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?
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.
Antifreeze goes into a water based cooling system to keep the water from freezing.
I read in a book about locomotives, that you couldn’t use antifreeze in a 2-stroke diesel, but you could in a 4-stroke. I wondered why the difference?
My guess would be that the 2 stroke is not water cooled, but I’m only guessing.
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.
Makes sense to me … so how do you keep the water from freezing?
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.
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 durin
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 system you are talking about exists and seems to be gaining acceptance in the industry. It uses an Auxiliary power unit which can deliver both heat and power to a shut down locomotive(not to be confused with “smartstart” type systems that turn the engine on and off when a certain temperture is reached and are also becoming common). There are also retrofits available that allow a locomotive to use auxiliary steam from a shop boiler to keep the coolant warm…
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)
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.
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“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.)
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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 facto
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.
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 locomotive
We only have a rough idea how much rail horsepower a “3000 hp” diesel locomotive is supposed to produce, and we have a much rougher idea how much it actually produces-- but it’s a safe bet it won’t be 3000.
If the engineer notches out to Run 8 with the locomotive still stationary, the prime mover may reach maximum speed but the brake horsepower will be nowhere near maximum. The main alternator/generator just won’t be that hard to turn, when stationary traction motors are connected to it.
Train comes apart with at least a broken knuckle.
Rodney
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
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 rat