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A truck delivers liquefied natural gas (LNG) to a refueling facility.

After dealing with this summer's high fuel prices, I suspect many fleet managers are now giving some thought to alternative fueling technologies. If you are considering such a change, you've probably looked at biodiesel or hybrid power. These green technologies have been grabbing headlines recently. And the light trucking world is accepting them.

Spurred by success, these technologies have entered the realm of class 8 vehicles. Several managers of waste-haul fleets and other heavy-duty applications have demonstrated improved economics with both diesel-electric and diesel-hydraulic hybrid systems.

But ready-mix trucks don't operate like trash collectors. Hybrids are most successful in delivery applications with a significant portion of their operating cycle as stop-and-go driving. As I explained in an article on hybrids, regenerative braking, the ability to capture kinetic energy and use it to accelerate back to speed, provides the operating energy that creates economy.

Since hybrids offer fewer advantages to a concrete producer, let's explore other fuel alternatives. Liquefied natural gas (LNG) and compressed natural gas (CNG) are practical fuel alternatives for vehicles in a producer's fleet. Many experts believe that because producers park their trucks at central locations, it's practical to install new fueling equipment.

This is an important difference from over-the-road trucking, where acceptance has been slow. There are few CNG and virtually no LNG refueling facilities other than in selected urban areas. But liquefied gas can be delivered and stored somewhat like diesel.

This slow acceptance may soon change. Last August, I test drove a Sterling LNG tractor on its way to the Port of Los Angeles. The truck was powered by a Cummins-Westport ISX-G engine, which produced 450 horsepower and 1650 pounds-feet of torque from its 14.9-liter (909-cubic-inch) displacement.

The clutch engagement torque, 1000 pounds-feet at 800 rpm, made it easy to drive. The rig moved from a dead stop easily, even when pulling more than 60,000 pounds. The natural gas' burn characteristics make the engine quite responsive to throttle input. Switching to gas-fueled trucks should have a minimal impact on drivers. In fact, I think many drivers will prefer the drivability of gas over diesels.

The selection criteria between CNG and LNG have more to do with the infrastructure of fuel delivery and storage than the operating characteristics of the fuels in an engine.

Natural gas is about three-quarters methane, the lightest and most easily burned of all hydrocarbons. Other gases in the mixture, mostly ethane, all burn completely and leave only carbon dioxide, water vapor, and trace amounts of other gases as their residue, not particulate matter.

Note that oxides of nitrogen, a smog-forming agent, are created when the nitrogen and oxygen from the air combine under the heat and pressure of combustion, no matter what the fuel.