Natural Gas Locomotive

[Mikeygaw]

I was looking over a leasing company roster (HLCX) and noticed that ex BN SD40-2 #7149 was noted as being a natural gas locomotive. Anyone have any kind of information on this locomotive, i.e. who's decision was it to turn the locomotive to natural gas usage, HLCX, BN, or factory? And wouldn't it be some what of a problem with additional infustructure (sp?) for the natural gas for a single unit rather than staying with standard diesel?

[edblysard]

BN had at least one pair of SD40-2 running on CNG, compress natural gas...with converted tank cars as tenders.
Do a Goggle search on the unit number you have, there are a lot of photos and info still around about them.

No more difficult to "fuel" as a CNG auto, and the infrastructure was not that complicated.

Ed

[Anonymous]

There is also LNG Locomotives (liqufied natural gas), I have no idea what is more cost effective: desiel, LNG, or CNG...

Does anyone know?

[Mikeygaw]

ok, one thing that didn't show up during the search... why were the units eventually reworked to use standard diesel, rather then continuing to use natural gas?

[joegreen]

BN 7149 and BN 7890 were converted by BN in 1991 to a natural gas powered loco and then converted back to a regular SD40-2 in 1997.

BN 7149 was sold to HLCX in June of 1999 and BN 7890 stayed with BN and was eventually painted into BNSF paint later and is still with BNSF.

[broncoman]

Does anyone know if the green goats are LNG or CNG?

[UPTRAIN]

The goats have a diesel powered generator that constantly recharges the large battery banks, it is neither LNG or CNG.

[tree68]

Probably the biggest drawback, IMHO, would be that , while the infrastructure is not complicated, it probably does not exist at the scale that would let the loco travel the system. I can see an application with a "captive" loco - local switching/industrial, where it can come back to one fuel point on a regular basis.

[broncoman]

Sorry got the MK1200Gs mixed up with the green goats.
Thanks for the correction, no wonder I was having a hard time finding them onine and they are LNG.

Dave

[UPTRAIN]

No problem, all high visibility cab and pug noses, all ugly!

[broncoman]

QUOTE: Originally posted by UPTRAIN

No problem, all high visibility cab and pug noses, all ugly!

Agreed!

SD 9s they're not.

[ericsp]

I got to see UPY 2004 up close, and I agree that thing is ugly.

[edblysard]

Having worked with MK1500Ds for the last 8 years, I kinda like the look.
Form does follow function.
And my engineer can see us no matter where we ride....

Ed

[Overmod]

Perhaps a logical confusion is that RailPower, the Green Goat folks, also are promoting their CINGL concept (which is natural gas).

A major problem with natural-gas locomotives is that the fuel has low energy density (even when liquefied -- and when liquefied you need a considerable amount of heat to re-gasify it for combustion). IIRC, you need something like 3.2 times the amount of natural gas for the same hp output from an internal-combustion engine, but the cost of fuel per gallon may even be higher for the natural-gas products as delivered. There are also 'alternative customers' for natural gas -- including peak power plants and millions of residential users -- that run the price up out of all proportion to utility as a transportation fuel.

RailPower has some economic analyses about why their natural-gas design is, overall, cost-competitive with diesels. (You can find some of the material at

http://www.railpower.com/products_td.html

although the following quote from that page may give some pause...)

"The cheaper price of natural gas than diesel, while maintaining similar thermal efficiencies, is what drives the cost savings on the CINGL"


Reading between the lines: Almost all the time, if you don't require the natural-gas fuel for pollution abatement or special operations, it simply isn't cost-effective compared to diesel. (And there are better technologies for particulate abatement in diesel exhaust...)

[broncoman]

I was under the impression that the pressure drop upon exiting the tank was enough for regasification. Its one of the cooler thing with regards to LNG over CNG in that you don't have to keep the regulator heated.
Is that right or wrong?

And Ed do you guys still have or are testing a MK2000C?

Dave

[Overmod]

Dave: Any time you get pressure drop, you get cooling. Not heat. If you have a compressed material with a very low boiling point, you'll get a gas coming out, and that gas may be suitable for piping to burners and subsequent ignition/combustion. But it will, of necessity, be colder than what comes out of the tank.

LNG, also by definition, is a cryogenic fuel: it was likely first compressed, then chilled so that it behaves as a liquid in handling and storage -- it inherently has low pressure and high density, so you get lots of combustion energy in a relatively small space. But you now need really competent insulation (multishielded vacuum bottles, high-performance foams, all that wonderful stuff from the Space Age) to keep it in liquid form, and you have to put heat back into it to return it to combustible natural gas at or near room temperature... or arrange to inject and burn it as a cryogenic liquid, which is how the SSME burns its oxygen and hydrogen, and perhaps more to the point how the methane... that's the major ingredient in natural gas... is burned in a PDWE. Unfortunately, the advantages of cryogenic fuel injection do NOT particularly apply to railroad applications in a cost-effective, or even particularly flexible in service, manner.

If you intend to burn LNG in any kind of engine that requires carburetion, you will have to regasify it. Yes, that step happens before you pass the gas through a regulator (to meter it for proper carburetion or combustion-air metering), and yes, you can do it with "waste" heat, for example from the engine exhaust or from a regenerative burner (using the same principle of the burners you see on some hot-air balloons). Not difficult to get a back-of-the-envelope calculation of the heat required -- take the fuel feed in gph or whatever, convert to mass, and look at the temperature rise from -256F up to ambient. As the LNG boils off, it 'autorefrigerates' the remaining fuel, which will reduce the pressure of the vapor above the liquid and hence the volume that will be available from the LNG tank without heating. In practice, it may make sense to use a positive-displacement pump and valves to move the cryogenic fuel (at its low pressure, probably under 5psi gauge) into a gasifier which does the heating up to 'normal' expected temp at required mass flow.

Now, if you have sufficient pressure to get something to exit the tank, at least part of what comes out will be a gas. CNG is pressurized up to 3000psi or so, without doing any cooling *other than removing the heat from compression*. Unfortunately that heat will be required from the environment when the pressure is relieved -- the CNG WILL expand, being a gas under pressure which will equalize according to the gas laws, but will chill down dramatically and freeze water in the gas, the metering apparatus, or any intake tract where ambient combustion air (usually containing some humidity) mixes with it. Since metering is often done with a small orifice, and even small amounts of freezing at the expansion side can foul up the flow through such an orifice, you often see some heating arrangement on CNG regulators. But don't mistake this for 'more heating being required' than is the case for LNG -- it's a matter of where the heat gets put back into the fuel.

Might be mentioned, also, that the effective heat content of fuels that are liquid at ambient temperature AND that don't require relatively high heat input to vaporize (like, for example, methanol or ethanol) will be higher than cryogenics with comparable combustible components.

Remember that one of the principal claims of researchers in both LNG and CNG locomotive development is that the engine systems are regenerative -- meaning that some of the 'waste heat' in the combustion exhaust is recaptured in the incoming fuel. In that respect, some of the nominal advantage of a Rankine cycle applies to gas-fueled engines... or perhaps a better way to phrase it is that the nominal thermodynamic disadvantage of expansion cooling or cryogenic storage is not a major efficiency factor in practical systems.

But it doesn't happen 'free' -- you have to design for it.

[broncoman]

I love this site!
One more question sir:
In the past in locomotive applications have they converted existing diesel engines to CNG or have they started with a clean slate? It seems in the medium to heavy truck categories the conversions were mediocre at best, and the purpose built (John Deere 8.1s for example) are very close to an equivelent sized diesel power-wise.

As always thanks for the answers, knowledge is power....


Dave

[Overmod]

First: the CINGL locomotive uses a gas-turbine powerplant, which is almost certainly built using modern 'microturbine' methods and materials... a high percentage of ceramics, self-adjusting magnetic bearings, etc.

On the question of locomotive conversions: there have been multiple attempts at 'dual-fuel' diesel/CNG locomotives. Bombardier did extensive research in the late 1980s (using the Alco/MLW 251 as the principal platform) -- results from this are available. A resource that, I think, will have answers for your questions is:

www.tc.gc.ca/tdc/publication/pdf/13400/13470e.pdf


My understanding is that the effective power output of the engine can be made very close (with volumetric concerns, and to an extent the 'clean burn' desired at high fuel rates when operating in CNG mode for pollution abatement, being the principal limits on developed hp in gas mode). Keep in mind, though, that this is a VERY different thing from saying that the fuel cost will be comparable for equivalent developed power.

My suspicion is that it wouldn't pay to design 'clean-slate' CNG engines for locomotive service alone; there's not enough amort for expected production runs vs. relatively simple conversions of existing engine tech. You will note that converting a 4-cycle diesel to CNG spark ignition, with modern ignition-timing methods (cf. HEI gasoline-engine tech), involves only a different set of top-ends on the cylinder heads/power packs -- lowered compression ratio and holes for spark being the things added. Situation is a bit more complicated for EMD 2-cycles, as you either pressurize the crankcase with carbureted gas (!!!) or have to arrange separate sets of ports for the gas mixture and the scavenge air, which in turn would require some different, probably CNC, machining on the powerpack assemblies and perhaps some additional fittings and components on the inside and outside of the crankcase.

The engines classically used in American locomotives turn so slowly, even at peak RPM, that control of gas mixture and ignition can be fairly optimized (imho) even in engines that have less-than-ideal spark-ignition characteristics.

[edblysard]

Dave,
The MK6201, a six axel 2000hp one off demo, was sold after our lease ran out,,,it is in Florida, last I heard.
Wish we could have kept it...loved switching with it!
Ed

[ericsp]

QUOTE: Originally posted by edblysard

Having worked with MK1500Ds for the last 8 years, I kinda like the look.
Form does follow function.
And my engineer can see us no matter where we ride....

Ed

Being an engineer (not the kind that operates locomotives) I agree with the function having precedence over form but I sure think those things are ugly.

[broncoman]

Overmod,

Would you think thank since LNG may experience major growth in the coming years and seeing that other big diesel engine companies (like wartsila-sulzer)are engineering purpose built power plants for marine and power applications that EMD and GE might also?

Thanks for the info Ed. I am really surprised that the c-c truck switcher didn't fly since many road still use short c-c for many tasks (SD9, 18, 24, 35). Were there any problems you came across?

Dave

[oltmannd]

What initially drove the BN to try nat'l gas was the price differential that existed between diesel and nat'l gas at the time. What killed it was the gap in price closed. This was primarily due to gas fired and dual fuel power plants increasing demand for gas.

[Anonymous]

The ex. converted natural gas tenders I believe are sitting in Staples, MN on a yard track and have been for quite a while. They have that natural gas paint scheme, white with green writing, very unique.

[CSSHEGEWISCH]

A couple of comments:
Unless the price differential opens up again, it looks like natural gas fueled locomotives will be limited to urban areas with tough clean-air requirements, such as the Los Angeles Basin or with state assistance programs, such as Houston.

I remember seeing MK 6201at Clearing a few years ago. I'm not sure if it was being tested by BRC or just passing through. The reason it never sold may be due to the price differential between a new MP2000C and a used de-turboed SD40.

[Overmod]

To broncoman:

I don't think there's a major future for LNG for locomotives -- a whole cryogenic infrastructure probably isn't worth it. The principal purpose of LNG is to reduce volume and pressure-related problems when transporting natural gas for long distances where pipelines are impractical, and for storing large volumes in manageable space with minimal explosion hazard. By the time you replicate all the supply and storage equipment for engine service facilities, even at low interest rate, then factor in the higher gallonage of fuel required by the lower heat content, the economics just don't work well.

CNG only requires a compressor and set of radiators; you can get the fuel supply from ordinary gas pipelines. I think that's a principal reason RailPower uses that technology for their road locomotive design.

As far as the actual engine is concerned, most "gas" engine designs don't care what the source of the gas is. An EMD or GE design would probably be second-sourced from an engine builder which specialized, as you note, in purpose-built powerplants. (Note that this is essentially the case both for the GEVO and H-series diesel engines already!) Other posts in this thread have already noted that MK, which had less capital and development tied up in their gas design, were unable to sell a large version -- and really haven't made much headway with the smaller versions. Remains to be seen if a hybrid locomotive that uses gas, rather than diesel, as its fuel can be successful... a big piece of the definition of 'success' in context being whether the locomotive in question operates a substantial part of its time in areas like the Southern California air-quality district...

[Paul Milenkovic]

Don't make me get out my tables from my thermodynamic textbook from engineering college!

Water has unusually high BTU's for changing from liquid to gas -- 1000 BTU's per pound compared with say 20,000 BTU's per pound from burning a pound of hydrocarbon fuel. That is why the coal bunker on a steam locomotive tender is large compared with the water tank. Don't remember the figures, but boiling liquid nitrogen requires much less heat than boiling water and I imagine methane is similar. Water is a special case because it is a lopsided molecule that forms an electric charge that holds it in the liquid state -- otherwise its heat of boiling as well as boiling temperature would be in a similar range as methane.

What takes a lot of energy in making liquid nitrogen is that it is so cold that the COP (coefficient of performance) of your refrigerator is low thanks to Mr. Carnot. The closer you chill to absolute zero, the more energy it takes to run the refrigeration cycle per BTU of cooling. Liquid methane, liquid nitrogen, liquid oxygen, liquid ammonia are all in the same ballpark of cryogenic temperatures.

So making liquid methane takes a good portion of the energy contained in the methane, but boiling liquid methane is not that big of a deal.

What about compressed methane? Don't know about the energy required to compress it, but as far as uncompressing it, are you sure it gets cold? If you expand a gas into a piston it can get cold -- that is how a gas-cycle refrigerator works, but if you expand a gas past a throttle or regulator nozzle, it pretty much stays the same temperature. The refrigerator expander is an adiabatic-reversible process while the throttle is an adiabatic-irreversible process, hence the difference. Now CO2 is a funny gas and it has something called the Joule-Thompson effect -- you can crack open a valve on a CO2 cylinder and get dry ice, but if you get air out of a scuba tank, you don't freeze the lungs of the diver.

How is it that letting Freon (or these days, the fake Freon) out of a needle valve makes things cold? The difference is that the Freon starts out as liquid and the cold comes from boiling liquid, not expanding a compressed gas through a throttle restriction.

So there is energy expenditure to compress methane into a pressure tank or to chill it into a liquid cryo tank (and liquid methane needs the same kind of vacuum Thermos insulation as liquid nitrogen), but getting the methane back out is no big deal.

On the other hand, Diesel engines inject their fuel and depend on the heat of compression for instantaneous ignition of the injected fuel while gasoline and methane or propane gas engines depend on the fuel/air mixture not igniting under compression until a spark initiates a flame front. I always thought there was a limiting cylinder size -- in the heyday of piston airliners, they had as many as 18 or even 28 cylinders on an engine, while Diesel engine cylinders can be much larger on account of the differences in the combustion process. But I guess methane must be high enough octane to work in the big cylinder Diesel-type engines.

As to the price of methane, methane would need to be much cheaper than Diesel to counter the convenience of a room-temperature liquid transportation fuel, a fleet of locomotives set up for Diesel, and the other factors.

[Overmod]

Heat of vaporization (aka latent heat of vaporization) for CH4 is given as 248.4 BTU/lb, or 138 kcal/kg. Not at all similar to liquid nitrogen (85.7 BTU/lb) or, for that matter, to 'normal' diatomic gases or noble gases.

Do you know how these cryogenic gases are actually liquefied? That should certainly relieve you on the point of what happens when compressed gases -- not liquids (yet!) -- are allowed to expand...

Gas laws, as I thought I mentioned before, indicate that if you saw heat evolved upon compression, you should expect similar heat 'required' upon expansion. This was first taught to me at age 5 (admittedly I went to a good and somewhat unusual school!) and amply confirmed by experience with a wide range of materials since. Throttle/regulator issues are not germane to the discussion of reheating cryogenic fuels from liquid phase, or allowing compressed fuel to expand.

As I'm sure you know, there's nothing more 'weird' about getting dry ice from expanding CO2 than there is about dry ice subliming rather than melting in ambient environments... you just need much higher atmospheric pressure to observe the liquid phase. And Freon at a metering nozzle is liquid for convenience in handling, efficiency in condenser thermodynamics, and much higher available mass flow to achieve a given level of cooling... did you bother to look up the heat of vaporization for dichlorodifluoromethane? (Hint: it's less than that for N2, which I think kind of pokes a hole in either one or the other of your arguments... ;-})

You've got the Diesel cycle backwards -- the heat of compression allows rapid combustion to occur in an excess of oxygen, and injection is used to get the fuel charge rapidly and effectively mixed with the oxygen by the time transition temperature for the combustion reactions is effectively reached in the fuel plume. If you are familiar with the Ricardo "Comet" and other swirl chambers, or with IDI in general, you'll understand more about how the process works in practice. You couldn't compress a gas mixture effectively -- it would detonate long before you reached the level of compression observed in the Diesel cycle! The whole point of "spark" engines is that they provide kernels of ignition energy short of spontaneous (and widespread) loci where the transition temperature is exceeded; when you in fact have such loci, you get... detonation, pre-ignition, call it by its wide variety of symptomatic names.

Limiting cylinder size has much more to do with dynamics and balancing than it does with pure combustion thermodynamics. You don't care how big the cylinder on a ship engine turning a couple of hundred RPM max might be, but you sure as hell would if it were spinning a propeller and having to be carried by aerodynamic lift! (BTW, diesels can be ideally suited to aircraft, and have been successfully used). You have problems with induction, valve shrouding, scavenging, etc. when using large cylinders at high engine speed. With spark (or laser) ignition, you can have a very rapid release of energy at precise points in the fuel charge, which allows injection timing and kinetics to be separated from combustion kinetics -- one of the reasons why DI gasoline engines can be nearly as "efficient" as diesels BUT require very precise fuel injection (on the diesel level of precision) to work. You could build a big, big spark-ignition engine, but you'd have to arrange some mechanical means of putting the spark in an appropriate place in the cylinder volume at the moment of ignition WITHOUT having its apparatus foul the piston at TDC. This usually isn't worth the effort (particularly when compression-ignition fuels are cheaper than volatile ones) -- BUT this is one of the places where polyspectral laser ignition has some interesting applications.

As a minor nit-pick, compression-ignition engines use cetane, not octane, as the rating -- and, as adrianspeeder probably knows, you can use propane in a diesel as a kind of analogue to nitrous oxide in gasoline engines... ;-} -- Just don't think that it'll run as smoothly if propane is the only fuel.

I believe you are correct on both counts regarding methane (of any kind) as a practical locomotive fuel. You must consider also, however, that politics trumps thermodynamics as well as economics -- if there's either a subsidy or a requirement that gas fuel be used, there will be positive incentives for railroads to overcome the objective disadvantages of the fuel and of the existing infrastructure optimized for diesel fuel. Be interesting to see what directions engine technology takes in the Southern California area, for example, and to what extent that technology takes hold and spreads in other areas, notably those with seasonal air-quality issues (Memphis being one!)

I'm hoping that Peter (M636C) will discuss some of the issues involved here, particularly with his knowledge or experience with dual-fuel conversions including those being researched in India.

[passengerfan]

I would think that the BN unitsd were like most of the trucks converted to run on Natural Gas they robbed the truck of about 1/3 of its power and most truck companies that experimented with road units burning the natural gas were disappointed and converted them back to diesel.
Boeing back in the late 1950's converted a Seattle Fire truck to a turbine powered truck and it lasted in the Seattle fire department for years.
The other truck converted was a Garrett Freight Kenworth Tractor. The burned kerosene and cosumed large amounts of fuel. The Garret unit was able to top Snoqualmie Pass at 70 mph grossing 80,000 lbs. something I don't believe todays trucks will ever come close to. Garret eventually sidelined the truck as it was to expensive to operate being a one of a kind. I believe it was converted to conventional diesel. Remember they had two glass windows on sides of hood and you could see right through without seeing the small size of the turbine inside. Where if their had been a conventional diesel their it would have filled the class.

[Paul Milenkovic]

QUOTE:
The Garret unit was able to top Snoqualmie Pass at 70 mph grossing 80,000 lbs. something I don't believe todays trucks will ever come close to.

Sorry, can't help asking -- did it chase actor Dennis Weaver all over the road in his little Dodge Dart (Speilberg's first movie was this TV Sunday Matinee classic called Duel)?

QUOTE:
Heat of vaporization (aka latent heat of vaporization) for CH4 is given as 248.4 BTU/lb, or 138 kcal/kg. Not at all similar to liquid nitrogen (85.7 BTU/lb) or, for that matter, to 'normal' diatomic gases or noble gases.

Well I guess boiling liquid CH4 is a bigger deal than I thought, but it is midway (in a ratio sense) between liquid nitrogen and water.

I stand by what I said about expanders and throttles. If you want to get any cooling by expanding a compressed gas, you have to do it against a piston or turbine expander and extract work from it -- if you expand it past a throttle, no cooling for an ideal gas. Gas cycle refrigeration needs an expander. Liquid cycle refrigeration (home or auto air conditioner) uses a phase change -- the flip side of this is a steam engine can get away with an injector to get water up to boiler pressure while a Diesel or gas turbine needs a compression stroke of the piston or a turbo-compressor. Gas phase engines or fridges need compressors and expanders while phase change engines and fridges (the ol' steam loco and the fridge in your kitchen) can get away with one without the other.

CO2 is not an ideal gas -- it has a significant Joule-Thompson coefficient -- meaning you can get substantial cooling by expanding it through a throttle. If CH4 has the Joule-Thompson effect, I stand corrected regarding tapping a CNG tank and needing to add heat. I know that air does not have a significant Joule-Thompson coefficient because otherwise scuba divers would freeze their lungs.

As to cylinder sizes, Otto and Diesel cycles, I am pretty sure there is an upper limit on Otto (gasoline) engine cylinders in terms of detonation -- you are compressing a fuel air mix ready to blow, and the trick is 1) to not ignite until the spark happens, and 2) to prevent the unburnt charge from blowing before the flame front gets to it. I was arguing that Diesel cylinders can be much bigger because the injected fuel burns on contact with the compressed and heated air -- yes, you need some kind of turbulence or mixing to get a good burn and low smoke, but Diesel cylinders can be really large as on low-speed ship Diesels.

Since Diesel cylinders are really not suited for gasoline-cycle (Otto) operation and spark ignition, I was wondering if methane fueling was a difficult problem or whether methane had such a high octane rating that you could easily convert medium-speed rail Diesels to spark ignition and methane.

[Anonymous]

UP ran one of their 4500HP gas turbines on gas for a while in the late 50s or early 60s.
I believe it was #70. This will require a trip to the Trains Mag archives.