Q6. Selective catalytic Reactors (SCR) are being extensively used in marine diesel engines for the compliance of Tier-III NOx emission requirements. Explain various types of SCRs in use with particular focus on the following:-
a) High-Pressure SCRs (HPSCR) vs Low-Pressure SCRs (LPSCR)
b) SCRs with static mixers.
c) SCRs installed upstream the turbocharger(s) Vs downstream turbochargers.
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.
Q9. NOx Tier – III requirements are getting mandatory as per MARPOL Annex IV. IN this context, briefly explain the following: -
a) Working principles and Components in a SCR system.
b) Operational sequence of a NOx control SCR plant.
c) Operational difficulties in SCR systems.
Q3): Exhaust emission control is a major global issue and under serious consideration by world shipping. In this context, comment on the following: -
a) Tier 2 and 3 emission regulation on main engine (4)
b) Primary NOx reduction vis-a-vis secondary NOx reduction measures. (4)
c) SCR for NOx Emission Reduction. (4)
d) Scavenge Air Moisturizing & Exhaust Gas Recirculation for ME. (4)
Q8. With reference to four stroke diesel engine emission control:
(a) Describe how the Miller Cycle operates to control NOx emissions;
(b) Describe, with reasons, the modifications needed for a medium speed engine to operate on the Miller Cycle;
Q7. Exhaust emission control is a major global issue and under serious consideration by world shipping. In this context, comment on the following: - A. Tier 2 and 3 emission regulation on main engine; B. Primary NOx reduction vis-a-vis secondary NOx reduction measures; C. SCR for NOx Emission Reduction; D. Scavenge Air Moisturizing & Exhaust Gas Recirculation for ME.
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.