Thermodynamic cycles with diluent that produce mechanical power, electrical power, and/or fluid streams for heating and/or cooling are described. Systems contain a combustion system producing an energetic fluid by combusting fuel with oxidant. Thermal diluent is preferably used in the cycle to improve performance, including one or more of power, efficiency, economics, emissions, dynamic and off-peak load performance, temperature regulation, and/or cooling heated components. Cycles include a heat recovery system and preferably recover and recycle thermal diluent from expanded energetic fluid to improve cycle thermodynamic efficiency and reduce energy conversion costs. Cycles preferably include controls for temperatures, pressures, and flow rates within a combined heat and power (CHP) system, and controls for power, thermal output, efficiency, and/or emissions.