ON THE SCENE: Truckin’ with gas, natural gas that is

| 12/17/2008

LONG BEACH, CA – Dec. 8, 2008. Switching over to natural gas is a pretty big deal.

This past week in California, ceremonies at the Port of Long Beach marked the delivery of 132 natural-gas-fueled tractors that will eventually replace older, heavily polluting diesels at the nation’s busiest container port complex.

The set-back, 113-inch Sterling day cab trucks were powered by 320-horsepower Cummins ISL G engines with liquid natural gas (LNG) fuel systems. Long Beach and a growing number of Southern California cities operate municipal buses on compressed natural gas (CNG), the alternative form of the same fuel, also to achieve near-zero emissions from their vehicles.

Representatives from both Long Beach and Los Angeles ports, air quality management and the U.S. Environmental Protection Agency joined officers of Daimler Trucks North America, makers of the Sterlings that were delivered at the port. California Cartage owns the new trucks.

Emissions reduction is not the only reason natural gas may emerge as a leading fuel for trucks. Once the initial development costs are paid off, natural gas-powered trucks should have a more economical lifetime costs of ownership.

Although LNG and CNG engines are 2010 EPA and CARB emissions standards compliant, they require no expensive diesel particulate filters. The engines are also certified to meet CARB Clean Idle standards. Recommended maintenance intervals are 30,000 miles.

Along with the economy angle, truckers want to know what it’s like to drive one.

I had an opportunity to get behind the wheel of the 132 Sterling LNG tractors, pulling a typical 36,000-pound standard container on a chassis. Our route simulated a typical urban drayage run, on a mix of freeways and city streets, with a few “hills” represented by bridge approaches.

The 9-liter Cummins engine was mated to a six-speed Allison automatic transmission. The trucks that these were replacing had Mercedes MB900 engines and 10-speed transmissions.

In a quarter-mile drag race staged for the event, the LNG truck beat the diesel by more than one truck-and-trailer length.

Ignition characteristics of gas and diesel differ, so the Cummins ISL G and its big brother, the Cummins-Westport ISX G, both require spark ignition in addition to fuel injection.

Power came on smoothly regardless of throttle setting, and the truck had no problems accelerating from traffic lights or going up hills. The ISLG was quiet, with almost no clatter usually associated with diesel engines. Its response is immediate, making the driving experience almost car-like.

The cost of fuel and fuel economy for natural gas is figured on per diesel gallon equivalent. This is done by calculating the energy content of the two fuels and comparing them.

On that basis, natural gas costs between $1.50 and $2.50 per gallon less than diesel. This past summer, when diesel was selling for more than $4.50, LNG was about $2.60. After energy prices dropped, natural gas was selling in some areas for less than $1 per equivalent gallon.

The 119-gallon LNG fuel tank in the Sterling provides an estimated 250- to 300-mile range.

 – By Paul Abelson, senior technical editor