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October 2011 www.sname.org/sname/mt HC, and PM emissions, these reac- tions allow for the reduction of NOX. Unfortunately, these catalyst- enabled reactions require contact with the catalyst. The catalyst is typically thinly deposited over an object with lots of tiny holes and lots of surface area, like a lter. ese l- ters have the detrimental eect of causing substantial backpressure in the exhaust passages, essentially a pumping loss. Catalytic converter. Catalytic converters, like those used in cars, dont achieve the NO X emissions reductions required for NO X ECA zones. The problem results from the fact that the cost and eciency losses associated with a catalytic converter vary exponentially with the amount of emissions reduc- tions required. e large reductions needed to achieve the radical emis- sions reductions being imposed in this decade require a catalytic converter to use large quantities of catalyst, making the solution extremely expensive. e resulting eciency losses are also large and can only be relieved by adding to the cost of the system. To make catalytic converter technology practical, something is needed to boost this performance, similar to what is done with the SCR and advanced catalytic converter (ACC) solutions. Selective catalytic reduc- tion. SCRs chemically enhance a catalytic converter by injecting a reduction agent, like urea or die- sel fuel, into the exhaust before the catalyst. e reduction agent allows the catalyst to achieve much higher NOX reductions. A History of IMO Emissions Control Standards e maritime industrys IMO emissions control standards began with the 1997 Protocol, which entered into force on May 19, 2005. is protocol mandated the IMO tier I emissions standards. e 2008 Amendments added tier II and tier III emissions standards. e tier I and tier II emissions standards mandate small incremental emission reductions globally, and were achievable by clean- ing up an engines combustion process. ese tier I and tier II engine improve- ments resulted in some small losses in fuel efficiency. On the other hand, the tier III standards required radi- cal emissions reductions only in IMO ECA zones starting in 2016. e tier III standards require the implementation of emissions control after-treatment equipment, which will impose larger losses of energy and cost eciency. The IMO ECA zones are specifically designated as to which tier III emissions standards apply, only NO X, only SO X, or both NO X and SO X emissions. ese ECA zones have been approved for the Baltic Sea (only SO X), the North Sea (only SO X), and around North America (both NO X and SO X).Two-part standards The IMO emissions standards have two parts. One is focused on NO X emis- sions and the other on SO X emissions by limiting fuel sulphur content. IMO regu- lations roughly paralleled those imposed upon the automotive/trucking market. For the automotive/trucking industries, the leaded or sulphur content of fuel was greatly reduced to make it possible for the general adoption of the catalytic con- verter NO X-reduction technology. Given the similarities, the maritime industry was also being guided into the adoption of catalytic converters. IMO NO X emissions directly limit the NOX emitted per brake horsepower hour measured in the exhaust stream. Since NOX is formed during high-temperature combustion when oxygen burns? with nitrogen, this limit can be achieved by either suciently cooling combustion temperatures, which hurts fuel eciency, or by using one of various emissions con- trol technologies to avoid the creation of, or reduce or remove the NO X from the exhaust once it has been created. SOX emissions are regulated indi- rectly by putting a limit on the sulphur content of the burned fuel. Sulfur content in fuel leads to both SO X and particulate matter content in the exhaust. is reg- ulation states that its compliance can be achieved either by using suciently low-sulphur fuel or by achieving equiv- alent emissions levels as if suciently low-sulphur fuel was being burned. Since low-sulphur fuel costs more than high-sulphur fuel, there are signicant benefits should an operator be able to stay with the high-sulphur fuel. IMO emissions control regulation compliance is demonstrated through- out a ships life. Fuel sulphur levels are demonstrated by fuel testing records, or by measuring the resulting SO X emis- sions level. Early in the life of a ships engine, the engine manufacturer can use test bed engine data to demonstrate NOX compliance. e regulations make it clear that the ship owner is ultimately responsible for overall compliance. Later in the ships life, ship owners are required to demonstrate compliance via in-situ testing and records. Cleaner, more expensive fuels make the implementation of emissions controls easier.