Among other things, it describes the technical advances in gas turbine technology that, in the author’s view, make their use in locomotives possible.
I know far too little about turbines to evaluate the article, but I see no advantages for the turbine in terms of exhaust emissions, including CO2, when using LNG and CNG from fracking.
Given the careless handling of methane slip at many wells and further methane slip during processing and transport, the CO2 equivalent advantage of LNG over diesel is negated.
The situation is different for climate-neutral fuels such as methanol. But it seems to me that it makes more sense to convert existing diesel engines to dual fuel for diesel and methanol or hydrogen or ammonia, etc. than to convert locomotives to gas turbines.
Wabtec and Progress Rail do not yet offer this, but examples from the shipping industry show that it is possible. Manufacturers such as MAN and Wartsilä offer new dual-fuel engines as well as conversion kits for existing engines.
Regards, Volker
The problem with gas turbines is that their efficiency drops dramatically with decreasing load - GE was rightfully proud in getting one of their industrial/powergen turbines to maintain a 40% thermal efficiency at 50% turndown. Going to a hybrid approach where a locomotive can run the gas turbine at full output providing propulsion power and power for battery charging would bge one way of getting around that limitation.
With respect to emissions, there is potential benefit in reducing NOx.
The article mainly deals with the improvements that are intended to remedy the shortcoming you describe.
I have my doubts about nitrogen oxides. I think the combustion temperatures are higher in gas turbines than in diesel engines. This means that nitrogen oxides are higher and particulate matter is lower in turbines than in diesel engines.
Regards, Volker
Harry Valentine was a regular on steam_tech before Yahoo Groups imploded. The last thing I remember him working on was the idea of small reactors providing process heat for local and canal shipping, using modern fireless-cooker heat storage. We had extensive correspondence on turbines (both steam and combined-cycle).
Modern turbines will be ceramic and cermet construction, likely with magnetic bearings, and in theory can have a service life of many thousands of hours even in comparatively high-vibration environments. Against this, they must be kept turning while hot, and have to be carefully packaged against various types of expected railroad shock (the likely-to-be-sabotage-on-some-level accident with the N&W TE1 being a graphic example).
They don’t make any better sense than oil engines if frequent or irregular ‘high turndown’ or selective deactivation is involved. As noted, you run them at a reasonable baseline, diverting the developed power to other purposes as needed, and do likewise with the bottoming recovery (whether as electricity or something else).
As noted, turbines make very little sense in a zero-carbon (rather than zero-net-carbon) economy. Probably the best of a bad lot would be as an alternative to fuel cells using blue hydrogen with sequestration (from natural gas) – but that’s not particularly cost-effective, as all carrier hydrogen is not. You need onboard hybrid traction battery and/or (ideally) at least punctuate catenary or third rail to allow best operation.
This amusingly is coming around to the passenger locomotive I was advocating in the early Seventies, which was 8 to 12 modular turboalternators in an E-unit carbody. This came after reading about the Essl locomotive in Trains and the Fell locomotive in the Encyclopedia of World Railway Locomotives – enough units would be running to keep the others on turning gear. (Strangely or not, by the time of the ALPS development, no one adopted that approach… we got the Jet Train and the aborted final rebuilds of Turboliners instead…)
Be interesting to see what someone will make out of the idea.
Reading the article reminded me of reading about Pratt & Whitney’s Variable Discharge Turbine proposal for the Wasp Major.
There is some interesting work on high entropy alloys, with some alloys showing brittle fracture at ~1100ºC. OTOH, I would guess that it would be at least 5 years before any of these show up in gas turbines.
My understanding is that peak combustion temperatures in gas turbines are lower than diesel engines, so that should mean lower NOx production. 2700ºF is the temperature where NOx production rapidly increases.
The key is that the same thermodynamics that apply to steam-turbine-electrics would apply to a ‘nuclear-electric’ cycle, which is why transporting the microreactor system by rail doesn’t show the microreactor in the locomotive.
A functional 50 MW plant would need external condensation, sufficient at least to dissipate residual exhaust heat from the secondary circulation down to the point of practical Holcroft-Anderson recompression. That’s going to be far too bulky for a practical ~8800hp locomotive, even if greywater-spray assisted. The practical heat-transfer surface needs to be enormous to get condensation of the steam mass flow in the required time, and effectiveness in potential high-temperature air drops dramatically (see the history of the GE Steamotive turbines, which used much higher-quality steam than a microreactor without external superheat (as for the original Indian Point I plant, and did not operate well on UP but did better on GN).
Get past that and we can take up the potential security and safety issues, including crash-resistant containment…
You can minimize the safety and security issues by locating the reactor in a fixed plant and stringing cantenary over the tracks. It might even help even out the load issue, too.
That’s an extension of the French model for ‘nuclear trains’ and a reasonable one, although I think it would be less likely to see a dedicated microreactor plant used for transportation than for, say, a large AI or crypto-mining facility. The most important thing is not to transport the nuclear heat source on a vehicle…
I would start with a NERVA (nuclear rocket engine) core and use a closed cycle gas turbine which would allow for a higher reject heat temperature. There have been major strides in metallurgy since the 1950’s.
Having said that, the French model makes a lot more sense. Similarly, burning natural gas in CCGT’s and electrified railroads has some advantage over nat gas fueled gas turbine locomotives.
Every heat engine has its “sweet spot” of maximum efficiency. A combustion turbine’s sweet spot should be more efficient than that of a diesel especially given the size difference vs power output. What I would like to see is a hybrid with the turbine-generator ramping up to its sweet spot and charging a large bank of batteries which then in turn feed the inverters and then the TMs. When the batteries are fully charged the turbine shuts down. When the batteries run low the turbine spools up and recharges them. Ergo the turbine runs at max efficiency only and train speed is dictated by battery draw.
What you’d rather have is each turbine running between peak efficiency and ‘idle’ with just enough fuel to keep the combustion-gas path hot and corresponding shaft speed achieved by motoring to give the effect of turning gear. Actually shutting a turbine down and then presumably starting it up again is likely to be false economy in a number of significant respects.
I had wondered if idling or shutdown would be more efficient. I would think it depends on how long it is between battery chargings. I’m two decades removed from my power plant days and my experience with gas turbines was tangential. A rail application should be significantly smaller than a stationary power plant and could be insulated to retain heat.
My understanding is that it is the other way around, diesel engines are generally more efficient than combustion turbines. I’ve seen reports of greater than 50% efficiency for diesel engines compared to mid to high 40’s for simple cycle combustion turbines. The intermittent nature of combustion in a piston engine allows for higher peak temperatures than is possible in a combustion turbine.
For fuel, shutdown is wildly more ‘efficient’ – idling a Braylon-cycle turbine requires the enormous compressor load be maintained to accommodate stable idle speed even with no turboshaft torque output. On the other hand, some form of turning gear has to be provided while the blading and shafts are hot, and there can be fretting and other damage to the bearings if there’s shock and vibration while the shaft is not suspended by lube film.
What I suggest is ‘motoring’ the engine like an amplified version of turning gear, with enough compressor flow that combustion adequate to keep the hot section hot (but not enough combustion flow to keep the engine idling under its own power) takes place before the engine is expected to spool up to make power. This is also fast enough to preserve tribology and fluid cooling
How efficient were the variously fueled rail turbines compared to diesel in past? My impression was they were not very efficient and required a lot more maintenance.
From what I’ve read, they weren’t as efficient as diesels, especially with varying loads and RPM’s, the turbines were most efficient at a high speed, for long durations
Where the turbines were attractive was in that they could run on “Bunker C” fuel, which was very inexpensive.
As technology advanced, it was possible to crack bunker C, and use it in more ways, increasing it’s value, as it’s price increased, it’s cost effectiveness declined, and it was no longer cost effective enough to offset its inefficiency and other factors
A medium size, medium speed diesel in locomotive service typically runs in the 40% efficiency range but this engine endures the full notch 1-8 spectrum. A quick look at simple combustion turbines shows peak efficiency in the same range. The advantage of the turbine in my proposal is the lighter weight, smaller size would make more room for batteries. In locomotives space is always at a premium.
Back last century when I was but a young nuke I wondered out loud why our (steam) turbine/generator set didn’t have roller bearings. It was explained that the service and application did not justify them. So, now I’m wondering about roller bearings on a combustion turbine/generator set. This application would be significantly smaller than anything in a power plant.
Something to remember is that before the advent of 2400hp six-motor units, ‘units’ such as GPs and Fs were very complicated and expensive for not that much road horsepower. Hence the promise of the Hamilton, then Lima-Hamilton, then Baldwin-Lima-Hamilton ‘free-piston engine’, combining the combustion efficiency of a compression-ignition engine with the mechanical simplicity of a gas-turbine expander. GM-EMD went so far as to build the carbody of a smaller (F9-size) version – the FG9 – before it was discovered that the noise these things made outweighed their efficiency.
The early attempts at using industrial gas turbines on locomotives were not so much about fuel efficiency as lower installed complexity and the ability to use very cheap fuel. UP did an interesting experiment with propane fuel in one of its early B-B+B-B turbines, in the smog-ridden L.A. basin – it ran beautifully but even in the early '50s cost too much. If I recall correctly, one of the Westinghouse selling points (to ATSF) was that no expensive and delicate cooling system would be needed for long, hot desert stretches.
John Kneiling called for small, relatively light turboshaft engines in his distributed-power integral trains, and one example (the Canadian Pratt & Whitney PT-6) was adopted for the UA TurboTrain. These worked reasonably well, but they were stinky in that early jet-engine way, and after the OPEC embargo they were hopeless; I don’t think their maintenance ever got out of the A&P price range – expensive. The French and British worked on the assumption that high/speed trains would use gas-turbine power (and indeed had reasonable success with the RTGs, but substantially-nuclear electric power came to be used for the former, and HST125 diesel trains at more conservative but still effective speeds.
As already noted, gas turbines are poor at operating at high turndown, so are not well-suited to most kinds of American train operation which may involve protracted delays or slow orders. The advantages of high power at low weight aren’t meaningful for freight locomotives, and prior to the recent craze for BEVs the provision of a sensible traction battery for use with a turboshaft-driven alternator was comparatively expensive to provide and maintain.