(a) Explain why highly efficient diesel engines tend to produce more NOx than low performance diesel engine (4) (b) Describe, with the aid of a sketch, a Selective Catalytic Reduction (SCR) unit for a marine propulsion diesel engine (8) (c) Explain why accurate monitoring of the exhaust gas flows entering and leaving a selective catalytic reduction unit are required and how these readings are used to control the reduction chemical supplied to the SCR unit (4)
Emission control

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