THEORETICAL EVALUATION OF THE EXERGETIC ANALYSIS AND EXERGOECONOMIC OF ORGANIC RANKINE CYCLE (ORC)/RANKINE HYBRID ENGINE SYSTEM IN TRACTOR APPLICATIONS

Abstract

Given the increasing fuel price and strict environmental regulations in agriculture, it is strategic to apply waste heat recovery (WHR) system on the tractor engine for energy-saving and environmental performance. A comprehensive theoretical investigation is presented in this study of a new combination system of the high-temperature steam Rankine Cycle (RC) absorbing the waste heat from exhaust gas and the low-temperature Organic Rankine Cycle (ORC) utilising supplement waste heat coming from cooling water towards a more efficient way at recovering energy in heavy duty diesel engine. The system has been modelled thermodynamically, analyzed exergetically and evaluated in terms of exergo-economics through optimizing multi-objective genetic algorithms to obtain the highest exergy efficiency with lowest specific electricity cost. Novelties include the combination of a regenerative preheater in the ORC loop and green refrigerants like R1233zd(E) for the ORC and water-steam for the RC carefully selected according to global warming potential (GWP) and ozone depletion potential criteria. The results show that the net power output, exergy efficiency and brake-specific fuel consumption (BSFC) of 38.7 kW, 42.8% and 12.5% are obtained in this cycle respectively. Unit electricity cost of 16.85 USD/GJ is obtained based on exergoeconomic analysis with a payback period of 3.5 years at varying load conditions. Sensitivity analysis demonstrates the resistance to variations in exhaust temperature (400-550°C) and environmental impact assessment indicates the annual reduction of 15.2tons of CO2 emission per tractor. The cascade topology attains 18-22% higher system efficiency compared with the single-loop, which is an evidence for its novelty in off-highway applications. Experimental validation in the future is suggested to relate theoretical analysis and practical use.