As the commercial marine industry adjusts their operations to meet EPA Tier 4 and IMO III emissions standards, Caterpillar Marine has introduced a solution built to maximize performance while meeting regulations. Caterpillar’s combination of a fuel-efficiency-optimized engine and a selective catalytic reduction (SCR) aftertreatment system is a solution that not only reduces NOx emissions, but can also lower a customer’s owning and operating costs in the process.
SCR technology has allowed Caterpillar to improve on marine engine designs and packages, while allowing systems to remain compact and easy to service, even improving overall fuel economy.
The dosing cabinet mixes the right dosage of compressed air [1A ] and urea [1B] drawn from the the urea tank and transfers it [2A]to the SCR module where it is injected in to the exhaust stream [2B]. In the SCR module  water evaporates and the urea is converted into NH3. When ammonia comes in contact with the SCR catalyst there is a reduction in NOx. The final output is carbon dioxide, nitrogen, water and oxygen.