Are Hybrids the Future for Locomotives?

By Noel T. Braymer

The Diesel-Electric locomotive has been around since the 1930’s. Since the 1950’s it has been the standard locomotive for most American Railroads. The Diesel-Electrics drove out the Steam locomotives for simple economic reasons: one Diesel-Electric could do the work of at least 3 steam locomotives. Will economics again drive out the Diesel-Electric with a new challenger?

One of the big problems with diesel locomotives and diesel engines in particular are emissions. Much of the problem is the diesel fuel which is cheaper and of a lower grade than gasoline. Railroads and trucking companies are under pressure from local communities and government to reduce their toxic emissions. For both railroads and trucking companies, fuel costs are a major part of their business expenses. Anyway of reducing fuel costs would be welcomed that would also reduce emissions.

The railroads, in particular the BNSF have been looking at Liquified Natural Gas (LNG) as a solution to their fuel costs and emission problems. Natural Gas is cheaper than diesel fuel and cleaner. The problem with Natural Gas is it doesn’t have the amount of energy for the same amount as oil. It is also difficult to carry enough Natural Gas in gas form to run trains.

The railroads are looking at LNG to run trains. As a liquid more Natural Gas can be carried for the same volume as compressed Natural Gas. But this will require a whole new infrastructure for facilities to cool Natural Gas into a liquid, store the LNG and pump it at fueling stations. Liquifying and keeping LNG cold also will cost money and extra energy. To run a freight train on LNG will require a tender holding enough LNG for all the locomotives with connections to it.Some trucking firms have already tried LNG on their truck fleets and have found problems using it. They didn’t get as much cost savings as they had hoped.

Some trucking companies are now trying Turbine-Electric Hybrid powertrains to save fuel and reduce emissions. These are being built by a company in San Jose, California called Wright Speed. Wright Speed doesn’t build trucks, they make kits that convert existing trucks from diesel to hybrid.

Turbine engines have a reputation from the past as being very fuel inefficient. Turbine engines are very efficient when run at full power. But they use almost the same amount of fuel when powered down or even at idle. Wright Speed gets around this by running the turbine constantly at full power as an electric generator. The power is then stored in a battery and used as needed by the truck for propulsion. Not a lot of battery is needed to run the truck since the batteries are constantly being recharged by the turbine generator. If the batteries are fully charged the turbine can be shut down, then restarted when the batteries need charging.

The results of using a Turbine-Electric Hybrid drive is fuel costs are cut by half while emissions are greatly reduced. Portable turbines are so clean that they produce fewer emission for the same amount of electricity than the power from many utilities. A diesel engine isn’t as clean and fuel efficient as a turbine when used as a hybrid.

Using basically the same system built by Wright Speed, such a powertrain should produce the same results for railroad locomotives. This could cut fuel costs by half and exceed future reduced emission standards coming for the railroads. This would avoid the cost needed for new infrastructure for the railroads for a conversion to LNG.

What would be even better would be to add capacitors to locomotives. The greatest use of energy needed in transportation is for acceleration. A great deal of energy is wasted as heat in braking. Capturing the energy from braking with regenerative braking and recycling it with capacitors for acceleration would save a great deal of energy for the railroads. This can also result in faster acceleration. This is especially useful for passenger trains with short distances between station stops.

The downside of capacitors is they don’t store very much energy. They charge and discharge energy quickly. They can also last a long time, longer than a battery.. But capacitors can’t hold as much power as a battery. Today it would require a separate tender on a train to hold enough power with today’s capacitors to get a passenger train moving from a dead stop.

The future for capacitors may lie in what are called ultracapacitors. These use exotic materials such as graphene and nanotubes to greatly increase the surface area of a capacitor to increase the energy density without increasing the size or weight of the capacitor. It will be a few years yet before an economical ultracapacitor is on the market. But with many groups working to produce them, they will likely be very popular and useful for future locomotives.

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