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Measuring and reporting vehicle emissions


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#1 Charlieman

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Posted 22 February 2019 - 13:16

I'm thinking out loud here. I just wonder whether "industry standard" statistics for new car emissions are meaningful to consumers.

 

In Europe, we have standard tests used to determine fuel consumption and emissions. I'm going to assume that the tests are indicative of real world conditions and that manufacturers aren't cheating. Both assumptions are true some of the time -- cars which perform highest in lab tests tend to perform highest in real world tests, and most manufacturers have not been caught cheating.

 

15 years or so ago, I looked at the mpg (km/litre) and CO2 emission (g/km) for cars listed by BMW. I picked BMW because most of their petrol and diesel engines were from the same generation. Multiplying mpg by CO2 emission for different petrol models with different engines, CO2 per litre of petrol was the same. That was pretty much what I hoped: Carbon input from fuel = Carbon output, consistently. I'd have been confused if there had been an outsider. Similarly for diesel engine BMWs, CO2 per litre of fuel was consistent across models.

 

What is the point of reporting CO2 emission (g/km) when it is the same pollution measure as mpg or km/litre? Petrol engines and diesel engines are different (calorific value of fuels, thermodynamic efficiency) but it is easy to provide a multiplier for CO2 emissions: 100 g/km of CO2 in a petrol car = 100 * Y for a diesel.

 

I am assuming conventional passenger cars with a modern ECU and sensors, with an efficient combustion process across different environmental conditions. I think that is a safe assumption. Carbon input = Carbon output, because the exhaust catalyser captures almost all non-CO2 carbon emissions. The UK MOT for petrol engines primarily checks CO2 emissions. It would be more useful if it measured other carbon emissions.

 

Many environmental campaigners have been surprised that their efforts to reduce CO2 have increased NOx emissions. They don't really know their own history. Problems related to car emissions were identified in the 1950s, and both CO2 and NOx were correctly identified as pollutants. NOx created problems that you could see for yourself -- smog, which was associated with California but cars also created the big smogs in UK cities in the 1950s. NOx pollution is also associated with tall buildings, poor air flow and high street temperature -- you can't just blame engine designers.

 

As I understand the combustion process in an internal combustion engine, you can have any two of three: thermodynamic efficiency, low CO2 emissions or low NOx emissions. So when car manufacturers were told to cut CO2 emissions and had an economic imperative to reduce mpg, the NOx went up. 

 

And we have the other stuff. Soot, unburnt fuel, particulates. They are a measure of engine inefficiency. They are mostly a diesel thing, old engines, which go away when hybrid electric/diesel power plants replace them.

 

 



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#2 Greg Locock

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Posted 23 February 2019 - 00:44

"I'm going to assume that the tests are indicative of real world conditions"

 

I don't agree, the tests are rather odd compared with real world driving. 

 

https://assets.publi...247/ppr-354.pdf

 

Note the very slow accelerations, if you drove like that in Australia you'd be beeped off the road!

 

"What is the point of reporting CO2 emission (g/km) when it is the same pollution measure as mpg or km/litre?"

 

None, for a technical audience.


Edited by Greg Locock, 23 February 2019 - 00:45.


#3 Kelpiecross

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Posted 23 February 2019 - 04:06

  I think the "pea soup"  fogs/smogs in early 1950s London were mainly due to the widespread use of coal for household heating/cooking etc.    



#4 Greg Locock

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Posted 23 February 2019 - 06:21

Yeah, I agree. I've never seen vehicle emissions blamed for smog in the UK. Not saying it didn't happen. 



#5 BRG

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Posted 23 February 2019 - 19:34

  I think the "pea soup"  fogs/smogs in early 1950s London were mainly due to the widespread use of coal for household heating/cooking etc.    

Exactly so.  Once the Clean Air Act of 1956 (and subsequent legislation) was enacted, smog became a thing of the past almost immediately.  Yet vehicle numbers increased whilst not having improved emissions until the 1990s.  So vehicle emissions were at most a tiny part of the problem.



#6 Charlieman

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Posted 25 February 2019 - 11:59

  I think the "pea soup"  fogs/smogs in early 1950s London were mainly due to the widespread use of coal for household heating/cooking etc.    

On reflection, I agree. Cars had low compression petrol engines and there were relatively few diesels. I should have limited my comment to California smog which is clearly linked with human/natural environment and vehicles emissions.



#7 Kelpiecross

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Posted 26 February 2019 - 02:11

  If England was like Australia in the early 1950s there probably weren't enough cars on the road to cause much smog.   

 

 I would have liked to have experienced a "pea-soup"  fog (but maybe not to have lived in one too long)



#8 MatsNorway

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Posted 01 March 2019 - 10:08

If we are going to talk about smog in a city you need to also look at wind conditions and ships. London had once the biggest port in the world. Back then they all ran on coal probably.

Smog being visible makes it easy to see the effect. Below is from some normally rather clean fjords.

Norway have started to realize that the pollution is a problem. Internationally no one wants to add the ship emissions to their national emissions.. so it has been overlooked for a long time.

They claim one big cruise ship pollutes more than 1 million cars pr year.

https://smp.vgc.no/v...e6a2187f316b512

https://www.kystogfj...ene_slimbox.jpg

 

https://www.sdir.no/...eritage-fjords/

 

 

As for wind the small city of Bergen has smog problems as the wind is consistently from the west. blocking the pollution against the mountains. The city has a population of less than 300k

https://www.business...llution-2011-11

"An inversion layer is formed, trapping the pollution hanging over the city. In January 2010, Bergen was the city most polluted in Europe "


Edited by MatsNorway, 01 March 2019 - 10:12.


#9 7MGTEsup

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Posted 21 March 2019 - 16:03

I am assuming conventional passenger cars with a modern ECU and sensors, with an efficient combustion process across different environmental conditions. I think that is a safe assumption. Carbon input = Carbon output, because the exhaust catalyser captures almost all non-CO2 carbon emissions. The UK MOT for petrol engines primarily checks CO2 emissions. It would be more useful if it measured other carbon emissions.

 

As far as I'm aware CO2 doesn't come into the MOT test in the UK, They measure lambda, CO and THC.

 

Nox can be quenched on a lean burn engine by running water injection but no one seems to have taken that path for some reason.


Edited by 7MGTEsup, 21 March 2019 - 16:07.