Despite a long history using natural gas to fuel many vehicles in its fleet, California utility giant Pacific Gas & Electric (PG&E) always got stumped in the heavy Class 8 vehicle category. Simply put, it couldn't get a truck in that weight class to run on natural gas without sacrificing a lot of horsepower and torque, thus making such tractors impractical for long-haul routes connecting farflung warehouses over the Sierra Nevada mountain range. Until now, that is.
The solution for PG&E comes from an innovative fuel system developed by Westport Innovations called high-pressure direct injection (HPDI). The system uses a small amount of diesel to ignite liquid natural gas (LNG) in the heavy truck engine. In Westport's case, a Cummins ISX model is used, thus generating diesel-equivalent torque and horsepower, along with a range of 400 to 450 miles.
As a result, PG&E is now putting into service five Kenworth Class 8 T800 highway tractors powered by Westport's engine and running on LNG to transport supplies from its main warehouse in Fremont, CA, to other warehouses in Fresno, Marysville, Ukiah and Templeton.
Four of the Class 8 LNG trucks will be used for two shifts per day, representing about 800 miles per day per truck. The fifth LNG tractor will serve as a customer demonstration vehicle to educate the utility's large trucking customers about the economic and environmental benefits of LNG-powered Class 8 units, says David Meisel, director of transportation services at PG&E.
Meisel notes that these LNG-powered tractors cut greenhouse gas emissions by 15% to 20% over equivalent diesel-fueled vehicles, while using LNG will cut the fuel costs for these trucks by about 50%.
“Our policy is to be an alternative fuel leader; that's why we're taking this step with these LNG-powered trucks,” he says. “Now, I'd love to tell you the science is perfect when it comes to using LNG to fuel Class 8 trucks, but it's not. Someone has to take the first step because the benefits are clear: reduced NOx [oxides of nitrogen], particulate matter, and greenhouse gas emissions, along with less reliance on diesel fuel by running the cleaner LNG fuel.”
Brian Pepper, senior program manager in transportation services at PG&E, notes that LNG replaces 95% of the diesel fuel typically consumed by these Class 8 tractors. The remaining 5% is a B20 biodiesel blend (20% biodiesel mixed with 80% regular diesel fuel) that acts as an “igniter” to get the LNG to burn under compression without a spark source.
The new LNG-powered trucks fuel up at PG&E's Fremont Service Center from an above-ground LNG fueling system built by Chart Industries, which can refuel the tractors with LNG at about 30 gallons a minute, roughly the same fill rate as with diesel fuel.
“LNG is a cryogenic liquid, meaning it's stored at extremely cold temperatures, so our truck operators go through extensive training to use the fueling systems,” Pepper notes. “The trucks themselves operate no differently than their diesel-powered counterparts, giving our drivers the same performance and handling. Our maintenance technicians get about half a day of training on these new engines, but they don't do too much differently — just change an additional filter.”
Down the road, Pepper expects to see other benefits from using LNG to fuel PG&E's highway tractors based on the company's experience using compressed natural gas (CNG) in its light truck fleet. “With CNG, we can theoretically double or even triple engine oil life, though we need to be careful about replacing the oil's additive package,” he says. “We should need fewer oil changes on the LNG-powered ISX engine in our tractors, but for now, we're sticking with the OEM's recommended drain. We'll look at the possibility of extending it later.”