Deere CNG Engine Runs Clean and Quiet

Sept. 28, 2010


It looks like a typical public utility company's dump truck, but this blue M2 has a green Deere gas engine that runs cleanly and quietly.
Three high-strength tanks store compressed natural gas at up to 3,600 psi. A regulator drops this to operating pressure of 200 psi. The engine will also burn super-cold liquified natural gas, which needs less space to store.
Under all the piping is a Deere 6081 inline Six that replaced the original Mercedes diesel. Custom installation was costly but worth it, says PG&E, which also runs 41 older Freightliners with the same Deere gas engine.
All gauges and controls are completely stock. The interior of the M2's aluminum cab is roomy and outward visibility excellent.
Test Set


Truck: Freightliner Business Class M2, BBC 106 inches, GVW 33,000 pounds

Engine: John Deere PowerTech 6081 Natural Gas, 8.1 liters (496 cu. in.), spark ignition, 250 hp @ 2,200 rpm, 800 lbs.-ft. @ 1,600 rpm

Transmission: Allison 3000 RDS 6-speed double-overdrive w/Chelsea 277 PTO

Front axle: 12,000-lb. Meritor MFS-12-143A on taperleaf springs

Rear axle: 21,000-lb. Meritor RS-21-160 w/5.14 ratio, on 23,000-lb. flatleaf springs

Wheelbase 180 inches

Brakes: Meritor S-cam w/Meritor Wabco ABS

Tires & wheels: 11R22.5 Michelin X2A2 front, XDY-3 rear, on Accuride steel discs

Fuel capacity: 56 diesel-equivalent gallons in three aluminum/glass- and carbon-fiber composite tanks

Body: 5-yard Heil steel end-dump

Someone went to a lot of trouble to build this truck. It looks pretty much like a standard Freightliner Business Class M2 with a dump body, but under the hood is a John Deere engine that burns compressed natural gas, and behind the cab there's a compartment with several gas tanks. Neither the Deere nor the CNG fuel system are factory options, so they had been custom installed — an expensive and time-consuming proposition.

Therefore, as I scooted down the sometimes narrow streets of Santa Monica, Calif., you can bet I was about as careful as I've ever been with a truck because I'd have felt awful banging up such a special vehicle. Pacific Gas & Electric, the San Francisco-based public utility that owns the truck, had it built as part of a continuing program to use natural gas as a motor fuel and to encourage other fleets to do the same.

Installing the engine and fuel system in this M2 costs about $80,000, said Brian Pepper, the senior project manager who oversees this and other clean-air programs for the utility. But he emphasized that this is a prototype; a production vehicle would be much less expensive, and in any case much of the extra cost would be paid for through government grants and tax credits.

Why natural gas? Pepper listed several reasons: clean exhaust, the geopolitical fuel situation, and favorable economics. The gas-fired engine emits almost nothing, so it can easily meet government air-quality regulations; natural gas is readily available domestically and from friendly countries; the cost of diesel engines is climbing steeply as more apparatus is added to meet upcoming emissions limits; and natural gas costs about a third less than the equivalent amount of diesel fuel.

Diesel fuel prices have been fluctuating so much in recent years that it has become a major problem for fleet executives trying to budget for fuel, Pepper said. Diesel is now at all-time highs and is not expected to get cheaper. Locking in gas in long-term contracts, as PG&E and other companies do, brings stability that adds further desirability to the concept, he contends.

PG&E has more than 850 gas-burning wheeled vehicles in its 8,500-unit fleet. Forty-one are older Freightliner FL70 trucks, also with the retrofitted Deere engine. That specific project ended when Freightliner introduced its M2 a few years ago, and PG&E had to start from scratch. This Class 7 M2 is the first and only one, but PG&E hopes there'll be a lot more.

That's why the company is sending the truck around California, letting managers and regular drivers at other utilities and municipalities check it out. Pepper welcomed my request to drive it because he figures the publicity will generate more interest. Everybody, especially those who already run gas-powered equipment, including the City of Santa Monica, seems to like it as much as PG&E's drivers do. Pepper says he's found enough interest for 200 to 300 copies of this chassis.

With that many potential orders, Freightliner might be able to afford to install the engine and the natural gas fuel system right in the factory, or at least in a nearby modification center, Pepper said. As it was, this M2's original Mercedes-Benz 900 diesel had to be yanked and the Deere fitted in. The work was done by a crew at Complete Coach Works in Riverside, Calif. Its sales manager, Don Allison, was my host for a drive on a pleasant summer day — pleasant in Santa Monica, whose western boundary is the cool Pacific Ocean. Inland it was a scorcher, but here we ran with windows down and enjoyed the breeze.

As I drove the truck along city streets and out the Pacific Coast Highway toward Malibu, Allison told me that the engine installation was "challenging." He's an old drag racer and race-crew member, and the people at Complete Coach are used to stripping down and completely refurbishing well used transit buses, so to them almost anything's possible. Still, they had to use the proverbial shoe horn to get the Deere in. One visible change was sculpting out a small alcove in the hood to make room for an air-inlet pipe atop the engine.

Motor mounts for the Deere are close to those for the original Mercedes, Allison said. The Complete Coach crew worked with Horton Industries to fashion a special compact fan drive to fit between the Deere's block and the radiator. The Deere's electronics package mated up rather easily to the chassis electronics.

The steel cabinet behind the cab holds three 18-×78-inch cylindrical tanks for the CNG. They're made of aluminum wrapped in glass and carbon fibers. Below them is the fuel panel with a regulator, filters, gauges and the filler. Each of the tanks holds 18.66 diesel-equivalent gallons, for a total of 56. That supplies enough range and operating time for a truck that returns home often.

Fuel storage pressure is as much as 3,600 pounds per square inch, and that gradually drops as the gas is consumed. Operating pressure is 200 psi, and if it gets that low in the tanks, you're essentially out of gas. One way to see how much gas remains is to read the pressure gauge. When we paused to shoot photos, it showed 2,200 psi, which is about three-quarters full, and that's what the fuel gauge on the instrument panel read. All gauges and controls on the dash are stock and there's no hint from looking at them that there's anything special about the truck.

The stock muffler was removed from under the cab and replaced with a 46-inch-long catalyst/muffler hung from the frame. A vertical stack is also possible, Allison said, and will be used on another M2 that PG&E is planning. Either way, there is absolutely no odor in the exhaust.

With the engine idling, I bent down close to the tail pipe to sniff the emissions, and could smell nothing, not even the faint aroma you might get from a gas-burning kitchen stove. This, of course, is one of the reasons for using CNG as a fuel — citizens can't smell anything so they don't complain unless it's about the very presence of the truck, and meanwhile they and the driver can breathe easy.

The exhaust is so clean, according to Don McCaw, John Deere's business manager for this gas engine, that it meets the federal EPA's current emissions limits with no exhaust-gas recirculation, as most diesels now must have, and already meets the 2007 limits with no particulate filter, which all will have for '07. The Deere 6081 is an in-line Six with displacement of 8.1 liters (496 cubic inches). It's based on a diesel and uses spark ignition and electronic controls. The natural gas version came out in '96, and there are about 2,500 running in transit buses and trucks. Customers reportedly like it because of its low emissions, performance and reliability. This one is rated at 250 horsepower and 800 pounds-feet of torque, so its performance feels like that from any other midrange diesel of similar size and output.

Deere has a 9-liter variant of this engine ready to meet the even stiffer limits in 2010, and an updated 8.1 will soon be available if California authorities decide, as they often do, that they want to be cleaner sooner than the rest of the nation.

The engine is quiet except at idle, when it makes a deep "bawww" sound. Above idle it quiets down and at highway speeds you can't hear it at all. There's a slight whining, probably from the transmission, and some general road and wind noise. But there's no diesel rattle or rumble, and you'd think you were driving a gasoline engine. In a sense you are, as the Deere uses spark plugs to ignite the natural gas.

Driving the truck is a snap because it has an Allison automatic and is relatively short. With no load, acceleration was brisk and the short wheelbase and tight turning ability made sharp turns easy. It was almost like driving a jacked-up pickup, but of course the truck is as wide as any medium-heavy vehicle. Outward visibility is excellent, and what I couldn't see through the windshield and side windows was visible through the dual-pane glass on either mirror. The cabinet housing the tanks is about the same width as the Heil dump body, so it did not hinder the view to the rear.

Natural gas requires expensive fueling stations, but the cost to operators can be quite small, PG&E's Pepper says. This is because grants and tax credits available from federal and state sources will pay much or all the cost of a station for a sizable fleet. Small operators can get access to private and municipal stations, though managers would have to work this out before considering the use of gas-fueled trucks.

Pepper believes that the total lifecycle cost of a natural gas-fueled truck will become less than a diesel, and as more operators learn of gas' benefits and the market grows, volume production should be possible. Freightliner does offer an engine/transmission-delete option for the M2 — a rolling glider or "slider," as Pepper calls it — as the builder did with the FL70. PG&E bought some of its FL70s that way, and this is about as far as Freightliner can go now.

Any line or mod center installation of the Deere gas engine would probably have to wait until '07, because engineers are now busy preparing and certifying the performance of the '07 diesels, says Chris Abarca, a Freightliner district manager who deals with Pepper on the program. Although Complete Coach has done the installation engineering, this would still have to be pulled into Freightliner's engineering system and its long-term soundness documented. So quite a few engineering hours would be needed at Freightliner.

If this has set you to thinking about natural-gas power, there's more information at And Brian Pepper would be happy to hear from you. His e-mail address is [email protected]. You can tell him I was impressed with his truck.