Diesel-Natural Gas Hybrid Engines, Going the Distance

With the recent boom in natural gas production in the United States and other parts of the world, it is no wonder that engineers are looking to use the new fuel in expanded capacity.

It’s not as if natural gas is new, as it’s been in use for at least a couple centuries, but production and distribution in mass quantities has never been suitable for the automotive market, whether it be light vehicles, or long-haul tractor-trailers, or even freight and passenger locomotives. There are light vehicles that run on compressed natural gas [CNG], but these are severely limited by a lack of infrastructure, fuel pumps, that is. Stations serving liquified natural gas [LNG], which are better for long-haul commercial applications, are even more scarce.

Still, the abundance of natural gas and its price, about a tenth compared to diesel fuel, for the same amount of energy, is compelling enough to get the attention of commercial transporters. Even though there are few LNG stations, the price differential of the fuel itself might even offset the cost of installing proprietary stations at transportation hubs. Locomotives, for example, don’t go off the tracks [much], so it’s easy to have LNG stations in place at the end of the line. Long-haul tractor-trailers would have the same benefit, many of them frequenting the same hubs that the locomotives, since these often form the final transportation link between cargo trains and warehouses.

There are engines that run on natural gas only, but limiting to a single fuel might not be a good idea for larger companies, whose fuel costs take a major part off the bottom line. Diesel-natural gas hybrid engines just might be the ticket, helping these companies take control of their fuel costs, since they can easily switch back to pure diesel fuel if the price of natural gas climbs again or the supply drops, which typically go hand in hand, anyway.

The new hybrid engine types are still basically diesel engines, using the heat of compression to ignite a small amount of diesel fuel and the rest of the natural gas charge, and can run on natural gas concentrations up to 80%. At the same time, natural gas emits up to 20% less carbon dioxide than diesel fuel.

My one concern, with all of this, is where the natural gas is coming from. Right now, the natural gas boom, and corresponding price drop, is due to greatly expanded use of hydraulic fracturing, or fracking. Fracking has been linked to a number of problems, only one of which is greenhouse gas emissions. Some estimates indicate that the Bakken Ridge Formation alone emits as much greenhouse gas in two weeks as does the entire United States in a year. If natural gas emits 20% less carbon dioxide, does that include the 26,000% increase on the extraction fields? Of course, maybe we could avoid fracking altogether and take natural gas from landfills.

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