Improving pre-turbine selective catalytic reduction systems in marine two-stroke diesel engines using hybrid turbocharging: A numerical study of selective catalytic reduction operation range and system fuel efficiency

In this article, a performance evaluation of a novel system solution combining a hybrid turbocharger and a pre-turbine selective catalytic NOx reduction system is carried out. Pre-turbine selective catalytic system are used with marine two-stroke diesel engines to comply with International Maritime Organization Tier III. The system solution focuses on expanding the selective catalytic reduction operation range which is limited by fuel sulphur content by increasing exhaust temperature at low engine loads. The extended operation range is to be achieved while minimizing any fuel consumption penalties. Increasing the operation range brings improvements to emission levels during manoeuvring operations which are often carried out close to populated areas. It also provides flexibility by enabling emission reduction during slow steaming operations in which mitigating fuel consumption penalties is paramount. In addition to system evaluation in still water conditions, furthermore evaluations have been carried out taking into consideration the effect of waves on the system performance. Investigating the effect of operating in waves bring additional insight that is relevant for predicting performance in operational conditions. Analysis of the system solution found that improvements in selective catalytic reduction operation range can be achieved while also improving fuel consumption. Fuel consumption is significantly improved in the high load range. Effect of realistic operation conditions where found to affect performance; however, significant effects are only found for harsh sea states in the load range below the design point.