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Can Someone Explain Diesel-Electric To Me?  
User currently offlineDocLightning From United States of America, joined Nov 2005, 19384 posts, RR: 58
Posted (3 years 9 months 1 week 1 day 22 hours ago) and read 3771 times:

Well, more broadly, I don't understand why you would want to couple a combustion engine of any sort to an electric engine in any application other than automotive.

In a car, the demand on the engine is constantly shifting, so it is often laboring under non-optimal conditions. Supplementing the engine output with a hybrid electric drive can help to reduce the load on the engine under the highest demand and significantly increases efficiency. That's why a Prius gets 35mpg tooling around San Francisco.

But in a ship or a train locomotive, the majority of the journey occurs under constant power. Given that any energy transfer involves energy loss, how is it beneficial to transfer the diesel (or turbine or whatever) power to a generator and then to an electric motor?

Even weirder, my Prius gets 50mpg (+/-) on the highway, which is relatively constant demand. The best diesel I know of gets about 40mpg on the highway. Why is a hybrid still more efficient than direct drive under constant load?

Can someone explain this without too many equations?

29 replies: All unread, showing first 25:
 
User currently offlineBMI727 From United States of America, joined Feb 2009, 15715 posts, RR: 26
Reply 1, posted (3 years 9 months 1 week 1 day 21 hours ago) and read 3751 times:

Torque. Electric engine provide max torque at 0 rpm, whixh is an obvious benefit when you are haulin a mile long train. Also they don't require heavy and complicated transmissions.


Why do Aerospace Engineering students have to turn things in on time?
User currently offlineTripleDelta From Croatia, joined Jul 2004, 1115 posts, RR: 7
Reply 2, posted (3 years 9 months 1 week 1 day 21 hours ago) and read 3733 times:
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PHOTO SCREENER

Quoting DocLightning (Thread starter):
Even weirder, my Prius gets 50mpg ( /-) on the highway, which is relatively constant demand. The best diesel I know of gets about 40mpg on the highway. Why is a hybrid still more efficient than direct drive under constant load?

Bearing in mind that the quality of the Diesel fuel itself may differ between continents, European Diesels usually have a much higher MPG. My Skoda sedan - about the same size and some 400 pounds heavier than the Prius - has a 1.9 liter 100 HP turbodiesel that had been designed in 1989 and updated here and there with a few bits of new technology; so hardly a cutting-edge modern engine. But, on the highways here in Croatia, I usually average 44-47 MPG - and that's at speeds between 80 and 100 MPH, with overtaking, often enough A/C, and in hilly and mountainous terrain (one of the country's main highways goes through the mountains, so you have a lot of ups and downs). A smaller Diesel city car can average anything upward of 60 MPG...

Back to the topic at hand, as BMI727 said, Diesel-electric systems are far less complicated and easier to maintain - not to mention lighter, given that you can do away with most the very stressed, and heavy, mechanical transmission system that has to deliver power to a number of axles. Plus, the energy losses incurred in the Diesel-electric can be significantly smaller than the energy losses incurred in the complex transmission system of a traditional Diesel.



No plane, no gain.
User currently offlineLOT767-300ER From , joined Dec 1969, posts, RR:
Reply 3, posted (3 years 9 months 1 week 1 day 20 hours ago) and read 3731 times:

Quoting DocLightning (Thread starter):
Even weirder, my Prius gets 50mpg (+/-) on the highway, which is relatively constant demand. The best diesel I know of gets about 40mpg on the highway. Why is a hybrid still more efficient than direct drive under constant load?

What kind of hybrid are we talking about? Specifically a Toyota parallel drive vs. a Diesel car engine or what? If that is the case then a really dumbed down answer is the fact that a regular combustion engine is inefficient at producing the right power over the whole range of speed that you drive at everyday. Hence you have transmissions that seek out the best power in a certain small range (say for example 3rd gear between 30-50mph). Electricity on the other hand doesn't have these limitations...which is why pure electric cars don't have multiple gears as there is no need for them.

A Toyota Parallel drive still is nowhere near as efficient as the most efficient diesels because again in a very dumbed down explanation it takes more gas to charge the batteries and simultaneously produce power for the wheels than just to produce power for the wheels in a regular diesel engine which has the advantage of being overall around 20% more fuel efficient via higher compression. The advantage of a pure hybrid drive such as in the Chevy Volt is the fact that in that system the the combustion engine focuses all of its energy on charging the batteries and helping the electric motor and not directly running the car. Why is this an advantage? Well think of it that when you press on the gas in the Prius, the gas engine sucks more fuel per second in order to meet your acceleration demand no matter if you just filled up or not, and this is not a fixed % increment but goes up faster and faster the harder you push the gas because of alot of factors (wind resistance for one among many others.) In theory if you hit the gas in a Chevy Volt all that happens is the batteries drain faster for the first 40-60 miles, then after your gas engine is kicking in to help the electric motor but again not primarily driving the wheels directly.

You must not have driven many diesels (or know much about cars as a matter of fact, which is actually rather obvious from the fact you bought a Prius) if you think the best diesel gets 40mpg on the highway.

From a financial standpoint a hybrid like the Prius makes about as much sense as a Pickup in downtown NYC.The ironic thing is if you dont keep your car for 7-12+ years it makes no sense buying a hybrid and thats taking into account the 10 year battery wont fail.


User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4488 posts, RR: 21
Reply 4, posted (3 years 9 months 1 week 1 day 19 hours ago) and read 3685 times:

Quoting LOT767-300ER (Reply 3):
From a financial standpoint a hybrid like the Prius makes about as much sense as a Pickup in downtown NYC.The ironic thing is if you dont keep your car for 7-12+ years it makes no sense buying a hybrid and thats taking into account the 10 year battery wont fail.

But you have to admit watching the commercials with all the faeries dancing in fields of posies while smiling at the Prius makes you feel better about yourself, doesn't it?   

The Prius is nothing but a semi-clever marketing gimmick.

Quoting TripleDelta (Reply 2):
Bearing in mind that the quality of the Diesel fuel itself may differ between continents, European Diesels usually have a much higher MPG. My Skoda sedan - about the same size and some 400 pounds heavier than the Prius - has a 1.9 liter 100 HP turbodiesel that had been designed in 1989 and updated here and there with a few bits of new technology; so hardly a cutting-edge modern engine. But, on the highways here in Croatia, I usually average 44-47 MPG - and that's at speeds between 80 and 100 MPH, with overtaking, often enough A/C, and in hilly and mountainous terrain (one of the country's main highways goes through the mountains, so you have a lot of ups and downs). A smaller Diesel city car can average anything upward of 60 MPG...

Different emission standards, not quality of gasoline. You can only get so much energy out of an amount of fuel. Euro IV diesel is equivalent to ultra-low-sulfur diesel in the US.

Quoting DocLightning (Thread starter):
In a car, the demand on the engine is constantly shifting, so it is often laboring under non-optimal conditions. Supplementing the engine output with a hybrid electric drive can help to reduce the load on the engine under the highest demand and significantly increases efficiency. That's why a Prius gets 35mpg tooling around San Francisco.
Quoting DocLightning (Thread starter):
In a car, the demand on the engine is constantly shifting, so it is often laboring under non-optimal conditions. Supplementing the engine output with a hybrid electric drive can help to reduce the load on the engine under the highest demand and significantly increases efficiency. That's why a Prius gets 35mpg tooling around San Francisco.

Many pieces of larger heavy equipment (haulers or "dump trucks" come to mind) utilize a diesel-electric drive and they are hardly laboring under "optimal" conditions (lots of start-stop with heavy loads). They're quite a bit less maintenance intensive than traditional mechanical-drive trucks.



I got my head checked--by a jumbo jet
User currently offlineflanker From United States of America, joined Aug 2005, 1627 posts, RR: 2
Reply 5, posted (3 years 9 months 1 week 1 day 18 hours ago) and read 3668 times:

Quoting LOT767-300ER (Reply 3):
What kind of hybrid are we talking about? Specifically a Toyota parallel drive vs. a Diesel car engine or what? If that is the case then a really dumbed down answer is the fact that a regular combustion engine is inefficient at producing the right power over the whole range of speed that you drive at everyday. Hence you have transmissions that seek out the best power in a certain small range (say for example 3rd gear between 30-50mph). Electricity on the other hand doesn't have these limitations...which is why pure electric cars don't have multiple gears as there is no need for them.

A Toyota Parallel drive still is nowhere near as efficient as the most efficient diesels because again in a very dumbed down explanation it takes more gas to charge the batteries and simultaneously produce power for the wheels than just to produce power for the wheels in a regular diesel engine which has the advantage of being overall around 20% more fuel efficient via higher compression. The advantage of a pure hybrid drive such as in the Chevy Volt is the fact that in that system the the combustion engine focuses all of its energy on charging the batteries and helping the electric motor and not directly running the car. Why is this an advantage? Well think of it that when you press on the gas in the Prius, the gas engine sucks more fuel per second in order to meet your acceleration demand no matter if you just filled up or not, and this is not a fixed % increment but goes up faster and faster the harder you push the gas because of alot of factors (wind resistance for one among many others.) In theory if you hit the gas in a Chevy Volt all that happens is the batteries drain faster for the first 40-60 miles, then after your gas engine is kicking in to help the electric motor but again not primarily driving the wheels directly.

You must not have driven many diesels (or know much about cars as a matter of fact, which is actually rather obvious from the fact you bought a Prius) if you think the best diesel gets 40mpg on the highway.

From a financial standpoint a hybrid like the Prius makes about as much sense as a Pickup in downtown NYC.The ironic thing is if you dont keep your car for 7-12+ years it makes no sense buying a hybrid and thats taking into account the 10 year battery wont fail.

How did you read my mind? HOW?



Calling an illegal alien an 'undocumented immigrant' is like calling a drug dealer an unlicensed pharmacist
User currently offlinevc10 From United Kingdom, joined Nov 2001, 1406 posts, RR: 16
Reply 6, posted (3 years 9 months 1 week 1 day 16 hours ago) and read 3624 times:

With regard to diesel -electric locomotives they could be attractive as the electrical out put can be used to energize more driving wheels than if it was a simple diesel mechanical drive. Also the heavy engine can be put where you like so making design easier.

The infra structure for diesel electric system is much cheaper than a pure electric train system.

littlevc10


User currently offlineDocLightning From United States of America, joined Nov 2005, 19384 posts, RR: 58
Reply 7, posted (3 years 9 months 1 week 1 day 15 hours ago) and read 3567 times:

Quoting LOT767-300ER (Reply 3):

You must not have driven many diesels (or know much about cars as a matter of fact, which is actually rather obvious from the fact you bought a Prius) if you think the best diesel gets 40mpg on the highway.

It's not what I think. It's what USDOT says. Maybe there are better diesels available across the pond.


User currently offlinecomorin From United States of America, joined May 2005, 4896 posts, RR: 16
Reply 8, posted (3 years 9 months 1 week 1 day 14 hours ago) and read 3548 times:

A Diesel Engine's (or any ICE) power output is lowest at low RPMs, and increases as speed picks up. This is why we have transmissions (Gearboxes). A pure Diesel Loco would need massive and lossy transmissions. A Series Wound Electric Motor, on the other hand has the most torque at standstill just when you apply the juice, which is what a loco needs.

So Voila, marry the two together and you have a brilliant combo. Trains need the most torque to get moving, which the electric motor is happy to provide. The Diesel engine is happy to rev up to high speed to provide the juice needed. You've sort of decoupled the power source from the traction source.

Hope this helps.


Comorin

Certified Electrical Engineer  


User currently offlinestar_world From Ireland, joined Jun 2001, 1234 posts, RR: 0
Reply 9, posted (3 years 9 months 1 week 1 day 14 hours ago) and read 3542 times:

Cars like the VW Golf TDI, even the US version, will regularly achieve an average of >40mpg, with 45+ mpg on highway driving.

Also, don't forget the difference between US MPG and UK (Imperial) MPG:

40 Miles per US Gallon = 48 Miles per Imperial Gallon = 5.88 l/100km.


User currently offlinefrancoflier From France, joined Oct 2001, 3735 posts, RR: 11
Reply 10, posted (3 years 9 months 1 week 1 day 14 hours ago) and read 3541 times:

Quoting DocLightning (Reply 7):
Maybe there are better diesels available across the pond.

There certainly are.

The US has kept its distances with diesel due, amongst other, to tight particulate emission restrictions and the availability of cheap gasoline. European manufacturers have had to develop diesels as the public demanded more economy due to punitive fuel prices. The manufacturers have come up with some amazing stuff. You can get something like 200 hp from a 2 litre turbo diesel these days, which is quite on par with a gasoline equivalent, except it'll burn much less.

They also become quite pleasant to drive, even if they'll never be as smooth or linear as gas engines, and they still sound like s**t.



Looks like I picked the wrong week to quit posting...
User currently onlinebohica From United States of America, joined Feb 2004, 2670 posts, RR: 0
Reply 11, posted (3 years 9 months 1 week 1 day 13 hours ago) and read 3523 times:

Quoting francoflier (Reply 10):
The US has kept its distances with diesel due, amongst other, to tight particulate emission restrictions and the availability of cheap gasoline.

Also, not too many gas stations in the USA sell diesel. I would be surprised if diesel is available in more than 25% of all gas stations in the USA.


User currently offlineracko From Germany, joined Nov 2001, 4856 posts, RR: 20
Reply 12, posted (3 years 9 months 1 week 1 day 13 hours ago) and read 3493 times:

A BMW 535d consumes 5,1l / 100km (46mpg) - and it has 300HP, does 0-100km/h in 5,7 seconds and has a top speed of 250km/h.

And it's a BMW 5er and not some ugly rice box.  


User currently offlineTSS From United States of America, joined Dec 2006, 3065 posts, RR: 5
Reply 13, posted (3 years 9 months 1 week 1 day 12 hours ago) and read 3483 times:

Quoting LOT767-300ER (Reply 3):
a regular diesel engine which has the advantage of being overall around 20% more fuel efficient via higher compression.

Diesel engines are more efficient because, unlike gasoline engines, diesels have no throttle plate restricting the intake airflow; the higher compression ratio (usually around 22 or 23 to 1 versus around 9 to 1 for gasoline engines) is necessary to get the air/diesel fuel mixture to ignite without a separate ignition system.



Able to kill active threads stone dead with a single post!
User currently offlineokie From United States of America, joined Jul 2003, 2986 posts, RR: 3
Reply 14, posted (3 years 9 months 1 week 1 day 12 hours ago) and read 3481 times:

Quoting DocLightning (Thread starter):
how is it beneficial to transfer the diesel (or turbine or whatever) power to a generator and then to an electric motor?


If you are comparing diesel/alternator/electric motor to a diesel/direct drive, then electrical wins out because of the complicated mechanical systems and mechanical energy losses involved to get the torque to the wheels.

Just remember Doc that the evolution of more fuel efficient diesel engines has transferred from industrial to automotive and industrial type engines are 30% plus more efficient than years ago. The down side on efficiency is that most industrial type engines have 20 year life spans and takes longer to get the old replaced with the new. This transition is only accelerated by higher fuel costs and environmental regulations. Right now industrial has to meet Epac II requirements and soon Epac III.

Okie


User currently offlineNorthStarDC4M From Canada, joined Apr 2000, 2990 posts, RR: 37
Reply 15, posted (3 years 9 months 1 week 1 day 11 hours ago) and read 3455 times:
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Diesel Electric allows all the following heavy mechanical bits to be omitted:

Clutch/Gearbox and associated control mechanisms
Differential for each axle
Geared connections to each axle

Additionally problems with ONE axle will stop all of them (at least in that truck) as the drive by nature MUSt be linked, not so in Diesel Electric (or Hydraulic for that matter)

It is also impossible to match diesel mechanical drives and slave them together (Multiple unit) unlike electric or hydraulic drives.

Maintenance is simpler as well. Any work on a mechanical drive is a big job.
Replacing a traction motor is much simpler (though i wouldn't call it easy)

Diesel Mechanical locomotives DO exist, but they are usually small in size and power. Industrial or switching engines.



Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety.
User currently offlineBMI727 From United States of America, joined Feb 2009, 15715 posts, RR: 26
Reply 16, posted (3 years 9 months 1 week 1 day 9 hours ago) and read 3387 times:

Quoting NorthStarDC4M (Reply 15):
Differential for each axle
Geared connections to each axle

Not small considerations considering how many axles a locomotive may have.

Quoting francoflier (Reply 10):
The US has kept its distances with diesel due, amongst other, to tight particulate emission restrictions and the availability of cheap gasoline.

That plus diesel's reputation in the US was ruined by some less than stellar models.



Why do Aerospace Engineering students have to turn things in on time?
User currently onlinebohica From United States of America, joined Feb 2004, 2670 posts, RR: 0
Reply 17, posted (3 years 9 months 1 week 1 day 8 hours ago) and read 3357 times:

Quoting BMI727 (Reply 16):
diesel's reputation in the US was ruined by some less than stellar models.

Back in the 1980's, I would avoid getting behind a smoke belching Oldsmobile diesel like the plague.   


User currently offlineMD-90 From United States of America, joined Jan 2000, 8502 posts, RR: 12
Reply 18, posted (3 years 9 months 1 week 1 day 7 hours ago) and read 3321 times:

Quoting DocLightning (Thread starter):
Even weirder, my Prius gets 50mpg (+/-) on the highway, which is relatively constant demand. The best diesel I know of gets about 40mpg on the highway. Why is a hybrid still more efficient than direct drive under constant load?

My mother has told me that she averages 46-47 mpg in her commute to work in a 2010 VW Jetta TDI wagon. That's not all highway miles either and in a car that weighs 3358 lbs vs the Prius' 2765 lbs.


User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 19, posted (3 years 9 months 1 week 1 day 5 hours ago) and read 3277 times:

An image to help illustrate the advantage of electrics vs. internal combustion:



As has been said already, electric motors can have linear torque/power curves and 100% torque can be delivered from 0 RPM. Therefore, a transmission is not required (though a reduction gear is usually used). Remember: Torque gets you moving. (Horse) Power keeps you going. (In really dumbed down terms).

Your average 4 stroke engine only makes usable torque at a given RPM. So you need a transmission to keep the engine within that usable range. (Again, in really stupified terms)

I just don't understand who thought it would be a good idea to start off with marketing parallel hybrids (like the Prius). It's not like their development is much cheaper. Series hybrids are infinitely superior. I remember reading an article of a Volvo C30 Series Hybrid prototype that could do over 100mpg and yet performed just as well as the normal car. Batteries need not be included.


User currently offlineKaiGywer From United States of America, joined Oct 2003, 12214 posts, RR: 35
Reply 20, posted (3 years 9 months 1 week 1 day 3 hours ago) and read 3253 times:
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FORUM MODERATOR

Quoting bohica (Reply 11):
Also, not too many gas stations in the USA sell diesel. I would be surprised if diesel is available in more than 25% of all gas stations in the USA.

To be honest, I can't think of a time I have seen a gas station that didn't sell diesel... Maybe it's because I live in semi-rural areas (suburban Mpls, and now in ND)...



911, where is your emergency?
User currently offlinecpd From Australia, joined Jun 2008, 4879 posts, RR: 38
Reply 21, posted (3 years 9 months 1 week 1 day 3 hours ago) and read 3245 times:

Quoting DocLightning (Thread starter):
Even weirder, my Prius gets 50mpg (+/-) on the highway, which is relatively constant demand. The best diesel I know of gets about 40mpg on the highway. Why is a hybrid still more efficient than direct drive under constant load?

Try Ford Fiesta Econetic Diesel. 3.0L /100km - or otherwise, around 75mpg (US). Not sold in your country as far as I know, but it is here - and is very economical motoring. And far cheaper than a Prius (although it is smaller).

The diesel-electric hybrids are the way to get more fuel efficiency. And modern diesels are very clean and quiet, far from the belching, clattering old things they used to be.

Take a look at the BMW 535D mention above, or even the Jaguar XF Diesel S (202kW), or even the Audi A8 4.2 TDI (a thundering monster) as an example of just how good they (as in modern diesel engines) can be.

[Edited 2010-10-21 17:24:01]

User currently offlineBMI727 From United States of America, joined Feb 2009, 15715 posts, RR: 26
Reply 22, posted (3 years 9 months 1 week 1 day 3 hours ago) and read 3242 times:

Quoting KaiGywer (Reply 20):

Yeah, even in cities diesel, while not universal, is not really difficult to get.



Why do Aerospace Engineering students have to turn things in on time?
User currently onlinebohica From United States of America, joined Feb 2004, 2670 posts, RR: 0
Reply 23, posted (3 years 9 months 1 week 1 day 2 hours ago) and read 3229 times:

Quoting KaiGywer (Reply 20):
Quoting bohica (Reply 11):
Also, not too many gas stations in the USA sell diesel. I would be surprised if diesel is available in more than 25% of all gas stations in the USA.

To be honest, I can't think of a time I have seen a gas station that didn't sell diesel... Maybe it's because I live in semi-rural areas (suburban Mpls, and now in ND)...

Maybe it's just where I live. Here in VA Beach about one in four gas stations sell diesel. The ratio gets better when you get closer to major highways though.


User currently offlineNoWorries From United States of America, joined Oct 2006, 539 posts, RR: 1
Reply 24, posted (3 years 9 months 1 week 1 day 2 hours ago) and read 3225 times:

Quoting comorin (Reply 8):
A Series Wound Electric Motor, on the other hand has the most torque at standstill just when you apply the juice, which is what a loco needs.



Yep -- traditionally done with DC -- series-wound tends not to work well with AC -- but IIRC there are some light rail systems in Europe that operate on 16 2/3 Hz AC with series-wound, almost as good as DC.

In the past, DE engines produced AC current and then rectified it to DC before sending it to the motors. For many decades, diesel engine designers have wanted the benefits of AC induction motors but have always been limited by starting torque. But, in the past 10-15 years or so, AC traction has been introduced to freight engines. Electronic inverters provide variable frequency variable and voltage to the drive motors that is optimal for speed and load.


25 okie : You can even put two series wound DC traction motors in series and get twice the torque but only half the speed. Good for switching operations in a r
26 Post contains images comorin : Thanks! Very helpful posts. I had forgotten about the DC vs AC thingy, did my Electrical Machines lab in '66, worrying about star vs delta circuits..
27 N1120A : That is the opposite of what is supposed to happen. Not really. USDOT/EPA testing is both outdated and geared to make gasoline cars look better. All
28 DocLightning : I understand that they use thyristors and other pulse sequencers to help the performance of the AC motors on the newer trainsets. That is why the Lon
29 NoWorries : That's a nice twist -- they have an infrastructure that provides 3rd rail DC power for older equipment with the newer equipment converting the DC to
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