Abstract
© 2014 The Authors.Organic Rankine Cycle (ORC) based engine waste heat recovery (WHR) has been recognised as a promising technology as it can potentially improve the total engine efficiency significantly and has no noticeable effect on engine operation. In this paper, a model based investigation in this technology has been presented. A semi-dynamic model has been developed which consists of a detailed 1-D engine acoustic model, an ideal ORC thermodynamic model and a bridging model that couples the two sub-models and enables a dynamic data transfer between these two models, thus enables a semi-dynamic simulation. A parametric analysis has been carried out for working fluid selection that allows the best match of the engine working conditions. Water, R134a and R245fa were selected as working fluid candidates, and the simulation results suggest that despite water has the highest cycle efficiency, it is unsuitable to use it because as a wet fluid, water cannot be heated to superheated steam in most of the conditions. For the two organic refrigerants, R245fa is superior to R123a in terms of cycle efficiency. A cyclic simulation following a WHSC engine operation cycle suggests that the control of working fluid flow rate is necessary to maintain a high ORC cycle efficiency. A preliminary optimal control can achieve 8.1% fuel economy improvement throughout the whole cycle.