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Brett, thanks for the reference pages. Still, I could not get enough info to compare apples-to-apples. The buses are about the same size and hold about the same number of passengers, but the rest of the info is too variable or not present. About the most you can say is that the BYD has wheel-motors that don't seem especially powerful and 324KWH of battery, and the Proterra has a single motor that doesn't seem especially powerful and up to 770 pounds of battery, which might be around 35KWH, so the BYD can go a lot further (which may or may not matter, depending upon route and charging speed).
It seems that the electric bus space is primarily occupied by Proterra and BYD. Subsidies aside, is there a site that has a spec comparison between the two? I'd think that the key comparisons would be the following: 1. Cost 2. Range 3. Recharge time 4. Passenger number 5. Acceleration It would also be nice to know expected battery life, but that might be speculative.
JCESR | Joint Center for Energy Storage Research www.jcesr.org/
Whenever discussing supercharged engines, displacement no longer matters, as it is effectively supplanted by boost pressure. The meaningful metric is power density (i.e., weight) and general fuel economy. They don't mention weight in the article, but Audi's 2.0 liter is now making about 1KW per 1KG, and I would expect this engine to have at least as good a ratio. In comparison, the other engines mentioned are probably also pretty close to that mark but not quite as good. As to fuel economy, well, I don't think any of these engines are built with that in mind, and so they may all pretty much suck. On a related subject, for those who are curious about such things, I was trying to determine the current production engine with the highest cylinder pressure. The Alfa 4C's 1.7 liter engine has 9.25 compression and 21.7 pounds of boost, and the Cadillac ATS's 2.0 liter engine has 9.50 compression and 20 pounds of boost. These were the highest combinations I could find.
Over the past several years we have had numerous lab reports of the excellent energy storage, life-span, and efficiency of graphene-based lithium or sulfur or lithium-sulfur batteries, using graphene for structural integrity. Now, it is time for this problem to be taken out of the realm of a lab chemists and put into the hands of applied-science engineers for mass manufacture -- what are the big players in this space waiting for?
Our experience: we had a Leaf for a couple of years, and with its effective 80 mile range we were regularly looking at the range guessometer while traveling around the Bay Area. With our Toyota RAV4 EV with effective 125+ miles range (we have driven this several times, it is quite real), we simply don't look at the guessometer and the anxiety related to range became nonexistent. Now I'm looking forward to getting the 150 mile range Chevy Bolt: I like that Chevy seems genuinely interested in EVs, as opposed to Toyota's disdain for its own excellent product.
I'd like to be corrected if I'm wrong, but give or take a few percentage points this is my understanding of various engine efficiencies: 1. conventional gasoline internal combustion: 20% 2. variable value timing gasoline internal combustion: 25% 3. direct-injection turbocharged gasoline internal combustion: 30% 4. microturbines: 30% 5. diesel: 35% 6. high-pressure injection turbocharged diesel: 40% 7. various split-cycle internal combustion engine designs: 45% 8. Stirling engine: 50% As it relates to engines for electric vehicle extended range generators, the larger the battery pack then the less the engine is used, and the less important its efficiency and the more important that it is light, small, and cheap.
To return to the question: why does Chevy stick with the T-shape battery pack instead under-the-floor-and-rear-seat design?
1. Good for GM to produce a technologically-sophisticated, good performing, great efficiency vehicle for not too much money. Perhaps it is not my idea of absolutely perfect, but there are a lot of people with a lot of ideas, and this seems a fine compromise. 2. I still don't get the T-shape battery pack instead of an under-the-floor-and-rear-seat pack: anyone want to opine as to why GM thinks this is better, despite that it takes out a middle rear passenger seat? Yes, the car is functionally a bit lower for it, but I don't see that this compromise is worth making. 3. While I would like GM (or anybody) to make a 150-mile EV for a reasonable price, I don't know that the Voltec platform is necessarily closer to enabling this than any other rolling chassis. Too bad.
Here's what I don't understand about this range extender design: with 25KW produced by the engine -- resulting in perhaps 20KW at the motor -- the car could maintain highway speed on level ground. But what if you throw it a long uphill? It would need, say, 60KW to go uphill, but the range extender yields 20KW, and the battery reserve would probably be readily depleted. So, the driver is stuck putt-putting up at half the speed of highway traffic. This seems quite dangerous. (It also explains the Volt, which has a range extender engine that can provide full power to the motor when needed.)
1. Ridiculously costly proposal. If there are 1000 spheres at $10,000,000 per (not to mention cost of specially-built ship, crew, chains, fuel, materials, etc.), the premise would cost $10,000,000,000. 2. Maintenance. 1000 spheres, each with pumps and valves, at a depth of over a 1000 feet? Good luck. 3. Pollution. Cement is, oh yeah, remarkably energy intensive. These are 1000 100foot spheres with 10foot think walls. The pollution caused through this solution is nuts. Frankly, it's not even a great thought experiment. I like the idea of renewable energy storage -- but not as much as I like true grid connectivity. Let's do the obvious first.
On a related note, I would think that the most logical place for a 2-liter direct injection turbo 4-cylinder (preferably with start/stop) would be in a minivan: it is often idling around town, it never needs ridiculously good performance -- 8-second 0-60 is fine, no need for 6-second 0-60 -- and it gets a lot of use and consequently mpg matters (especially to these owners). But, interestingly, only GM and Ford make these engines, and yet they are the only manufacturers that don't make minivans. I like my Grand Caravan, but I don't like dealing with the transverse V6. I don't even think Chrysler, Toyota, or Honda even have plans for a large DI turbo I4, and Nissan only has a 1.6. Surprising lack of connect between engine and target vehicle in this regard.
The article and linked post does not state whether this license is exclusive or nonexclusive. I hope for the later, as I would not want the technology to be tied up by one party. Further, I suspect the magic now is not in the product but in the manufacturing which appears to necessarily involve 'gas phase deposition that embeds nanoscale silicon particles into the graphene layers' (and there may be more than one way to skin that cat).
Wait, here's a possible answer to my own question: perhaps the clutch between the motor and the transmission is necessary to allow the motor to be put into action to start the engine (i.e., momentarily disengage the motor from the transmission so as to allow the motor to start the engine at the correct RPM, then reengage everything with both the motor and the engine at the correct RPM (using the motor to 'pick up the slack' in terms of the appropriate torque to get everything moving together harmoniously).
Perhaps someone can explain the need for a clutch between the CV and the motor: given that, through the controller, the motor can drive the CV, or act as a generator, or simply freewheel, why is there a need for this clutch?
Comparing apples to apples, we are in this instance discussing a genset in a series hybrid used for the express purpose of replenishing the batteries with electricity. Therefore, it seems apt compare by using the highest efficiency mode, as it will only be operating in that generator mode. For such a purpose, it appears fair to use the 28% microturbine (with recuperator) figure (which comes from Capstone's own analysis) and then compare that to other maximum efficiencies, such as up to 40% for TDI diesel. However, that being said, it is also certainly worth noting that the microturbine is clean and multifuel-capable. And, the microturbine is potentially lighter than even a purpose-built TDI diesel generator, and so if it is not regularly used the tradeoff of lighter weight should be considered.
Rosen Motors -- the founding company of Capstone microturbines and Pentadyne flywheels -- created a lovely design in the mid-1990's with a microturbine, flywheel, and battery system. This is the same thing, with the flywheel being replaced by ultracaps. But much as I would delight in seeing their success, the same or similar impediments may exist: 1. each component -- motor, controlling electronics, batteries, ultracaps, and now carbon body -- is quite expensive; 2. limited efficiency microturbine (max 28%); 3. space limitations (if the microturbine is inclusive of a recuperator -- and without which efficiency falls even more); and 4. battery weight, if this is truly to travel 200 miles (!) on battery power alone. Even using Tesla-style high-power battery packs and pushing the definition of max distance, that's still probably a 40KWH battery pack @ approx. 800 lbs., 150 lb. motor and 50 lb. controller, and then perhaps 300 lbs. for microturbine, fuel system, generator, and recuperator and something for the ultracaps. (Frankly, with a battery pack that large, I don't know why you'd need ultracaps for power flow either in or out, as the batteries should be able to produce/absorb the needed electricity.) So, in total, over 1300 lbs. for the propulsion system -- and just to throw a price on there, even at some volume given the expense of microturbines and ultracaps the whole system has got to cost over $50K. Add the carbon body, and the balance of the car for top components, and the simple production costs have got to total at least $150K. (Then there's marketing, distribution, sales, service, cost of capital, overhead, etc.: perhaps Velozzi is a nonprofit corporation?) In any event, I love the concept, and I wish them the best of luck. Maybe they want to bite off a little less, and just focus on the big motor for best-in-class performance?
Aside from the gibberish extrapolations from bad or useless data, the other sin is abject failure to actually look at the source of profits: either very high volume, or very high content cars. Let's make a blanket assertion: no one is going to be selling a tremendously high volume of cars in the foreseeable future. So no great profit stream there. As to high content, while Mercedes, BMW, Audi, and Toyota all make wonderful high mpg, high content, and doubtless very high profit cars, I can't think of even a single high content high mpg car in the pipeline at any American car company, let alone actually for sale. We have totally missed the boat on this, and it is a sad example of a fundamental misreading of the market to fail to recognize the importance of this segment -- American can makers still equate small high mpg cars with a 1980 Celica and just can't seem to shake that mental equivalence. So, no profit there. I know: huge SUVs! Oh, wait...