, though, and facing a lot of resistance, holding your speed constant at low revs takes a lot more torque, and boosts your efficiency.

There are of course other well-known factors like how ICEs in town waste energy idling and braking. But even when you account for these factors, this is the reason why your efficiency peaks at the bottom of the rev range of your highest gear: high torque, low RPM. Same reason why towing with an ICE doesn't cause as much range loss as towing with an EV - that trailer means your engine needs to put out more torque to maintain your speed!

EVs and the electric motors on hybrids, by contrast, have efficiencies that look like this:


(Varies a lot depending on the type of electric motor... this one is from an early Prius) Note that while there are variations, it's efficient everywhere. Even the absolute worst efficiency is only 83% of the best efficiency. By contrast, in the gasoline vehicle's chart, you'll see labeled values 45% of the best efficiency - and it gets even worse from there at even lower torques. So while electric motors are affected by driving conditions, it's not nearly as much.

That said, it's easy to overstate this as "EV motors are not affected by torque and RPM conditions". You can see that - to some extent - they still are. And it's this that causes Tesla's dual motor configurations to have longer range than their single motor vehicles, despite their greater mass. They sleep whichever motor is less efficient under current conditions ("torque sleep") or in order to subject one motor to higher torque demands - only waking the sleeping motor when it's actually needed (rapid acceleration, etc). So while it's not a huge increase in performance, it's enough to give greater range regardless.

Clear? :)
 
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KarenRei

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#24
The EV graph is pretty clear. But I don't know what the X and Y axis units are on the first graph, nor do I understand the numbers in the middle of the graph. Can you explain them? :)
X axis = engine rotation rate in RPM
Y axis = engine pressure (directly related to torque) in bar
Labels = fuel consumption in g / kWh.

This particular engine is a large diesel, so it's fairly efficient as far as ICEs go. Diesel is around 45kJ/g (0,0125 kWh/g), so the energy in the fuel burned is:

0,0125 * value

And thus the efficiency (energy produced divided by the energy in the fuel burned) is:

1 / (0,0125 * value)

So this engine's peak efficiency is 39%, while the lowest label they show is 18% (and it goes down from there).
 

mkg3

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#25
I'm sure one of the new owners will drive for short period at 87+MPH and can report back how much charge was drained by doing the increment soon enough....
 

Akilae

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#28
Thomas is closest, but still not completely there. And it's actually quite simple.

Here's your answer:



That's called a "brake specific fuel consumption" graph; google image search for more. It means "fuel consumed divided by power produced", so obviously, low numbers are good. A car engine may have a 35% thermodynamic efficiency at its peak but average only 20% in operation, because that peak efficiency is only available in - as you'll notice - low RPM / high torque situations. Torque in particular is the killer issue - if you're not producing a lot of torque, your efficiency is terrible.

Now, you have a gearbox, whether manual or automatic. So, you can trade off - to some extent - RPM and torque. So you try to keep your engine at low revs / high torque as much as possible. But the simple fact is that at low speed, you simply can't do that very well. The air and rolling resistance are so low there that even at low revs, holding your speed constant just isn't going to require much torque. Cruising even at highway speeds generally requires much less torque than your engine can provide, so that your car doesn't feel sluggish or have trouble climbing hills; at low speeds, cruising power is a tiny fraction of what your engine has the potential to provide. Which means that you're low down on that graph, which means that your efficiency sucks. When you're on the highway, though, and facing a lot of resistance, holding your speed constant at low revs takes a lot more torque, and boosts your efficiency.

There are of course other well-known factors like how ICEs in town waste energy idling and braking. But even when you account for these factors, this is the reason why your efficiency peaks at the bottom of the rev range of your highest gear: high torque, low RPM. Same reason why towing with an ICE doesn't cause as much range loss as towing with an EV - that trailer means your engine needs to put out more torque to maintain your speed!

EVs and the electric motors on hybrids, by contrast, have efficiencies that look like this:


(Varies a lot depending on the type of electric motor... this one is from an early Prius) Note that while there are variations, it's efficient everywhere. Even the absolute worst efficiency is only 83% of the best efficiency. By contrast, in the gasoline vehicle's chart, you'll see labeled values 45% of the best efficiency - and it gets even worse from there at even lower torques. So while electric motors are affected by driving conditions, it's not nearly as much.

That said, it's easy to overstate this as "EV motors are not affected by torque and RPM conditions". You can see that - to some extent - they still are. And it's this that causes Tesla's dual motor configurations to have longer range than their single motor vehicles, despite their greater mass. They sleep whichever motor is less efficient under current conditions ("torque sleep") or in order to subject one motor to higher torque demands - only waking the sleeping motor when it's actually needed (rapid acceleration, etc). So while it's not a huge increase in performance, it's enough to give greater range regardless.

Clear? :)
Thank you for this really great explanation. :)
 

EValuatED

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#29
Great explanations & discussion and thanks @Thomas Mikl and @KarenRei !

Here's what I 'heard' in reading your excellent posts:

At low speeds & stop/go -- application of the ICE motor is inefficient (re: % extracted from fuel by motor/drivetrain system) -- in its use of its higher power density fuel (in relation to power density of battery storage 'fuel').

At high speeds -- mode of application of ICE is less inefficient -- so on a relative basis it appears as not much change in fuel economy at higher speeds (until aero effects become more & more impactful).

At low speeds & stop/go -- application of EV is efficient (in use of stored energy 'fuel') but is noticeably impacted by repeated accelerations. (Regen helps EV overall system efficiency but you don't get back 100%.)

At high speeds -- application of EV is efficient but increasingly impacted by aero effects. (Again, Regen helps EV overall system efficiency but you don't get back 100%).

Repeated accelerations have a noticeable impact on both systems.

With ICE v. EV, we see effects of different propulsion system characteristics, in application.
 
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#30
Thomas is closest, but still not completely there. And it's actually quite simple.

Here's your answer:



That's called a "brake specific fuel consumption" graph; google image search for more. It means "fuel consumed divided by power produced", so obviously, low numbers are good. A car engine may have a 35% thermodynamic efficiency at its peak but average only 20% in operation, because that peak efficiency is only available in - as you'll notice - low RPM / high torque situations. Torque in particular is the killer issue - if you're not producing a lot of torque, your efficiency is terrible.

Now, you have a gearbox, whether manual or automatic. So, you can trade off - to some extent - RPM and torque. So you try to keep your engine at low revs / high torque as much as possible. But the simple fact is that at low speed, you simply can't do that very well. The air and rolling resistance are so low there that even at low revs, holding your speed constant just isn't going to require much torque. Cruising even at highway speeds generally requires much less torque than your engine can provide, so that your car doesn't feel sluggish or have trouble climbing hills; at low speeds, cruising power is a tiny fraction of what your engine has the potential to provide. Which means that you're low down on that graph, which means that your efficiency sucks. When you're on the highway, though, and facing a lot of resistance, holding your speed constant at low revs takes a lot more torque, and boosts your efficiency.

There are of course other well-known factors like how ICEs in town waste energy idling and braking. But even when you account for these factors, this is the reason why your efficiency peaks at the bottom of the rev range of your highest gear: high torque, low RPM. Same reason why towing with an ICE doesn't cause as much range loss as towing with an EV - that trailer means your engine needs to put out more torque to maintain your speed!

EVs and the electric motors on hybrids, by contrast, have efficiencies that look like this:


(Varies a lot depending on the type of electric motor... this one is from an early Prius) Note that while there are variations, it's efficient everywhere. Even the absolute worst efficiency is only 83% of the best efficiency. By contrast, in the gasoline vehicle's chart, you'll see labeled values 45% of the best efficiency - and it gets even worse from there at even lower torques. So while electric motors are affected by driving conditions, it's not nearly as much.

That said, it's easy to overstate this as "EV motors are not affected by torque and RPM conditions". You can see that - to some extent - they still are. And it's this that causes Tesla's dual motor configurations to have longer range than their single motor vehicles, despite their greater mass. They sleep whichever motor is less efficient under current conditions ("torque sleep") or in order to subject one motor to higher torque demands - only waking the sleeping motor when it's actually needed (rapid acceleration, etc). So while it's not a huge increase in performance, it's enough to give greater range regardless.

Clear? :)
Nice explaination. You know this from intrest/looking up? Or has this something todo with mabye your job/studies?

Incase you ever said that somewhere else sorry for the question. I'm intrested in you informative/useful remarks(when i saw them).

Thanks!
 

KarenRei

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#31
Nice explaination. You know this from intrest/looking up? Or has this something todo with mabye your job/studies?

Incase you ever said that somewhere else sorry for the question. I'm intrested in you informative/useful remarks(when i saw them).

Thanks!
I once ran a company making EV range calculation software. :) Understanding where vehicles lose energy was literally my job.
 
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#33
I once ran a company making EV range calculation software. :) Understanding where vehicles lose energy was literally my job.
<Encyclopedia>

Alright! Thats pretty interesting. Thanks for the quick reply though I appreciate it.

Never thought I'd post something on a forum to a person. Being in the dark and nerding out is more fun :) (Been reading this since the very start, just never made an account because there was not alot of pics and stuff back then). But this ain’t so bad. Have to make sure I don't get addicted. It's still a while for the M3 here in Belgium.
Cheers!

</Encyclopedia>
 
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Akilae

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#34
I once ran a company making EV range calculation software. :) Understanding where vehicles lose energy was literally my job.
That's why on July 27th we thought that you might work for Tesla after they where taking down their code snippets right after your post ;).
 
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4701

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#36
Faster you go on battery the more cooling of the batteries needs to happen??
Load difference is too small compared to extra cooling. Most of the cooling is done by glycol loop. The faster you go the more air passes through the radiator, cooling the coolant faster.

I can bring some extremely nice numbers from BMW 5-series, 2010, diesel, 180kW
Fuel economy at 90kmh 56mph is 5l/100km 47mpg. (around 30kW load?)
Fuel economy at 180kmh 112mph is 10l/100km 23,5mpg (around 100kW load)
Fuel economy at 250kmh 155mph is around 20l/100km as engine hardly keeps up at around 4200rpm (170kW load)
(Model S draw is also somewhere around 170-200kW at that speed, which makes me wonder about efficiency)

I was stunned. Drove at 180-220kmh for one hour. Engine at 2500-3000rpm.
And that RPM is the key. Turbo is blowing hard, engine has low rpm while enough torque.
Also gains due to intercooler chilling that pressurised air better.
Engine is operating at extremely high efficiency (can anybody estimate?) while cruising at 180-200km/h.
 

tivoboy

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#37
Load difference is too small compared to extra cooling. Most of the cooling is done by glycol loop. The faster you go the more air passes through the radiator, cooling the coolant faster.

I can bring some extremely nice numbers from BMW 5-series, 2010, diesel, 180kW
Fuel economy at 90kmh 56mph is 5l/100km 47mpg. (around 30kW load?)
Fuel economy at 180kmh 112mph is 10l/100km 23,5mpg (around 100kW load)
Fuel economy at 250kmh 155mph is around 20l/100km as engine hardly keeps up at around 4200rpm (170kW load)
(Model S draw is also somewhere around 170-200kW at that speed, which makes me wonder about efficiency)

I was stunned. Drove at 180-220kmh for one hour. Engine at 2500-3000rpm.
And that RPM is the key. Turbo is blowing hard, engine has low rpm while enough torque.
Also gains due to intercooler chilling that pressurised air better.
Engine is operating at extremely high efficiency (can anybody estimate?) while cruising at 180-200km/h.
the only thing I'll say about this, is that this is most likely only reported by the trip computer or ECU from the car.. real world consumptions could be dramatically different if one takes into account actual fuel consumed and miles travelled.. it's very hard to actually calculate unless one simply actually does the speed, distance and the mileage and then does a re-calculation based on actual fuel consumption.

I can get my ECU to display pretty much anything I want based on hypermiling or drafting or simply lifting off, and it doesn't recalculated dynamically at all taking into consideration more distance based consumption.

I'll add, this is also based on a 750il, BMW M5, alpina 7, and every benz out there.
 
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4701

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#38
Well, the average consumption per 4350km was exactly what trip computer said (error was within 0.1 units, as display can't show more).
5 refills within 2 days, keeping all receipts and verify to be absolutely sure.
If car doesn't know exactly how much fuel it is burning, it will not run with good emissions.
Also I can see 20l/5gal of fuel tank missing after 60 minutes of driving. And hidden menu shows exact
fuel amount in the tank left and fuel wasted during last trip-reset.

Range of 1400km / 870 miles on 70 litres (18.5gal) verifies one specific driving scenario (56mph limited countries).

But yes, I've driven with vehicles that have incorrect consumption display. I suspect main problem is injectors
that inject more (known as leaking, due to wear) than ECU asked. Therefore more fuel actually used than asked.
But that is offtopic.

Proof, but another trip with more limited speeds (we bought 302l of fuel):
 
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