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Old 05-30-2007, 09:18 AM   #1
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Diesel electric?

Works for trains, why not cars? A diesel electric has an engine that's whole job is to turn an electrical generator. That generator powers the wheels, no direct connection between the engine and the wheels. This lets the diesel run at its most efficient range, and allows a smaller engine than would be required to move the train from a dead stop. Think about it, it's a lot easier to get a generator spinning than get the wheels on a heavy vehicle spinning, and an electric motor can apply max torque at 0RPM.

This being said, anyone know exactly what size motor would be needed to move a 4000LB vehicle at highway speeds with decent acceleration? And where would you source these engines from? Seems like this would be a far more friendly way of getting electricity to the ground, since there would be no need for large battery packs (a standard car battery would work) and you could use a very small diesel engine to get the generator running at speed. If a 2 liter diesel is enough to run a car at normal speeds and accelleration, then a half liter diesel is all that would be needed to run a generator strong enough to power electric motors, I'd think. It would also be a lot simpler to set up, since there doesn't need to be a way to interface both the ICE and the motor to the driveline, and the ICE only has to be sized to run the generator, not the whole vehicle. Only bad thing, the ICE would be running whenever the car was running, about the only place you could get away without running the ICE would be at a stoplight. I do think that these negatives would be outweighed by the positives, IE power steering, AC, ect all running, unlimited range as opposed to possible recharge needs, and mileage in the hundreds based on a much smaller engine than would normally be needed to run the vehicle. Plus, this could be made to fit where the existing drivetrain is now. And if you really, really wanted to you could make it a plug-in model by adding a larger battery bank between the motor and generator, and set it up so the diesel only comes on when the battery pack reaches X amount of power. This would require a separate motor to run vehicle accessories, however.

Such a vehicle would be almost like a conventional car is, it would just have gobs of torque and very high mileage. Such a thing would be just what you need to boost that electric car image, and would make an excellent bridge vehicle to an all-electric setup, and would extend petroleum reserves until a viable replacement could be made.

Thoughts? I'm kinda considering this for a project, perhaps for my truck, if I can't come up with a proper RWD car direct injection turbodiesel engine for it in the next year or two.
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Old 05-30-2007, 11:09 AM   #2
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If you're gonna bother with a serial hybrid, there's no huge reason to run a diesel genset versus gas because at peak efficiency, the differences are minimal. Off peak efficiency from diesels is generally far better than their gasoline counterparts, which is why they're great in cars, can't always run at WOT, but in gensets, we can. Barring biofuels, imo there's no advantage in running a diesel instead of a gas genset.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 05-30-2007, 01:08 PM   #3
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Actually, torque at a specific RPM would be higher on a diesel than a gasoline, meaning a smaller diesel could be used. In a gasser the gasoline is burned almost instantly and motive force after the explosion is inertia, while in a diesel the fuel is burning almost the entire power stroke, which is what makes a diesel make so much more torque.

An analogy would be bowling, a gasoline engine would be the equivalent of standing at the end of the aisle and throwing the ball down the lane, which is a quick burst of power followed by momentum. A diesel would be the equivalent of walking behind the ball pushing it the whole way, or slow, but constant power applied the entire way.

As a rough guess, I'd need a 1.5L gasoline engine to make the same torque at a specific RPM that I could do with a 0.5L diesel. HP doesn't matter here, since the function is a constant RPM/constant load application.

Then there is the whole biofuel/veggie oil thing

For my own application, I'd want an electric motor capable of delivering the equivalent of 300 ft lbs of torque up to 2000RPM for a direct drive (1:1) rear gear ratio, or 6000RPM if I were to keep my 3.42 gears. This may not be possible though, from what little bit I've looked at the motors that can turn these kinds of numbers weigh in at a ton by themselves, would still then need the diesel engine and generator. No hurry though, it'll be years before I can spend the first dollar on this.

Yes, that's right, if I can make this work I'd be wanting a street racer. IF it works, I could have a street racer that got triple digit mileage
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Old 05-30-2007, 01:28 PM   #4
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Originally Posted by Telco View Post
Actually, torque at a specific RPM would be higher on a diesel than a gasoline, meaning a smaller diesel could be used.
Nope, not for anything within the last couple decades anyway. Off load torque is different, but peak/WOT torque is pretty much a function of displacement for both NA gas and diesel engines. For instance, a 3L DOHC NA gasser made in the early nineties and a 1.6L SOHC NA diesel made in the early 80s.


Now, the gasser has a slight advantage because it's newer/DOHC/more efficient per BTU at peak eff, but, the main point is the same. At 2k rpm the 1.6L diesel makes ~115nm, and at 2k rpm the 3L gasser makes ~230nm. So, roughly twice as much displacement means roughly twice as much torque, with torque available at a given rpm/WOT being about the same between the two. I think you should do a bit of googling.

Diesels are more efficient at part load, since there aren't pumping losses on the same order of magnitude compared to gassers, which is why they're more efficient in cars, but for basic WOT power generation, there isn't much of a difference in engine efficiency.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 05-30-2007, 03:45 PM   #5
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bsfc

The BSFC map! Saves the day again... (I'm teasin', it's a great tool to quantify such assumptions)

Actually, I've had similar thoughts of using the same principle as a Locomotive "Hybrid" for a vehicle -- complete with "dynamic braking" to recharge the system on heavy decel or braking. But there are too many fluctuations in a daily commute -- possibly better for long-interstate trips for consistent speed and less variation in load. More thought could go into how it would serve the big-rig industry for long over-the-road applications.

Also, newer locos have the option of AC traction motors that apparently can be modulated better than the older DC variants (of course a bit difficult to integrate/convert in a 12V DC ignition system and components of a modern vehicle).

But I digress -- WOT is efficient, but seems to generate quite a bit of emissions comparatively. That's the rub.

RH77
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Old 05-30-2007, 04:42 PM   #6
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It's a series hybrid in order to serve as a transmission, not because it is efficient.

Really really really smart guys at Honda and Toyota thought about how to make the most efficient hybrid, and you see what we got.

Series hybrid would be really cool from a packaging standpoint, though.

Actually, it seems like what Telco is describing is a TZero with a diesel generator trailer... Pretty cool, but not so efficient.
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Old 05-30-2007, 05:28 PM   #7
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The BSFC map! Saves the day again... (I'm teasin', it's a great tool to quantify such assumptions)
Hallelujah!
It's just the easiest way to illustrate points about engine eff, just like the aerodynamic drag force and high speed salt flat runs are the best way to show vehicle efficiency. Personally I'd drop/strip a metro exactly like the EV album version, put in enough lead acids to go 70miles@55mph, and a ~15hp direct drive Honda motor geared for cruising on the highway from ~45-65mph. If pulled off right, on batteries it'd be less than 3 cents per mile, and on gas a little less than 4 cents per mile.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 05-30-2007, 06:55 PM   #8
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Originally Posted by Bill in Houston View Post
It's a series hybrid in order to serve as a transmission, not because it is efficient.
Uh oh! Don't tell that to the guy I met this week who just built a series human electric hybrid bicycle:


http://www.twobikes.ottawa.on.ca/sha...756-169-1d.htm


http://www.twobikes.ottawa.on.ca/sha...922-171-1d.htm

The photos aren't great, but there's no mechanical drive from the pedals to either wheel.

(Actually, he's quite aware of the losses involved. There are several reasons for him doing it like this... I'm just not sure what they are )
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Old 05-30-2007, 07:07 PM   #9
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Sorry, I was referring to locomotives. I guess I should be more specific. :-)

Even for the bike, though, pretty inefficient. But I don't think efficiency is what the bike guy was going for...
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Old 05-30-2007, 07:09 PM   #10
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Sorry, I was referring to locomotives.
I know. I've been waiting for an excuse to stick this bike in a thread for a couple of days now.

Sorry for the hi-jack. I'll move the bike stuff to a new thread:

http://www.gassavers.org/showthread.php?t=3604
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