Aiming at the recovery of exhaust energy for a diesel engine, a set of ORC (organic Rankine cycle) system is designed. The characteristics of the exhaust gas under various operating conditions are studied through experiment. Based on experimental results and theoretical calculation, effects of eight kinds of zeotropic mixtures on the performance of ORC system for exhaust energy recovery are discussed for vehicle engine under various operating conditions. Variation of net power output, thermal efficiency, exergy efficiency of ORC system and mass flow rate of zeotropic mixture under various operating conditions of engine is investigated. Two concepts - WHRE (waste heat recovery efficiency) and POIR (power output increasing rate) are - defined and studied. The results show that when the evaporating pressure is 2.0 MPa, the net power output of ORC system can reach up to 24.65 kW. Using this ORC system, the maximum WHRE is 8.5% and engine power output can be increased by 10.63%. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.