Test Drive: Peterbilt Model 536 with Cummins L9N Natural Gas Engine

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Gray Peterbilt Model 537 in garage with no trailer
Test driving Peterbilt's 537 with Cummins natural gas engine
Peterbilt

Fleets bemoaning the current cost of diesel fuel – and feeling pressure from customers' environmental, social and governance plans – already have a relief outlet with compressed natural gas (CNG).

Prices at the pump vary significantly across various states but, for the most part, a diesel gallon equivalent of CNG can be had for about half the cost. However, while offering a greenhouse gas emissions reduction of about 20% compared to a modern diesel engine, CNG is not a zero-emission solution. 

The natural gas infrastructure is also not expansive by any measure. As of 2021, there were nearly 900 public CNG fueling stations in the U.S., according to the Department of Energy, but its footprint is fairly widespread except for a natural-gas no man's land in the Dakotas, Montana and most of Idaho. 

By comparison, the DOE estimates there are roughly 55,000 Level 2 and DC Fast Charging EV stations coast-to-coast. While there is a massive cluster in California, the number of EV terminals across the rest of the U.S. is significant. 

Natural gas for now, EV for later?

Peterbilt has been building medium-duty trucks for 27 years, and the company claims that 95% of that truck population is still in service. The company refreshed its medium-duty line about a year ago, but that process is ongoing. Peterbilt is phasing in a new hood design that aligns more closely with the brand identity found on its on-highway flagship models, adding a signature fender valley and dual-side air intakes – style features absent on prior medium-duty models.

Once my Model 536 rolled off the Peterbilt assembly line (equipped with the "old-style" hood), it was shuttled next door where it got its CNG upfit from Momentum. It still needed a 26-foot box, but I wasn't making any deliveries so I jumped in.

Momentum CNGMomentum Fuel Technologies' upfit facility is next to Peterbilt's Denton, Texas assembly plant.Peterbilt offers two natural gas powertrain options in its medium-duty line: the Cummins B6.7N (as of March this year) and the L9N. My test truck was outfitted with the in-line six cylinder, spark-ignited, L9N for the horsepower bump. The B6.7N is rated for 200 to 240 horsepower and 520-560 pound-feet of torque, compared to the L9N's 250 to 320 hp and 660 to 1,000 lb.-ft. torque. My truck was spec'd to 300 hp at 2,100 RPM and 860 lb.-ft .torque at 1,300. 

This Class 6 truck was configured to run from a distribution center and make multiple stops before heading back, so Peterbilt's Medium-Duty Product Marketing Manager Phil Hall and I headed out on about a 90-minute route that mixed some urban with some on-highway driving and a lot of left- and right-hand turns, all wrapped up in a blend of stop-and-go traffic and highway speed cruising. 

Inside, the natural gas version of the Pete Model 536 looks just like the diesel version – mostly. The cab featured a methane detection system (natural gas engines emit unburned methane because catalytic converters operate less efficiently at low temperature). Otherwise, it's the same. The dash layout is customizable by application with available space for optional gauges, switches and RAM mounts. My truck was outfitted with Allison's 3000 Highway Series, so the customary push-button shifter was affixed to my wing panel. 

The aluminum cab is 8 inches wider than the old 1.9-meter cab and has room for three adults. It features a floor height of 40.5 inches and a roof height of 74 inches. Phil and I are fairly average size guys (for truck drivers, anyway), and the cab was comfortable with room to spare. In its redesign, Peterbilt moved things like RAM mounts and cupholders – both of which traditionally have crowded the passenger's side of the cab – more center of the dash and away from the passenger's knee.

The cab also sits 3 inches lower, improving ingress and egress, and stair-style steps and knurled-grab handles improve safety. Once this truck is deployed to its customer, I think they'll find climbing in and out of it four dozen times a day less physically taxing. 

Injection molded body panels are scratch/scuff and glare resistant, and they resist warping in the summer heat – handy features since it was a broiling 98 degrees when we hopped in the cab.

Visibility is excellent. The truck has a turning radius of about 51 feet. This isn't a small vehicle but it maneuvers like one a lot smaller than its 109" BBC.

A 7-inch graphic display screen is smartly centered in the instrument cluster, splitting the speed-o and tachometer. 

Steering was light, and there's almost a nimbleness to the low-end power and its quick acceleration. Yes, we were missing the box body and its corresponding payload, but this truck is almost always going to cube out before it grosses out. With 300 hp at my disposal, I don't foresee any challenges at 26,000 GVWR. 

The engine responds and sounds exactly like you'd expect from its diesel counterpart. Worth noting: the L9N – certified to the California Air Resources Board and Environmental Protection Agency's Optional Low NOx emissions standard of 0.02 g/bhp-hr – has 90% fewer NOx emissions than the current North American EPA standard. 

If I didn't know in advance this was a natural gas powertrain, I wouldn't have been able to tell from the driver's seat. And I think that's the biggest compliment you can give an unconventional powertrain solution: that it doesn't feel or act unconventional at all.