Many varied replies to your question, but here are the correct answers.
Diesel locomotive horsepower rating is the engine power delivered to the traction generator. The output of the traction generator (alternator/rectifier or a DC generator) is connected to a Load Box or on units that have Self-Load to the locomotive's dynamic brake grids which provide a resistance load that converts the DC electrical power to heat. While the engine is running loaded in throttle 8 and conditions are stbilized the traction generator voltage and current are measured. The formula for converting electrical power from watts (volts x amps) to horsepower is V x A / 746 (- % efficiency of the generator). The actual conversion formula used in railroad shops is V x A / 700 which assumes that the traction generator is 94% efficient. Other loads on the engine (parisidic, compressor, cooling fans, traction motor blowers, auxiliary and exciter generators) are not considered. The locomotive's excitation control system is designed to keep the traction power constant while auxiliary loads on the engine are variable such as compressor pumping for a short period then unloading or radiator fans running then stopping depending on cooling demand.
Your second question about anti-freeze in engines designed primarily for locomotive application has a 2 part answer. In the early 1990's Union Pacific's mechanical department and EMD made a serious effort to use antifreeze (ethelene glycol) in the upcomming production of the SD90 with both the 4300 hp 710 engine and the 6000 hp "H" engine which was still in the design phase. Anti-freeze was not employed on either of these engines for two reasons: costs and cooling efficiency. The costs associated with the use of anti-freeze are of course the price of the anti-freeze solution but also included is the cost of equiping every shop with a coolant recovery system that would save and permit re-use of drained anti-freeze coolant (coolant must be drained from an engine for such work as a power assembly replacement). The anti-freeze coolant is too expensive to just drain away and re-fill the engine with new coolant. Also there are costs associated with the disposal of the anti-freeze solution which is environmentally hazardous. While all railroad shops today have facilities to treat drained coolant from the shops and inspection pits, the current anti-corrosion chemicals in engine coolant are not highly toxic and are within the capacity of shop treatment plants to reduce the drain water toxicity to acceptable levels. Use of anti-freeze would require special handling or a re-design of shop treatment facilities at a considerable expense to the railroad. There is also concern of the possibility that the engine coolant could be unintentionally drained on the railroad line, worse case is near a lake or river. The plain water with corrosion inhibiter currently employed is not an environmental concern if it spills or the engine is drained (such as the opening of a automatic freeze drain valve) on the rail line.
The second reason that the use of anti-freeze was dropped has to do with something that came as a surprise. Experiments with the 710 engine showed no signs of engine corrosion or cooling system problems. However the coolant efficiency was reduced, particularly the ability of the anti-freeze coolant to absorb heat within the power assembly jacket and cylinder head which is designed to be cooled with plain water. With the existing design of the 710 power assembly fixed, use of anti-freeze would not provide the engine cooling efficiency required. This problem would also exist in 645 and 567 power assemblies which are of similar design.
Though the EMD "H" engine was designed to use anti-freeze coolant, none of the engines actually used it in service. Now that the 6000 hp SD90 is a dead issue, the point seems moot.
Alan Robinson, timz, and GP40-2 -
Thank you all for a very informative and concise discussion. I realize there are a few minor points of disagreement and/ or clarification to be had among you, but overall I think for 15 minutes or so of reading this is the best exposition of the topic outside of an engineering class. Thanks again !
- Paul North.
In freezing conditions, engines equiped with 'APU's (Automatic Power Units) will have the APU monitor they ambient and engine temperatures and automatically start the APU to create and circulate coolant to the everything above the freezing point.
Engines not equipped with APU's are kept running. If the engine is not kept running during freezing conditions then it must be drained to keep it from freezing and can no longer be used for power until it has coolant added and the engine restgarted.
Never too old to have a happy childhood!
I think we are WAY over-thinking this. A SD40-2 produces 3000 HP (or there abouts, very common to see them produce 2800-3400 on a load test) All this says is the engine+main alt- parasitic loads/losses (air compressors, fans, aux. gens etc.) is capable of powering 3000 HP worth of electric motor.
As for the antifreeze. ANY engine can run anti-freeze, The reason many choose not to run it is because it in EXTREMELY hard on engine seals. especially lower liner seals on EMD's. The shortline I used to work on ran antifreeze in all it's units, EMD's Alco's and GE's. now on the UP only the 8900's (6000 hp EMD's now retired) had anti-freeze. water is cheap, effective and engine and environmentally friendly.
Alan Robinson When we say that a diesel electric locomotive is a 3000 horsepower unit, we usually mean that the locomotive can exert 3000 horsepower at the rail once it has achieved the speed at which it is generating its maximum continuous tractive effort.
When we say that a diesel electric locomotive is a 3000 horsepower unit, we usually mean that the locomotive can exert 3000 horsepower at the rail once it has achieved the speed at which it is generating its maximum continuous tractive effort.
That is not exactly correct. A diesel-electric is rated in nominal horsepower available to the traction generator/alternator. The rating does not include electrical and mechanical losses to the rail. The rail horepower is lower.
In the case of the the 2000 HP EMD E7, 2000 HP was available for the traction generators. The E7's electrical and mechanical losses to the rail were 18% (a modern AC unit has less than a 7% loss). The true rail horsepower of an E7 was 1650 HP per unit. 2 E7's had 3300 rail horsepower, while 3 were producing right around 5000 rail horsepower. The Niagara produced around 5000 HP at the rail, so its easy to see why it took 3 E7's to equal the horsepower of 1 Niagara. It's incorrect to state the Niagara could generate more than its rated horsepower. Both the E7s and the Niagara were producing EXACTLY their rated rail horsepower.
Timz--"By the way-- who said that two E7's "should" be enough to replace a 4-8-4?"
I would say experience showed this. Until 1-1-1958, the N&W used one J 4-8-4 between Monroe, Va., and Bristol, Va., to pull the Southern trains that ran through Bristol. The Southern used two E's south of Bristol on the Pelican and the Birmingham Special, and two PA's on the Tennessean. I do not have an accurate memory of the number of cars on any of these trains, but I would say that the Southern brought thePelican in with at least a dozen cars, and the N&W took the train on to Monroe after two sleepers had been added. After 12-31-1957, two E's ran through with each train.
Johnny
Alan Robinson...trains such as the 20th Century Limited and the Empire State Express. When E units were placed in service on these trains, it was found that instead of the two unit locomotive (4,000 horsepower total) that should have been adequate to replace one 4-8-4, it was necessary to use three in order to maintain schedule.
By the way-- who said that two E7's "should" be enough to replace a 4-8-4?
Alan RobinsonSteam locomotives were quite conservatively rated and could frequently exceed their design specifications.
As for the conservative rating-- you'd probably agree the engine's rated TE wasn't particularly conservative? If its nominal TE was 65000 lb it would be an exceptional engine that actually produced, say, 75000 lb?
So you probably meant its horsepower "rating" was conservative. Well, when the designer calculated Z he could use a conservative formula, or not-- he probably didn't give the matter a lot of thought, in any case. He would do his best to make the engine powerful, within the specified limits of weight and so on, and didn't waste time trying to predict just how powerful it would be.
Alan Robinson When a traction motor isn't turning there is no back EMF to lower the current. The current is limited only by the resistance losses in the motor windings. So, the current is at a maximum when the train is first starting.
Alan RobinsonThe load on the generator/alternator is at a maximum at this point.
Alan RobinsonSimilarly, the prime mover brake horsepower is at a maximum even though the power at the rails is zero.
Nope. Like I said, the main generator/alternator simply won't absorb the prime mover's full horsepower-- the rotor turns too easily.
Say the prime mover isn't connected to anything. We shove the throttle to Run 8 and the prime mover speeds up to its governed maximum RPM, but still producing zero brake HP (and not burning much fuel). Now put on your gloves and grab the output shaft and try to stop it. You can't, of course, but you are putting some drag on it, so now it's producing some slight BHP. But you can't grasp it hard enough to make it produce its full horsepower-- and neither can the generator/alternator, when the locomotive is stationary. Maybe it could, if the excitation current were high enough, but the locomotive control system won't permit that-- the traction current would instantly melt everything it touched.
Rodney, this is an unwarranted assumption. For starters, we may be dealing with a pusher. No broken knuckles here. Then again, a light single unit switcher with a starting tractive effort lower than the coupler strength could be tied onto 100 loaded hoppers. Both of these scenarios would allow the locomotive to exert maximum starting tractive effort without necessarily being able to move the train.
In any event, the discussion was meant to illustrate the fact that horsepower at the rail is more than tractive effort. It is the product of the tractive effort and the speed. Hence, no speed, no horsepower at the rail despite a very high starting tractive effort.
When we say that a diesel electric locomotive is a 3000 horsepower unit, we usually mean that the locomotive can exert 3000 horsepower at the rail once it has achieved the speed at which it is generating its maximum continuous tractive effort. Below that speed, the horsepower is time limited.
The brake horsepower of the prime mover may be somewhat more than the maximum rated continuous horsepower at the rail, but one must know how the prime mover horsepower is apportioned out to all uses. Some may be used for head end power in these days of electrically powered passenger car mechanical systems.
Also, keep in mind that a diesel electric locomotive is a constant horsepower machine. This means that as speed increases, tractive effort must fall so that the product of the two is always less than or equal to the rated unit horsepower. You can't overload a diesel electric unit. The prime mover can never generate any more power than it's peak capability.
This is not necessarily true for a steam engine. It is easy to overload a steam engine and many no doubt were frequently operated in overload condition. You could overfire them, shoveling excess fuel into the firebox and generating more steam than the boiler was otherwise rated to generate. Almost all steam locomotives could use more steam in the cylinders than the boiler could produce. There would be lots of black smoke and efficiency would go to hell, but for a short overload period this would be acceptable. Steam locomotives were quite conservatively rated and could frequently exceed their design specifications.
An example was the 4-8-4 Niagara type on the New York Central. This locomotive was built as a dual service machine and was often used to pull the famous name trains such as the 20th Century Limited and the Empire State Express. When E units were placed in service on these trains, it was found that instead of the two unit locomotive (4,000 horsepower total) that should have been adequate to replace one 4-8-4, it was necessary to use three in order to maintain schedule. The Niagara could generate more than it's rated horsepower, especially at high speed.
tims, this simply isn't so. When a traction motor isn't turning there is no back EMF to lower the current. The current is limited only by the resistance losses in the motor windings. So, the current is at a maximum when the train is first starting. The load on the generator/alternator is at a maximum at this point. Similarly, the prime mover brake horsepower is at a maximum even though the power at the rails is zero. Essentially, all the power is converted into heat within the motor windings. Clearly, this condition can't continue for long or the motors will be destroyed. However, there may be a practical limit to prevent the engineer from simply slamming the throttle in Run 8 while the train is stainding still. This may well cause the wheels to slip. But for the sake of arguement, suppose the locomotive is heavy enough that it won't slip it's wheels even at full throttle.
As the train begins to move, and the motors begins to generate back EMF, the current begins to drop. During this acceleration period, the tractive effort drops, too. Horsepower at the rails begins to creep up and heating in the motors drops as less power is wasted as heat. Brake horsepower can remain at its peak all during the period of acceleration.
Finally, speed increases to the point that the back EMF counters enough of the generator/alternator output that the current drops to within the safe continuous limit. This typically happens somewhere between 9 mph and 13 mph, depending on the number of traction motors and the gearing. If the train can't accelerate to this speed within the time limit of the electrical system, the engineer must reduce the throttle position to drop the brake horsepower (and thus the current) to within the safe continuous limits. Since the tractive effort has been dropping, and will certainly drop if the engineer needs to reduce the throttle, the train may stall.
Since a traction motor can generate a starting torque that is greater than the continuous running torque for a limited time, a diesel electric locomotive can start a train it can't necessarily pull. This is just the opposite of a steam locomotive, which can generally pull any train it can start.
Train comes apart with at least a broken knuckle.
Rodney
Alan RobinsonWhen the train is just starting, brake horsepower may be at a maximum even though horsepower at the rail may be zero!
trainfan1221 A diesel engine is usually rated a little higher so that a 3000 hp unit gives that at the rail.
The type of mechanical brake mentioned in an earlier post utilizing a brake pad resting against the rim of a flywheel and attached to a long arm fastened to a scale was called a prony brake (not a pony brake) and is useful for only relatively low horsepower measurements. This is because prolonged operation makes the brake shoe get HOT! For high horsepower applications, the same principle is used but another means must be used to load the engine. Three common methods in use today are a "club" propeller (common for aircraft engine testing), an electrical generator of some kind (useful for such things as diesel locomotive engines) and hydraulic pumps of various kinds. All of these can easily dissipate all the heat generated in loading the engine. The heat goes into the air (club propeller), into a body of water (hydraulic pump) or into an air-cooled resistor grid (electric generator.) The torque can be measured by means of an arm or set of arms working against a load cell or by measuring the electricity generated or the water pumped directly and then calculating the power input to do the work. This only works if the efficiency of the generator or pump is well known.
Diesel locomotives have two main power ratings. One is brake horsepower measured at the output of the prime mover. The second horsepower rating of great importance is the horsepower at the rail. This is what counts in actually pulling the train. It can never be even equal to the brake horsepower because of losses in the electrical transmission. When the train is just starting, brake horsepower may be at a maximum even though horsepower at the rail may be zero! (No train speed, no horsepower at the rail, regardless of tractive effort exerted.)
Steam locomotives also had several different horsepower ratings. One was boiler horsepower reflecting the ability of the boiler to generate steam. Another was cylinder horsepower, a calculated number used to design locomotives and to compare (approximately) the performance of one locomotive with another. Yet another was indicated horsepower measuered by means of an indicating mechanism attached to the cylinders and valves and measuring the pressures in the cylinders and positions of the pistons as the locomotive actually worked. This device "drew a picture" of the pressures and allowed the horsepower generated to be directly measured at the cylinders. Then there was drawbar horsepower measured at (you guessed it) the drawbar. This was done with a dynamometer car coupled between the locomotive and the train. It essentially measured directly the drawbar pull and combined this with the train speed to show the horsepower the locomotive could produce at any speed.
Brake horsepower is the horsepower measured at the flywheel of the engine In an auto engine, the horsepower may be determined with the alternator, water pump, fan, etc., operating, or without any of them. The term "brake horsepower" comes from the old method of attaching a braking mechanism (shoe and drum) on the flywheel. The brake was attached to an arm whose opposite end rested on a large scale (like they used to weigh sacks of feed, etc.). As the engine ran, the brake was applied to give the engine a load. The force on the scale exerted by the arm, being the reaction to the braking force, measured the torque (force on scale times the arm length). Horsepower was then calculated from the measured torque and the revolutions per minute. We used to perform this experiment in mechanical engineering lab when I was getting my mechanical engineering degree.
Murphy Siding I've seen references to locomotive horsepower refered to as brake horsepower. What does that mean? Unrelated question: Why can you put antifreeze in a 4 stroke diesel, but not a 2 stroke?
I've seen references to locomotive horsepower refered to as brake horsepower. What does that mean?
Unrelated question: Why can you put antifreeze in a 4 stroke diesel, but not a 2 stroke?
1. "Brake horsepower" is jargon with identical meaning to "gross horsepower" -- the horsepower of an engine not subtracting for the parasitic power consumption of auxiliaries such as water and oil pumps, and not subtracting for any transmission losses beyond the flywheel or output shaft. The "brake" comes from a device called a De Prony Brake invented in 1821 to measure the output of an engine. (I had to look that up because I don't think anyone has used that device in more than 100 years, but the name stuck.)
2. There's no either/or capability for ethylene glycol as an antifreeze additive in 4-stroke vs. 2-stroke diesel engines. Depending upon the design of the engine, antifreeze can be compatible or incompatible with either. In turn, that depends upon original design parameters that are established when a new engine design is begun. Those parameters are derived from assessments of the market for the engine and what customers will most highly value. Customers who will regularly use an engine 8-12 hours a day only, such as in the trucking market and earthmover market, value antifreeze compatiblity because the alternative is block heaters and the cost of all the infrastructure that goes with that, or draining and refilling the engine every shift.
Class 1 and 2 railroads, and marine users, which are the customers for the overwhelming share of the locomotive engine market (as opposed to short lines and industrial users), place a very low relative value on antifreeze compatibility because they want to keep the locomotive or engine busy around the clock, 365 days a year, and thus place a very high value on engine design factors such as high fuel economy, high availability, low maintenance cost, and low initial purchase price. It's not possible to design an engine to achieve perfection in all categories at any given time as some of those categories are often technologically incompatible. Antifreeze compatibility, for example, can be designed into a locomotive engine but until recently it was at the cost of significantly higher initial capital cost, higher maintenance cost, and lower fuel economy. So, if you asked the railroad customer, "Would you rather have an engine with lifetime cost X and no antifreeze capability, or lifetime cost X+1 and antifreeze capability," the answer from the railroad customer was always, "You can highball the antifreeze."
Note that "antifreeze-compatible" is similar to "bullet-proof"; there is no such thing. Only degrees of safety.
More recent designs from EMD and GE are antifreeze-compatible due to improvements in materials science and engineering, but few railroads want to use antifreeze even so, because of its cost to add and replenish, the environmental issue of disposal, leakage, and drainage, and because in the overwhelming majority of their fleets they still do not need it.
Auxiliary heaters and the like are not free-rides either. They cost money to install, a lot of money to service and maintain, decrease availability, require more training and supervision of employees, and on a broad basis in the Class 1 environment not deemed economically effective. In specific applications they have high return on investment, such as locomotives that are regularly worked only a partial day and tied up remote locations. But those applications are typically narrow because they're often marginally economic in the first place as they tie up an expensive asset (the locomotive) and generate a limited revenue and profit stream.
RWM
Horsepower seems to be a nominal term and can mean different things, and there are different kinds such as brake horsepower and actual, and I believe the other term is Drawbar(?) HP. A diesel engine is usually rated a little higher so that a 3000 hp unit gives that at the rail. I remember reading that Amtrak F40s actually had closer to 3200 hp than the given 3000.
In a passenger locomotive with an alternator for lighting the power from the engine lessens with train length, or at least a basic amount is taken off right from the start. The engine had to run at a constant speed and I don't know how many still are set up like this. NJTransit rebuilt their F40s so they had an auxiliary engine instead.
Part of me kinda figured that there was, considering that the automotive industry (which I'm a part of) has the same deal where you either hook a small electrcially powered water pump/heater into the cooling system of your car and it'll keep the coolant not only circulating, but also keep it warmer than the OAT, of course there are also dipstick heaters that work the same way by heating the lubricating oil in the engine (really nice on diesels since most of them are cold-natured anyway)
BamaCSX83 the only other option that I would know of would be to add some form of heater into the cooling system to be able to keep the water temp above freezing when shut down in extremely cold weather (kinda like what someone would do to their car or truck up north when it runs a risk of freezing).
the only other option that I would know of would be to add some form of heater into the cooling system to be able to keep the water temp above freezing when shut down in extremely cold weather (kinda like what someone would do to their car or truck up north when it runs a risk of freezing).
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
The use of antifreeze does not depend on whether an engine is 2 or 4-cycle. It depends on whether an engine is made of cast iron components or of fabricated steel components. EMD engines are in the latter category, and they happen to be 2-cycle. Therefore the 2-cycle aspect is associated with the antifreeze issue, but it is not a cause of it.
Engine made from fabricated components are more prone to leakage from internal seals that are less perfect that those in cast iron engine components. Such leakage can allow engine coolant to get into the crankcase oil. Antifreeze kills the lubricating ability of the engine oil, which can result in serious damage to the crank bearings.
Caterpillar diesels, for instance, are built with cast iron bodies, so they can be run with antifreeze without risk of internal leakage resulting in bearing failure. This gives them the advantage of being able to be shut down during idle times to save fuel during freezing weather. Whereas an engine with water instead of antifreeze needs to be drained if shut down during freezing weather.
When I was with the NSRR we left the locomotives idling when there was a freeze danger- none had antifreeze due to an EPA regulation. or so I was told.
Makes sense to me ... so how do you keep the water from freezing?
Dave
Lackawanna Route of the Phoebe Snow
Antifreeze and main bearings don't get along. Most EMD 2-cycles are a bit leaky. If a little water gets in the lube oil, it is not a big concern.
Mike WSOR engineer | HO scale since 1988 | Visit our club www.WCGandyDancers.com
My guess would be that the 2 stroke is not water cooled, but I'm only guessing.
Phoebe Vet. Antifreeze goes into a water based cooling system to keep the water from freezing.
Antifreeze goes into a water based cooling system to keep the water from freezing.
Thanks to Chris / CopCarSS for my avatar.
Brake Horsepower is the power the engine makes on the test stand. When you install it, add a transmission and accesories that drain power, it will be reduced.
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