U.S. trucking companies, trash haulers and transit agencies continue to invest in new vehicles fueled by compressed natural gas or liquefied natural gas, in part to meet corporate or agency carbon-footprint goals. But the economic rationale for switching trucks and buses from diesel to CNG or LNG is weaker than it was a few years ago, when diesel cost two-thirds more than natural gas fuels on a per-BTU basis — prices for diesel, CNG and LNG are now in the same ballpark. Also, developing regional or national networks of CNG/LNG fueling stations doesn’t come cheap. Today, we discuss the growing use of natural gas in trucks and buses — and threats to that trend.
LNG has been a frequent topic in the RBN blogosphere, but mostly in the context of large-scale natural gas liquefaction and export (All Down the Line); from time to time, we’ve also considered LNG’s role in supplementing pipeline gas deliveries of natural gas to New England during the winter months (Baby Come Back). CNG has been blogged about occasionally too — mostly relating to CNG exports to the Caribbean (Down to Kokomo) or CNG use at well sites (You’re As Cold As Ice).
CNG and LNG also can serve as transportation-fuel alternatives to diesel or motor gasoline. To make CNG, you compress natural gas to more than 3,000 pounds per square inch (psi) — typically 3,600 psi. Compression reduces gas’s volume to about 1% of what it would be at normal atmospheric pressure, but CNG still takes up 3.8 times more space than diesel on a per-BTU basis. To make LNG, you supercool natural gas to minus 260 degrees Fahrenheit in a liquefaction plant (at normal atmospheric pressure); LNG takes up 1.7 times more space than diesel per BTU, but unlike CNG, you need to keep LNG supercooled (at fueling stations and on the LNG-fueled truck) until it’s converted back to a gas.