Featured　Application　A　control　strategy　for　an　ORC　is　designed　and　a　transient　simulation　is　performed　together　with　an　ICE.　The　method　can　be　used　to　develop　the　coordination　control　of　ICE-ORC　combined　system.　Abstract　Currently,　internal　combustion　engines　(ICEs)　are　still　the　main　power　for　transportation.　Energy　conservation　and　emission　reduction　for　ICEs　have　become　the　driving　force　of　the　industrial　R&D　in　recent　years.　Organic　Rankine　cycle　(ORC)　is　a　feasible　technology　to　recover　the　waste　heat　of　an　ICE　so　that　the　energy　efficiency　can　be　enhanced　apparently.　However,　there　are　still　many　obstacles　needed　to　be　overcome　for　the　application　of　an　ORC　together　with　an　ICE.　When　a　vehicle　is　driving,　the　operation　conditions　of　the　ICE　vary　in　a　large　range.　The　operation　of　the　ORC　needs　to　be　regulated　accordingly　to　achieve　maximum　efficiency.　In　this　study,　the　operation　characteristics　of　an　ICE-ORC　combined　system　is　investigated　and　the　transient　performance　is　analyzed.　First,　an　integrated　simulation　model　of　the　ICE　and　the　ORC　was　built　in　GT-POWER　software.　A　5　kW　single-screw　expander　was　employed　for　the　ORC　system.　The　working　characteristics　of　the　ORC　system　were　evaluated　under　various　working　conditions　of　the　ICE.　The　matching　principles　of　the　ORC　with　the　ICE　were　discussed　and　the　optimal　operation　conditions　of　the　ORC　over　the　entire　engine＇s　working　range　were　obtained.　Subsequently,　a　feedforward　control　strategy　for　the　ORC　system　was　designed　in　MATLAB/SIMULINK.　Finally,　the　entire　model　was　simulated　under　a　transient　driving　cycle　of　a　vehicle.　The　results　indicate　that　the　pump　speed　and　the　expander　speed　are　two　important　parameters　and　must　be　adjusted　according　to　the　engine＇s　working　condition.　The　speed　of　the　single-screw　expander　maintains　in　the　low-speed　region　and　the　pump　speed　is　tuned　to　achieve　a　high　evaporation　pressure　and　a　proper　superheat　degree　of　the　working　fluid　at　the　inlet　of　the　expander.　Thus,　the　net　power　output　can　be　maximized.　The　designed　feedforward　control　strategy　can　adjust　the　working　condition　of　the　ORC　automatically　to　match　with　the　working　condition　of　the　ICE.　The　ORC　operates　intermittently　and　an　impulse　power　is　output　under　the　urban　driving　conditions.　However,　the　working　time　of　the　ORC　is　increased　significantly　and　the　power　output　is　relatively　higher　under　the　highway　conditions.