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# Heavy-duty LNGPUBLIC ACCESS

Designers are Taking Most of the Diesel Out of the Cycle.

[+] Author Notes

Executive Editor

Mechanical Engineering 124(05), 59 (May 01, 2002) (1 page) doi:10.1115/1.2002-May-5

## Abstract

This article focuses on the natural gas advocates who have set their sights on the diesel engine, and some of their new ideas are getting a workout in California. Otto-cycle engines fueled by natural gas are common in cities as the operators of buses and other vehicle fleets try to keep emissions in check. Natural gas mixes with air before it enters the cylinder. An electronically controlled injector introduces a small amount of diesel fuel at the end of the compression stroke to begin ignition. According to Caterpillar, more than 85 percent of the fuel consumed can be natural gas in some applications. Cummins Westport Inc., Vancouver, BC, is testing a 400-hp diesel engine that burns natural gas. The system injects diesel as a pilot and then follows it with natural gas. Electronic controls determine the timing and quantity of natural gas.

## Article

Natural gas advocates have set their sights on the diesel engine, and some of their new ideas are getting a workout in California.

The big attraction is that natural gas burns cleaner than other fossil fuels do. It churns out no sulfur oxides or particulates. Burning it yields fewer nitrogen oxides and less carbon dioxide than you get from liquid petroleum fuels.

Otto-cycle engines fueled by natural gas are common in cities as the operators of buses and other vehicle fleets try to keep emissions in check.

Now, a move is on to bring diesels into line. Caterpillar markets dual-fuel diesel engines ranging from 190 to 410 horsepower. They are electronically controlled to burn conventional diesel fuel and a variable mix of natural gas, which can be stored in compressed or liquefied form.

Natural gas mixes with air before it enters the cylinder. An electronically controlled injector introduces a small amount of diesel fuel at the end of the compression stroke to begin ignition.

According to Caterpillar, more than 85 percent of the fuel consumed can be natural gas in some applications. The engines can run on diesel fuel alone if they run out of natural gas on the road, where they can’t refuel.

The feedlot operation of Harris Ranch Beef Co. in Coalinga, Calif., has 20 Freightliner trucks with the 410-hp engine, a version of the Caterpillar’s Cat C-12. Manny De La Ossa, special projects manager at Harris Ranch, said the trucks have a range of 430 miles when they are fueled to capacity, with about 100 gallons of LNG and 20 of diesel.

A similar idea has been demonstrated by Alternative Fuel Systems of Calgary, Alberta. The company, however, is concentrating on natural gas Otto-cycle engines, including the conversion of diesels to spark ignition, according to its vice president of engineering, Paul Newman.

Cummins Westport Inc. of Vancouver, British Columbia, is testing a 400-hp diesel engine that burns natural gas. According to a spokesman, the engine compresses air, unmixed with fuel, like a conventional diesel. The system injects diesel as a pilot and then follows it with natural gas. Electronic controls determine the timing and quantity of natural gas. The company hopes to have a model on the market late next year.

Cummins Westport is a joint venture of Cummins Inc. of Columbus, Ind., and Westport Innovations Inc. of Vancouver. The 400-hp engine, a 15-liter diesel called the ISX-G, uses liquefied natural gas for onboard fuel storage. It is modeled on Cummins’ ISX engines, rated for 400 to 600 hp. At last check, the ISX-G was edging toward 500,000 miles of road service in 17 trucks.

Cummins Westport has 240,000 km on an in-house LNG diesel truck.

Cummins Westport estimates that 95 percent of the fuel consumption over a duty cycle will be natural gas. According to the company’s spokesman, the ISX-G’s fuel economy is comparable to that of a conventional diesel engine. A gallon of diesel fuel contains about 140,000 Btu, or something near 148 million joules. Its energy equivalent in liquefied natural gas is about 1.7 times the volume.

Dave Lynch, regional sales and marketing manager for Cummins Westport, said the next step will be to apply the concept to the ISM range of Cummins engines, which are rated up to 370 hp.

Most trucks testing the Cummins Westport ISX-G belong to Norcal Waste Systems Inc., which uses them in the Bay Area of California. Norcal owns 14 Peterbilt trucks fueled by LNG and has ordered nine more. The company built a natural gas fueling station in San Francisco in March.

The Bay Area Air Quality Management District, a regional branch of a state pollution control program, has helped pay for the trucks by funding the difference in cost between conventional diesel and LNG diesel.

According to Lynch, the premium represents not only the engine, but other components, such as a stainless steel tank to hold the gas at -258°F and pumps to keep the pressure at 3,000 psi when the gas enters the combustion chamber.

So far, the air quality district has chipped in $2.2 million. That covers the 14 trucks on the road and the nine ordered, and approves the purchase of another 15. It also includes$50,000 toward construction of the LNG station.

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