Q5. With reference to marine diesel engine selective catalytic reduction (SCR)
(a) Explain, with the aid of a graph, the influence that fuel sulphur content has on the operation of an SCR unit (4)
(b) Explain how the operation of a turbocharger system can have a detrimental effect on the unity when burning fuels with higher sulphur content (4)
(c) Describe, with the aid of a sketch, a system which maintains good engine performance of the turbocharger system and good NOx reduction when burning fuels with higher sulphur content, explaining how conflicting conditions are met (8)
Q3. (a) Describe, with the aid of a sketch, an external system for reducing engine NOx emissions, explaining the chemistry of the process (8)
(b) Explain why Urea is used in the Selective Catalytic Reduction process instead of ammonia. (4)
(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 (4)
Q2. (a) Describe, with the aid of a sketch, a diesel engine NOx reduction system using chemical supply, explaining the safety and pollution avoidance systems required. (12)
(b) Explain chemical reactions involved in the NOx reduction system described in part (a)
of the question. (4)
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