Natural gas as a fuel for internal combustion engines isn’t a new idea. What is new is the scope of its penetration into

new vehicle applications in the wake of rising diesel prices – and nowhere is that trend more prominent than the fuel’s current inroads into the heavy-duty truck market.

Fleet interest in natural gas as a viable Class 8 fuel skyrocketed during the unprecedented 2007-08 fuel price spike, but that brief affair ended as prices returned to more manageable levels in recent years.

Today, interest is returning because fleets realize that yesterday’s lower fuel prices truly are a thing of the past, says Robert Carrick, vocational sales manager of natural gas for Freightliner. “Every time the prices retreat, they’ll stay at a higher level instead of dropping all the way back down,” Carrick says. “Fleets are looking at ways to combat that.”

Even if the natural gas infrastructure is lagging, competition is driving the heavy-duty truck marketplace, says Jonathan Burke, vice president of global market development for Westport.

“The challenge for fleets that looked to natural gas in the past was that there were very few vehicle models and engines available,” Burke says. “Now we’re seeing all of the major truck OEMs step up and invest significant amounts of capital in making a huge range of new factory-built vehicles available today. That’s the sea change.”

The right path

Both compressed natural gas (CNG) and liquefied natural gas (LNG) fuels behave exactly the same once introduced into an engine’s combustion chamber, but the manner in which they are delivered, stored, packaged on a vehicle and transported to the combustion chamber are radically different.

The nation’s fleet included about 105,000 natural gas engines in 2010, with larger vehicles such as those used by UPS accounting for a larger share than in years past.

“Fleets operating on longer routes should ensure they are running on a defined natural gas corridor,” says Steve Weiner, alternative fuels marketing manager for Peterbilt. “If the routes are stable, then you can put fuel where you need it. If the routes change frequently, then it can be challenging to ensure fuel availability.”

Fleet managers can follow a simple rule of thumb when looking to convert from diesel to CNG or LNG, says Nadine Haupt, director of alternative fuels for Navistar. Take a gallon of diesel fuel, and consider the amount of energy that it creates; to get that same amount of energy using LNG, about twice as much fuel is needed. The ratio for CNG is about four times as much as diesel.

On smaller routes, fleets tend to spec CNG because the tank packaging and weight considerations on the chassis are more doable. But anybody on longhaul, or even regional haul, might look at LNG depending on weight and packaging. “Then you have to take a look at what’s available in terms of infrastructure,” Haupt 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 a cryogenic (cold) fuel, protective clothing and eyewear should be worn.