erikemAirliners typically shut their engines down when arriving at the gate and I don't recall seeing any jet engines equipped with turning gears
I don't have my gas-turbine reference at hand to give you specifics, but there ARE spin-down parameters for aircraft turbines, if for no other reason than heat soak in the bearing lube.
Yes, most of these turbines are very, very short compared to the ones used in the GE locomotives, and use better modern alloys and fabrication techniques, too. If I remember correctly the wheel section of the PT6 is only two stages in the power turbine. Helped to split the compressor turbine into sections,, too...
Will give better detail when I can.
RME
If it is important to idle a turbine at lower fuel flow, that could be built into the design.
For example, one could use an electric motor to turn the turbine at a slower rate than a self-sustaining idle on turbine power, and one could have some kind of pilot light in the combustion cans to keep the turbine at some desired temperature.
I had read in an Aviation Week article many years back on the French Turboliners used by Amtrak that they would put the turbine in one power car at idle and use the second power car turbine to run to train at cruise speed -- that was said to save fuel over running both turbines at part load. Maybe Jerry could weigh in, but maybe that turbine design had such a low-fuel idle setting .
If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
Paul MilenkovicFor example, one could use an electric motor to turn the turbine at a slower rate than a self-sustaining idle on turbine power ...
That is exactly what the turning gear does (NOTE: it's 'gear' in the sense of apparatus, not 'gears' in the sense of things with teeth on them, although the turning on steam turbines is usually done with gears). For shaft sag the required turnover speed is really quite slow, IIRC on the order of 2-3 rpm for the early series (someone look at the reference books and insert the correct value here -- it is in there, I just don't remember it)
... and one could have some kind of pilot light in the combustion cans to keep the turbine at some desired temperature
With the turning gear, there's no need for that -- and a good thing, too, because if your compressor isn't turning there is nothing blowing the fire through the cans anyway...
You shut the turbine off when not using it, following the automated shutdown sequence (described in a couple of references, including iianm Classic Trains a few years ago) and then put it on the turning gear. Doesn't matter if it gets cold -- the automated STARTUP sequence (which I remember as being a bit longer than 90 seconds to develop working power state, but again it's in the references) is spec'd for cold start anyway. Remember to purge your fuel lines any time you shut the turbine down, even for a short period!
Better check the fuel consumption on an idling turbine. Compressor and all, ifuel consumption will be relatively high even at 'low power' because you'll have to maintain necessary rpm with the compression loss scaled to rpm. In a different context, a bit like "saving" fuel by "idling" a diesel that can't be slowed because it's running inline HEP...
Having the prime mover shut down going down hills sounds like a major train handling headache to me. I run in undualating territory, where you change from power to drifting/braking very frequently. I can't imagine a system which could crank the engine and have power available in anywhere near as quick as typical train handling demands. Might work on some of those super long grades out west if you overcome the cooling fan and air compressor problems.
Just ask a engineer that uses a multi-engine Genset locomotive how quickly it loads up to full power when full power is required, as each additional prime mover has to fire and then come up to power in sequence.rfpjohnHaving the prime mover shut down going down hills sounds like a major train handling headache to me. I run in undualating territory, where you change from power to drifting/braking very frequently. I can't imagine a system which could crank the engine and have power available in anywhere near as quick as typical train handling demands. Might work on some of those super long grades out west if you overcome the cooling fan and air compressor problems.
rfpjohnHaving the prime mover shut down going down hills sounds like a major train handling headache to me. I run in undualating territory, where you change from power to drifting/braking very frequently. I can't imagine a system which could crank the engine and have power available in anywhere near as quick as typical train handling demands. Might work on some of those super long grades out west if you overcome the cooling fan and air compressor problems.
Never too old to have a happy childhood!
BaltACDJust ask a engineer that uses a multi-engine Genset locomotive how quickly it loads up to full power when full power is required, as each additional prime mover has to fire and then come up to power in sequence.
Yeah, but any proper Genset consist will either be GPS-aware of the track profile, much as DPU units can be, and bring modules on line, stabilize them, and load them down well in time to suit the track profile.
Barring that -- a sensible engineer would know how long the 'latency' of his additional engines would be, and just pre-actuate them, no different in principle from how you modulate the brakes to keep the train slack right when running over undulating road...
Andof course, if it's *that* much of an issue, no one said the engines of a hybrid consist HAVE to be shut down when idling -- even the EPA regs on idling only involve the situation when trucks are not moving. While I don't recommend it for diesels, you could implement alternate-cylinder firing to keep the engines spun up and cylinders hot on minimum fuel; this would produce loading within about 20 revolutions of resumption of fueling...
Meanwhile: How many gensets in a given CONSIST need to be running to provide power for dynamic braking on all axles in that consist? Bet it's not many...
Overmod BaltACDJust ask a engineer that uses a multi-engine Genset locomotive how quickly it loads up to full power when full power is required, as each additional prime mover has to fire and then come up to power in sequence. Yeah, but any proper Genset consist will either be GPS-aware of the track profile, much as DPU units can be, and bring modules on line, stabilize them, and load them down well in time to suit the track profile. Barring that -- a sensible engineer would know how long the 'latency' of his additional engines would be, and just pre-actuate them, no different in principle from how you modulate the brakes to keep the train slack right when running over undulating road... Andof course, if it's *that* much of an issue, no one said the engines of a hybrid consist HAVE to be shut down when idling -- even the EPA regs on idling only involve the situation when trucks are not moving. While I don't recommend it for diesels, you could implement alternate-cylinder firing to keep the engines spun up and cylinders hot on minimum fuel; this would produce loading within about 20 revolutions of resumption of fueling... Meanwhile: How many gensets in a given CONSIST need to be running to provide power for dynamic braking on all axles in that consist? Bet it's not many...
Railroads are not operating on Popular Mechanics what it will be like in the future with GPS track profiles, while some elementry aspects of such technology are being 'played' with in a testing enviornment there is nothing in 'production'. Present day Genset's fire up power on load demand - not enough load the additional engines don't fire up. This is one reason why Gensets are not being used for line of road movements. The I am aware of, Gensets, at least on my carrier are not equipped for dynamic braking.
The starting and stopping of prime movers in railroad locomotives is not the simple act of turning the key to start your Chevy or Honda.
BaltACDThe starting and stopping of prime movers in railroad locomotives is not the simple act of turning the key to start your Chevy or Honda.
We are discussing genset engines. These are no more involved than large truck engines ... or someone very stupid has done the systems integration. Even the large 'railroad' style Caterpillar 20-cylinder engines should fall in this category. True, it is not 'turn the key like a car' -- but then, neither are most diesel cars...
I assure you that GPS add-ons to PTC are well in hand, and will interface with all the various kinds of hybrid and modular-power locomotives now being developed. This is most certainly not Popular Science grade engineering or development. (Whether or not the equipment is 'currently in production' is of minor importance to future PTC implementation as I expect a number of aspects of that system to change within the next year or so)
Balt. Assistant chief dispr, "turning the key to start..." is the solution, and am I risking losing a patent (?) to the problem.
Suppose you're descending from the eastbound side of the Martinez bridge, or at Andesite in the shadow of Mt Shasta or crossing the river at Benson, Az.
What works, practical, legit, but not in the rulebook or train-handling guide, is to slam the db-control-lever to Off, slam the throttle to maximum power, stretching the train while the downgrade is shoving the mass towards the point (node) where the forces change.
It works, and it can't be a secret.
Turning the key to start would make this kind of train-handling work with gen-set's of all flavors.
Key start (soft-ware) to have the gen-sets on the line, ready....prior to needing them....is that an impossible....
I have enough trouble trying to figure out if and when the big GEs are going to bestow some power when I open the throttle coming out of a dip! At one time, back in the early 80's some RF&P loco's had some sort of selector system with which the engineer could isolate trailing units. I believe it was on our GP40-2's (141-147). It seemed like a pretty good idea, except that the GP35's which frequently trailed had a bad habit of not loading after being put back on line. I know things have advanced tremendously, (too far for my taste) but I seriously doubt that a unit that shuts down on descending grades could be made responsive enough to meet the demands of real world train handling. As for GPS feed, we now have GE's trip optimizer which has some whiz-bang technology to run our trains absent brains. At best it gives a vanilla performance. Letting it go through it's fumbling attempt to get down the road makes my skin crawl. I know it's the future, but I find it near impossible to swallow! I guess I'm getting too old and grouchy, or perhaps I take too much personal pride in my job. OK that rant took me way off course.
efftenxrfe Balt. Assistant chief dispr, "turning the key to start..." is the solution, and am I risking losing a patent (?) to the problem. Suppose you're descending from the eastbound side of the Martinez bridge, or at Andesite in the shadow of Mt Shasta or crossing the river at Benson, Az. What works, practical, legit, but not in the rulebook or train-handling guide, is to slam the db-control-lever to Off, slam the throttle to maximum power, stretching the train while the downgrade is shoving the mass towards the point (node) where the forces change. It works, and it can't be a secret. Turning the key to start would make this kind of train-handling work with gen-set's of all flavors. Key start (soft-ware) to have the gen-sets on the line, ready....prior to needing them....is that an impossible....
Present GenSets are for yard use - not road use.
Engineers I have discussed them with report they have no 'direct' control of the secondary gensets, they are started and stopped based on load the locomotive is pulling at any point in time. It is next to impossible to 'kick' a car in switching, the time and distance it takes load the locomotive up to 'kicking speed' with a cut of cars makes this a ineffective swtiching technique. When the throttle is closed, the secondary genset go off line and shut down as there is not 'demand' for their additional power, when the throttle is notched up and the load meter rises the gensets come back on line as necessary. Engineers normally consider GE products to be slow to load - GE's are cheeta's in comparison to gensets.
As a result of this performance, gensets are not used for general yard switching, for the most part they are being utilized for industrial switching in and around customer facilities - locations where cars are normally not 'switched' but are shoved to precise spoting locations and/or couplings - with and without air.
Personally, I view genset development to be at the stage of the EMD FT demonstrators, ie barely scratching the surface of the technology. Time, money and effort should improve their performance.
That's a good question that energy-conscience people might ask. It could work (with the right battery technology) for short trains on level ground where there are frequent stops (such as commuter trains) when the dynamic brake energy of each stop could be stored in batteries within the locomotive then delivered to the traction motors upon start-up. However, with 6,000 ton trains descending long grades the dynamic brake energy storage would require a large warehouse full of batteries, and then some. Equipping locomotives this way would limit their use to such trains and severely limit flexibility with the power pool.
In addition, frequent starting and shutting down of large diesel engines creates other issues that are not easily addressed. Diesel engines use considerably less fuel at idle than similar sized gasoline engines so the fuel savings would be so marginal as to be off the radar. Thermal stresses caused by shutting down an engine of this size just after climbing a grade, cresting a hill, then shutting it off on the other side would pretty dramatically shorten their lives if not cause outright failure.
Electrification is the only way to recover a useable quantity of energy from traction motors. Power can be put back in the grid or used to help lift an opposing train climbing the hill, but the cost of that is nothing short of enormous... then there is the ongoing maintenance of catenary. The mountain railroads that used electricification abandoned it many years ago.
Dennis
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Overmod Jerry PierA gas turbine can be shut downwithout consequence and full power can be attained in 90 seconds on restart. OH would UP disagree with you there! If you don't have turning gear and USE IT, shaft sag will turn your pretty turbine into a mass of expensive scrap in a comparatively short time -- and as I recall UP found this out by experience. Thermal cycling of the burners and cans, and clearances inside the engine, will not benefit from random startup and shutdown, even if you follow the 'recommended' autostart procedure. (Not to mention what happens if you're using heavy oil and the lines to the turbine were'nt properly purged with diesel at shutdown, and things have cooled off a bit...)
Jerry PierA gas turbine can be shut downwithout consequence and full power can be attained in 90 seconds on restart.
OH would UP disagree with you there!
If you don't have turning gear and USE IT, shaft sag will turn your pretty turbine into a mass of expensive scrap in a comparatively short time -- and as I recall UP found this out by experience.
Thermal cycling of the burners and cans, and clearances inside the engine, will not benefit from random startup and shutdown, even if you follow the 'recommended' autostart procedure. (Not to mention what happens if you're using heavy oil and the lines to the turbine were'nt properly purged with diesel at shutdown, and things have cooled off a bit...)
AGREED! Gas turbines (I run 6,000hp units regularly) would suffer from thermal shock and "rotor bow" (you called it "shaft sag") which is VERY hard on bearing structure. Also starting an essentially cold gas turbine and going to anywhere near full power in 90 seconds would render it useless in a short period of time.
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