The future of diesel as the fuel of choice for big trucks is in little doubt.
Nothing presently available comes even close to the efficiency of diesel, both in terms of energy yield, price, or availability. The only real contender at the moment is liquefied natural gas (LNG), and it’s closer than you might think to becoming a practical alternative to diesel in some applications.

More than 12,000 LNG-powered vehicles are working in various markets around the world — predominantly in urban transit applications and in areas where environmental concerns have led to innovation through publicly funded incentives to offset development costs. Mid-range trucks have been running spark-ignited LNG engines in some markets for years, but heavy trucks — especially in long-distance service — have been lagging behind. Until now.

Vancouver-based Westport Innovations, the world’s leading developer of LNG fueling technology for diesel engines in a joint venture with Cummins, has been running 14 trucks in daily service hauling municipal waste out of San Francisco since 2001, averaging over 100,000 miles per month for the fleet. And last May, the company began a one-year project called The Clean Air Corridor, testing five trucks hauling loads between Ontario and Michigan.

Partners in the Clean Air Corridor include Challenger Motor Freight of Cambridge, Ont., Natural Resources Canada, Sustainable Technology Development Canada, and Toronto-based natural gas utility, Enbridge.
“The Ontario project was meant to prove the performance of the engine and show that it would work in a practical application,” says Bryan Zehr, manager of heavy-duty demonstrations and deployment at Westport Innovations.

The five Challenger trucks are 2005 Volvo VNL 670s, equipped with 450-hp, 1,650-lb ft Cummins ISX engines, modified to accommodate Westport’s High-Pressure Direct-Injection (HPDI) LNG fueling technology. The trucks run two shifts per day along the Highway 401 corridor hauling 100,000-lb GVW loads of beer to Jackson, Mich., from Toronto, and 140,000-lb GVW loads of garbage from Toronto to Lenox, Mich. The round trip mileages are 560 and 470 respectively, and since the test began, the fleet has logged nearly 600,000 miles.

Three of the 14 trucks in the California test program have reached or exceeded 500,000 miles, and are currently being upgraded with the next generation HPDI hardware. Those three engines, claims Zehr, are showing normal or better than normal wear characteristics.

How Does It Work?

Westport is developing its HPDI technology exclusively with Cummins at this point, and only for the ISX engine, having signed a technology development agreement with the engine maker in 1999.

It’s a duel-fuel engine of sorts, as it burns about six or seven-percent diesel (by energy yield) across a typical duty cycle. Natural gas has a higher ignition temperature than diesel does, so cylinder temperatures generated by compression aren’t enough to ignite the LNG. “We inject a small amount of diesel on each compression stroke, acting as a pilot ignition, which is immediately followed by a larger injection of natural gas,” Zehr states. “That happens across the entire duty cycle.”

The amount of diesel is almost constant across the duty cycle, whether idling or pulling 140,000 lb — just enough to initiate ignition. As the load increases, so does the volume of natural gas. At idle, the LNG/diesel ratio is about 20 percent (or five parts LNG to one-part diesel) by energy. At full load, it’s about two percent by energy.

The fuel tanks are a proprietary low-heat-leak design, integrated with a heat exchanger from the engine’s cooling system to turn the liquid stored in the tank to a gas. The liquefied natural gas provides 2.5 times the energy storage per volume compared to compressed natural gas. It’s stored in the tank at about 100 psi, but it’s pumped up to 5,000 psi before it reaches the injectors. The fuel is injected directly into the cylinder. Direct injection allows for sophisticated control over timing and quantities of fuel, allowing the engine to perform like a diesel, and providing more flexibility in calibrating the engine.

The stock Cummins injectors are replaced with a dual-fuel injector that flows both liquid diesel and LNG gas.

The same internal fuel rails are used to get the fuel to the injectors, but there’s a high-pressure diesel injection pump in there, too. The hardware modifications are neither extensive nor expensive. We can’t quote a price yet because the parts are mostly pre-production prototypes.

The base-engine ECM remains the same, doing all the basic fuel calculations and commands. Westport’s controller takes and reads the basic fueling commands from the engine ECM, and uses them to manage the natural gas fueling. The torque and horsepower curves remain the same as a standard ISX, but Westport is currently working on a 500-hp/
1,850-lb ft version.

These 2004 — compliant engines use the same cooled-EGR systems as their full-diesel counterparts, but the emissions are said to be running near 2007 levels — without the exhaust aftertreatment. In fact, Westport recently received California Air Resources Board (CARB) certification for its HPDI engines to run at 1.2g/bhp-hr (NOx), and 0.02g/ bhp-hr (PM).

Westport followed the CARB certification announcement by saying the ISX LNG engine would become available to select fleets in the Southern California market with the appropriate Cummins 2004 to 2006 model-year (new or retrofit) diesel ISX engines beginning in 2006. The engine will be offered in two ratings: 400 hp/1,450 lb ft torque, and 450 hp/1,650 lb ft torque, matching the diesel-fueled base ISX engine.

Ready for Market?

The fuel used in the Challenger test was trucked to London from Montreal in relatively small quantities. The cost of the diesel-energy-equivalent volume of LNG would be extraordinary. There’s a lot of equipment required to run five vehicles, said Kurtis Wadley, Wesport’s field service technologist at Challenger’s London terminal. “It wouldn’t cost that much more to support 50 or 100 vehicles.”

Areas of the country that have marine access to world supplies of LNG, or areas where pipeline access and storage facilities exist — or can be built –are prime candidates for LNG fueling depots. Thus, carriers located near such facilities could soon see advantages in switching to LNG-particularly carriers that can run a truck in close proximity to the fuel supply, such as local, regional, or some linehaul operations.

The Canadian East Coast is a favorable location for LNG HPDI deployment, as is Vancouver. There’s a natural gas liquefaction plant near there that releases some product on an occasional basis. The U.S. East Coast has LNG import terminals as well, but California remains the most likely place to stage the initial roll-out.

As for the pricing of the fuel, Zehr stresses it’s impossible to toss out a number at this point. The raw material is reasonably priced, but the spread between diesel and LNG isn’t yet that dramatic.

To date, Westport has proven that LNG works in a heavy-duty diesel engine with comparable performance and efficiency, and lower emissions. Fueling infrastructure will be an issue for some time, but with diesel’s increasingly volatile price, and the propensity toward lowering our dependence on foreign oil supplies, LNG could establish itself in certain areas sooner than some might expect.