Locomotive horsepower

[Virginian]

Todays diesel engines are computer controlled as to both air and fuel (injectors) metering, but neither have ever been constant flow.  Ideally you would want to have a nearly constant ratio of fuel to air, but rarely has this ever been accomplished throughout the range.  When the operator asks for more power or speed, the diesel will produce more torque and/or a higher speed, which will be utilized by the generator due to it being also stepped up via the field currents at the same time.  Torque will be effected by how much fuel is burned on every combustion stroke, and power will be determined by how fast the torque is produced (i.e. engine RPM).  The traction control will monitor every wheel and control the electrical power going to each motor to limit slip.

[selector]

Thanks for the illucidation.  I still don't know how the prime mover in a locomotive responds to an increased demand for work.  If the operator notches up, take me through the "system" so that we understand what happens as a result of what.   Does the diesel increase revolutions by nearly two times, or does it merely aspirate more, get more fuel, and how does that affect the torque output, which I now understand is the primary motive force once converted to tractive effort by the motors?  (I had always understood that a diesel gets air metered, while fuel is constant.  Probably outdated knowledge now that we have common rail and other improvements...although I don't know if common rail has any application here....what does?)

[Virginian]

Torque is twisting force.  Horsepower is work.  The characteristics of a diesel usually cause it to operate at considerably slower speeds than a gasoline engine.  Hence it must produce more torque at a slower speed to achieve like power.

One horsepower equals 550 foot pounds per second.  From that you should be able to calculate anything.    (But, I'll bet 4000 Budweiser Clydesdales could drag any loco anywhere !  If you could only find the right harness. )

[beaulieu]

And they're geared 85:16? So their motors can exceed 9729 lb-ft of torque?

The 85:16 ratio is for the SD70MAC.  The SD70ACe is 83:16.  I don't know what either of their torque limitations is (although the SD70ACe does have a higher limitation than the SD70MAC has) -- to me it's whatever the software thinks that it is.

SD70MAC uses Siemens 3-phase equipment, SD70ACe switched to Mitsubishi for the 3-phase drive.

[GP40-2]

Dynamometers do not measure horsepower, they measure torque!

Bingo! We have a winner!

That's because torque is the ONLY force a reciprocating engine (gas or diesel) produces. I'll repeat that for the "experts" on this forum: The diesel engine on a locomotive is designed to produce "X" amount of torque to turn the traction alternator. "Horsepower" ratings are derived from the torque output at a given RPM; it is never the other way around.

Diesels rely more on torque than do gas engines, application for application....or am I wrong?

Both types of engines rely on torque and ONLY torque to produce useful work. Torque is the only force they produce. The difference between a (typical) gas and diesel is their torque curves occur at different RPM's.

[chefjavier]

Try this link for locomotives power.

http://www.locophotos.com/

Enjoy!

[chefjavier]

http://www.geocities.com/guilford_350/

Fix your link.. You need give an space after the quote in order for the link to establish.

[trainfan1221]

I am just gonna sum things up this way.. Horsepower is a basic rating and from what I understand has just as much to do with speed.  A 5000 hp locomotive can pull a 5000 ton train, so can a switcher, just a lot slower.  Lets also look at it this way, a muscle car can have 600hp, and a small switch engine also has same rating.  Do you think the car is gonna pull the same kind of weight as the switcher? Doubtful.  It explains that there are other forces than horsepower at work.  An intermodal train will be given the same power as a large drag freight which could be a lot heavier, because it needs to move fast.  The Contemporary Diesel Spotter's guide explains a lot of this also at the end of the book.

[JayPotter]

And they're geared 85:16? So their motors can exceed 9729 lb-ft of torque?

The 85:16 ratio is for the SD70MAC.  The SD70ACe is 83:16.  I don't know what either of their torque limitations is (although the SD70ACe does have a higher limitation than the SD70MAC has) -- to me it's whatever the software thinks that it is.

[timz]

rail conditions permitting, it can produce up to 191,000 lbs of TE within that speed range.

And they're geared 85:16? So their motors can exceed 9729 lb-ft of torque?

[oltmannd]

Torque is a measure of work.  Horsepower is a measure of how fast the work is done.  A tractor and a motorcycle may both have 100 hp.  The tractor runs slower, does more work.  The motorcycle does less work, but does it faster.

The hp-torque curves of any engine should cross at 5252 rpm (assuming the engine can run that fast) .  I'm sure there are formulae for figuring torque at a given hp and rpm level. 

I think you're confusing "work" with "force".

Torque is a measure of rotational force.

Work is "energy usefully expended".  Linearly, it's force X distance.  Rotationally, it's torque X revolutions  (both with the proper fudge factor to get the English units to work out)

If you apply a force to an object and it doesn't move (or a twist and there is no rotation), then no work is being done. 

Power is a measure of how fast you can do work.  Force X distance / time.  Since distance/time = speed, Power = force X speed.  The rotational equivalent is torque X revolutions/time or torque X RPM (with appropriate English fudge factors)

[silicon212]

Horsepower measured on a rotating power source, is definitely measured using this formula -

Horsepower = torque*rpm/5250

This applies to engines, motors etc.

Dynamometers do not measure horsepower, they measure torque!

[WSOR 3801]

Torque is a measure of work.  Horsepower is a measure of how fast the work is done.  A tractor and a motorcycle may both have 100 hp.  The tractor runs slower, does more work.  The motorcycle does less work, but does it faster.

The hp-torque curves of any engine should cross at 5252 rpm (assuming the engine can run that fast) .  I'm sure there are formulae for figuring torque at a given hp and rpm level. 

[JayPotter]

So if adhesion allowed, an SD70ACE could generate 177,200 lb TE continuously, minus the gear loss? At what speed, I wonder.

At least on CSXT, the nominal continuous speed of an SD70ACe is 8.8 MPH.  It can be relied upon, under normal rail conditions, to produce 157,000 lbs of TE at or below that speed; and rail conditions permitting, it can produce up to 191,000 lbs of TE within that speed range.

[timz]

So if adhesion allowed, an SD70ACE could generate 177,200 lb TE continuously, minus the gear loss? At what speed, I wonder.

[beaulieu]

1TB2630 traction motors used in the SD70MAC are rated at 9729 lb-ft. of torque. 

That's continuous, or maximum? What's the usual gear ratio? SD70MACs use ... 42-inch wheels, or what?

It's continuous and effectively maximum torque. The motor has a higher figure called "Breakdown Torque" but this can only be achieved instantaniously and is followed by the motor stalling and torque dropping to zero.  

All SD70MACs were built with 85/16 gearing and 42" wheels. SD90MACs also used this motor and gearing, some of them had 44" wheels. 

[selector]

Let me....ahem...play devil's advocate for a moment.  First, I am only as knowledgeable as the next guy about gas and diesel engines.  I make no claims to training or experience that places me in a position to catch any of the responders in such a way as to make a cheap point.  So, please just take the question at face value as an academic exercise.

My understanding is that a diesel is different from a gas engine by virtue mainly of its ability to generate a lot of power at low rpm's, and this is because of various characteristics such as compression and efficiencies that accrue thereby.  Diesels rely more on torque than do gas engines, application for application....or am I wrong?  That is, a diesel is not meant to generate tons of hp, whereas a higher revving gas engine does just that.

Another question: as the load demand on the traction motors is either realized or imposed, will the diesel prime movers not have to rely more heavily on their torque characteristics (vice a gas engine's hp from revs) to keep the alternator/generator at speed to supply the power?

My questions, as naive as they may appear to be, could be at the root of the fracas a few posts back.  If there is a fundamental misapprehension by some or many of the readers (including me) of this thread, perhaps some of you could fill us in a bit?

Thank-you for helping us out.

[wabash1]

Maybe we should start at the beginning.

One would build an engine only to be able to harness it to some sort of machine to do some useful work.  The characteristics of the engine (torque/speed curve) need to be known in order to match it to the requirements of the machine. 

In the case of a lawnmower, the engine's design fits a direct drive of the blade.  In the case of a chainsaw or leaf blower, a single reduction gear set makes the match.

In the case of an automobile, a transmission with several gear ratios is needed.

In the case of a DE locomotive, the engine is mated to the traction alternator by direct drive.  The traction alternator was designed to match the engine's characteristics, providing an electrical transmission of nearly infinte effective "gear ratios".

Once the traction alternator is designed to be matched to the engine, the issue of diesel engine torque/speed characteristics is a moot point.  For everything "downstream" of the traction alternator, it doesn't matter what's making the electricity. As long as the HP is there, the locomtive will perform.

For the greater part of a locomotive's operational speed range, the performance is strictly governed by HP.  So, knowing what the diesel engine's speed/torque characteristics won't tell you anything useful about the locomotive's performance.

You can nit-pick this around the edges all you want.

Now im gonna nit pick. is that going forward or backwards. LOL and dare i need to say anything about dynamic????

[YoHo1975]

Thanks for making the point eloquently.

[oltmannd]

Maybe we should start at the beginning.

One would build an engine only to be able to harness it to some sort of machine to do some useful work.  The characteristics of the engine (torque/speed curve) need to be known in order to match it to the requirements of the machine. 

In the case of a lawnmower, the engine's design fits a direct drive of the blade.  In the case of a chainsaw or leaf blower, a single reduction gear set makes the match.

In the case of an automobile, a transmission with several gear ratios is needed.

In the case of a DE locomotive, the engine is mated to the traction alternator by direct drive.  The traction alternator was designed to match the engine's characteristics, providing an electrical transmission of nearly infinte effective "gear ratios".

Once the traction alternator is designed to be matched to the engine, the issue of diesel engine torque/speed characteristics is a moot point.  For everything "downstream" of the traction alternator, it doesn't matter what's making the electricity. As long as the HP is there, the locomtive will perform.

For the greater part of a locomotive's operational speed range, the performance is strictly governed by HP.  So, knowing what the diesel engine's speed/torque characteristics won't tell you anything useful about the locomotive's performance.

You can nit-pick this around the edges all you want.

[timz]

1TB2630 traction motors used in the SD70MAC are rated at 9729 lb-ft. of torque. 

That's continuous, or maximum? What's the usual gear ratio? SD70MACs use ... 42-inch wheels, or what?

[YoHo1975]

I'm sorry this thread got a little heated, but it's always nice to be courteous even when you disagree.

 

Of course, Given the double negative in GP40-2's post, he is unintentionally agreeing with me anyway.

Also thanks to Wabash1 for backing me up. 

I will say that even though you typically deal in group ratings, the tractive effort is still the relevent measure. You just don't need to know the actual value, because that work has been done for you to increase efficency.

We've also discussed in other threads how Horsepower relates to speed and so, Tractive effort isn't the only relevent measure. 

 

[beaulieu]

Stroke length is an important factor in torque, the EMD engine is slightly longer stroke. But like everything else there are trade-offs. With the longer stroke there is greater stress on bearings, etc.

 

The 1TB2630 traction motors used in the SD70MAC are rated at 9729 lb-ft. of torque.  

[wabash1]

Well of course torque is important from a physics perspective, don't be silly, and don't try and be a smart alec.

 

However, the poster was asking for torque numbers similar to what one would get for automobile performance. In the case of a Diesel Electric locomotive, Torque doesn't represent the same thing at all.  In fact, a very very brief glance through EMD's website doesn't show a single reference to the Torque of any of the 710 product line.

 

Torque isn't relevent in the same way and therefore in the context of the question asked, it isn't a relevent measure.

The Torque of the Engine is such that it will generate the correct power output at the correct RPM

The tractive Effort of a loco is the functional equivelent of torque in a car and that is where the comparison should be made.

 

Now, I'm sure somewhere you can find the torque numbers and given that we're talking about Diesels that are so large that you could stuff one or more rat motors in one cylinder (in terms of displacement) those numbers would be impressive, but they aren't really relevent in the same way.

  

Blah, Blah, Blah.

Again, if you don't think the torque of a prime mover isn't relevent to locomotive proformance, you are clueless. Good thing you don't actually work in this industry.

The torque of the prime mover is not measured and doesnt matter, the prime mover only turns the altenators ( which there is 3) this is why there is no torque numbers. the numbers you gave are effort reading of the traction motor in which you ( for your own satisfaction) changed to read in ft. pounds of torque , Ive only seen electric motors rated in horse power units and effort , never torque. Oh and i do work in the industry, and even though i dont study engines like i use to ( cars trucks and motorcycles and locomotives ) I do know what the locomotives will do and its really not that important to a railroader what the traction effort of a engine is. these engines are alread broken down into groups so all i need is model of engine and look up what the group rating is, but since there isnt anything new in the last 15 years worth bragging about or any real change the ratings are pretty much the same

[JayPotter]

GEVO (4400 Traction HP) engine produces 23,550 lbs-ft torque @ 1050 RPM
EMD 710 (4300 Traction HP) engine produces 26,500 lbs-ft torque @ 900 RPM

Is torque inversely proportional to RPM; and/or is there some other reason why the engine with higher horsepower and higher RMP produces less torque than the engine with less horsepower and lower RMP?  Thanks very much.

[silicon212]

Let's keep the tone a bit more civil, please.  If you find that you cannot convince the person with the contrarian view from yours with your words or with documents linked in your message, just agree to disagree and move on.  No one gets points or an award for persevering at the cost of civility.

Thanks.

 

THANK YOU!

[AlcoRS11Nut]

Let's keep the tone a bit more civil, please.  If you find that you cannot convince the person with the contrarian view from yours with your words or with documents linked in your message, just agree to disagree and move on.  No one gets points or an award for persevering at the cost of civility.

Thanks.

 

[selector]

Let's keep the tone a bit more civil, please.  If you find that you cannot convince the person with the contrarian view from yours with your words or with documents linked in your message, just agree to disagree and move on.  No one gets points or an award for persevering at the cost of civility.

Thanks.

[GP40-2]

Well of course torque is important from a physics perspective, don't be silly, and don't try and be a smart alec.

 

However, the poster was asking for torque numbers similar to what one would get for automobile performance. In the case of a Diesel Electric locomotive, Torque doesn't represent the same thing at all.  In fact, a very very brief glance through EMD's website doesn't show a single reference to the Torque of any of the 710 product line.

 

Torque isn't relevent in the same way and therefore in the context of the question asked, it isn't a relevent measure.

The Torque of the Engine is such that it will generate the correct power output at the correct RPM

The tractive Effort of a loco is the functional equivelent of torque in a car and that is where the comparison should be made.

 

Now, I'm sure somewhere you can find the torque numbers and given that we're talking about Diesels that are so large that you could stuff one or more rat motors in one cylinder (in terms of displacement) those numbers would be impressive, but they aren't really relevent in the same way.

  

Blah, Blah, Blah.

Again, if you don't think the torque of a prime mover isn't relevent to locomotive proformance, you are clueless. Good thing you don't actually work in this industry.

[YoHo1975]

Well of course torque is important from a physics perspective, don't be silly, and don't try and be a smart alec.

 

However, the poster was asking for torque numbers similar to what one would get for automobile performance. In the case of a Diesel Electric locomotive, Torque doesn't represent the same thing at all.  In fact, a very very brief glance through EMD's website doesn't show a single reference to the Torque of any of the 710 product line.

 

Torque isn't relevent in the same way and therefore in the context of the question asked, it isn't a relevent measure.

The Torque of the Engine is such that it will generate the correct power output at the correct RPM

The tractive Effort of a loco is the functional equivelent of torque in a car and that is where the comparison should be made.

 

Now, I'm sure somewhere you can find the torque numbers and given that we're talking about Diesels that are so large that you could stuff one or more rat motors in one cylinder (in terms of displacement) those numbers would be impressive, but they aren't really relevent in the same way.