Natural Gas – Conversions, Vehicles and Technology

A Fleet Manager's Guide to Switching to Natural Gas Medium-Duty Trucks

May 2014, Green Fleet Magazine - Feature

by Sean Lyden - Also by this author

Queens-based Ferrara Brothers Building Materials employs a Kenworth T440 CNG truck equipped with the 8.9L Cummins Westport ISL engine to haul cement around New York City.
Queens-based Ferrara Brothers Building Materials employs a Kenworth T440 CNG truck equipped with the 8.9L Cummins Westport ISL engine to haul cement around New York City.

Natural gas is touted as a cheaper, cleaner-burning fuel than diesel and gasoline — and this has a growing number of medium-duty truck fleets (Class 4-7) considering making the switch to natural gas.
According to Navigant Research, global annual sales of medium- and heavy-duty natural gas trucks will more than double, from 170,200 in 2013 to 398,400 by 2022, primarily driven by fuel-cost savings for natural gas of almost $2 per gallon equivalent to diesel.

But, with an up-front investment from $20,000 to more than $50,000 per truck, what medium-duty applications make the most financial sense for natural gas conversions? What is involved with acquiring natural gas trucks? What should fleet managers expect with order logistics and delivery times? What are the factors to consider with fueling and service infrastructure?

Work Truck spoke with experts at Clean Energy, Freightliner, Cummins Westport, GE Capital Fleet Services, and Ryder to get their advice on these questions and more.

Auditing Medium-Duty Fleet

When identifying ideal candidates for natural gas conversion within a medium-duty fleet, fleet managers should look for applications suitable for natural gas, including regional haul and distribution, pick up and delivery, food and beverage, refuse, and utility, according to Robert Carrick, vocational sales manager — natural gas, Freightliner Trucks.
“One of the key drivers is fuel use,” said Jeff Campbell, director of marketing for Cummins Westport Inc., which manufactures dedicated natural gas engines as a factory-direct option for several truck and bus OEMs. “The higher the fuel use — in terms of both miles and engine hours — the better the business case.”

The converse is also true. The less fuel consumed, the harder it is to justify the investment, especially in the medium-duty market.

“Since medium-duty vehicles generally operate in lower mileage applications and consume far less fuel than Class 8 tractors, there are a limited number of medium-duty applications that generate a compelling business case for natural gas in the current market,” said Scott Perry, vice president of supply management for Ryder System, Inc, which operates roughly 400 natural-gas-powered vehicles, ranging from Class 4 trucks to Class 8 tractors. “But, we expect that advancements in natural gas technology in both the passenger car and heavy commercial markets will both have meaningful impacts on medium duty technologies, in terms of bringing down the cost over time.”

In other words, the lower the incremental cost for the natural gas system, the fewer miles or engine hours required to recoup the investment, which will make natural gas more financially feasible for a wider range of medium-duty applications. But, for now, natural gas is most practical for trucks that perform jobs requiring high-fuel consumption.

“The best applications for natural gas are those where you’re running 80,000 miles or more per year, such as regional hauls; you’re burning 10,000 to 15,000 or more gallons of fuel per truck per year,” Carrick said.


Compressed natural gas (CNG) is natural gas that’s “compressed” to less than one percent of the volume it occupies at standard atmospheric pressure and stored at pressures as high as 3,600 psi. Natural gas that’s cooled to minus 260 degrees Fahrenheit becomes a liquid — that is, liquefied natural gas (LNG) — shrunk to a volume even lower than CNG, allowing for smaller fuel tanks for LNG to achieve an equivalent range to CNG.

But, which is better for medium-duty trucks? It depends on the specific job.

“LNG is best suited for high-mileage applications where the fuel is consumed more quickly so that the fleet is not exposed to fuel venting (a characteristic of LNG),” said Perry of Ryder. “LNG fueling infrastructure is more limited than CNG, which also has an impact on the applications that can be supported. CNG is much more widely available and provides a lower cost per diesel gallon equivalent and overall operating costs under current conditions.”

According to Carrick with Freightliner, CNG has gained greater traction than LNG in the medium-duty market.

“We have only sold a handful of LNG vehicles in straight-truck [medium-duty] configurations. The challenge with LNG in vocational markets is that the trucks are not constantly running like over-the-road tractors are. If LNG fuel is not used, you risk losing it.”

This is because LNG that sits in the tank will eventually get too warm, reverting back into a gas form and expanding, causing it to vent out of the tank. “So, in essence, LNG is a ‘use it or lose it’ fuel. You don’t have that issue with CNG,” said Carrick. 

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