Comparison of different procedures for the optimisation of a combined Diesel engine and organic Rankine cycle system based on ship operational profile

At a time of strong challenges for shipping in relation to economic and environmental performance, the potential of waste heat recovery has been identified as among the most important technologies to lower fuel consumption. This paper presents the comparison of four different procedures for the optimisation of a combined Diesel and organic Rankine cycle system with increasing attention to the ship operational profile and to the inclusion of engine control variables in the optimisation procedure. Measured data from two years of operations of a chemical tanker are used to test the application of the different procedures. The results indicate that for the investigated case study the application of an optimisation procedure which takes the operational profile into account can increase the savings of the installation of an organic Rankine cycle from 7.3% to 11.4% of the original yearly fuel consumption. The results of this study further show that (i) simulating the part-load behavior of the ORC is important to ensure its correct operations at low engine load and (ii) allowing the engine control strategy to be part of the optimisation procedure leads to significantly larger fuel savings than the optimisation of the waste recovery system alone.