Hi
thjakits,
Those two articles that you provided links for are fascinating. Not sure what to make of them. All the more so, not sure how to read them in light of Wrightspeed's counterclaim, regarding its pathbreaking 80 KW dedicated "
Fulcrum" automotive turbine generator......?? See
https://www.wrightspeed.com/technology/the-fulcrum/. Wrightspeed claims that the
Fulcrum is a very fuel-efficient range-extender, because it uses energy recovery by re-feeding its hot exhaust.
Agreed that the weight of the engine itself does not make huge difference at low HP, and that at low HP fuel consumption is more important. But personally, I don't know of a diesel engine that can produce 1500 HP and yet weighs just 150 kg, as per a helicopter turbine. As far as I know, if 1500 HP were the goal in a piston-driven diesel generator, then we can add an extra zero to the weight, because only big marine diesels that weigh 1500 kg or thereabouts can produce 1500 HP.
Remember, the key here is to imagine the TerraLiner carrying
two separate generators, with different power ratings and uses, and just one of them dedicated to powering the electric motors when climbing an incline. Climbing a sustained incline like the one running from Sacramento up to Lake Tahoe is not a peak power "moment" of accelerating for a minute or so on a flat surface to get up to 90 kph. Rather, it's a sustained, multi-hour slog that would seriously drain any battery bank, unless that battery bank were stupidly large and hence heavy. So the solution, it seems to me, is to simply accept that one needs to burn serious fuel to do it. And this means a generator at least as big as the continuous power consumption of the electric motors. So at least 420 KW minimum. We're back in Oshkosh territory, where the generator's engine becomes as big in terms of HP or KW as a diesel motor driving the axles more directly and conventionally would have been.
But if a hybrid TerraLiner will need six large 250 HP electric motors to function as retarders in any case when descending slopes, then why not snatch victory from the jaws of retarder necessity, and "go wild"? Have one
just one of the generators be a fuel-drunk 1500 HP lightweight helicopter-turbine powerhouse that will feed all the electricity that six 250 HP electric motors could ever want? For long ascending inclines in particular we let fuel economy go to hell, maximizing performance instead. And then for 95 % of the rest of the time the TerraLiner has a terrific, much lower HP turbocharged piston-diesel, one that keeps it running nice and fuel-economical on flats, slight slopes, and slight descents?
I am not an engineer. But I've done tons of mountain driving because I lived for years in both Switzerland and Italy. Even when I don't mountain drive I still "transmission brake" out of habit. As such, I guess I feel that I've become keenly sensitized to how long ascents and descents are a kind of driving that's fundamentally different from all of the other kinds of driving one might do on flat-land, whether highway or city. When I was still quite young I burnt out two transmissions: a car driving up to Tahoe towing a U-Haul trailer, and a U-Haul 24-foot moving truck descending from the Sierras down to Bishop, where we had to trans-load to a different truck. I transmission-braked the whole way, but the 24-foot U-Haul truck just couldn't handle the descent.
These are scenarios where I'd love the TerraLiner to literally eat the pavement of anti-hybrid doubt. That's why
Iain's observations about trucks jake-breaking and using engines to dissipate energy on extended descents hit home with such force. Or why I find those humungous 250 HP electric motors in the Wrigthspeed drivetrain endlessly fascinating. I can "feel" the potential as a possible end-user. Wrightspeed's drivetrain "feels" just like what a big truck with electric motors would want. There's no point going with smaller electric motors, because then one would still have to fit electromagnetic-induction retarders in any case. Which is just another name for a generator, but one that produces heat instead of electricity. So why not cut through the complexity, and use super-big electric motors instead, motors that do double-duty as retarder-generators when descending slopes?
It makes total sense, at least to me. But again, I am not an engineer, so I'd love to see this debated and kicked around for a while by others.
Just for the record: thanks for using argument and evidence, and thanks for providing links, and not merely asserting. Those two links to very relevant and interesting articles made all the difference in the world. Without those links, I would have felt zero motivation to take your post seriously.
Remember, here on ExPo we can claim to have tons of "experience", and we can claim to be "experts". But since this web forum is largely anonymous, how do we know that someone who merely asserts their epistemic authority, is not in fact lying through their teeth? Even in a formal university context where the institutional setting creates a hierarchy, and the professor at the front of the lecture hall is supposedly credentialed and hence presumed authoritative, I still found myself refusing to accept his or her authority as a
fait-accompli. No doubt because I am a philosopher both by disposition and training, and so I will expect even fully-credentialed authorities in formal academic contexts to provide me with arguments and evidence that I can assess for myself, independently. All the more so then on an anonymous web forum, where I have no idea who I might be talking to. If someone merely asserts on a web forum, I swiftly develop a strong anti-authoritarian allergic reaction, and I just tune out.
Also, thanks for not fielding any of the standard objections to turbines as found in the
cruiser's forum thread, eg. heat and noise. Presumably Wrightspeed addressed all the standard objections with its 80 KW
Fulcrum. Yours is a different kind of objection, basically, a fuel-consumption worry. Yours strikes me as a legitimate worry, with the possible exception of the scenario I've been sketching vis-a-vis sustained uphill climbing. A scenario, again, where I'd probably want to at least
experiment with a super-powerful helicopter turbine or a jet aircraft APU, and see what happens if one were to let fuel consumption go to hell.
Finally, remember that no matter what the outcome of this debate at the level of mere words, if the TerraLiner ever gets past the vaporware phase, the most intelligent thing to do would be design the two generator side-lockers in such a way that they might accommodate a wide variety of possibilities: a wide range of piston-motor diesel generators, yes, but also a cute little 1500 HP helicopter turbine that weighs just 150 kg......:sombrero:
All best wishes,
Biotect
PS -- One more important point, regarding altitude. The articles that you referenced made the excellent observation that turbine efficiency degrades with altitude. Whereas piston-driven diesel engines tend to be turbocharged, and turbocharging does a good job compensating for loss of air pressure due to altitude. An important consideration for the TerraLiner, which will need to glamp the Tibetan plateau.
..
