To　improve　the　energy　efficiency　of　internal　combustion　engines,　this　study　develops　a　single-piston　free　piston　expander-linear　generator　(FPE-LG)　for　a　small　scale　organic　Rankine　cycle　(ORC)　in　a　waste　heat　recovery　system.　The　prototype　can　operate　continuously　and　stably,　thereby　indicating　that　the　single　piston　FPE-LG　has　a　feasible　working　principle.　The　operation　characteristics　of　FPE-LG　are　revealed,　and　the　effects　of　the　intake　valve　opening　time　(IVOT)　and　the　exhaust　valve　opening　time　(EVOT)　on　the　output　performance　are　investigated.　The　experimental　results　reveal　that　the　piston　can　run　at　a　relatively　high　velocity　near　the　dead　centers,　and　peak　acceleration　is　typically　achieved　when　the　piston　arrives　at　the　operation　left/right　dead　centers　(OLDC/ORDC).　The　piston　stroke　length　is　decreased　significantly　as　the　operating　frequency　is　increased.　The　peak　power　output,　peak　in-cylinder　pressure,　peak　velocity　of　the　free　piston,　and　utilization　ratio　of　the　piston　stroke　(eta)　are　increased　as　the　external　load　resistance　is　increased.　In　addition,　n　increases　with　longer　IVOT　and　can　reach　up　to　67.4%　when　the　IVOT　is　40　ms.　The　exhaust　pressure　decreases　as　the　EVOT　is　increased,　and　the　power　output　can　be　improved　by　regulating　the　IVOT　rather　than　the　EVOT.　(C)　2018　Elsevier　Ltd.　All　rights　reserved.