Marine Cat

NSCR Catalyst for Marine Engines


Engine exhaust has been effectively treated by catalytic converters since the 1970’s when the first automobile catalysts were placed on cars. Now EPA has a new requirement for catalytic converters on spark ignited, marine gas engines. The Environmental Protection Agency determined that for engines built after January 1, 2010, that are less than 500 HP, they would need to meet certain emission requirements. Why catalytic converters? Catalytic converters use chemistry to remove most of the hydrocarbons, nitrogen oxides and carbon monoxide from exhaust fumes. The emissions removed are some of the most harmful to our environment and air quality.

For recreational boat owners, the engine and exhaust system is now more complicated with additional sensors and electronics. To make sure the catalytic converter is working properly, oxygen sensors are required in the exhaust stream before and after the catalytic converter to measure the fuel/air mix in the exhaust. The oxygen sensors report to the engine’s electronic controls to adjust the fuel/air mixture as necessary (to achieve the stoichiometric air to fuel ratio of 14.7 to 1) and to deliver an exhaust gas mixture that the catalytic converter can clean up, leading to the fewest harmful exhaust emissions. At these stoichiometric conditions, a “three-way” catalyst can be employed, which allows the catalyst to eliminate Carbon Monoxide (CO), Hydrocarbons (HC) and Nitrogen Oxides (NOx) all at the same time with the same catalyst.

Marine Spark-Ignition Engines and Vehicles: Exhaust Emission Standards
Further EPA information regarding Recreational Marine Engines

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