Parametric study for small scale engine coolant and exhaust heat recovery system using different Organic Rankine cycle layouts

This paper presents the study of four different engine coolant and exhaust heat recovery Organic Rankine Cycle systems using R245fa as working fluid and scroll expander as expansion machine. The parametric investigation suggested the fluid superheating temperature has limited influence on the simple structured ORC system (ORC_sim) with overall efficiency about 6.2% and average produced power around 0.59 kW under engine rated condition. The maximum rotational speed of the scroll expander is around 4000 rpm under different ratio of coolant and exhaust ratio of the Yanmar engine (6.8 kW), which means the designed ORC system can be easily used for electricity generation by directly connecting expander shaft to a conventional electrical generator. The BSFC reduction ratios of ICE + ORC_sim, ICE + ORCR_1 and ICE + ORC_pre under engine rated power are respectively 6.1%, 7.4% and 5.2%. And the overall effective energy efficiency by integrating ORC_sim, ORCR_1 and ORC_pre to the ICE can be improved by 6.5%, 8.0% and 5.4% under engine rated power condition.