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

"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.

> 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.

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

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 :-/

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!

wrote:
> I don't know how well diesel-electric would work for semis/18
> wheelers.But as far as diesel Locomotives are concerned, they
> can't/aren't suppose to sit too long without the engine running.Too much
> water moisture from the air would get into the generator coils.
> cuhulin
>
As a locomotive engineer with 10 years experience, that information is
total bull****. Rainwater falling in the exhaust stacks may be a problem
but the traction motors/alternators are not affected by moisture unless
submerged in water.
AL G

Al G, you want to argue with Wendell Miller (I am not Wendell Miller)
about that?
cuhulin

wrote:
> Al G, you want to argue with Wendell Miller (I am not Wendell Miller)
> about that?
> cuhulin
>
Why not let Mr. Miller argue on his own? I was merely responding to a
post containing bull**** information that I know not to be accurate.

Locomotives sit idle, not running, all over the U.S. every day. I work
for CSX Transportation as an engineer. I am instructed in my several
thousand page rule book to shut down a locomotive any time it is not to
be used for more than 30 minutes and the ambient air temperature is
above 40 degrees Fahrenheit.

It is not uncommon to leave a locomotive shut down for days in some
situations. There are short-line railroads all over the USA that leave
their locomotives shut down in remote terminals for weeks on end.

Most north American locomotives do not use anti-freeze compounds in the
engine's coolant so it is important to drain a locomotive of coolant if
it is to be left shut down in sub-freezing temperatures.

Al G

Wendell Miller and his wife and my old buddy and his wife are smart.They
don't own a computer.
cuhulin