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.
As a cryogenic product, LNG requires special equipment and handling. To reach its liquid state, the gas must be chilled and stored at -256° F. Vehicle fuel tanks and LNG storage tanks are insulated pressure vessels, more like thermos bottles than traditional fuel tanks. Thus, while training to handle CNG takes five minutes or less, more specialized training and protective gear is required for LNG filling operations.
CNG is better for domiciled vehicles that return to a fueling station each night or day, such as refuse vehicles, street sweepers, and buses. LNG provides greater range for long-haul operations.
Finally, refueling equipment isn't the only thing that's costly about natural gas. According to the Diesel Technology Forum (DTF), an $110,000 drayage truck can cost as much as $200,000 when equipped for LNG. Conversions of diesel pickup and medium-duty trucks to natural gas cost $20,000 or more.
Public works fleets generally don't qualify for federal financial incentives offered to private-sector fleets that offset the vehicles' higher purchase prices.
But departments that operate CNG and LNG vehicles and onsite fueling stations may very well qualify for the alternative fuel excise tax credit, which is 50 cents/GGE (see IRS Publication 510 and Notice 2006-92). If a buyer is a non-tax-paying entity, tax credits can go to the seller. That gives you, the buyer, the opportunity to negotiate those credits as price reductions for equipment, infrastructure, or fuel.
In addition to grants from foundations — such as the William and Flora Hewlett Foundation in California, the National Energy Foundation, and various Clean Cities Coalitions — cities and counties can apply to federal agencies for funding to partly or completely mitigate investing in new vehicles, conversions, or projects.
Probably the most well-known is the Federal Highway Administration's Congestion Mitigation and Air Quality Improvement Program. Designed to enhance collaboration among state DOTs, municipal planning organizations, and transit agencies, eligible activities include converting diesel vehicles to cleaner fuels.
Over at the EPA, the agency has rolled virtually all emissions-reduction initiatives, such as Clean School Bus USA and Clean Ports USA, under a single umbrella: the Diesel Emission Reduction Program. Although a state match isn't required, 35 states participated this year; and states that fully match federal funds receive a “bonus” worth half the grant amount.
One of this year's grantees was Community Development Transportation Services Inc., which provides low-interest loans to rural public and nonprofit transportation providers in rural areas to develop self-insurance pools or pay the premiums on short-term insurance coverage.
The EPA has awarded the entire $50 million appropriated for 2008, but additional funding probably will be available next year.
Cities and counties have tapped into opportunities made possible through the Department of Energy's State Energy Program, which provides grants to energy offices and sponsors much of the department's Clean Cities program though its Special Projects division. In Texas, it's paid for backup compressors for the natural-gas fueling stations operated by the cities of Lake Jackson and Austin. West Virginia gives local governments grants to offset the higher sticker prices of alternatively fueled vehicles.
This year, State Energy Program appropriations totaled $50 million, which was divided evenly between competitive and formula grants. So far, $7 million of the competitive amount has been awarded. The department has asked for another $50 million for 2009.
The federal government's goal is to reduce the nation's carbon footprint. With programs spread across various departments, figuring out how to pay for greening your fleet is a matter of identifying other public agencies that would benefit and calculating the overall reduction in pollution.
So while the initial investment for natural gas is larger than for diesel vehicles, at $2.60/gallon-equivalent or less, the savings on fuel and the positive public relations benefits may outweigh the disadvantages.
— Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.
Same style, different color
Light- and some heavy-duty natural-gas vehicles work like gasoline vehicles: with spark-ignited engines. Some heavy-duty vehicles use high-pressure direct-injection engines that burn the natural gas in a compression-ignition (diesel) cycle, but additional spark ignition is needed to sustain combustion.
Here's how a vehicle running on compressed natural gas (CNG) works:
Gas enters the vehicle through the fill valve (A) and flows into high-pressure cylinders (B). When the engine needs power, the gas leaves the cylinders and passes through the master manual shut-off valve (C), travels through the high-pressure fuel line (D), and enters the engine compartment. It then enters the regulator (E), which reduces the pressure used for storage (up to 3,600 psi) to the required fuel-injection system pressure. The solenoid valve (F) allows the gas to pass from the regulator into the mixer or fuel injectors and shuts off the flow when the engine isn't running. Gas mixed with air flows down through the fuel-injection system (G) and enters the engine combustion chambers where, like gasoline, it is burned to produce power.
Source: U.S. Department of Energy Alternative Fuels and Advanced Vehicles Data Center