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395 messages, Last post on Aug 29, 2007 at 7:27 AM
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Replying to: lensman (Jun 01, 2006 8:01 am) that is a very hard question to answer. Generally speaking optimal efficiency is when variable losses equals fixed losses. An engine running at fixed speed will have a constant frictional loss. On the other hand its variable loss will be dependent on the power it handles. Consequently as long as the engine runs at full power (which will be at its top rpm) its efficiency can be made high. But when cruising or decelerating its variable loss (dependent on power) will drop to a low or almost zero value. Meanwhile the fixed loss incurred by having to run at full speed will be maintained and therefore fixed loss will no longer equal variable loss, so mathematically you will start drawing away from your optimal efficiency point. The conclusion I derived from all this was that engine speed will have to vary with power demand. You may counter by proposing that the battery can act as a energy buffer so that the engine need only be called upon infrequently when the battery SOC has dropped below 60% say. Here's what you should know about batteries - GM required 840lbs of lead acid to give them enough power density to provide the amps needed by the EV1 for its 0-60mph eight second ramp. Perhaps it would be safe (ie with good longevity) for a Prius 57kw engine 21kw battery if you installed a 400lb NiMH battery and downsized its engine to 15kw. But that would be a $10,000 battery ! I still believe that series hybrid is the correct approach but without a battery. The advanced hybrid engineering board has some more posts fleshing out the idea. Diesel hybrids for cars is a different application than for ships or freight trains where they are more frequently employed. To my knowledge neither ships or trains use batteries for load levelling. Cars are what we can describe as being heavily motorised. The huge mass of ships and trains precludes them from attempting to have 0-60mph acceleration ramps in the 8 second range. Since low mass is of great importance, putting a large battery in a light vehicle is a bad idea. Think how much faster the EV-1 would be divested of its 840lb battery. Battery installs are an attempt by vested interests in the resource industries that got shut out when the alchemist for really hi energy chemistries didn't show up and interest for pure electrics waned. They are now trying to hijack hybrid vehicles to adopt their expensive products instead. Neither series hybrids nor the Toyota HSD need those large storage batteries as an enabler. It's not just my opinion, it happens to be good physics as well. With the battery out of the equation we can consider the diesel. I will start considering diesels for fuel efficiency when I see Boeing start using them in their 747 jumbo jets. Diesels are heavy for their power. Yes lots of torque. If I want torque I'll use a higher ratio in my gearbox. And I hear the VW Jetta TDI is a slug when it comes to acceleration. 'Nuff said. For me the real interest is replacing the gearbox/clutch system with a system of higher efficacy where the road wheels are not locked to the crankshaft. So when you wrote: "I mean a design encorporating a smaller engine, no clutch or gearbox and possible motors in both wheels at the front or back hence no drive shafts, could result in a car which weights the same if not lighter than a standard setup." You could have added "and cheaper to boot" T2 |
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Replying to: toyolla2 (Jun 01, 2006 1:07 pm) Jet "A" is number 1 diesel. That is all we ran in our trucks most of the year in the Arctic. Does not lubricate well so we used 9/11 additive. |
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Replying to: toyolla2 (Jun 01, 2006 1:07 pm) Could I ask to clarify a few points you made; 'GM required 840lbs of lead acid to give them enough power density to provide the amps needed by the EV1 for its 0-60mph eight second ramp' Do you mean that you need that much battery to get the car from 0-60mph and then they are flat, or do you mean you need that much in order to provide the PEAK amperage necassary? Couldnt the ICE provide enough amperage in conjunction with the battery for the 0-60 sprint? I know Im assuming any power inverter used would have to be made out insanium  with all this amperage around, but, suppose you were to use a heavy duty high amperage capacitor for those instantanious bursts of speed. On a side note was the EV1 a pure serial hybrid, this I didnt know, anyone have any links I could read up about the EV1, tis a real shame GM decided to crush them rather then let interested parties have them, I know the risk of getting sued was one of the reasons sighted, but surely some form of waiver signed by anyone taking the cars would have sufficed...!!! Cheers again for the quick replies.
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Replying to: lensman (Jun 01, 2006 2:19 pm) It was purely electric. The way many of us feel is the best and simplist way to go. When they get batteries that will be adequate. This is a good link covering the GM EV-1 from cradle to graveyard. EV-1 |
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Gagrice, I know you are more knowledgeable on fuels than I but if Jet "A" is number 1 diesel. Then why do I smell paraffin when exiting the plane ? T2
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Replying to: lensman (Jun 01, 2006 2:19 pm) Gagrice's link will be useful, but regarding the necessity for 840lbs of lead acid in the EV-1. In answer to : "you mean you need that much in order to provide the PEAK amperage necessary?" Yes you do. However its possible to draw the same current from a lot less lead but risk the possibility of buckling plates and overheating. Few than ten discharges could destroy the smaller pack under those conditions. You might note that secondary cells like lead-acid and NiMH have two parameters to look out for. 1. Power density (the max allowable amps you can draw). ie how fast you can accelerate. 2. Energy density (for how long you can draw those amps). ie how far you can go When these are known plus the cell voltage and mass per cell you can compute max amps. A subsequent calculation using the energy density parameter and knowing or estimating the current drawn at cruise speed will give you the expected mileage range. I apologise if I misled you on the EV1 as a serial hybrid, I was just making a point on how large and expensive the battery was going to be in order to carry a 100kw rating. T2 |
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Replying to: toyolla2 (Jun 01, 2006 6:39 pm) |
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Replying to: lensman (Jun 01, 2006 2:19 pm) "Couldn't the ICE provide enough amperage in conjunction with the battery for the 0-60 sprint? I know Im assuming any power inverter used would have to be made out of insanium with all this amperage around." Using a battery and ICE together sounds a neat idea initially. It is an idea that is easily grasped by anyone not in the engineering community. Unfortunately it doesn't hold water scientifically. In the long run you would be better off to bore out those cylinders and get your power the old fashioned way or better still raise the ICE towards 15,000 rpm when required, after that you can dispense with the battery entirely and all that energy it was requiring to lug it around the streets. An energy waste that went unquestioned. In the '04 Prius as I have already stated 57kw is augmented by only 21kw so you don't need to do much drilling or speeding up to pick up 21kw from the ICE. And who says the ICE has to be SULEV on a full time basis ? Isn't that an unreasonable engineering restraint given that it's still OK to allow 5.4 litre V8 hemi's on the roads ? At 15000 rpm MG1 could generate 45kw (100A  450vac) and could be direct drive from a gas ICE. A diesel on the other hand cannot speed beyond 4000rpm so would need to be geared up to its generator, incurring gear whine and a 7% transmission loss which counts against its better thermal efficiency that it was selected for in the first place. insanium ? Not required. There have been godzilla inverters in the 150hp range for some time. I think the new inverter in the 2007 TCH is rated 105kw so that would put Toyota in a good position to graduate to series hybrid providing the inverters in those vehicles behave. They are also running MG1 and MG2 at 13,000 and 14,000 rpm on that vehicle. All Toyota is missing is a high speed engine. Perhaps Yamaha will help them with that. T2 |
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This year's Challenge X, a Department of Energy and corporate-sponsored advanced vehicle technology competition, pushes university teams to re-engineer their Equinox into a vehicle that is more fuel efficient and cleaner running while maintaining the utility for which the vehicle was originally designed. To meet these goals, the Penn State team has replaced the gasoline V6 engine with a very compact, common rail turbo-diesel engine, according to Matthew Shirk, a graduate student in mechanical engineering and Penn State Challenge X student team leader for this year's competition. The engine is mated to a continuously variable automatic transmission. The engine and transmission are computer controlled, and work together with a powerful electric motor that is powered by a 300-volt lithium ion battery pack.The vehicle is a parallel diesel-electric hybrid with an all-wheel-drive system that works similarly to that found in the stock Equinox.The small engine allows for greater fuel efficiency, while the electric drive components aid the small, less-powerful engine when more power is required. Diesel Hybrid challenge |
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Lensman, things have quietened down since I posted. If you have further questions please indulge. Hi Gagrice, I see you have dug up the Challenge X initiative for University students. I can't help feeling that there is not much opportunity for inventiveness when the architecture is so well laid down at the beginning. Looks like a train wreck in the making to me. So I'm going to address the title of this group "Diesel Hybrids". The first problem is the idea itself. That diesels will be the 'answer' as opposed to other prime movers like gas turbines or wankel engines. It's as if changing the engine can suddenly give improved mileage -if that is indeed the aim of the exercise. The real problem is not with the type of engine but the type of transmission it is using. Although mechanical efficiences of mechanical transmissions approach 80% the real parameter we should be looking at is the efficacy not the efficiency of the transmission. Most prime movers exhibit constant torque characteristics. Consequently if the engine is connected temporarily to the wheels via one of five or so different gear ratios the fact is despite whether they are changed manually or automatically, the road wheels are limiting the prime movers ability to reach and maintain its top rpm and hence its maximum power. Typically an efficacy of less than 60%is achieved in the real world. The effect of which is to require the capacity of the prime mover to be almost twice as large as it needs to be for a given performance. The efficacy of the HCH cvt is difficult to estimate without published graphs and I am not sure any dealership has the equipment to measure how well it does its job either. A diesel hybrid with its low rpm hi torque characteristic would be quite severe on this system incidently. The Prius brings its prime mover speed to its max 5000rpm providing the vehicle is in the 50mph to 100mph range. The higher torque of a diesel would require merely a change in the 2.6 planetary ratio but would diesel stopping and starting vibration be noticeably reflected through to the vehicle ? Anyway 50mph base speed is much too late for a 76Hp engine, at 20mph only 55Hp is available. Allowing MG1 to approach 13,000rpm would bring 76hp sooner at around 30mph and significantly improve efficacy as I have been advocating. Diesel or no diesel. How viable would a diesel hybrid be, seeing as how I would incur both hybrid and diesel premiums in the pricing ? T2 |
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