Energetic and exergetic assessment of a two-stage Organic Rankine Cycle with reactivity controlled compression ignition engine as a low temperature heat source

Abstract

The waste heat from exhaust gases and cooling water of Reactivity Controlled Compression Ignition are used to launch a two-stage Organic Rankine Cycle. Considering the chemical kinetic mechanism, a Computational Fluid Dynamic model is presented to simulate the gasoline-diesel fueled RCCI engine. In addition, the performance of ORC is simulated by applying the Engineering Equation Solver software. By linking these two codes, a detailed Computational Fluid Dynamic-thermo analysis is carried out for the proposed heat recovery system and also the potential effects of some decision parameters on the performances of the combined Reactivity Controlled Compression Ignition – Organic Rankine Cycle system are studied in detail. The obtained results show that coupling Organic Rankine Cycle to the engine, improves Fuel Conversion Efficiency, break specific of Oxides of Nitrogen and Carbon Monoxide emissions as well as exergy efficiency to compare with sole engine operation state. According to the parametric analysis, can be seen that the temperature and pinch point differences of the evaporators, expanders’ efficiencies as well as the temperatures and mass flow rates of the engine exhausted gases and cooling water should be taken as the effective parameters to evaluate the proposed system in terms of the first and second laws of thermodynamic. Moreover, a comparative study is performed between Reactivity Controlled Compression Ignition engine and a conventional diesel engine as the heat source of the heat recovery system. Results indicate that the energy and exergy efficiencies of Reactivity Controlled Compression Ignition – Organic Rankine Cycle system are higher than diesel – ORC under the same operations load, although, using a diesel engine has a greater influence on the net output power of the attached cycle, regardless of the engines’ power.