I've been thinking about the potential for gas turbine electric locomotives, in the context of increasing pressure on railroads to reduce diesel engine emissions (notably in the Los Angeles area where I live).
I know that there have been some experimental gas turbine electrics built in the past, and that a major problem with them was inefficiency at less than full throttle. My thinking is that you could reduce the scope of that problem by running a series of fairly small gas turbines in parallel, bringing more turbines online only as needed -- like power utilities do with power plants.
To give some scope to the concept, I constructed (mentally) a gas turbine locomotive using off-the-shelf microturbines made by Capstone Turbine Corp., which is, I think, the largest maker of gas turbines for on-site power generation in the U.S. They can run on diesel fuel, natural gas, and a lot of other stuff.
To take a specific example, Capstone's CS1000 model generates 1,000 kW of electricity, and can be run with up to 30 units in parallel. One such turbine measures 3 meters x 3 meters x 9 meters, or roughly 10 feet x 10 feet x 30 feet. Two such turbines would approximately fit in the footprint of an EMD SD40 locomotive, (65 foot length) and with about the same power output (2,200 kW for a 16-cylinder diesel engine). The electrical efficiency of the turbines is 33%, which is roughly comparable to diesel engines, and if running on LNG would have much lower fuel cost than a diesel-burning unit. The cost of natural gas per BTU is one half to one third of the cost of fuel oil.
My thinking is that you'd design such a locomotive with one cab unit combined with one or more "slugs" that would have turbines and traction motors but no control cab. They'd be connected together so that the cab unit could disipense the electrical output of one to four of the turbines (or one of six, or one of eight) to all the connected traction motors. This modularization could offset the inefficiency of turbines at partial output.
I have no idea whether such a product would be economically attractive to railroads or not, because I don't know the relative capital costs of turbines vs. diesel engines for a given output, and I don't know the relevant fuel cost per GTM for comparison purposes.
I am fairly certain that the turbine would be a winner on air pollution grounds, since it would not produce the high NOx output that inevitably come with diesel engines, due to the inevitable presence of oxygen in the diesel exhaust stream (making conventional catalytic converters less efficient) and the high compression ratios of diesel engines. If burning methane, the turbine also would have almost no SOx emissions, and less CO2 as well.
I'm hoping someone with deeper knowledge of motive power design than I possess can weigh in and comment on the basic feasibility of the concept.
Is it time to begin thinking about a gas turbine electric locomotive consist powered by LNG?
Just curious.
Lew Phelps, Pasadena CA
Interesting idea- but this isn't a busy part of the forum. Try reposting it in the Locomotives section.
The big question is whether or not this would be more cost effective than the current strategy of powering a standard diesel locomotive with LNG that is being tried on the FEC. In addition to using largely standard parts, there is protection against price increases in LNG as the locomotive can simply return to diesel. Natural gas may be cheap now, but won't be if everyone starts using it and demand for the limited supply increases.Granted, as you have noted turbines can do this as well.
I'm waiting on more information out of Russia on how the GT1 and GT1h are working out in somewhat similar services to that in the US. They are traditional one-turbine units, though.
The genset idea is interesting, and potentially workable if reliable. The question is whether or not it works economically. A JetTrain style turbine-with-diesel is another option.
The advantage of using slugs is that they can also be used as LNG tenders, but the module flexibility advantages that helped the diesel vanquish steam are lost. For example, many services in the LA Basin would be hauling a lot more locomotive around than is needed.
You should definitely post this in the Trains Magazine 'locomotives' forum, and have Northwest, M636C, and some of the other experts comment on it there.
I had a similar proposal many years ago, but the individual turbine generators were smaller than the Capstones you're using. They were arranged in modular frames with all the connections to common manifolding, so any one unit could be pulled for service with minimum cost and complexity. The original 'proposed' carbody was a used E8 shell, with (as you noted) additional traction, motor capacity on trailing units -- this was in the heyday of the GE MATE concept, so that's what I called them -- that were fitted with corner castings and connections to use fuel tankage inside ISO standard tank container framing. Any combination of jet A, diesel or LNG could be used (I personally think using CNG on a locomotive is as suicidal as trying pulverized coal) depending on how you set things up. At the time I gave some thought to steam bottoming (small-scale combined-cycle) but didn't think it would be easy to provide the necessary HRSG and exhaust cross-connections to make reasonable power density for the cost involved.
A later thought was to put the turbine section in the center, and the cabs on the outboard ends of the MATEs ... with real good soundproofing!
I think there have been a couple of proposals using both Capstones and the Solar ceramic turbines. You would mount them with the same provisions used for tuned mass dampers, with primary and secondary compliance, so that no combination of ride or buff/draft shock would damage the blading. You might cautiously approach the people who developed the old CINGL approach, or ask some of Ross Rowland's design team for advice, if you disagree with me on the utility of CNG..