by chrismb » Mon Jan 10, 2011 6:39 pm
The fastest motors I know are the Dyson vacuum cleaner motors that run at 104,000 rpm. I do not think they would last very long if they were run constantly as generators.
'Turbo-compounding' is the term applied when mechanical geared shaft is taken directly off a turbocharger (rather than a turboprop, which is designed to drive a prop and is usually axial flow type rather than centrifugal, for efficiency). Some trucks even have [had] turbo compounding that feed directly to the transmission, but this tends to work only on long straight flat roads at constant speeds.
This idea gets close to where I think the internal combustion engine will eventually end up - I think the future of the ICE is as a gas-supply to drive a turbine when it is in a low-efficiency regime.
So the way this would evolve is; STEP 1: turbos in cars get bigger to the point that they are used to drive electric generator sets, rather than directly connected to an intake compressor. (Intake compressors would be electric and be driven independently of, but electrically from the turbine-generator).
STEP 2: The turbo-generators then evolve in size (and become axial-flow) to the point where fuel can be injected directly into the turbo under certain load regimes for extra, and efficient, power - hence we end up with a 'turbine' engine bolted on to the back of an ICE.
STEP 3: Then the ICE is disconnected from direct transmission to the wheels, and instead those are driven electrically from the turbine. The piston engine remains, as a gas-feeder to keep the turbine running, and to fire it up, when it is not in an efficient regime of operation.
All elements of this have, actually, already been done. There is nothing actually radical about this, apart perhaps from the integration and overall 'technology roadmap'. During the war, there was a British tank that ran off two Daimler engines that did not directly drive a transmission but whose exhaust powered two turbines that were mated to a transmission.