Q6. (a) Explain why highly efficient diesel engines tend to produce more NOx than low performance diesel engines.
(b) Describe, with the aid of a sketch, a Selective Catalytic Reduction (SCR) unit for a marine propulsion diesel engine.
(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.
Q2. NOx Tier-III requirements are getting mandatory as per MARPOL Annex VI. In this context, briefly explain the following:
a) Working principles and Components in a SCR system. (6)
b) Operational sequence of a NOX control SCR plant. (5)
c) Operational difficulties in SCR systems. (5)
Q7. (a) Describe, with the aid of a sketch, an external system for reducing engine NOx emissions, explaining the chemistry of the process (6)
(b) Explain why Urea is used in the Selective Catalytic Reduction process instead of ammonia. (5)
(c) Explain why the exhaust gas quality must be monitored before and after the Selective Catalytic Reduction unit, stating how such monitoring influences operation of the SCR unit (5)
Q4. a) Describe, with the aid of a sketch, an external system for reducing engine NOx emission, explaining the chemistry of the process
b) Explain why Urea is used in the selective catalytic reduction process instead of ammonia.
(c) Explain why the exhaust gas quality must be monitored before and after the selective catalytic reduction unit, stating how such monitoring influences operation of the SCR unit.
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