Agency switches fuel, engines to lower emissions

The Ann Arbor (Mich.) Transportation Authority (AATA) has begun using ultra-low-sulfur diesel fuel to power its buses. It also is replacing its current diesel engines with engines fitted with particulate filters. In combination, the fuel and the engines are expected to reduce emissions of particulate matter, hydrocarbons and carbon monoxide from the authority’s buses by 90 percent.

For several years, AATA has been studying alternative fuels and searching for a way to reduce emissions from its 100 buses. “We found over the years that a diesel engine will run on just about any kind of fuel base that you put in it, but what kind of emissions you get out is the important thing,” says AATA Executive Director Greg Cook. “We’re after an alternative fuel that will run our fleet and will give us a clean burn.”

AATA has been using low-sulfur diesel fuel in its buses since 1995. Last summer, AATA tested ultra-low-sulfur diesel fuel produced by London-based BP in its buses and found a 10 percent reduction in particulate emissions. Concurrently, the authority’s engine manufacturer, Detroit-based Detroit Diesel, upgraded the exhaust gas recirculation (EGR) control and the particulate filter aftertreatment systems on its Series 50 engine.

In July, the agency contracted with BP to supply approximately 1 million gallons of ultra-low-sulfur diesel fuel annually. Additionally, AATA ordered 19 buses with the new engines from Hayward, Calif.-based Gillig to replace aging vehicles. All new buses purchased by the agency will be fitted with the new engines, and all other buses will be retrofitted with particulate filters.

AATA is paying 12 to 15 cents more per gallon for the ultra-low-sulfur diesel fuel than its previous fuel, but Cook expects that price to drop as more fleets begin using the fuel.