LNG has its own problems
Of the 117,000 natural gas-fueled vehicles in the United States, about 3,100 run on liquefied natural gas rather than compressed natural gas, according to the Energy Department.
LNG as a transportation fuel has its advantages, and its problems.
LNG is in limited use in the U.S. in some trucks in the Long Beach and Los Angeles ports and in garbage trucks in several cities, according to a new report on natural gas from the Massachusetts Institute of Technology.
The long-haul trucking industry also is looking at LNG but hasn't embraced it.
The advantage LNG has over CNG as a fuel for long-haul trucks is that the trucks can be driven farther before needing more fuel - two and a half times as far for a given tank size. That's because you can squeeze more super-cooled, super-compressed LNG into a tank than CNG. Still, a truck fueled with LNG will travel only 60 percent of the distance on a tank than a similarly equipped diesel-fueled truck, MIT said.
LNG carries the same disadvantage of CNG: A lack of refueling stations.
A recent Canadian report on natural gas vehicles said the Lower 48 would need 66,000 more LNG refueling stations to match the nationwide system of diesel pumps.
LNG trucks also need special tanks. With LNG, natural gas is super-chilled to convert it into a liquid that is denser than gaseous methane and thus can be stored in smaller spaces. On a vehicle, LNG is stored at minus 260 degrees in a double-walled tank with a vacuum between the walls to help with insulation. "Over time, the LNG warms, the methane gas boils and eventually a pressure relief valve must be opened if the tank is not refilled within a relatively limited period of time (about a week)," MIT said.
An LNG long-haul truck costs about $70,000 more than a diesel version. It takes about four years to recoup that price through lower fuel costs, MIT said. But U.S. trucks often get resold into foreign markets after a few years, and part of the trucking industry's reluctance to embrace LNG is the difficulty finding buyers of the converted trucks.
K.C. Elliott from the Office of the Federal Coordinator contributed reporting to this article.