Alternative Fuels Displace "Pure" Diesel

Sept. 28, 2010

Twenty-two years ago in southern Brazil, a fleet manager was telling reporters what he thought of alcohol he was testing as a fuel for his diesel engines. In response to a question about the concept of alternative fuels, the manager declared without hesitation, “The best fuel for a diesel is diesel, and the best alternative fuel for a diesel is diesel.”

That's still largely true, except oil prices have made “pure” or “straight” diesel painful to burn. And what is becoming the mainstream product — ultra-low sulfur diesel (ULSF) — is getting panned for its slightly lower tank mileage and loss of lubricity that higher sulfur levels once provided. By federal mandate, ULSD had to be available since autumn of 2006 to fuel EPA 2007-powered trucks. It's becoming more common at fueling stations across the country, and anyone running an EPA '07 diesel should use it or risk damaging the exhaust system's aftertreatment devices.

Natural gas

Among the alternatives to diesel, natural gas is gaining the most monetary and patriotic backing. America has an abundance, and more reserves are being found. Natural gas is touted as an extremely clean fuel, emitting fewer greenhouse gasses than diesel.

Caterpillar and Cummins have long built stationary spark-ignition engines based on diesels, and experience shows that the clean-burning performance of filtered gas lengthens the time between crankcase oil changes and allows pistons, valves, cylinders, rods and crankshafts to last longer.

Cummins has worked with Westport Innovations to develop advanced combustion systems. One is high-pressure direct injection (HPDI), which uses a small amount of diesel to ignite the natural gas in the engine. This provides diesel-equivalent torque and horsepower, along with a range of 400 to 450 miles, the companies say.

Pacific Gas & Electric recently bought five Kenworth tractors powered by Cummins-Westport HPDI engines that burn liquified natural gas. Fuel costs should be half that of straight-diesel trucks. PG&E now has 1,300 natural gas-powered cars and trucks, some of them Freightliner medium-duty dump trucks with Deere gas engines. The company paid many thousands of dollars to have the trucks' original diesel engines yanked and the Deeres installed, but felt the emissions-reduction performance and the resulting “green” reputation made the conversations worthwhile.

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Biodiesel storage
Domestically produced biodiesel can displace more expensive imported oil and cuts some exhaust emissions. But it needs more filtering,and its storage life is only about six months.
PG&E's latest natural-gas vehicles are five Kenworth T800 tractors with Cummins-Westport high-pressure direct injection engines. They'll haul construction materials throughout the utility's service area.
LNG fueling takes a bit of know-how, but is not difficult, users say. 
LNG fueling stations use cryogenic vessels like these spherical tanks to keep natural gas liquified at super-cold temperatures. Such stationscan cost $350,000 to $1 million, but lower-cost stations are under development.
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