Jim Park: Cummins says its new X15N natural gas-powered 15-liter engine offers diesel-like performance. Does it really? Let’s find out. And if you haven’t already seen it, check out our X15 walk-around video, too — see what makes this engine so special.

Our 579 test truck had the flagship 80-inch ultra-loft sleeper and a fully electronic dash display with all the bells and whistles. It also had the latest safety and driver assistance features, like lane keeping assist, Bendix Fusion, lane departure warning, autonomous emergency braking, stationary vehicle braking, active cruise with braking to full stop, following distance alerts, and a whole lot more.

We scaled out the gate at Peterbilt’s Denton, Texas plant at 67,800 pounds. That’s a pretty typical load for a truckload carrier. We drove about an hour out from Denton to Bowie, Texas, on US Route 380 and Route 287. The route was mostly a four-lane limited-access highway over rolling terrain, along with a couple of towns with traffic lights. I left the cameras off while I got used to the truck.

Patrick Wallace, how are you, sir?

Patrick Wallace: I am doing well, how are you?

Jim Park: What do you do at Peterbilt?

Patrick Wallace: I’m the marketing manager for alternative powertrain, so I have natural gas and electric vehicles.

Jim Park: I should ask you what your favorite is, but I won’t because that means you have to commit to something and you’ll be in a ton of trouble. But, how do you find working with the natural gas product?

Patrick Wallace: It’s a great product. So at Peterbilt, we’re leaders in natural gas for commercial trucking. We have a full range of offerings, all the way from medium duty to heavy duty, and we cover lots of different segments. So, like, vocational, over the highway, medium duty pickup and delivery, and refuse, as well.

Jim Park: After grabbing a quick lunch and taking a few pictures of the truck, we turned on the cameras and headed back to Denton. While bobtailing around Denton, I thought the accelerator pedal was a little bit sensitive, but it was quite manageable under a loaded trailer.

Patrick told me the engineers spent a lot of time getting that pedal feel just right.

So one of the things I noticed when I first got in, we were bobtailing, was that the throttle pedal was a bit sensitive at really low RPM and low speed. So, we’re just gonna pull off and take up a little bit of a hill here, and I wanna see how the throttle pedal reacts under a load, which is a bit different, and see if it’s quite as sensitive. It wasn’t bad, but I would probably dial that down a bit if I could.

Patrick Wallace: Yeah. A lot of special attention was paid to the throttle calibration with this engine. On a previous natural gas engine, there was some feedback that it was a little hard to maneuver and a little hard to pull away from a stop. And so there was a lot of special attention paid to making sure that it was very responsive in low-speed situations.

Jim Park: And as our experience just indicated, coming up that little grate out of our parking spot, that was perfect. I have no issues with that whatsoever.

Patrick Wallace: It works very well when it’s loaded up.

Jim Park: Leaving the truck stop in Bowie, I wanted to see how fast the truck got up to speed on a freeway on ramp. We had a little bit of help from a slight downhill grade, but we pulled uphill for the final couple of gear changes.

Forty five miles an hour now just entering the freeway. Forty eight, forty nine. Today, we’re gonna in the right lane here, we’re gonna verge on. Fifty at 1500 RPM and in 11th gear.

Now we’re loaded about 60,000 pounds of gross weight here, by the way. So we’re still accelerating. Fifty five now. Still climbing this slight grade. We’re obviously at a nice, safe merging speed.

There’s my shift to 12 at 60 miles an hour, 1400 RPM, and we’re gonna just get her up to 65 [miles] and, throw the cruise control on.

That was a nice, smooth acceleration, wouldn’t you say?

Patrick Wallace: Yeah, so the powertrain is very well integrated and optimized. So this engine was developed with, the Eaton Endurance HD. So that’s a twelve-speed, and so they work seamlessly together.

Jim Park: Seamlessly is a good word for it.

Naturally, I wanted to put Cummins’ claim of diesel-like performance to the test. It’s hard to find any serious hills in East Texas, so I had to make do with some rolling interstate freeway-type grades.

So we got a bit of a grade coming our way. Again, it’s Texas. You’re not gonna see too many mountains here, but, coming into this at 66 miles an hour, 1500 RPM. We’ll probably lose two or three hundred RPM, couple of miles an hour, but I’m not gonna touch the shifter, obviously, and it’s not gonna shift on its own. Plenty of torque behind this.

We’re in the, solid part of the torque band here, so we’re getting a full 1850 out of it, at 1400 RPM now. Now we’re getting into a steeper part of the hill. Cruise control on, 12th gear, 63 miles an hour, 1400 RPM, and we’re over the top. Didn’t drop a gear.

Drivability wise, once the cruise control’s on, you really don’t have to touch this. But as far as losing speed, we lost three miles an hour and made it up again in no time. So, I think that’s a good indicator of what this engine’s capable of.

We’ll get to the engine brake in just a minute. But first, I wanted to ask Patrick about some of the upsides of this engine compared to diesels or to previous natural gas engines.

Patrick Wallace: So there’s a lot of good reasons. If your if your company has carbon reduction credits, or carbon reduction goals, you can use renewable natural gas to meet those goals.

And I wanna point out too that, you know, before maybe you wanted to go to natural gas, but you didn’t have what you needed. You couldn’t get the engine horsepower rating or the torque rating that you needed. You couldn’t get the gross combination weight up high enough. With this new introduction of the X15N and the integration with the Allison and the Eaton powertrains, we’re really opening that up. So you’ll be able to get a natural gas engine to meet almost every application, cover really broad swaths.

Jim Park: The engine brake on the X15N isn’t quite as powerful as the current X15 diesel. The diesel delivers about 525 breaking horsepower at 2100 RPM, while the natural gas version produces about 460 horsepower at 2300 RPM.

Cummins programmed the fan to come on when peak braking power was commanded. The fan creates about 75 horsepower of drag on the engine adding to its retarding capability.

I think we’re gonna come down a grade here in just a second, so we’ll fool around a little bit with the engine brake, which is it’s gonna surprise a lot of you. It surprised me how much retarding power it has. It’s not quite what a diesel will do, but it’s pretty darn close. So, we’re at 65 [miles] now. I’ve got the engine brake in the first position.

It should hold us at about this speed on this little grade, 66, so we gained a mile an hour. That’s not anything to worry about. And you notice that even though the engine brake is on, you can’t hear it, which is I know all the fun with an engine brake. But so this is a slightly steeper part. I’m gonna go to the second position on the engine brake now. You can hear it. You can hear how quiet it is.

Gaining a bit of speed, 70 [miles] now. Pull her in the number three position, and we’ll get off that as we’re going up the hill.

You may have just heard the fan cut in at the end of that clip. That’s what I was referring to earlier.

The X15N delivered the desired retarding power, albeit a bit noisily thanks to the fan, but, honestly, I don’t think the extra braking power is gonna be missed all that often.

Reports and comments on social media from drivers and fleets who have trialed the X15N are overwhelmingly favorable. Fundamentally, the only difference between the X15N and its diesel cousin is that it burns cleaner and cheaper fuel. The wheels don’t care what energy source makes the 500 horsepower and 1850 pound-feet of torque.

I firmly believe this engine will get the regional and long-haul sectors over the low-carbon hump. Hydrogen might yet prove to be a viable zero-emission alternative, but natural gas is here now, and it works.

Waiting for something better to come along is like stepping over a dollar to pick up a dime.

Click on the links down in the description if you wanna read more about the engine and renewable natural gas on trucknews.com.

Reporting from Denton, Texas, I’m Jim Park.