CNG vs diesel: Advancements, costs, and future outlook for commercial trucks
Key takeaways
- Advancements in CNG engine performance now rival diesel engines in power and torque, making them more attractive for commercial use.
- CNG trucks incur higher initial costs due to complex fueling systems but benefit from lower fuel and maintenance expenses over their lifespan.
- Natural gas is domestically produced, providing stable and predictable fuel pricing unaffected by global market fluctuations.
- Upcoming EPA27 regulations are expected to reduce emissions significantly, bringing CNG trucks closer to cost parity with diesel and boosting market adoption.
Two years ago, a head-to-head comparison of trucks fueled by diesel and compressed natural gas (CNG) would have resulted in a clear winner. But a lot has changed in two years, especially with the performance of CNG engines.
Will the changes to diesel engines starting MY 2027 and the advancements in CNG engines make the alternative fuel rival tried-and-true diesel?
Cummins’ X15N CNG engine now rivals diesel power and torque
The CNG engine offerings of the past were fine for some applications, but their sluggish performance compared to diesel left something to be desired.
Ready to try a CNG truck?
Hexagon Agility works with truck manufacturers, dealers, and fleets to spec and design CNG-powered trucks tailored to fleet needs. The company’s demo program, which allows fleets to demo a CNG-powered truck for a period of time at no charge, has helped Hexagon Agility collect performance data and driver feedback. Fleets interested in taking part in the demo should contact Hexagon Agility.
Two years ago, “we would have seen less power, less torque,” Ian MacDonald, VP of Hexagon Agility, a provider of natural gas fueling systems, told FleetOwner. “We had a 12L engine—that was the largest engine—[offering] 400 hp and just over 1,400 lb.-ft. of torque.”
Compare that to a diesel engine. Cummins makes some of the most popular engines in the industry, and even its most efficient engine, the 15L X15 Efficiency Series, delivers up to 550 hp and 1,850 lb.-ft. torque. of torque. Comparing that CNG engine to Cummins’ X15 Performance Series hurts even more, as the engine offers up to 565 hp and 2,050 lb-ft. of torque.
But that was two years ago.
By September 2024, Cummins had already designed and started full production of its CNG-powered engine, the X15N. This 15L engine, now the largest CNG engine available, delivers up to 500 hp and 1,850 lb.-ft. torque. of torque.
“The feedback we're getting from drivers is that the X15N engine feels much more like a diesel when they drive it,” MacDonald said. “I think that's exactly what Cummins was going for, and really, what the industry wanted.”
CNG engines cost more up front—but deliver lower fuel and maintenance costs over time
Aside from performance, another common talking point in engine comparisons is cost. A CNG engine costs more than a diesel engine—for now, at least. The reason for this additional cost lies in the more complex fuel system.
Diesel’s fueling system is simple. As a liquid, diesel fuel is housed in an aluminum or steel tank, and the delivery system for that liquid is simply a pump, MacDonald explained. However, because CNG is a gas, its fueling system and fuel delivery process are less straightforward. Natural gas molecules must be compressed at high pressure and stored safely on a truck. Therein lies the extra cost.
Hexagon Agility’s CNG fuel system includes a carbon-fiber tank that keeps the natural gas compressed. Then, Hexagon Agility attaches the tanks and the fueling system to the trucks. Depending on the application, the tanks could be installed behind the cab, on the roof, or on the truck rails.
But where it costs more up front, MacDonald said CNG makes up for it in lower fuel and maintenance costs.
“Natural gas fuel is always less expensive, so you get a fuel savings that helps you pay that increment down, and … you don't have to buy DEF (diesel exhaust fluid), so you're also saving,” MacDonald explained.
What’s more, CNG engines produce significantly fewer emissions than diesel engines and don’t have aftertreatment systems that diesel engines have. This also reduces costs over the life of the vehicle.
“I spent a lot of time in the emissions arena for diesel trucks; I know that those [aftertreatment] systems can be very expensive when they do fail,” MacDonald said. “It's a bit of a shock to the system when you do have after-treatment expenses to account for, as opposed to being predictable and manageable over time.”
The more predictable and manageable CNG engine maintenance requirements MacDonald referred to include spark plug replacement.
CNG offers predictable pricing and flexible depot or public fueling options
Where to fuel CNG
CNG fueling can be done similarly to diesel fueling, either in public or on-site at the fleet depot. The U.S. Department of Energy offers a map of public CNG fueling stations, and those can be found at popular diesel-fueling stations, such as Chevron and Love’s.
Fleets that prefer to fuel their trucks on-site can install CNG fueling infrastructure at their depot. This does come with a cost, but fleet owners might find the investment to be worth it. Fleet owners can often negotiate the price of CNG when buying in bulk. Additionally, a CNG supplier might build a private, on-site fueling station that it owns and operates for the fleet, such as with this fleet in Ohio.
Regardless of where a fleet gets its fuel, the price it pays for CNG is more predictable for two main reasons, according to Advanced Clean Transportation (ACT) News. The first is that CNG is a domestically produced commodity, immune from “import costs and other price variability.” Second, domestic market forces determine the cost of CNG relative to diesel prices, which are set by the global market. For example, when gas and diesel prices rose during the COVID-19 pandemic or after Russia invaded Ukraine, CNG prices remained stable.
How to fuel CNG
Fueling a truck powered by a CNG engine is “straightforward,” according to MacDonald. Simply pull up to the CNG pump like you would a diesel pump and then grab the hose. While the setup is similar, there is no mistaking a diesel pump for a CNG pump. The CNG pump doesn’t have a curved nozzle, and it locks into place before dispensing any CNG.
"It's just a quarter turn that locks the nozzle onto the truck nozzle, and then it automatically fuels to the fill point,” MacDonald said. It takes 15 minutes to fill a CNG tank.
Unlike diesel fuel, which can drip onto a driver's boots and jeans when moving the nozzle from the truck to the pump, if any CNG is released into the air, it evaporates almost immediately. Drivers who’ve filled with CNG have told MacDonald how much they appreciate not smelling like fuel after pumping CNG.
EPA27 could put CNG trucks at cost parity with diesel and accelerate adoption
While warranty requirements for model year 2027 trucks are yet to be determined, the EPA27 regulation requiring trucks to lower their emissions output from X to X is set in stone. Cummins’ X15N natural gas engine already meets this requirement, but reducing emissions this much in diesel engines requires significant equipment changes that many truck manufacturers have confirmed will come with a price increase just as significant. This will put CNG-powered trucks nearly at cost parity with diesel-powered trucks. MacDonald expects EPA27 to act as a “boon" to the CNG market.
Already, “lots and lots of fleets are very, very interested [in CNG trucks], but the freight market has been in a really difficult spot,” MacDonald said. But when EPA27 kicks in, “that’s going to make the economics much more compelling.”
About the Author
Jade Brasher
Senior Editor Jade Brasher has covered vocational trucking and fleets since 2018. A graduate of The University of Alabama with a degree in journalism, Jade enjoys telling stories about the people behind the wheel and the intricate processes of the ever-evolving trucking industry.