I have read at some point, that the pressurized intake charge can partially negate pumping losses from the increased exhaust pressure in a turbocharged engine. How much fact is there in this theory? I have my doubts as to how effective it could be.

 

This doesn't seem to follow conservation of energy. The exhaust causes the pressurized intake in the first place. Now, it is possible to eliminate the effect of reversion by having more intake pressure than exhaust pressure.

However, turbines always increase back pressure, and increased back-pressure always increases pumping losses. After all, when the intake valve is closed, how could any pressure on that side possibly reduce pumping loss? Having a higher cylinder pressure due to boost doesn't change the fact that a higher back-pressure will result in more work being done against the piston while on the exhaust stroke.

Hopefully, I'm not being to blunt with my answer, but it just doesn't make any sense to me,

Chris

 

I could be totally wrong here (and if I am, please correct me) but on the intake stroke, you have positive pressure (boost) pushing on the piston, pushing the piston down its stroke instead of N/A where the piston has a vacuum trying to get the air in the cylinder. So the intake stroke is actually making power instead of drawing power. Now on the exhaust stroke, after the piston has reached BDC, and the exhaust valve is opened (I know that normally the exhaust valve opens before BDC, but this is just for a example), some of the exhaust pressure can vent into the exhaust, even before the piston has to move up the cylinder, which helps on reliving some of the work the piston has to do. Then the piston just has to move whats left out. Plus exhaust in a boosted applcation is going to be less dense than the intake charge. Again I could totally be wrong on this, but this is JMO..
Bowtie Guy

 

That's the theory the way I understood it. I read it on another board, and there it was not worth discussing. Here, however, I like to hear people's opinions and theories. The question is not if it would "even out", I highly doubt that, but if it would reduce in any significant way the pumping losses. Thanks for your responses!

CR

 

Tom (Boost Engineer) just responded to one of my questions with this in his answer:

So, the way I read that, having a turbo can decrease pumping losses overall. I don't understand how that is possible, but am very interested to learn.

Chris