Quote:
Originally Posted by serialk11r
Not as a "windmill", but as a turbine. As I noted in the second post, it doesn't work very well unless the rotor chamber volume is significant compared to the intake manifold volume.
Ideally you have a mini-supercharger placed where independent throttle bodies go, then it would work. Otherwise there is too much blowdown loss. If the supercharger were electrically powered it could have very good transient response too.
Unfortunately you can't really do this if you want boost since an intercooler has to go somewhere in there and such. Additionally, say you take an Eaton M62 with ~1L displacement, with 6 lobes that makes only 0.166L displacement per lobe, so it will depressurize quite a bit in the manifold which probably has a lot more volume than that. If you use a giant supercharger and turn it slowly that would work better, but turning a supercharger too slowly is bad for boost efficiency, although having reduced intake manifold volume is good for boost efficiency.
I was thinking a twin small supercharger setup where you can bypass one of them and disconnect it from the manifold altogether when under light load circumstances, but the remaining supercharger would have so much blowdown loss that the parasitic loss from running the supercharger would probably overcome whatever tiny gains there may be from throttling reduction.
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I follow your reasoning on the non-isentropic expansion but your idea is fundamentally circular math and logic.
So you assume isentropic expansion of the air in the manifold from the piston descending creates a pressure differential across the blower from high-atomspheric to low-manifold pressure. And you create an ideal system where all process remain adiabatic and the piston must draw in air and therefore the roots blower must spin because it is both connected by the mechanical belt and is subject to the pressure differential that is acting across it.
OK so this also must be a reversible process in that the if the piston was providing air to the system then the process would remain isentropic.
To remain isentropic and adiabatic the must be no heat transfer so the process must take place instantaneously. There must be no work performed by the working fluid. In order for the work to be transmitted to the rotor you have by definition created a non isentropic process. Lower temperature in the manifold will be subject to heat transfer. It is probably small though.
Fundamentally I don't see how performing work on the working fluid will be able to produce a situation where the work is recovered in a significant amount by the blower to an extent that it is a worthwhile investment from both a fuel and power standpoint. There is so much frictional loss that will be unavoidable in the system. Also the reduced pressure going into the the Otto cycle creates problems. You now have a much bigger pressure differential to overcome between the intake and exhaust sides of the otto cycle which requires more work and therefore entropy creation.
VW created a twin charger system for the 1.4L where they had both a super charger and a turbo to create low end boost quickly but the more efficient turbo for high end. The roots type blower was on a clutch and only engaged for short periods of time at high loads situations.