Interest in natural gas as a fuel for commercial trucks has been rising, thanks to the low cost of the fuel, and the desire of fleets to be "green" and reduce dependence on foreign oil.

However, a limited number of engine options has meant it's just not a viable strategy for some fleets, especially the type of regional linehaul fleets that may be best poised to take advantage of the limited but growing fueling infrastructure.

That's set to change significantly in the next two years, starting with the launch of the Cummins 11.9-liter ISX12 G early in 2013.

Recent changes in EPA regulations have increased the aftermarket conversion kits available, and now the domestic Big Three producers of light-duty pickups are also in the business.

None of these options is cheap, but the low cost of natural gas, whether purchased in compressed or liquefied form, should pay off price premiums in a few years, suppliers say. The higher the cost of conventional fuels, the better the argument for natural gas.

Upcharges for natural gas options are changing, too, but the trend is downward, according to supplier representatives who spoke at a meeting of the Truckload Carriers Conference's Refrigerated Division in July.

A couple of years ago, the up-charge for a natural gas engine and fuel system on a new Class 8 truck or tractor was around $60,000, but that is now about $40,000, the reps said. For trash collection trucks, whose owners are embracing natural gas fuel most enthusiastically, the per-truck premium is as low as $15,000 to $20,000 to the major refuse fleets.

Available now

These engines are currently available for heavy and midrange trucks:

Westport Innovations 15-liter HD dual-fuel:

Based on the Cummins ISX15 with Westport's high-pressure direct injection components, the HD uses diesel fuel as a pilot ignition method with natural gas as the main energy source. This results in greater fuel economy than with natural gas alone, the company says. But it requires exhaust aftertreatment equipment similar to that used on straight-diesel engines.

The HD has ratings of 400, 450, 475 and 550 horsepower with torque of 1,450, 1,650, 1,750 and 1,850 pounds-feet, and comes with the Cummins Intebrake retarder. It can be used with manual transmissions and Eaton's UltraShift Plus automated mechanical gearboxes. The HD is available in Kenworth's T800-LNG and Peterbilt's 386, 388, 367 and 367SB models.

Cummins Westport 8.9-liter ISL-G:

This is a spark-ignition engine based on the midrange-size but heavy-duty ISL9. It runs on 100% natural gas, so it needs only a simple three-way oxygen catalyst in its exhaust system to meet emissions regulations.

The ISL-G has five ratings, from 250 to 320 horsepower and 730 to 1,000 pounds-feet. That is modest output for Class 8 applications, but the torque converter in the mandatory Allison automatic transmission compensates by multiplying torque at startup, and constant power flow during upshifts makes acceleration brisk.

The ISL-G is available in various models from Freightliner, Kenworth, Peterbilt, Mack, Volvo and Crane Carrier Corp. Later this year it will be available in an International Tran-Star daycab tractor and next year in the new LoadStar.

Emissions Solutions Inc. 7.6-liter Phoenix 7.6L:

ESI modifies Navistar's DT466E and MaxxForce DT with patented parts (some of them cryogenically treated), a proprietary electronic control unit and an electronic throttle body. The rating is 285 horsepower and 820 pounds-feet, and it's been certified by EPA and California Air Resources Board to more than meet emissions limits.

The Phoenix 7.6L is available in new International WorkStar and DuraStar vehicles, and can be retrofitted to existing trucks with the base engines. ESI says it's also certified a Phoenix 7.3L, based on Navistar's V-8 diesel, now in fleet testing, but Navistar says it currently has no plans to use it.

Coming soon

Due out early next year is the Cummins Westport 11.9-liter ISX12 G, a spark-ignition natural gas engine based on Cummins' ISX12 diesel. The 12 G will have six ratings from 320 to 400 horsepower and 1,150 to 1,450 pounds-feet of torque. Higher output (compared to the ISL G) means the ISX12 G can be used with manual transmissions and not just automatics.

Most truck makers say they'll offer the ISX12 G: Freightliner in a Cascadia 113 daycab, Volvo in a VNL daycab, Kenworth in its T660, T800 and W900S, and Peterbilt in the Model 367 LNG and Model 386 LNG. Navistar will offer it in the ProStar in the 2013-2014 timeframe.

Many in the industry say there's pent-up demand for this engine, which will be the first to fill a gap between the 8.9-liter Cummins Westport ISL G and the 15-liter Westport HD.

"We had a conference in October, we had Kenworth, Peterbilt and Freightliner on the panel," says Rich Kolodziej, president of NGVAmerica, a national trade association promoting vehicles that run on natural gas. "They all said when that 12-liter comes out, Cummins Westport will not be able to sell it fast enough." In May, Freightliner made a coast-to-coast trip promoting the ISX12 G in a new Cascadia 113 day cab tractor, running on compressed natural gas.

In 2014, Cummins says it will begin production of an ISX15 G, also a spark-ignition engine based on the 15-liter ISX. Like the ISX12 G, the 15 G will use a maintenance-free three-way catalyst packaged as a muffler with no other aftertreatment needed. Like most such engines, it will burn compressed or liquefied natural gas or biomethane. Cummins has not announced ratings yet.

A Volvo 12.8-liter dual-fuel engine, based on the D13 diesel, is due out sometime in 2014. It will use liquefied natural gas as the main fuel with "trace amounts" of diesel for pilot ignition. This is 30% more efficient than spark ignition and will add range to the truck it powers, which is important for over-the-road operations, according to company executives. Like other natural gas engines, it will have a three-way catalyst in its exhaust system, plus a downsized DPF and urea injection equipment because of the small amounts of diesel fuel it will burn.

Navistar also is working with an outside company, Clean Air Power, to investigate the potential of developing a Navistar large-bore dual-fuel engine. It will be based on the 12.4-liter MaxxForce 13 and, like the upcoming Volvo and current Westport HD engines, will use a small amount of diesel fuel for pilot injection and run mainly on natural gas. Thus it will need only a small DPF and might or might not use urea injection.


Bi-fuel CNG gasoline systems are now options on Class 2 pickups from General Motors Fleet and Commercial Operations, Chrysler's Ram brand and Ford Commercial Truck. The ability to use gasoline addresses "range anxiety" - If an owner can't find a CNG station, he'll still be able to drive, albeit on the more expensive fuel.

In principle there are many similarities among the three companies' products, though each one's system is offered in slightly different pickup models. The systems all use gasoline V-8s with hardened exhaust valves and valve seats, separate gas injectors and fuel lines, pressurized gas tanks and conventional gasoline tanks, and electronic controls programmed to operate the systems. CNG tanks are in cabinets at the front of the pickup bed, and the gasoline tank is below the bed, as usual. All will run primarily on CNG and when those tanks are empty, will automatically switch to gasoline. All lose some power and torque while running on natural gas, but drivers will hardly notice, the builders say. Here are brand-specific details:

Ford-Westport WiNG:

Westport Light Duty partners with Ford for a "WiNG" bi-fuel system for SuperDuty F-250 and F-350 pickups.

WiNG, for Westport Natural Gas, consists of CNG components added to freshly built Fords with specially prepped 6.2-liter V-8s. A WiNG engine will run primarily on CNG, and will start on gasoline or CNG. The WiNGed trucks will come with Regular, Super and SuperCrew cabs, with short or long pickup beds, and with two- or four-wheel drive. Other configurations might be added later. Westport says the CNG system's weight is 200 pounds with tanks empty.

Using both fuels, range will be as much as 630 miles. Westport adds the CNG equipment in a facility next to Ford's Kentucky Truck Plant east of Louisville, Ky, where it also stocks parts for overnight delivery. Sales are handled through certain Ford truck dealers, perhaps as many as 200, willing to train technicians to service and repair the bi-fuel trucks.

General Motors also has chosen one basic model for its bifueler: a 2500 HD Extended Cab, though it can be had with a short or long box and two- or four-wheel drive. The trucks are produced in GM's Fort Wayne, Ind. plant, then go to nearby Union City, where IMPCO Automotive installs the Bosch CNG equipment, which weighs 450 pounds. The gas-prepped Vortec 6-liter V-8 starts on gasoline, then switches to CNG. The gas tank holds 17 gasoline-gallon-equivalents and the gasoline tank holds 36 gallons; combined range is more than 650 miles.

The CNG tanks are in a special cabinet attached to the frame, not the bed floor. They've been crash-tested and operated in extreme temperatures, GM says.

Ram factory built system:

Ram will install bi-fuel equipment in its own plant in Mexico. The bi-fuel package was engineered with the help of engineers at Fiat, Chrysler's parent and a major supplier of natural gas vehicles and equipment to Europe and other markets. It includes a gas-prepped 5.7-liter Hemi V-8 that uses gasoline for start-up, switches to CNG until that's exhausted, then switches back to gasoline.

The CNG tanks hold 18.2 GGEs and the gasoline tank is 8 gallons. CNG-only range is 255 miles, and the backup gasoline supply extends that to 367 miles. The system is initially available only on a four-wheel-drive 2500 Heavy Duty Crew Cab with an 8-foot-long bed.

Aftermarket conversions

Scores of products are available for truck operators wanting to convert existing trucks from gasoline or diesel fuel to natural gas, according to NGVAmerica, a trade association representing the industry. It has compiled a 29-page list of suppliers and their products, and the vehicle models and engines they're designed to convert.

Some products make complete conversions to gas; others are bi-fuel mechanisms that burn one fuel or another (like the Big Three products); and some are dual-fuel, using diesel for pilot ignition (like the Westport HD and upcoming Navistar and Volvo engines); or displacing it with gas in a process called fumigation. The long list is posted at

It's become easier for suppliers to offer conversions, thanks to a recent change in EPA. The change allows companies to market approved aftermarket conversion kits without having to undertake the same certification testing required for OEM engines. The cost to develop these systems is a lot less, so they cost less to buy. However, they are limited to older trucks, those the EPA classifies as "outside of useful life" (greater than 435,000 miles), or "intermediate useful life," which is older than two years up to 435,000 miles.

"Expect to see more of these conversions out and in use," says Stephen Ptucha, director of product management for Westport HD. "Especially with the infrastructure expanding where a fleet doesn't have to have its own refueling station, this could be a very good option for companies with a small number of older trucks in their fleet, or to con vert the entire fleet if they have the age of the engine that fits."

Learn more about natural gas and the fleets using it, including an extensive list of online resources, on our website at

From the September 2012 issue of HDT.

Natural Gas: What Fleets Need to Know, Part 1

Natural Gas: What Fleets Need to Know, Part 3 - What's the Payback?