4 ms·

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 aggre

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.
    - King-Aaron 5y ago
      The comparison was originally EGT for turbocharged engines vs non-turbocharged engines. Yes, the temps right out of the head are higher before the turbine vs after for sure, but temperatures going into the cat converter are still generally higher in a turbocharged application compared to an aspirated engine.
      - WhisperingShiba 5y ago
        I was just salty I got down voted or 'Flagged' or whatever. I completely believe the turbo's higher combustion efficiency means higher temp downstream of the >Turbine< Was I pedantic? Yes. Still salty though.
- bsagdiyev 5y ago
  Tell that to the hot dog I cooked on a red hot turbo manifold, back in my teen years.
  - WhisperingShiba 5y ago
    'hot' vs 'hotter'. Unless I'm fundamentally misunderstanding physics, when flowing gasses do work, they decrease in temperature. They might increase in velocity, but they decrease in temperature.
mulmen 5y ago
Turbochargers do not compress exhaust air, they compress intake air using already-expanded escaping exhaust gas. It is possible this restriction preserves (localizes?) some heat but based on my very, very basic understanding of thermodynamics I would expect some exhaust heat to be "lost" to the work of compressing the intake air. I'm not sure how this would manifest. In the end I suspect exhaust gasses are still hotter in a turbo setup but as a side effect of ramming more air through the intake and burning more fuel per cycle.
- Dork1234 5y ago
  Turbochargers take exhaust pressure and convert it to intake pressure. The normally work on a ratio of about 2:1, where 2 pounds of back pressure (exhaust pressure) is converted to 1 pound of intake pressure. Since this pressure(and gas expansion) is normally wasted (except in aircraft where it can be used to propel the craft forward) it is a consider more efficient than supercharged setup.
aunty_helen 5y ago
Retarded* timing Advanced timing + turbo = boom. Increased charge density from >atmospheric pressure causes faster flame propigation and pushes the fuel closer to its knock point when compressed. Turbos also run a richer mixture under load to cool the intake charge. Richer mixture and a comparitively later burning and therefore hotter exaust stream increase exhaust temperature (along with the ability to produce more power aka burn more fuel)
- King-Aaron 5y ago
  Yeah sorry, brain fart while I was writing that. In saying that mine is set very close to the knock threshold
- wcunning 5y ago
  Except that you then hold the exhaust gas in a big aluminum tube past a cooled bearings and other things that pull heat out of a naturally low mass thing.

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.
  - King-Aaron 5y ago
    The comparison was originally EGT for turbocharged engines vs non-turbocharged engines. Yes, the temps right out of the head are higher before the turbine vs after for sure, but temperatures going into the cat converter are still generally higher in a turbocharged application compared to an aspirated engine.
    - WhisperingShiba 5y ago
      I was just salty I got down voted or 'Flagged' or whatever. I completely believe the turbo's higher combustion efficiency means higher temp downstream of the >Turbine< Was I pedantic? Yes. Still salty though.
bsagdiyev 5y ago
Tell that to the hot dog I cooked on a red hot turbo manifold, back in my teen years.
- WhisperingShiba 5y ago
  'hot' vs 'hotter'. Unless I'm fundamentally misunderstanding physics, when flowing gasses do work, they decrease in temperature. They might increase in velocity, but they decrease in temperature.

mulmen 5y ago

Turbochargers do not compress exhaust air, they compress intake air using already-expanded escaping exhaust gas. It is possible this restriction preserves (localizes?) some heat but based on my very, very basic understanding of thermodynamics I would expect some exhaust heat to be "lost" to the work of compressing the intake air. I'm not sure how this would manifest. In the end I suspect exhaust gasses are still hotter in a turbo setup but as a side effect of ramming more air through the intake and burning more fuel per cycle.

Dork1234 5y ago
Turbochargers take exhaust pressure and convert it to intake pressure. The normally work on a ratio of about 2:1, where 2 pounds of back pressure (exhaust pressure) is converted to 1 pound of intake pressure. Since this pressure(and gas expansion) is normally wasted (except in aircraft where it can be used to propel the craft forward) it is a consider more efficient than supercharged setup.

aunty_helen 5y ago

Retarded* timing Advanced timing + turbo = boom. Increased charge density from >atmospheric pressure causes faster flame propigation and pushes the fuel closer to its knock point when compressed. Turbos also run a richer mixture under load to cool the intake charge. Richer mixture and a comparitively later burning and therefore hotter exaust stream increase exhaust temperature (along with the ability to produce more power aka burn more fuel)

King-Aaron 5y ago
Yeah sorry, brain fart while I was writing that. In saying that mine is set very close to the knock threshold
wcunning 5y ago
Except that you then hold the exhaust gas in a big aluminum tube past a cooled bearings and other things that pull heat out of a naturally low mass thing.