0 Members and 1 Guest are viewing this topic.
I tried to understand it - 'onest guvner, but the Geezobrain sort of iced up. Maybe a piccy would help?
I'm not sure I really understood the question but; if you change the amount of air you let into an engine, don't you mess up the compression ratio?
Where a turboexpander downstream from a supercharger (turbo or mechanical) can improve efficiency by noticeably lowering the induction air temperature (admittedly a the cost of slightly higher pumping losses).The principle is that a t-expander in conjunction with an intercooler can allow far higher heat rejection than a standard turbo. Thus, the exhaust pressure is now adding overall efficiency as opposed to more power alone - as with a simple turbo'd engine.
The second thing that occurred to me is that the regulation of charge that is so critical in a S.I. engine can be adjusted by controlling the instantaneous density of the charge air rather than throttling the flow.A potential way to do this would seem to control the air's temperature (independent of ambient temp.) to 'pack-in' the charge in full power mode and thin out (by less cooling) in part load conditions.
I looked at the paper (well, I sort of skimmed it!) and I can see how you can get a greater air mass per cycle and therefore more power for a certain displacement, but it was not too clear to me why the efficiency improves.
"can be adjusted by controlling the instantaneous density of the charge air rather than throttling the flow" But isn't that what a throttle does? The air after the throttle is less dense than the atmospheric air.