Quote:
Originally Posted by serialk11r
Depends on how you look at it. If you look at it as a proportion of exhaust energy, then turbo reduces it. If you look at it in absolute terms (or in relation to total power output), turbo increases it because when you have close to equal compression and expansion, the gas ALWAYS has energy leftover. When you turbocharge you bring up the pressure in the exhaust as well. The pressure in the exhaust is always greater than the pressure at the intake; The energy in the exhaust is greater than the energy needed to supercharge the engine. The higher the boost, the bigger the gap becomes. A turbo behaves pretty similarly to a supercharger (okay, with its own electric drive) with a slightly lower energy input requirement (turbo still produces significant backpressure).
A few pages earlier (edit, in another thread rofl) I ran some very rough calculations for turbocompounding a typical gasoline engine (which has more pressure in the exhaust than diesel), and what you can pick up is rather small with a naturally aspirated engine. I believe turbocompounded diesels today have >2 bar boost, which as I said greatly increases the amount of pressure in the exhaust, allowing a turbine to be particularly effective. Turbocompounding a high boost gasoline engine would yield even better results, but at the end of the day the turbine is not going to be as good as a piston, and you ultimately dump more energy out the exhaust either way compared to a similarly powered naturally aspirated engine (of course high rpm friction makes things slightly complicated but...).
Actually something I'd like to try is connecting the shaft of a turbo to the crank via reduction gearbox. The turbine would have to be replaced of course, with a larger turbine with lower A/R to produce excess turbine power. One day when I have money...
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I don't even know where to start with the pile if misinformation posted, really. I also am going to guess you didn't look up the turbine driven shaft technology that I mentioned
I'll simply say that I do this for a living (oem level, not some 'tuner' at a shop) and you way off base or misinformed.
Edit: you do realize that lower compression pistons actually have fewer pumping losses than high compression, right...LOL