Marine engine makers gear up for stiffer emissions standardsOct 1, 2013 11:04 AM
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The Tier 4 regulations begin to take effect in January 2014 for commercial engines with maximum power greater than 600 kW (804 hp). The EPA Tier 4 regulation represents a 90 percent reduction in particulate emissions and an 80 percent reduction in NOx compared to the Tier 2 standards.
Because these largest engines pump out the most pollutants, the requirements start in 2014 with the largest engines, from 2,682 to 4,962 hp (2,000-3,000 kW). All engines in the class must meet Tier 4 standards by 2017.
While the jump from Tier 2 to Tier 3 will be relatively easy, moving to Tier 4 is “a game changer,” according to Aufdermauer.
“It requires something more extreme than in-cylinder technology to get you to Tier 4,” he said.
To meet the Tier 4 NOx emission regulations, marine diesels will use after-treatment systems to clean the exhaust gases outside the engine. A common method will be selective catalytic reduction (SCR), using urea treatment found on highway semi truck engines since 2010.
A urea and water solution, or diesel exhaust fluid, scrubs nitrogen oxide to near-zero levels from the exhaust. Urea is also used as a nitrogen fertilizer in the agricultural industry.
The urea solution is carried in a separate tank and injected as a fine mist into the hot exhaust gases, reducing pollution to near zero and providing a small boost in fuel economy.
Urea bottles and pumps are a common sight at truck stops, and soon they’ll be part of marine fuel bunkering as well. Consumption of urea is about 3 percent of the diesel consumption.
For marine manufacturers that also offer diesels for the highway market, urea injection is a familiar proven technology.
“We see the on-highway products go through growing pains and the marine products lag on-highway and industrial off-highway for smaller products,” Aufdermauer said.
Sherman with MTU said the company has been running SCR systems for about five years. “It’s something we understand really well,” he said.
Additional engine tweaking will be required as well. For instance, the fuel system will have to operate at even higher pressures than Tier 3.
“For Tier 3 injection, pressure is at 1,600 bar and we’ll have to go to 2,200 bar which is pretty consistent in the industry,” Aufdermauer said. “And we’ll do a lot of work with piston and power cylinder valve overlap so we can control particulate matter in the cylinder and the NOx will be handled through SCR.”