EVs and Particulate Emissions 3

[TugboatEng]

I would have posted to the old thread but it's closed.

Original thread:

https://www.eng-tips.com/viewthread.cfm?qid=493416

Here is some affirmation of my previous suspicion about EVs and it's worse than I thought. 1850x the particulate emissions from all EVs vs all combustion powered vehicles.

https://nypost.com/2024/03/05/busin...missions-are-worse-for-the-environment-study/

Of course, the methodology needs to be examined. Secondly, article mentions tires and brakes as the source of PM. Is road wear not included?

Note that particulate emissions from all properly running on-road diesel engines post 2008 is 0pmm so 1850x may still not be a very large number.

 

[BrianPetersen]

There is absolutely no possible way an EV without an engine is going to emit 1850 times as much PM as an otherwise comparable combustion-engine vehicle. It completely fails the smell test. There is no tailpipe, so there's that. The EV relies less upon its mechanical brakes - regenerative braking doesn't use them - at 50 000 km the brake pads and rotors on my Bolt look like they're practically new, so there's less PM from brake pad and rotor material. There's much hubbub about EVs having more tire wear due to more weight; I think it's because a bunch of them have automatic ride-height-adjustable suspension and they can't have steering geometry optimised for minimum tire wear throughout the ride-height adjustment range (Rivian, Tesla, probably others, not mine). At 50 000 km (of which about 12 000 were on the winter tires) the OEM tires on my Bolt are probably a third worn, and they'll be replaced before legal minimum, so they're heading for probable replacement around (guess) 80 000 km which I would consider to be in a normal range.

There is no shortage of FUD circulating. Fear, Uncertainty, Doubt.

Certain EVs - some Teslas come to mind - come with high-performance summer tires as original equipment. Long life is not a design priority with those. Combine that with having 600 horsepower on top and perhaps a heavy-footed driver and there's gonna be tire wear. But not 1800 times as much tire wear as some other vehicle!

Certain EVs - Rivian comes to mind - seem to be getting a reputation for excessive tire wear. Those have ride-height-adjustable suspension with a pretty large height adjustment range. I'm suspicious about this being the real problem. Those vehicles have an independent upper and lower unequal-length wishbone suspension design front and rear.

- Unless the suspension is designed for zero camber gain - and that's not normally the case, and impossible if the upper and lower arms are either non-parallel or unequal length with the normal case being both - there is only going to be one or maybe two ride heights at which the camber is zero (or at the minimum-tire-wear condition). At any other ride height, it's going to have positive or negative camber. If the suspension is the usual arrangement - upper arm shorter and inclined more - then the lowest suspension setting (for highway range) is going to have significant negative camber. OR, if the alignment is set up for minimum tire wear at that ride height, it's going to have significant positive camber at any other ride height. It would be interesting for someone who has one of these vehicles, to put it on a good alignment machine, and post a camber curve (camber as a function of ride height).

- Unless the suspension is designed for zero bump steer at both ends - and if there is any designed-in roll understeer, which would normally be the case - it's only going to have one or maybe two ride heights at which the toe is zero. Roll understeer means heading towards front toe-out and rear toe-in with suspension compression (lower ride height). Toe-out is bad at both ends, so in the interest of not having actual toe-out, more likely it has zero front toe and some non-zero rear toe-in at low (highway-cruise) ride height and goes towards toe-in at higher ride height up front and towards zero out back. Again, front and rear toe curves would be interesting to see.

The Ford Lightning should not have this problem. For one thing, it doesn't have ride-height-adjustable suspension. For another, the rear suspension (which is going to change in ride height more due to cargo loading) is a rare modern example of pure trailing arm geometry, which (ideally) does not change toe or camber with suspension movement.

My Bolt does not have this problem. Not ride-height-adjustable. Rear suspension is a twist-beam axle, which has insignificant toe or camber change with ride height. Front is MacPherson strut same as practically any other modern GM car.

 

[TugboatEng]

I mentioned it above, 1859x a very small number is still a very small number.

I am annoyed that quantities are not included for this reason.

Modern diesel engines with particulate filters and gasoline engines with oxidation catalyst emit almost zero particulate matter. When testing diesel engines with DPF the result is always 0% opacity. I don't know what that correlates to in ppm but it must be very low.

Do note that combustion engines breath through high efficiency air filters do it's quite possible their PM is lowered than the inhaled air. We participated in the certification of a Cat 3500 series EPA Tier 3 engine. This was during one of the bad California fire years. The testers were commenting that the PM of the exhaust was lower than the air in. This could have been an exaggeration, the final data was proprietary so I never got to see it

 

[LittleInch]

The article does include a logarithmic graph, but this is just not comparing the same thing.

It's comparing particles from brakes and tyres from EVs to tail pipe emissions. It doesnt try to compare the same particles from the same source. So we don't know how EVs compare to ICE or hybrid vehicles for tyre and brake emissions.

So yes, being pedantic. EVs are not zero emissions, but the amounts here different to other vehicles are just minute. And it's CO2 which really matters.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BrianPetersen]

The brake particle contribution has to be lower, simply because the actual mechanical brakes are used A LOT less: Regenerative braking. Mine defaults to using that even if you apply the normal brake pedal. It only applies the mechanical brakes if it has to (because you're asking for more than what regen can achieve). The actual brake parts are the same as on a bunch of other compact GM cars (Encore, Trax, Sonic which are platform-cousins), but the Bolt brakes last way longer.

 

[BrianPetersen]

Here is the actual source article, which contains a good explanation of not only what the original intent was, but also how it has been misinterpreted.

https://www.emissionsanalytics.com/news/gaining-traction-losing-tread

The real point is that exhaust tailpipe PM emissions in the EU, which has regulations for this, are basically irrelevant compared to PM emissions from tire wear. There was no measurement of tire wear on a representative BEV compared to a comparable petrol vehicle. The article made some logical inferences based on vehicle weight (the possibility exists), but no actual measurement.

My Bolt weighs 1600 kg. A current VW Golf, which is practically the same size, weighs about 1400-1500 kg. That's the EV weight penalty for comparable-passenger-space vehicles in the same class, comparing a vehicle that was designed as a combustion-engine vehicle from the outset to a vehicle that was designed as an EV from the outset. (Add: 400 kg battery pack. Cancel: Front drive motor and gear reducer are about the same mass as a transaxle. Subtract: 150 kg combustion engine. Subtract, which VW could have done on the Golf but didn't, a lot of the body panels are made from aluminium, don't know what those weigh. Subtract: Petrol tank.)

Now, current vehicles in general are enormously heavy compared to their predecessors, but that's safety equipment, noise insulation, crash structures, and they've gotten bigger because no advertising manager ever wants to have to deal with the new model having less trunk space or passenger volume than the outgoing model. And people keep on buying ever bigger and bigger trucks and SUVs to get to and from work and the grocery store ...

 

[TugboatEng]

Shoot, I wish I had posted this instead of the news link. This has real numbers (quantities).

https://www.emissionsanalytics.com/news/gaining-traction-losing-tread

Yes, the news article is comparing tire wear to tail pipe emissions. That's not fair because both EV and combustion powered cars have tire wear.

However, in the improved link the tire emissions were measured to be 8.03 mg/km. Adding 500kg weight to the car nearly doubled the PM with an additional 7.67mg/km.

For comparison, tailpipe PM was measured to be 0.02mg/km. The correct conclusion should be that EV's likely emit double the PM (8.05 ICE and 15.70 EV) of a ICE driven vehicle if we assume the EV is 500kg heavier than its ICE equivalent.

 

[LittleInch]

Further correction? 7.67 mg/km... not kg?

[Now fixed in post above]

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[rb1957]

you may want to change your signature line ... I read it as "remember minus more details" ... ok, that's just me !

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[BrianPetersen]

Their tire wear measurements were based on tests conducted on one vehicle, stated to be a Mercedes C-class, presumably a fairly new one. Those weigh about 1600 kg.

So ... how does a +30% increase in vehicle mass (+500 kg) result in a +90% increase in tire wear?

Probably ... because the tires and wheels and car remained the same and inflation pressure presumably remained at nameplate, and the tires are thus operating close to the upper bound of their load ratings as opposed to the lower bound. And the suspension would be riding at a lower ride height, probably affecting the alignment a little. The tires will be flexing more, running hotter, scrubbing more against the pavement due to the increased deformation around the contact patch. I can see that leading to an out-of-proportion increase in tire wear with the same vehicle and same tires and same inflation pressure.

So ... What happens to the tire wear if you accept the increase in mass as part of the vehicle, and re-specify either the tires or the inflation pressure or the suspension settings and/or ??? so that the combination is reset to the best combination for the new loading situation?

My Bolt came with low-rolling-resistance self-sealing Michelin tires with the highest specified inflation pressure of any car I've ever owned.

 

[GregLocock]

Wear type problems increase as Fz^(4-6) depending on what is wearing. This is surprisingly similar to long term fatigue life of metals

https://www.researchgate.net/figure...ds-and-particle-sizes-T60-min_fig7_273181609.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[TugboatEng]

Maybe there needs to be some clarification.

The baseline weight loss was 36.50 mg/kg. Of that 8.03 mg/kg became airborne / was sub 10 micron. The question is whether the 7.67 is the tire weight loss or the increase in PM? If it is tire weight loss then that 30% increase in weight corresponds with a 36% increase in wear. That seems reasonable, no?

If the 7.67 mg/kg is only airborne particles then that would be a 95% increase in PM. The language makes me think it's the first case, though.

However let's assume the same ratio becomes airborne. 8.03/36.5*7.67 equals 1.69 additional airborne mg/km.

That means the EV makes 9.99 mg/kg PM while the ICE is 8.05 mg/kg. That's stil 24% more PM from an EV vs ICE.

Here in California some say that PM kills 50k annually.

 

[BrianPetersen]

They're still only looking at tires, and not brake components. They're also not considering photochemical smog, which is from HC and NOx. It all adds up. And still, the disbenefit from choosing to drive a huge SUV instead of something more sensibly sized for driving one person to and from work overwhelms all this, and walking (no cars) would be best of all.

Good luck.

 

[TugboatEng]

The study was looking at PM which is a different pollutant than HC or NOx.

Something to keep in consideration is that power plants don't have particulate filters, oxidation catalysts, selective catalytic reduction, or even intake air filters. ICE engines are cleaner than grid power. In some cases they can be more efficient as straight steam cycles are very limited.

 

[BrianPetersen]

Right, but power stations aren't generally located next to residential areas. (PM gets scrubbed out of the air by, for example, rain, fog, clouds, and are primarily a local and short-term pollutant as opposed to a long-term climate-change issue.)

And, nuclear plants, solar, wind, hydroelectric (which account for 90+% of grid supply where I live) don't need any of that.

 

[TugboatEng]

You're fortunate for that to be your case but this isn't true for the majority of the rest of the world. All things need to be looked at critically. This study is interesting because it's one of the first I have seen that produces real numbers.

In much more densely populated California our fossil fuels power stations are located within cities including Pittsburg, Antioch, Martinez Crockett, Hayward, Santa Clara, San Jose.

 

[BrianPetersen]

https://www.sciencedirect.com/science/article/pii/S0269749123014021

 

[waross]

Using tailpipe emissions and ignoring tire and brake contributions of an IC vehicle compared to tire and brake contributions of an EV vehicle is not oranges to apples. It is a peanuts to elephants comparison.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

In the tire PM study the total quantity was separated from the airborne emissions. Airborne was 23% of total. Is the brake study airborne or total? I haven't figured that out yet. It seems like brake emissions are minimal except for city driving.

 

[BrianPetersen]

Urban conditions are where you have the most people in closest proximity to the vehicles, though. That's where people are breathing this stuff in the most. The situation is not simple.

Still ... Compare the air quality in any large urban centre now, to how it was 40 years ago back when most vehicles on the road had rudimentary emission controls at best. A lot of progress has been made, and no, it still isn't perfect. Tailpipe nasties (HC, CO, NOx, PM) are now minimal for modern vehicles, with the remaining challenge being CO2, and that's a big one.