In　order　to　improve　the　electric　efficiency　of　a　stationary　compressed　natural　gas　(CNG)　engine,　a　set　of　organic　Rankine　cycle　(ORC)　system　with　internal　heat　exchanger　(IHE)　is　designed　to　recover　exhaust　energy　that　is　used　to　generate　electricity.　R416A　is　selected　as　the　working　fluid　for　the　waste　heat　recovery　system.　According　to　the　first　and　second　laws　of　thermodynamics,　the　performances　of　the　ORC　system　for　waste　heat　recovery　are　discussed　based　on　the　analysis　of　engine　exhaust　waste　heat　characteristics.　Subsequently,　the　stationary　CNG　engine-ORC　with　THE　combined　system　is　presented.　The　electric　efficiency　and　the　brake　specific　fuel　consumption　(BSFC)　are　introduced　to　evaluate　the　operating　performances　of　the　combined　system.　The　results　show　that,　when　the　evaporation　pressure　is　3.5　MPa　and　the　engine　is　operating　at　the　rated　condition,　the　net　power　output　and　the　thermal　efficiency　of　the　ORC　system　with　IHE　can　reach　up　to　62.7　kW　and　12.5%,　respectively.　Compared　with　the　stationary　CNG　engine,　the　electric　efficiency　of　the　combined　system　can　be　increased　by　a　maximum　6.0%,　while　the　BSFC　can　be　reduced　by　a　maximum　5.0%.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.