ENGINE EXHAUST SYSTEM
Your engine expels the by-products of the engine operation through
an exhaust system, just like cars do. In boats however, this exhaust
system mixes the debris left over after the power stroke of the engine
with the hot water that is expelled after cooling the engine. Basically
the exhaust system contains the exhaust manifolds, exhaust vent and
most likely a catalytic converter. Basically the exhaust fl ows through
the catalytic converter to purify the exhaust before expelling the
exhaust through the stern drive either just above the propeller, or
through the prop shaft.
Catalytic Converter
The catalytic converter is now required on modern engines. These
catalytic converters sit at the top of the exhaust manifolds on either
side of the engine. These boxes grow very warm and burn excess
hydrocarbons emitted by the engine, resulting in cleaner emissions.
These converters require oxygen to fuel the burning process of these
hydrocarbons, and will often times have an upstream oxygen sensor
that will adjust the fuel injection process to add more oxygen in the
fuel ratio. These converters have been implemented to provide cleaner
emissions.
Typical Catalytic Converter Diagram
3-10
Chapter 3
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