What should be a factor that make diesel engines designed for locomotives differ from any other engines? I can only think about the overall width that fit under the hood. Somebody help please.
Karn[:)]
Thanks a lot M.W. Hemphill!!!
Is weight actually a positive or negative factor of a locomotive??? I have heard that the more the loco weigh, the higher the tractive force a loco use to pull the load. An electric loco does not have diesel engine(s), and big, heavy fuel tank, how do they get the weight from?
Karn[:)]
For one thing, there’s easily such a thing as too MUCH weight for a given locomotive. That’s true both in absolute terms and, perhaps more importantly, in terms of excessive weight on one or more axles due to the placement of the engine or its weight distribution inside the locomotive.
A consideration here is the weight rating of bridges, which can limit the number of locomotives permissible in a single consist, for example, even if the standard track design can tolerate high axle weight.
In almost all respects other than tractive effort, weight (and inertial mass) become drawbacks for locomotive operation. Lateral and curve-entry flange forces increase. Shock force into the track, and on low spots and other defects, increases. Springing has to be heavier, which causes implicit shock to traction motors, etc. to be greater.
Most slow-speed engine designs tend to be rather tall, too, which puts much of the required mass up high in the carbody. This causes all sorts of problem with roll, riding quality, etc.; it’s usually not possible to drop the engine down in the carbody because the trucks and fuel tanks are best provided under the frame, and that leaves no room for a crankcase, flywheel, etc.
Electric locomotives usually carry ballast to make up their relative lack of adhesion weight – the GG1, for example, had a ballasted deck of 4 inches of concrete.
When you hear people say that early diesel motors were ‘too heavy for locomotives’, they really mean it. The output of these motors was relatively small for their very substantial mass; it doesn’t make sense to use a substantial part of your efficient-range output just to move the locomotive!
One other factor that makes railroad diesel engines different from marine and standby power supplies - altho I don’t know if it is significant - is that the first two tend to run at max RPM’s constantly vs. a RR diesel running at Run 8 one minute and Run 1 the next and then in idle as you are going down a hill and using dynamics.
Excellent posts by Bro. Hemphill…worth noting is the marine application of railroad-sized diesel engines.
EMD is still the most common prime mover in tugboats, oil field work boats, inland river towboats and certain larger marine applications involving diesel-electric drive. So is Caterpillar.
GE, which has been in the diesel engine business for a while, is almost a non-player in the marine engine business. Even tho the company has attempted to make inroads, it’s been thwarted by many factors and one of the few GE converts, Crescent Towing in New Orleans, is reengining GE’s with something else…Cats, I think.
Kind of funny that EMD and Caterpillar are such major players in the marine world and GE is not. Yet in the rail world, it’s GE and EMD, with Caterpillar never really able to make much noise in mainline railway applications.
Alco, btw, is still alive and well in the marine world, with the US Coast Guard and CSX-owned American Commercial Barge Lines being the biggest users of the Alco 251 engine.
Another great reference for marine diesel news is http://www.marcon.com
Their quarterly tugboat market report is a great source of marine propulsion news.
Aren’t the diesels on tugs the primary form of power on the propellor transmission? Seems to me the constancy of load would be different; the difference being that a railroad diesel engine turns a generator, while a marine diesel actually turns the propellor of the boat.
Erik
One thing that I have seen in my experience is that marine application engines are always rated the highest horsepower for any given engine.
In marine engines, annual overhaul of the cooling system is a must; marine engines live and die by the cooling system.
Stationary application engines are always the lowest in power for a given engine, with standby type engines being the lowest. Standby engines can sit for weeks and months and suddenly be expected to instantly go to full power and rpm. Stationary engines that are constant duty run for long periods of time and run into problems with varnishing of cylinder walls, and buildup of deposites in the lubrication passages; this can also happen from excessive idling. In addition to being lowest rated power, stationary engines also have different injectors or injectors with different timing/ output, and different cam timing. The biggest difference between stationary and other types is main bearings have the largest oil clearences, meaning the shells are thinner or possibly that the crank journals are slightly smaller, this is especially true for standby engines. Cylinder varnishing can also mean different specs for the rings.
Stationary engines typically show a lot of wear for relatively few hours of service, especially standby engines where bearings can show scoring and patterns indicative of lack of lubrication.
One thing I do not know about locomotive engines is the arrangement of thrust bearings. Locomotive engines sit pretty level and flat, so I imagine they should have thrust bearings facing foreward and aft. It seems mobile engines always have a slight rise from back to front and so the thrust bearing is at the rear of the crankshaft after the last main journal. It is typical for engines that have thrust in both directions to have the thrust bearings located on either side of the center main journal.
One thing for sure is that you can look at two engines, the same make and model, and the
Interesting post re: mechanical differences in various large diesel engines. Not being a propulsion engineer, I would only guess that there’s not a great deal of difference between, say an Alco 251 in a “Reliance” class Coast Guard cutter and 251 in a diesel locomotive, or an EMD 645 in a tugboat and the same engine in an SD45. The used equipment market is chock full of such engines listed as “rto’s”–running-take-outs–and various published reports I’ve read indicate that power swaps from water to rails, and vice-versa are not uncommon.
Ditto “standby power” or “diesel peakers.” There’s an Alco S-1 near me that runs very nicely with a meticulous Alco 539 inside that began life as standby power plant at Disneyland. Someone familiar with that particular 539 told me the original owners were notorious for regularly running the engine several times weekly for the reasons stated in the post above.
I do know that the 645 turbo’s have to be shock resistant for marine applications. The last turbo prices I saw at the UP were about $65,000 new from EMD. A marine turbo was $140,000. Don’t ask me why. I donthave a clue.
I guess it’s my fault, I should have made it clear when I said in my experience that that is with high speed engines from Cummins, Detroit, and Caterpillar, for which I know these differences exist.
The last thing I would want to do is mislead, and for that I apologize.
I’ve tried to find out information on marine-turbo shock absorption, but haven’t succeeded; I’m waiting for responses from the boatnerd community.
Marine engines are rigidly bedded in boats that are generally of high mass. When these come in contact with docks or other obstacles, the shock would be communicated through to the sensitive turbo bearings. There is no way to predict what direction the shock would ‘come from’, either (whereas I think in locomotives the principal source of shock would be slack run-in, essentially axial to the turbo and hence accommodated by a stronger thrust bearing…)
I don’t think better ‘thrust bearings’ would fix the situation on a boat engine. Turbo bearings IIRC are generally hydrodynamic bearings (no balls; a machined floating center member between polished shaft journal and outer ‘race’); you can’t use a resilient bearing surface as in steam turbines because the shaft in a turbo is comparatively short, so you’re looking at a larger bearing surface, higher pressure in the bearings, etc.
I do look forward to hearing expert opinions.
It seems that between marine, stationary, and locomotive diesels, the loco diesels dont operate in a narrow power band, dont have an engineering crew watching every second, and dont have the benefit of just sitting calmly on a concrete pad. In my opinion this makes locomotive diesel engines one bad mother…ALCO, yeah ALCO.
By the way, im going through diesel withdraw, as dad is borrowing mine to go upstate with a camper and some friends, so keep the diesel stuff coming, or “Cummin”. Ha ha, ok cheap shot. Hey i try.
Adrianspeeder
PS: I think Rudy Diesel would be proud.
Great thread guys! I’ve learned more in the past 10 minutes than any ten minutes since… anyway.
For a bit of history, Marks point 3 in his first post on this thread is important: maintenance. There were two engines use in early rail diesels which disappeared very rapidly: the Beardmore, which was used in an early diesel for CN, and the Fairbanks-Morse, an excellent opposed-piston engine. Both of these, if memory serves, were originally used on submarines, where space is a problem (to put it mildly) and were very good reliable medium speed engines. On submarines. The problem was, they required tender loving care all the time from highly experienced mechanics (we called them ‘tiffies’ – Engine Room Artificers’). Transported into railroad locomotives, they just couldn’t get the care they needed, with predictable results.
Many of the very large marine diesels (low speed) such as are made by MAN etc. can really be thought of as a group of so and so many individual engines (single cylinder/piston/connecting rod/injector) sharing a crank, and will run quite happily with one or more cylinders out of service, provided the crank isn’t damaged. Nice if you’re a thousand miles from land… also, many very large marine diesels with reduction gear drive are engine-reversing: to go ahead, you start the engine in the ahead direction; to go astern, you stop the main engine and restart it in the astern direction. They run in either direction equally happily. Needless to say, this takes time… large ships are even harder to stop than trains!
I would imagine that relatively low power (!) applications for marine use the propellor thrust can be taken quite nicely in the engine; but keeping in mind that the thrust from the shaft can be either forward or reverse; engine slant has little impact. In any large direct drive (through reduction gears) application, the thrust (both ways) is taken by bearings in the reduction gear.
Of some interest to this discussion might be the tugboat “Lauren Foss” operated by Foss Maritime here on the west coast, primarily engaged in the sea-towing of retired naval vessels. She flies the flag of the west’s premier tugboat operator, but her story (and her Alco innards) make for good reading.
See Marcon’s report from a year ago.
http://www.marcon.com/marcon2c.cfm?SectionGroupsID=35&PageID=153
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Then, check out this page: the World’s Largest Diesel Engine, which puts out 108,920 hp at maximum speed – 102 rpm! Makes an EMD look kinda’ small.
http://www.bath.ac.uk/~ccsshb/12cyl/
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YEAH MARK !!! [:D] NOW THATS MY KINDA ENGINE!!! OHH OHH OHH !!![bow][bow][bow][bow][bow][bow][bow][bow]
I don’t think better ‘thrust bearings’ would fix the situation on a boat engine. Turbo bearings IIRC are generally hydrodynamic bearings (no balls; a machined floating center member between polished shaft journal and outer ‘race’); you can’t use a resilient bearing surface as in steam turbines because the shaft in a turbo is comparatively short, so you’re looking at a larger bearing surface, higher pressure in the bearings, etc.
I do look forward to hearing expert opinions.
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What I have read is that a floating bearing is used in turbos to reduce the relative speeds between the surfaces - the floating bushing turns at an intermediate speed.
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Originally posted by M.W. Hemphill
Jamie: According to the marine engineering websites I’ve read, attempts to take up the thrust with the reduction gears will result in the fatal destruction of the reduction gears.
This is true, and is why the thrust generated by a ship’s props are isolated from the plant by large thrust bearings. I have an old navy training manual “Principals of Naval Engineering” that explains the use of a Kingsbury or segmented pivoted shoe thrust bearing. I wish I knew how to post the illustrations. According to the book, this is the most common type of bearing used in modern ships.
From what I have read and seen in actual experience aboard ships is that the area of the hull that supports the reduction gears is the most deeply honycombed and rigid part of the ship.
Imagine a long rod thrown through the air flexing along its length “whiffle, whiffle, whiffle”, that’s exactly what a ship does! This oscillation can vary from a gentle shimmying to violent shaking in almost any plane and even tortionally along the length of the hull. It’s totaly common to see some feature of the ship rocking forcefully in some sea, and the next day perfectly calm while something else is affected.
Props really vibrate! when a prop is cavitating from a major change in speed or direction, which is common in naval ships, stuff on the fantail will literally dance around on the deck! accompanied by a loud roar, the ship vibrates like an earthquake. These are things that I experienced while on a 980 ft., 180,000 ton AOE, which is a pretty large ship.
All of the stuff on the site about warships is right on, vibrations and all.
Marine engines have watercooled exhaust manifilds, which are pretty heavy compared to a regular exhaust manifold, but I do not think that type of manifold would be used if the exhaust were to go out a vertical stack.
Oh, reading the page on the world’s biggest engine reminded me of the reason medium and slow speed engines are so tall, the crossheads! According to the article, the crossheads are for isolating torque, which is partially true. Another reason for using the crosshead design is to acheive an “ultra long stroke”.
The length of a rod in comparison to the radius of a crank’s throw is called rod ratio. I have noticed that steam locomotives all have a very long rod ratio, and have been curious why. Anway, rod ratios in IC engines are far shorter, but diesel engines almost always have rod ratios longer than gas engines. I suspect that it is because a long rod ratio is of greater benefit to a constant pressure cycle, and a short rod ratio is better for a constant volume cycle.
What’s the big deal? Rod ratio affects the acceleration-decelaration curve of a piston, and the curve determining the mechanical advantage based on the angle between a crank and a connecting rod.
A con rod swings outside of a crank’s radius in the upper 180 deg. of a crank’s rotation, and swings on the inside a crank’s radius on the lower 180 deg. of rotation. This causes the piston’s accelaration-decelaration in the upper 180 deg. of crank rotation to have a much steeper, v-shaped curve, and the same curve for the lower 180 deg. to have a much more circular curve.
In other words, a piston moves farther for fewer degrees of crank movement in the upper 180 deg. of crank rotation. Acording to the math involved in determining the shape of these curves for a given rod ratio, as a rod’s length approaches infinity, the difference between the curves for upper and lower crank movement approaches zero, and as a rod’s length becomes shorter, a maximum in difference is reached.
The point of maximum mechanical advantage between a crank and a rod is achieved when there is a ninety deg. angle between the crank and the rod. In most engines, this happens around 67 deg. B/ATDC, but varies wit
Well, first I messed up the order of the paragraphes when I came back from a break and I’m not sure how to fix it without retyping the whole thing, I see my edit came after your first read, sorry.
The reason I brought it up was overmod said earlier that marine engines are tall, and the web site for the worlds largest engine showes an engine with a crosshead design, which is common for marine engines and is the reason that they are “tall”. The article gives a reason for using the crosshead design, but in the past I have read that another reason is to have an extremely long or “ultra long stroke”, so to help somebody understand why does there need to be such a long stroke, I decided it would be helpfull to explain rod ratio.
I guess it ended up being pretty long winded.
Sorry.