Emissions challenge falls to local mtu distributor
The emissions specification was placed in the contract WETA offered for four new ferries for San Francisco Bay. After the contract was awarded, the task of meeting the stringent pollution requirement fell to local mtu distributor, Pacific Power Products Company, Ridgefield, Washington. Pacific Power is the mtu distributor in the Pacific Northwest and provides sales and aftermarket support to marine, industrial and power generation markets. “Pacific Power was confident that an environmentally friendly mtu marine engine could do the job with an assist from an accompanying pollutiontreatment system,” says Bill Mossey, corporate sales manager, Pacific Power.
For the engine, Pacific Power chose the mtu Series 2000, which can operate on a blend of biodiesel and ultra-low-sulfur diesel fuel. Even without a pollution-treatment system, the mtu engine exceeds EPA Tier 2 marine emission requirements. “The Series 2000 engine was a key part of our solution to this tough emissions problem,” says Mossey.
Besides being environmentally friendly, the Series 2000 engine features the highest horsepower in its class. A pair of these powerful engines helps each ferry meet WETA’s demanding 25-knot speed requirement.
SCR aftertreatment controls emissions
“The penalty for failure to meet the standard was complete rejection of the vessel — not just financial penalty, as is customary,” said Mossey. “That represents a much greater risk for boat builders, so it was an absolute must to meet the requirement.”
That meant deciding what type of pollutiontreatment system would be paired with the mtu engines to bring emissions down to the required level. The firm had previous experience equipping a ferry with a system for selective catalytic reduction (SCR), an aftertreatment that uses an aqueous urea solution to form ammonia for converting smog-producing NOx in diesel engine exhaust into harmless nitrogen gas and water vapor.
When used to treat diesel exhaust, SCR can reduce NOx in excess of 95 percent and can allow for combustion optimization for lowest fuel consumption and particulate matter emissions. SCR has long been used to reduce pollution from stationary sources. But the size and weight of SCR systems have made them impractical for many mobile applications.
Nevertheless, Pacific Power decided that SCR would be the best pollution-treatment option to package with the mtu engines. But the WETA ferry application would require a custom-designed treatment solution that would be less bulky and lighter than conventional SCR equipment. So the distributor worked with one of its suppliers to design a “compact SCR” system about one-fifth the size and weight of SCR systems developed for stationary pollution sources.
Results satisfy demanding customer
Acceptance testing done by WETA confirmed that Pacific Power’s mtu engine/SCR package did the job — and then some. Actual emissions were nearly 97 percent below EPA emission standards for Tier 2 marine engines, easily surpassing WETA’s 85 percent requirement. What’s more, Mossey notes, no particulate filter was required to reach the emissions target due to the exceptionally clean-running mtu engine. The mtu engine/SCR package is so clean, he adds, that it would meet the WETA requirement even if the engine were burning low-sulfur No. 2 diesel fuel rather than the ultra-low-sulfur diesel fuel mandated by California.
The testing results equate to net tailpipe emissions that would approximate EPA Marine Tier 4 standard levels which go into effect beginning in 2016 for marine diesel engines. Tier 4 requires reduction in NOx and HC emissions of up to 75 percent and a reduction in particulate matter of 80 percent from current Tier 2 requirements.
With the mtu engine/SCR pollution-control package approved for duty, two of the ferries ordered by WETA, Gemini and Pisces, are now in operation in San Francisco Bay. The other two vessels should be plying the same waters by the middle of this year. Equipped with their capable and super-clean power systems, the four ferries should please both environmentalists and passengers for years to come.