Overmod Erik_Mag My original post was missing two very important words... 4,500hp GTEL consumption at full throttle was on the order of 450gph. I take it you mean that the idle sfc of the turbine is comparable to sfc of one of the various 4400hp prime movers in Run 8 reasonably fully loaded?
Erik_Mag
My original post was missing two very important words... 4,500hp GTEL consumption at full throttle was on the order of 450gph.
I take it you mean that the idle sfc of the turbine is comparable to sfc of one of the various 4400hp prime movers in Run 8 reasonably fully loaded?
More like just plain "fc" (fuel consumption) as opposed to specific fuel consumption. I'm very sure a modern 4,500hp combustion turbine would have a much lower sfc than the ~1949 vintage GT used in the Little Blows.
What I'd think would be an ideal Turbine locomotive is to use a turbine with reasonably good efficiency with a 50% turndown along with a battery capable of handling about 2 hours of the turbine's rated output. If the locomotive is going to spend an extended time running below 50% power, the turbine can be shut down. This would also allow for recovery of braking energy.
On a slightly different subject, did you see the reports of a "ducted injector" for diesel engines from Sandia? They're claiming that the ducted injector will lower particulates AND NOx. The inspiration was from the Bunsen burner, guessing that the duct promotes evaporating the fuel before significant combustion takes place so that the combustion process is more like a gasoline (spark ignited mixture) engine.
Another Steveo fan!
Who would have thought that on a railroad forum.
Erik_MagMy original post was missing two very important words... 4,500hp GTEL consumption at full throttle was on the order of 450gph.
I have to wonder whether in the age of AC synthesized drive from smoothed DC-Link, the general idea of the GTEL (running on the same gas-oil fuel used for practical high-speed diesels) might be resurrected using a variant of genset operation. Here the turbine would be paralleled with one (or more, if warranted) reasonably-sized piston-engine gensets (which themselves could be effectively shut down and restarted using their load-management software) which would provide the loading to run a given train at low speed or start it moving up to "Run 8 compatible" speed until the turbine could be spun up and preheated for emissions and brought on line. The pony engine in the GTELS was only about 800hp in my recollection, and only acted on a couple of the TMs for hostling. My version would have reasonable turndown and, presumably, corresponding idle and low-power fuel efficiency, but still allow a reasonable QSK or C175 engine to co-exist with the ceramic turbine in a reasonable carbody and frame length...
Overmod Erikem What impressed me was that the fuel consumption at idle for the 4,500HP GTEL's (~200 gal/hr) is about the same as a Tier III 4,500HP diesel. You're probably looking at efficiency at design horsepower -- where this is less surprising; the turbine would be most efficient there, and the benefits both of turndown or slower rpm operation of the piston engine would be minimized. When you're burning fuel with comparable efficiency to get heat release, expect comparable burn mass flow...
Erikem What impressed me was that the fuel consumption at idle for the 4,500HP GTEL's (~200 gal/hr) is about the same as a Tier III 4,500HP diesel.
You're probably looking at efficiency at design horsepower -- where this is less surprising; the turbine would be most efficient there, and the benefits both of turndown or slower rpm operation of the piston engine would be minimized. When you're burning fuel with comparable efficiency to get heat release, expect comparable burn mass flow...
My original post was missing two very important words...
4,500hp GTEL consumption at full throttle was on the order of 450gph.
Champlain DivisionJetTrain is, or was, a Diesel Turbine-Electric locomotive. Its ST-40 powerplant did not drive a transmission; it drove a generator/alternator.
That's correct. The stuff I was talking about is all gas-turbine-specific; the 'transmission' I was referring to didn't have to be hydrokinetic or mechanical (like the Turboliners). A contrast between the JetTrain and the ALPS locomotive alternative being engineered at UT was the form of transmission in the latter, which involved a very different design of alternator (using a principle designed for SDI) and forms of energy storage to facilitate high sustained speed at minimal fuel consumption. There's electric and then there's electric...
To an extent I was crippled by 'wishful thinking' -- the original brief for the train was more ALPS-like, like a full TGV with its gas turbine instead of catenary, and Bombardier made some expedient changes in what actually got built.
Also, I know it’s been a long time (close to 20 years ago), but I don’t remember it having a diesel genset for HEP service. IIRC, the turbine provided that too.
I don't remember that either -- it would be better common sense to take the HEP load off the turbine in any case for a variety of reasons, unless you want to use the GE-style hostling arrangement (a relatively small diesel engine -- relatively being as I recall about 800hp) to provide the lighting load at times the turbine would be command idle or on the turning gear. As I recall though the APU follies with the SPV-2000 were painfully memorable, so the idea of running all the ancillary systems from a dedicated separate genset with efficient turndown might not have been "preferred" in a pure high-speed design.
Tell more stories! You're ahead of the edge of history, which is not a common thing in railroading, and this whole page of the story is in danger of being lost or trivialized.
ErikemWhat impressed me was that the fuel consumption for the 4,500HP GTEL's (~200 gal/hr) is about the same as a Tier III 4,500HP diesel.
The JetTrain in happier days, in Montreal in 2003:
Greetings from Alberta
-an Articulate Malcontent
I was being conservative in guessing fuel consumption at idle, nice to know I guessed high instead of too low. One of the implications of low consumption at idle is that thermal efficiency of diesel engines won't take a big hit at low throttle positions as compared to combustion turbines.
What impressed me was that the fuel consumption for the 4,500HP GTEL's (~200 gal/hr) is about the same as a Tier III 4,500HP diesel. OTOH, the 4,500HP GTEL's were using ca 1950 technology, where a modern turbine would do much better.
erikem a 4,500HP diesel engine may use 5 to 10 gallons per hour at idle.
Actually, closer to 3 gph in low idle. But, your point is solid. Locomotives spend nearly half their time in idle.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
Overmod,
I was closely involved from an advocate point of view when JetTrain was testing and touring corresponding with several different Bombardier and TTC/DOT personnel.
A few technical points, if I may;
JetTrain is, or was, a Diesel Turbine-Electric locomotive. It’s ST-40 powerplant did not drive a transmission; it drove a generator/alternator. Also, I know it’s been a long time (close to 20 years ago), but I don’t remember it having a diesel genset for HEP service. Iirc, the turbine provided that too.
The TF40 is the engine used in the LCAC, rated at 4000HP each.
I assume that was the rating in the Jettrain car.
The Navy is buying upgraded versions with full electronoc control, called ETF-40B.
Peter
Don't know about the TPE331, but Jerry Pier sent me some info on rail applications for the TF40, which was a 4,000shp engine versus the ~1,000shp for the TPE331. The TF40 was also a dual spool design versus the single spool for the TPE331.
What would make most sense with a TPE331 design would be 3-4 of them in one carbody acting as a genset.
erikemhe advantage of the TPE331 was much quicker throttle response as the constant speed props kept the whole engine turning at constant speed along with lower fuel consumption at high power.
This is true, but the analogue for a train (a CVT of some kind) is not really practical even for TurboTrain tare weight. You may recall (if I recall correctly, it's in a Popular Mechanics article from 1966) that the PT6/ST6 was specifically chosen for being a free-turbine design providing immediate torque at low speed with the 'gasifier' turning at high rpm.
Most of the recent multispool designs (a couple of geared-fan engines are three-stage) involve driving a fan load for direct aerodynamic thrust; the provision of a 'switch-pitch' vane system (as in some torque converters in the '60s) would be difficult if not dangerous to implement in the power turbine of a lightweight-train style turboshaft engine. The same issue would probably apply to long-term effective clutching of the compressor turbine to the power turbine at speed, That's not a happy place for actuators, even those remoted via a sliding torquemeter shaft, to live...
Having said that -- weren't there proposed rail uses for the TPE331 'back in the day'? I can't find any on the Web, and I wouldn't dare defend them as an engineering solution (vs. an optimized free turbine) but for something like an original-style integral train or HPIT, might they might have been considered?
The PT6/ST6 design is often referred to as a "free turbine", and also referred to as a gasifier/power turbine combination. The competing Garrett TPE331 engine had a common turbine stage driving both the compressor and the output shaft. The advantage of the TPE331 was much quicker throttle response as the constant speed props kept the whole engine turning at constant speed along with lower fuel consumption at high power. OTOH, the PT6 has a reputation for being an extremely reliable engine and is easier to start as the starter doesn't have to turn the props.
Back around 2008-09, GE was making noises about their new large frame stationary simple cycle combustion turbine having a 46% thermal efficiency at 100% power and 40+% thermal efficiency at 50% power (i.e. 50% turndown). GE's J79 engine of B-58, F-104 and F-4 fame had movable compressor stator blades to improve efficiency a les than 100% power.
blue streak 1Point is the Jet train did not use a power plant for close to sea level operation. A turbo prop or the now proposed external fan jet ( essentiallly a turbo prop with many blades ) would have been the best for fuel consumption but still the idle fuel flow would have been too much.
The Bombardier JetTrain was like an evolutionary step backward from the ALPS locomotive toward the Amtrak turboliners -- it involves no more than a turboshaft engine driving a transmission. To my knowledge this involves the same general construction idea as the PT6/ST6 in the TurboTrain, where the traction turbine is free from the stages that drive the compressor and therefore can turn at any required speed while the compressor speed is optimized. There is no point for 'fan bypass' in these designs, as there is neither prop or reaction thrust; the only output that matters is torque via the power turbine shaft. This is not a design like the NYC jet RDC that might benefit in some way from high bypass or geared-fan engines.
The high "idle" fuel consumption is a consequence of the required power to run the compressor at required volumetric throughput and pressure to keep the combustors stable in firing. (That's a different way of looking at what erikem was calling 'turndown') How much of the resulting combustion gas goes through a power turbine is optional in this design, but any of it that isn't directly used will have to be wasted.
It is a lot more complicated than at first blush. First it is the aircraft design. Higher altitude means less air resistance so less power needed. There are aircraft that are actualy more efficient at lower altitudes. The A-300 is one and its most efficient trip altitude ( not fuel consumption ) is between 25,000 ft and 27,000 feet. It has a high lift wing that akes a lower altitude better. Since it flies at a lower altitude its true airspeed is much faster than at high altitudes. Total fuel cosumption is less for a trip.
Outside air temperature is the controlling factor. The speed of sound is dependent exclusively on air temperature. Most aircraft are designed to cruise at a defined fraction of the speed of sound (mach ) . Usually about Mach .80 although a large differences for biz jets. Standard temperature "usually" decreases 2C per thousand feet. Starting at sea level's 15C temp decreasing to about -50C above that temp remains same so less air resistance, Now that is just standards and know there are major variations espeially at the poles or equator.
Jet engines actuallly produce less thrust at higher altitudes but the aircraft differences more than make up. Each model is different of course but as a general rule fuel flow equals thrust . Better later designs have more thrust per pound of fuel flow.
Jet engines, turbo props, turbo shafts that just operate at close to sea level have different designs than a jet designed for high altitude service. GE's CF6-50s -80 s are major block cores for back up generators and many navy ships
Norm48327 Turbine engines do not fare well at low altitude when it comes to fuel consumption. The denser air at low altitude demands more fuel than it does in the rarified upper reaches of the flight levels. That should explain why long range flights strive to get as high as possible in the fupper flight levels. There is substantial fuel savings to be had at those altitudes.
Turbine engines do not fare well at low altitude when it comes to fuel consumption.
The denser air at low altitude demands more fuel than it does in the rarified upper reaches of the flight levels. That should explain why long range flights strive to get as high as possible in the fupper flight levels. There is substantial fuel savings to be had at those altitudes.
The issue with turbine powered airplanes fuel consumption at low altitudes is that turbine engines lose efficiency when "turned down" - i.e. they do their best running near max power. Most energy efficient flying speed is usually said to be 1.3 times stall speed - at 40,000' feet cruising speed isn't much past the 1.3 times stall speed at that altitude. 100% power at 40,000' feet is quite a bit lower that at sea level, so the engines are running close to flat out at cruise.
Issue with turbines in trains is similar, as the prime mover would be running considerably less then full power most of the time and thus at a lower efficiency. The 4,500HP UP GTEL of the 1950's used about 450 gallons per hour at full throttle and 200 gallon per hour at idle - a 4,500HP diesel engine may use 5 to 10 gallons per hour at idle.
- Erik
Jet engine performance limited by temprature.
Early turbojets used water injection on takeoff to reduce inlet temprature, also the cooler air is denser and when compressed provide a better fuel/air ratio providing more thrust generation.
Interesting question. One of the You Tube channels I subscribe to is a flight channel where the pilot flies a Daher TBM-850 turboprop with a Pratt & Whitney Canada PT-6 engine. If the flight is long enough he flies at around 30,000' depending on direction of the flight. This is for efficiency, cruising speed, and weather.
https://www.youtube.com/watch?v=MwNI8d2-V7s
Naturally aspirated piston engines lose power as you gain altitude, with a loss of 2-3% for every 1000 feet gained. Turbocharging or other forms of forced induction can reduce or even eliminate this derating.
Not sure how gas turbines react though.
Seems to be varying answers online, but here's one that matches what I thought was the reason behind it.
https://www.quora.com/Why-are-jet-engines-more-efficient-at-higher-altitude
Lots of stuff out there about air density though as well. I wonder if we have anyone here with a degree in aeronautical engineering that could shed some light now that I'm curious?
Perhaps lower air resistance in the thinner air too?
About 15 years ago this thing came out to Alberta for a promotional tour, pulling one Amfleet coach. At the time a study had just been completed which recommended upgrading the existing Canadian Pacific Edmonton-Calgary line to handle much higher speeds. The JetTrain would have allowed this without the initial expense of electrification, and would also have solved the clearance issues around overhead wires.
But nothing ever came of that proposal, and the prototype never returned to western Canada after that tour.
I was always under the impression that fuel efficency rises because of the lower air temperatures, not because of air density.
Thanks,M636C,
I did not know that about the turbine lease. Even though it’s carcass is rotting in the desert in CO, at least we know where it is.
Can anybody zero me in on where it might be on Google Earth or is it stored inside?
There are hazards that high off the ground where a sudden decompression of the plane could be instanty fatal to passengers and crew but they are taken into consideration before the flight.
I enjoy flying private and like flying below 15.000 ft. Oxygen is requieremt a that altitude but I did not find it a problem.
Norm
Frankly, there's nothing the Jet Train could do that a Charger can't do more efficiently.
Editor Emeritus, This Week at Amtrak
Champlain Division What I'd like to know at this late date is what happened to the JetTrain prototype? The last I heard is that it was languishing in storage at TTI in Colorado Springs.
What I'd like to know at this late date is what happened to the JetTrain prototype? The last I heard is that it was languishing in storage at TTI in Colorado Springs.
IIRC correctly ,Bombardier pinned much of it's hopes for production orders for the Jet Train on proposed Florida and Texas high speed rail projects that failed to be built.
The thought being that the high fuel consumption would be less of an economic deficit when compared to the cost of building and maintaining catenary..
"I Often Dream of Trains"-From the Album of the Same Name by Robyn Hitchcock
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