Canadian truckers like their big engines, and they were, once upon a time, willing to give natural gas a serious try. Cummins’ ISX12 G 12-liter natural gas engine never caught on here because its 400 hp/1,450 lb.-ft. rating was insufficient for most Canadian applications.

Several Canadian fleets did find limited success with the Westport Innovations 15-liter HPDI (high-pressure direct injection) engine, but production of that ceased in November 2013, fueling a near decade-long wait for a suitable replacement.

Excitement in Canada was palpable when Cummins first announced the X15N in the fall of 2021. It went into production at the company’s Jamestown Engine Plant in western New York last September. Peterbilt and Kenworth are the first two OEMs to offer the engine, and units are now in production.

Freightliner will offer the X15N in sleeper and day cab versions of the Cascadia beginning this year.

New to North America

While we keep saying the X15N is a new engine, it comes to North America with more than 2.5 billion miles logged by production engines in Asia and Australia. More than 50,000 of these engines are already running globally.

Presently, 16 North American fleets are field testing the engine, including two in Canada. They are testing linehaul, regional, and vocational duty cycles, and have accumulated more than 2.1 million miles of real-world evaluation — including hot and cold weather and high-altitude exposure.

“We’ve been researching and developing this particular engine for six years now,” says Mario Sanchez, Cummins’ on-highway sales director. “It has run more than 40,000 hours of dyno testing and 6 million miles (8 million km) of pre-production on-road testing. Yes, it’s new to North America, but it’s already a well-proven product.”

New to the X15N

The first and most obvious improvements over the previous heavy-duty natural gas engine are the ratings. It’s available in 400, 450 and 500 hp with torque ratings of 1,450, 1,650, 1,750 and 1,850 lb.-ft. Also offered are optional SmartTorque and EX ratings for improved drivability, such as predictive gear shifting, predictive engine braking, on-ramp boost and hill roll-out.

These are available when mated to the Eaton Endurant transmission.

The lower X15N ratings align with the top ratings of the ISX12N, which will appeal to some regional and vocational customers already using that engine. Cummins claims the X15N offers 10% better fuel economy and lower GHG emissions over the ISX12N with comparable rating and duty cycle.

The big news here is really the torque profile of the X15N. With the 500/1,850 configuration, you get 1,700 lb.-ft. at 900 rpm.

Peak torque of 1,850 comes on at 1,100 and runs out to 1,400 rpm, providing strong pulling power through the typical top-gear range. Our test truck cruised at 1,450 rpm at 65 mph in 12th gear, giving us a 300-rpm plateau of peak torque at cruise speed to manage the slight grades on our route.

There’s more about the drive below, but I’ll say the higher torque improves the drivability of the X15N immensely over the ISX12N.

The higher torque is a direct result of the larger displacement as well as substantial changes to the air handling and fuel systems. This engine uses a dual-entry wastegated turbocharger, rather than the complex and expensive variable geometry turbo (VGT) found on the big diesels. Sanchez says the VGT wasn’t necessary to achieve the desired results.

Rather than using a single large throttle valve, to control the gas and air mixture, gas intake is now metered by eight individually managed solenoids. They respond to fuel demand faster and more precisely than a single large throttle plate.

In principle, it’s like what a common rail injection system does for diesel engines.

“You have these actuators that can open very quickly to meter the amount of gas flow that you need,” Sanchez says. “It’s more accurate, and and it improves the transient response of the engine.”

The X15N also has a combustion chamber/cylinder head designed exclusively for the way natural gas behaves in the cylinder during intake and combustion.

Longer maintenance intervals

Maintenance intervals for the X15N have been extended and synchronized allowing for oil drains and spark plug changes at the same time. This was a significant concern with previous generations of heavy-duty natural gas engines.

Changes to the architecture of the cylinder head allow for better cooling of the spark plugs and further design changes to the plugs themselves and the ignition system contribute to longer service life.

The piston design has been improved to reduce oil consumption, and a higher capacity oil pan allows drain intervals to run out to 60,000 miles (96,000 km) under normal operating conditions. Short-haul and severe-service applications have shorter intervals of 50,000 and 25,000 miles (80,000 and 40,000 km) respectively.

The aftertreatment system used with the X15N is an upgraded design of the familiar passive three-way catalyst used in other natural gas engines. It requires no additional fluids or prescribed maintenance.

How does it drive?

The trip started at Peterbilt’s production facility in Denton, Texas. We headed west on US Rte. 380 and then northwest on US Rte. 287 to Bowie, Texas. We returned the same way.

It a 60-mile (96-km) ride each way, and the route was mostly four-lane limited access highway with rolling hills as well as some side roads through town with lights and traffic. We were loaded to a gross vehicle weight of 67,790 pounds (30,750 kg) – a pretty good example of how the X15N will operate in fleet service.

Cummins has touted the X15N’s “diesel-like” performance, and my test drive confirms that’s a very accurate description. It’s got the big torque of a big-bore diesel and the sustained pulling power through the lower end of the torque curve, down through 1,000 rpm, but it rolls on more “softly” than does a diesel. That’s not to suggest it’s lazy or sluggish. Far from it. It’s just not as aggressive feeling as a diesel.

I set the cruise for 65 mph (105 km/h) once we were up on the highway and the transmission never downshifted on the 1- to 2-mile-long rolling hills along the route.

The engine is very quiet to begin with, but it was odd not hearing the turbocharge spooling up as the engine drifted down into the lower regions of the torque curve. The feeling was that of a strong, steady pull.

I found the throttle pedal to be a little sensitive while bobtailing, but it felt very, well, diesel-like, when pinned up to the trailer. Sanchez said that might have been a calibration issue and assured me the sensitivity could be dialed back electronically.

The integrated powertrain, featuring the Cummins Eaton Automated Transmission Technologies Endurant HD N transmission, made the overall driving experience fantastic. The up- and downshifts were smooth and confident, even when making a full-throttle application. There was just no fooling that engine/transmission combination.

I hesitate to call this a downside because it’s hardly noticeable, but the engine brake in the X15N is a little weaker than that of the current generation X15 diesel.

The diesel delivers about 525 braking horsepower at 2,100 rpm while the X15N produces about 460 hp at 2,300 rpm with the engine fan on. That’s a feature Cummins has programmed into the engine when peak braking power is commanded. The fan creates about 75 hp of drag on the engine, adding to the retarding capability.

I never needed full retarding capability on the test drive but tried it to see how it felt. It performed well, albeit noisily. Honestly, I don’t think the extra braking power will be missed all that often.

Final thoughts

I firmly believe this engine will be key to migrating over to a cleaner alternate energy source for trucking. Battery-electric trucks won’t work in longhaul service, and hydrogen fuel cells are still horribly expensive and there is still very little fuel distribution in place.

Natural gas is widely available in most of North America, and this engine is here now and ready to work.

It already beats the dreaded 2027 NOx emissions limits, and in terms of vehicle weight and operating range, is very competitive with a similarly spec’d diesel.

If you’re still worried about natural gas as a less-than-stellar alternative to diesel, don’t be. The X15N checks almost every box. This is the engine that will get us over the hump and keep us running clean and green for a long time to come.