trucks: Dual Fuel Trucks Come Clean in California

December 1, 1998

5 Min Read
trucks: Dual Fuel Trucks Come Clean in California

Paul Harder

A new spin may be put on natural gas as a fuel for heavy duty trucks.

Taormina Industries, Anaheim, Calif., is using refuse trucks with dual-fuel engines that can switch from dual-fuel to diesel, reduce operating costs and reduce exhaust emissions by as much as 50 percent in particulate volume. And, the Sanitation Districts of Los Angeles (LACSD) has been using landfill methane gas (LFG) as an alternative truck fuel for two years.

Taormina manages solid waste collection and processing for six Orange County, Calif., cities in addition to recycling and processing the waste from another 55 surrounding communities - a total of some 4,000 tons per day.

Its fleet is made up of 271 Peterbilt, International, White/GMC and Volvo/White collection roll-off trucks and transfer tractors.

One year ago, Power Systems Associates (PSA), a Los Angeles Caterpillar Engine distributor, repowered 38 of Taormina's trucks, replacing mechanical diesels with dual-fuel versions of Caterpillar 3176B, C-10 and C-12 electronically controlled engines.

The repowering was the outgrowth of a joint research project that includes Taormina Industries, California's South Coast Air Quality Management District, AMOCO Oil Company, MVE/Drexel, PSA, Caterpillar Engine Division and Clean Air Partners of San Diego, who developed the technology. The consortium's goal is to demonstrate liquified natural gas (LNG) as a practical and clean-burning fuel for highway diesels.

Taormina's goal was to reduce exhaust emissions without escalating fleet capital and operating costs, or sacrificing on-highway engine performance. So far, the company reports that drivers are pleased, and there has been no significant impact to the firm's bottom line.

Most alternative fuel engines require spark ignition to burn natural gas. By contrast, the dual-fuel engines use diesel as a pilot for combustion ignition in an injected fuel mix ratio of 15 percent diesel to 85 percent natural gas.

Achieving combustion ignition helps these engines retain the operating characteristics of the conventional diesel engine: power and fuel efficiency. Taormina chose natural gas in liquefied rather than compressed form because its high density simplifies storage and handling. The trucks can run for 12 hours on a 90-gallon tank of LNG, a third the tankage needed for compressed natural gas.

Computerized control and coordination of the diesel and natural gas combustion events are what make the technology work. The engine's electronic control module and an interconnected electronic control unit on the natural gas circuit are programmed to start the engine on full diesel, switch to dual-fuel when the engine accelerates above idle speed, then return to pure diesel when the engine drops back to idle. Drivers report that there is no power drop when switching from diesel to dual-fuel.

Caterpillar has an exclusive license to this technology for use on its electronically controlled diesels, models 3126, C-10 and C-12.

Converting the engines requires replacing the conventional intake manifold with a manifold machined to accept Servojet natural gas injector valves. PSA's Kevin Campbell reports that neither the valve cover nor oil pan are removed during the conversion.

Changes to the truck are similarly modest: A 97-gallon cryogenic fuel tank and a related vaporizer, pressure regulator, solenoid valve and the gas injector valves on the intake manifold are added. These convert the high-pressure cryogenic LNG to low-pressure natural gas.

A malfunction in the natural gas circuit will cause the solenoid to instantly stop the natural gas flow and simultaneously switch the engine back to full-diesel.

Taormina's drivers report that the dual-fuel engines have the same power but run smoother and quieter than diesels.

Ron Stewart, Taormina's director of fleet maintenance, adds that oil analysis shows significantly lower oil contamination in the dual-fuel engines, allowing for extended oil change intervals. This has reduced lubricant and filter costs, lowered maintenance labor costs, reduced shop time and increased on-road time.

"If the engine wear rates stay as low as our oil samples indicate, then we could see engine life extended significantly," Stewart notes.

Until now, most alternative fuel vehicles are in home-at-night service because CNG tankage and limited fueling facilities limit their range. By tripling truck range, LNG and dual-fuel engines can lift this stricture, giving Taormina the flexibility needed to maximize the return on increasingly expensive equipment and crews.

When it is time to trade or sell the trucks, dual-fuel components can be removed easily, returning the trucks to the configuration and value of electronic diesels.

In another application of dual-fuel technology, the LACSD Puente Hills' 70,000-ton landfill operates three Caterpillar dual-fuel Class 8 truck conversions. The trucks use LNG that is produced and processed on-site instead of natural gas as the alternative fuel. According to LACSD and PSA, the LFG is the British thermal unit-equivalent to natural gas as the substitution fuel for these dual-fuel engines.

Hill climb tests performed by LACSD show that the power of the high-torque, dual-fuel engines closely matches that of diesel engines at normal power demands but can drop as much as 15 percent when these engines are pushed to their upper limits.

LACSD prefers dual-fueled trucks over those with dedicated alternative fueled engines because of the greater range, driver acceptance, reliability and ability to switch to full-diesel.

Acquisitions Eastern Environmental Services Inc., Mt. Laurel, N.J., has completed the acquisition of the Savino Companies, which provides solid waste collection in New Jersey and New York City.

Superior Services Inc., Milwaukee, has closed on acquisitions in central Illinois, northern Missouri and eastern Pennsylvania. It has acquired Santangelo Hauling Inc., Norristown, Pa., Macon County Landfill Corp., Decatur, Ill., and a transfer station owned by the city of Mexico in Audrian County, Mo. It also has announced the purchase and sale of assets in Wisconsin and Illinois with Browning-Ferris Industries, Houston.

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