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#21
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Any reason semis do not use diesel-electric engines?
On Jun 7, 12:55 pm, Patok > wrote:
> Harry K wrote: > > On Jun 6, 9:03 pm, 223rem > wrote: > >> Harry K wrote: > >>> On Jun 6, 5:44 pm, 223rem > wrote: > >>>> ? > >>> Errm...fuel economy? Every time you convert energy from one form to > >>> another you lose energy in the conversion. > >> Yes but the diesel engine driving the electrical generator runs at a > >> constant, most efficient RPM, as opposed to a diesel engine running the > >> transmission directly. That ought to more than compensate for the losses > >> in converting mechanical work into electricity. > > >> Besides, isnt this the principle behind "hybrid" vehicles? > > > I suspect the additional weight and cost of the generator and motor(s) > > would more than offset any loss due to varying speeds. They would > > have to pack that weight all the time. > > Wouldn't the loss of the transmission offset that? And there is > already a generator (alternator), it just needs to be bigger now. > > To recap: > + smaller more efficient IC engine (diesel or gas, or even a turbine) > + no transmission > + regenerative braking > - larger heavier battery (pack) > - larger heavier generator > - electric motors to drive the wheels > > It's all a matter of proper compromise, I think. It is workable for some > applications right now, and will be for all, when sufficient advances in > battery technology are made.- Hide quoted text - > > - Show quoted text - Haven't seen many diesel/electric rigs I take it. The generator is huge, not just a minor size increase over the current alternator and the electric motor(s) are no slouch themselves. No, the loss of the tranny wouldn't make up for both the genny and the electric motor(s). Size of engine: It takes x amount of HP to move a semi load down the road. Assume 400 for a conventional rig. It will take 400 plus some additional to make up for loss of energy converting from mechanical (conventional) to electric and back to mechanical for the diesel/ electric. Harry K |
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#22
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Any reason semis do not use diesel-electric engines?
"Tim B" > wrote in message news:O_L9i.3504$xq1.946@pd7urf1no... > > "223rem" > wrote in message > . .. > > ? > > Hybrid semis are being developed. > > http://www.peterbilt.com/index_new_mor.asp?file=2100 > Interesting. A fuel economy improvement of 5-7% doesnt seem to be anything to beat your chest about, on first glance, but as fuel prices rise (and as a worst case scenario-God forbid- availability declines) the difference could be considerable. I seem to remember gas turbines being looked at for freight haulers too, some years ago, but the time was not right. It may never be right, who knows. |
#23
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Any reason semis do not use diesel-electric engines?
> wrote in news:mWeai.16730$C96.8337
@newssvr23.news.prodigy.net: > > "Tim B" > wrote in message > news:O_L9i.3504$xq1.946@pd7urf1no... >> >> "223rem" > wrote in message >> . .. >> > ? >> >> Hybrid semis are being developed. >> >> http://www.peterbilt.com/index_new_mor.asp?file=2100 >> > > Interesting. A fuel economy improvement of 5-7% doesnt seem to be > anything to beat your chest about, on first glance, but as fuel prices > rise (and as a worst case scenario-God forbid- availability declines) > the difference could be considerable. > > I seem to remember gas turbines being looked at for freight haulers > too, some years ago, but the time was not right. It may never be > right, who knows. > > > THat would equate to roughly $6300.00 a year savings Min. A long hauler would save much more. KB -- Thunder Snake #9 "Protect" your rights or "lose" them. |
#24
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Any reason semis do not use diesel-electric engines?
In article >,
223rem > wrote: > ? Up to now a hybrid hasn't had much advantage over an all-mechanical drivetrain in this market. Think of a hybrid as simply an extremely fancy transmission that has the ability to store some power in batteries. In a car you have the advantage with a hybrid of staying at the engine's power band, some regenerative braking, and higher momentary peak power without a big engine. In a semi the rules are different. A diesel engine is more efficient across the RPM range than a gas engine simply by nature of the combustion cycle. Then the large engines have a narrow RPM band (1,000 to 2,100 RPM typical for most driving, best economy near 1,500) and therefore just can't get too far from the sweet spot unless you have an exceptionally horrible driver. And semis spend hours at a time driving at one speed. They usually see far less stop-and-go driving than cars. Finally, the ECMs in modern engines have pretty tight control over power output and can hammer out surprisingly high peak power as-needed without going to a larger engine. Most horsepower uprates these days are strictly software changes. There are even driver-reward schemes that give the driver so many minutes of high-horsepower driving for each hour of drive time. The new Cummins engines all have variable-geometry turbo chargers that can make the engine feel about twice its size on acceleration. A straight diesel-electric would be a loss in fuel economy because at highway speeds a typical semi is in direct drive (or slight overdrive) and transmission losses are near-zero. OTOH, a motor-generator setup usually loses at least a third of the power to heat, getting worse as it gets hotter. Add transformers, rectifiers, and inverters for charging batteries and running from and it gets even worse. A hybrid could do better because at cruising speeds the electrical system's inefficiency could be cut completely out of the equation. As far as electrical-assist power goes, most semis have three or four batteries, each rated for at least 600 amps at cranking. All of that amounts to only around 16 horsepower at the starter motor, and even that can fry that motor in a hurry. You would need a very large battery pack and a very sturdy motor to get enough additional power to notice. Granted, starter motors are inefficient as hell, so it won't be as extreme in a well-built system. A roadranger transmission weighs in at 700 to 1,000 pounds, depending on gearing, IIRC. You'd be lucky to find just a battery pack that light before adding on the motor, generator, gearbox, power equipment, and any other extras, like a hot-water storage tank. Each pound added to a truck is a pound taken away from the load. Besides, most of the free space in large semis has been taken up recently by the new emissions-required DPFs. One other thing: there are more bad car drivers than bad truck drivers. A lot of the hybrid's design is to compensate for poor driving: jackrabbit starts, hard braking, minimal coasting. Most truck drivers do a better job than that. Buses are a better market since they're almost 100% stop-and-go, have plenty of room for batteries, and weight isn't much of a concern. I've seen Eaton's hybrid drop-in hybrid transmission and it seems to work quite well in that application. Paccar's hydraulic brake and booster setup will likely be best for big truck applications since it will only come into play during stop-and-go driving, is relatively light, and otherwise leaves the drivetrain unchanged. -- B.B. --I am not a goat! thegoat4 at airmail dot net |
#25
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Any reason semis do not use diesel-electric engines?
Harry K wrote:
> On Jun 6, 5:44 pm, 223rem > wrote: > >>? > > > Errm...fuel economy? Every time you convert energy from one form to > another you lose energy in the conversion. Trains use it as it makes > it easy to drive multiple axles plus other reasons. > > Harry K > Trains also use it because they need big time traction control. Try putting 6000 horsepower to the rails, steel-on-steel :-/ |
#26
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Any reason semis do not use diesel-electric engines?
Patok wrote:
> Harry K wrote: > >> On Jun 6, 9:03 pm, 223rem > wrote: >> >>> Harry K wrote: >>> >>>> On Jun 6, 5:44 pm, 223rem > wrote: >>>> >>>>> ? >>>> >>>> Errm...fuel economy? Every time you convert energy from one form to >>>> another you lose energy in the conversion. >>> >>> Yes but the diesel engine driving the electrical generator runs at a >>> constant, most efficient RPM, as opposed to a diesel engine running the >>> transmission directly. That ought to more than compensate for the losses >>> in converting mechanical work into electricity. >>> >>> Besides, isnt this the principle behind "hybrid" vehicles? >> >> >> I suspect the additional weight and cost of the generator and motor(s) >> would more than offset any loss due to varying speeds. They would >> have to pack that weight all the time. >> > > Wouldn't the loss of the transmission offset that? Probably not. One transmission vs an alternator and at least 4 traction motors, plus heavy gauge wiring and control systems? Doesn't sound like a win to me. And there is > already a generator (alternator), it just needs to be bigger now. You're kidding, right? The alternator that is already there is just a bigger version of a car alternator, it absorbs maybe 15 to 20 horsepower max. You're talking about an alternator that can absorb the whole 500 horsepower of the engine for a hybrid or diesel-electric drive! |
#27
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Any reason semis do not use diesel-electric engines?
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#28
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Any reason semis do not use diesel-electric engines?
Al G, you want to argue with Wendell Miller (I am not Wendell Miller)
about that? cuhulin |
#29
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Any reason semis do not use diesel-electric engines?
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#30
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Any reason semis do not use diesel-electric engines?
Wendell Miller and his wife and my old buddy and his wife are smart.They
don't own a computer. cuhulin |
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