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I work for a competing car company and I once saw a presentation showing that turbos significantly increased CO2 emissions because the cooling of the exhaust ai

I work for a competing car company and I once saw a presentation showing that turbos significantly increased CO2 emissions because the cooling of the exhaust air causes the catalytic converter to operate a few hundred degrees Fahrenheit cooler, lowering reaction efficiency. This can be mitigated by hybrid setups, since you can avoid pumping cold air down the exhaust path on decelerations, but without that, it’s actually not clear that the emissions efficiency of smaller, turbo motors is necessarily better at similar power outputs to larger naturally aspirated engines.

stickfigure 5y ago
You must mean something other than CO2? Catalytic converters aren't intended to reduce CO2.
- wcunning 5y ago
  Might have been more NOx, but the presentation also referred to COx. I’m not an emissions specialist, so I might have misinterpreted parts of it. Or it could have been related to combustion efficiency in addition to reaction efficiency.
  - cirrus3 5y ago
    > I’m not an emissions specialist, so I might have misinterpreted parts of it. Maybe just delete your comment then, it is distracting
- ardit33 5y ago
  This is specific to small Turbo engines (eg. 1.1 l three cylinder turbo). They get great MPG ratings in official testing, but in real world usage they perform worse than a larger non-turbo counterpart (for the same amount of power/HP). Small turbos get good mpg ratings, but their real world use is different: https://www.greencarreports.com/news/1109366_small-turbo-engines-get-good-mpg-ratings-real-world-use-may-be-a-different-story https://www.greencarreports.com/news/1109366_small-turbo-eng... The trouble with turbos: Why fuel economy can be worse, not better https://www.theglobeandmail.com/globe-drive/adventure/red-line/the-trouble-with-turbos-why-fuel-economy-can-be-worse-not-better/article29705614/ https://www.theglobeandmail.com/globe-drive/adventure/red-li... Could we be reaching the end of the road for small-capacity turbocharged engines? https://arstechnica.com/cars/2017/02/could-we-be-reaching-the-end-of-the-road-for-small-capacity-turbocharged-engines/ https://arstechnica.com/cars/2017/02/could-we-be-reaching-th...
sbierwagen 5y ago
It increased CO2 emissions? The cat doesn't touch CO2, it only affects unburned exhaust gases. And CO2 is a primary emission, if it was "significantly" increased then you would also see a significant increase in... fuel consumption. Where else would the carbon be coming from?
- ardit33 5y ago
  This is specific to small Turbo engines (eg. 1.1 l three cylinder turbo). They get great MPG ratings in official testing, but in real world usage they perform worse than a larger non-turbo counterpart (for the same amount of power/HP). Small turbos get good mpg ratings, but their real world use is different: https://www.greencarreports.com/news/1109366_small-turbo-engines-get-good-mpg-ratings-real-world-use-may-be-a-different-story https://www.greencarreports.com/news/1109366_small-turbo-eng... The trouble with turbos: Why fuel economy can be worse, not better https://www.theglobeandmail.com/globe-drive/adventure/red-line/the-trouble-with-turbos-why-fuel-economy-can-be-worse-not-better/article29705614/ https://www.theglobeandmail.com/globe-drive/adventure/red-li... Could we be reaching the end of the road for small-capacity turbocharged engines? https://arstechnica.com/cars/2017/02/could-we-be-reaching-the-end-of-the-road-for-small-capacity-turbocharged-engines/ https://arstechnica.com/cars/2017/02/could-we-be-reaching-th...
King-Aaron 5y ago
So I think you misunderstand, a turbocharged engine generally produces hotter exhaust due to the gases being run through a compressor, and often have more aggressively set timing than a similar layout aspirated engine. I don't know where you got "the cooling of the exhaust air" from?
- WhisperingShiba 5y ago
  Exhaust gas runs through a turbine, hence 'Turbo'. Typically this cools exhaust. Whether or not the higher combustion temperature from the compressed inlet gas makes up for this is not known to me.
  - post_break 5y ago
    Exhaust gas is hotter on turbo engines. It’s why you have to watch exhaust gas temperature like a hawk when off road. High revs with little movement causes EGRs to melt down. 450-650C.
    - WhisperingShiba 5y ago
      I acknowledged that this could still be true in my comment, but that I would have to actually do some analysis. However, what the parent comment said is wrong. Your gas is going to lose internal energy to shaft work as it moves through the turbine, which then compresses the inlet air. Not saying its not hot or hotter, I'm saying the air is not moving through a compressor (which /would/ heat the gas as it does work on the gas to move it to higher pressure), it moving through a turbine, which is recapturing the internal energy of the exhaust gas to improve the efficiency of the engine. Because this site always needs ""SOURCES"" https://www.theturboforums.com/info/article/why-are-exhaust-gas-temperatures-so-important.378413/ https://www.theturboforums.com/info/article/why-are-exhaust-... >EGTs are usually measured close to the head. This provides a much quicker response time as well as a more accurate reading. In fact, the temperature of the exhaust gas following the turbocharger can be as much as 200 to 300 degrees lower than the temperature upstream of the turbo. Air resistance caused by the turbo itself can also cause increases in the temperature upstream that would not be detected past the turbo.

stickfigure 5y ago

You must mean something other than CO2? Catalytic converters aren't intended to reduce CO2.

wcunning 5y ago
Might have been more NOx, but the presentation also referred to COx. I’m not an emissions specialist, so I might have misinterpreted parts of it. Or it could have been related to combustion efficiency in addition to reaction efficiency.
- cirrus3 5y ago
  > I’m not an emissions specialist, so I might have misinterpreted parts of it. Maybe just delete your comment then, it is distracting
ardit33 5y ago
This is specific to small Turbo engines (eg. 1.1 l three cylinder turbo). They get great MPG ratings in official testing, but in real world usage they perform worse than a larger non-turbo counterpart (for the same amount of power/HP). Small turbos get good mpg ratings, but their real world use is different: https://www.greencarreports.com/news/1109366_small-turbo-engines-get-good-mpg-ratings-real-world-use-may-be-a-different-story https://www.greencarreports.com/news/1109366_small-turbo-eng... The trouble with turbos: Why fuel economy can be worse, not better https://www.theglobeandmail.com/globe-drive/adventure/red-line/the-trouble-with-turbos-why-fuel-economy-can-be-worse-not-better/article29705614/ https://www.theglobeandmail.com/globe-drive/adventure/red-li... Could we be reaching the end of the road for small-capacity turbocharged engines? https://arstechnica.com/cars/2017/02/could-we-be-reaching-the-end-of-the-road-for-small-capacity-turbocharged-engines/ https://arstechnica.com/cars/2017/02/could-we-be-reaching-th...

sbierwagen 5y ago

It increased CO2 emissions? The cat doesn't touch CO2, it only affects unburned exhaust gases. And CO2 is a primary emission, if it was "significantly" increased then you would also see a significant increase in... fuel consumption. Where else would the carbon be coming from?

ardit33 5y ago
This is specific to small Turbo engines (eg. 1.1 l three cylinder turbo). They get great MPG ratings in official testing, but in real world usage they perform worse than a larger non-turbo counterpart (for the same amount of power/HP). Small turbos get good mpg ratings, but their real world use is different: https://www.greencarreports.com/news/1109366_small-turbo-engines-get-good-mpg-ratings-real-world-use-may-be-a-different-story https://www.greencarreports.com/news/1109366_small-turbo-eng... The trouble with turbos: Why fuel economy can be worse, not better https://www.theglobeandmail.com/globe-drive/adventure/red-line/the-trouble-with-turbos-why-fuel-economy-can-be-worse-not-better/article29705614/ https://www.theglobeandmail.com/globe-drive/adventure/red-li... Could we be reaching the end of the road for small-capacity turbocharged engines? https://arstechnica.com/cars/2017/02/could-we-be-reaching-the-end-of-the-road-for-small-capacity-turbocharged-engines/ https://arstechnica.com/cars/2017/02/could-we-be-reaching-th...

King-Aaron 5y ago

So I think you misunderstand, a turbocharged engine generally produces hotter exhaust due to the gases being run through a compressor, and often have more aggressively set timing than a similar layout aspirated engine. I don't know where you got "the cooling of the exhaust air" from?

WhisperingShiba 5y ago
Exhaust gas runs through a turbine, hence 'Turbo'. Typically this cools exhaust. Whether or not the higher combustion temperature from the compressed inlet gas makes up for this is not known to me.
- post_break 5y ago
  Exhaust gas is hotter on turbo engines. It’s why you have to watch exhaust gas temperature like a hawk when off road. High revs with little movement causes EGRs to melt down. 450-650C.
  - WhisperingShiba 5y ago
    I acknowledged that this could still be true in my comment, but that I would have to actually do some analysis. However, what the parent comment said is wrong. Your gas is going to lose internal energy to shaft work as it moves through the turbine, which then compresses the inlet air. Not saying its not hot or hotter, I'm saying the air is not moving through a compressor (which /would/ heat the gas as it does work on the gas to move it to higher pressure), it moving through a turbine, which is recapturing the internal energy of the exhaust gas to improve the efficiency of the engine. Because this site always needs ""SOURCES"" https://www.theturboforums.com/info/article/why-are-exhaust-gas-temperatures-so-important.378413/ https://www.theturboforums.com/info/article/why-are-exhaust-... >EGTs are usually measured close to the head. This provides a much quicker response time as well as a more accurate reading. In fact, the temperature of the exhaust gas following the turbocharger can be as much as 200 to 300 degrees lower than the temperature upstream of the turbo. Air resistance caused by the turbo itself can also cause increases in the temperature upstream that would not be detected past the turbo.