My FE/Performance Project

[pgfpro]

Originally Posted by theholycow

Ah, but the turbo doesn't work on exhaust heat, it works on exhaust velocity. There have been discussions of scavenging exhaust heat too; to do so, you would change the exhaust gas's density, producing more pumping loss (though I don't recall if there was any data showing whether the recovered heat outweighs the increased pumping loss).



Forcing more air into the engine requires you to put in more fuel. More air, more fuel, more power. Now you have to back off the throttle, introducing extra pumping loss at the intake (in addition to the turbo's pumping loss at the exhaust).



I wasn't talking about superchargers at all. I know someone else was, but I was just addressing turbochargers.



It is not my forum. My responsibilities beyond those of a regular user are mainly to keep out troublemakers and spammers; I do NOT direct discussions unless they are grossly misplaced.

It's not that I didn't want to discuss it, just that I didn't want to pollute your thread with a tangent off-topic discussion. I was trying not to step on your toes.

Where does the exhaust gas's movement come from? The pistons pushing it out. A turbocharger is driven by the pistons, using the exhaust as a linkage. It is not using free energy to do its job of shoving more air (and the resulting more fuel) into the engine.



This. Many factory turbocharged cars are more efficient because they have a more efficient, less powerful engine plus a turbocharger to provide the missing power only when needed.

In a very short description I will try to explain why a turbo engine can be more fuel-efficient.

I believe that the exhaust gases create a pressure and temperature drop across the turbine of the turbo. This is what harnesses the energy to turn the turbine wheel. Today?s turbo?s are very efficient i.e. they can take this energy and utilize it. To the point that at very light engine load there will be very little exhaust pumping losses. Even if there is a slight exhaust pumping loss the advantages on the intake side will out weigh it.

The intake side is where a turbo-charge engine has a few major advantages.
From my data-logs I have noticed that at the same cruise speed with light engine load a turbo charge engine will run at a higher absolute manifold pressure (measured in Kpa). This helps with the intake pumping losses and is a major contributor in fuel atomization. This in turn reduces the BSFC numbers at light load.