After dealing with the summer's high gasoline and diesel prices, as well as the uncertainty about future energy costs, I suspect many of you are giving some thought to alternative fueling technologies. If so, you've probably looked at bio-diesel or hybrid power.
But there are other options, including natural gas: liquefied (LNG) or compressed (CNG).
No fuel emits zero pollutants, but natural gas is close. Though its exhaust contains traces of benzene, cyanide compounds, phenol, toluene, and other contaminants, natural gas is about 95% methane, the lightest and most easily burned of all hydrocarbons. Other gases in the mixture, mostly ethane, burn completely, leaving only carbon dioxide, water vapor, and trace amounts of other gases — instead of particulate matter — as residue.
At press time, natural gas was selling for the gasoline-energy-equivalent of less than $1/gallon for CNG (85 cents in Utah) to more than $2/gallon for LNG, depending on geographic location and demand. Savings after all storage- and dispensing-related costs are about $1 to $1.50/gallon on an energy-equivalent basis.
The energy content of natural gas is referred to in “gasoline gallon equivalents,” or GGE. One GGE is 5.66 pounds of natural gas, or 125 standard cubic feet.
FUELING: BUILD OR BUY?
Switching to natural gas has a minimal impact on drivers because its burn characteristics make engines quite responsive to throttle input. In fact, I think many operators will prefer the drivability of natural gas over diesel. I did when I drove a Cummins-Westport LNG-powered Sterling.
Deciding whether to convert to natural gas has more to do with delivery, storage, and safety than its operating characteristics.
The United States has an extensive natural gas delivery system for homes and industry, but few CNG and virtually no LNG refueling facilities (see map).
CNG must be compressed to less than 1% of what its volume is at standard atmospheric pressure, and stored at up to 4,900 psi. It takes $350,000 to $400,000 to build a modest industrial-sized compressor facility with related storage and dispensing equipment to service a reasonably large fleet, with related operating and maintenance costs running from 15 to 35 cents/GGE. There are, however, smaller refueling devices that compress gas delivered to structures.
Another factor limiting the popularity of natural-gas-powered vehicles is weight. Pressurized tanks must be used for CNG, and thermos-type tanks are needed to maintain LNG at cryogenic temperatures. Both are heavier than those for gasoline and diesel equivalents.