Natural gas: Ready for prime time? Part 1

| August 16, 2012

There’s a simple rule of thumb when looking to convert from diesel to CNG or LNG, says Nadine Haupt, director of alternative fuels for Navistar. For LNG, about twice as much fuel is needed compared to diesel. CNG requires about four times as much as diesel.

On smaller routes, CNG is usually more practical because the tank packaging and weight considerations on the chassis are more doable. But for long haul or regional haul, LNG often works, depending on weight and packaging, Haupt says. “Then you have to take a look at what’s available in terms of infrastructure,” she says.

CNG fuel systems store compressed gas in cylindrical tanks at pressures up to 3,600 psi. CNG requires compression to get the fuel into the tanks, and stations are designed for refueling vehicles to meet fleet requirements ranging from a few minutes (fast fill) to several hours (slow fill). Fast fill can increase the temperature of the gas, which can result in a lower fill volume. LNG, stored as a liquid, is pumped into vehicle tanks in a similar fashion as diesel or gasoline, but since LNG is extremely cold, protective clothing and eyewear should be worn.

A look at refuse and many medium-duty applications showcases the differences between CNG and LNG, says Steve Gilligan, vice president of product and marketing for Navistar. “These are trucks that typically come home every night to the same location, and they’re generally fueled overnight,” Gilligan says. “That scenario lends itself perfectly to CNG. The trucks can be hooked up to a slow fill, fill overnight and the next day are ready to go.”

Running Class 8 trucks over the road is much different, Gilligan says. If the trucks are not coming home every night, they need enough range to get to the next available fuel station. “If you’re running longer distances or need a more compact vehicle, you need to look at LNG because you get a better packaging on the vehicle and faster refueling times,” he says.