Thermodynamic analysis of waste heat recovery using Organic Rankine Cycle (ORC) for a two-stroke low speed marine Diesel engine in IMO Tier II and Tier III operation

In the frame of the EU-funded project ECCO-MATE, new emission reduction strategies, as for example Exhaust Gas Recirculation (EGR), have been analyzed in order to decrease low speed marine diesel engine emissions, with emphasis on nitric oxides (NOx). In developing a cleaner engine, it is important to maintain performance at acceptably high levels, without increasing fuel consumption, as expected when using EGR. To this end, waste heat recovery technologies, such as Organic Rankine Cycles (ORC), appear as attractive alternatives. In this work, a 1-D gas dynamic model of a two-stroke, crosshead, low speed, 13.6 MW marine Diesel engine of Winterthur Gas & Diesel (WinGD) has been developed using Ricardo WAVE. The model has been first validated against experimental data. A Low Pressure (LP) EGR architecture has then been implemented in order to assess the engine performance under IMO Tier III operating conditions. The boundary conditions regarding the engine heat rejection, in particular for exhaust gas economizer, Scavenge Air Cooler (SAC) and High Temperature (HT) jacket cooling water, have been computed with the engine model developed, both for the baseline case (IMO Tier II) and the case with LP EGR (IMO Tier III). The computational results have been used as inputs to a thermodynamic process simulation model, developed in Engineering Equation Solver (EES), able to quantify the performance of different Organic Rankine Cycle (ORC) architectures and working fluids, with the scope of obtaining the maximum net power output for all engine operating points considered. The outcome of the present study is that, through the combined use and integration of innovative emission reduction strategies, as LP EGR, and waste heat recovery systems, such as ORC, it is possible to develop marine diesel engines which exhibit fuel consumption levels comparable to those of Tier II operation, at substantially reduced levels of pollutant emissions.