QUESTIONS Model cycles Otto – SIIC – gasoline engine Diesel – CIIC – diesel engine Dual –IC Brayton – gas turbine & jet engine Brayton cycle Gas power Uses • • • • Auxiliary power generation Stand-alone power generation Naval propulsion Jet engine Brayton cycle 1→2 Isentropic compression 2→3 steady pressure heat addition 3→4 isentropic expansion 4→1 steady pressure heat rejection Brayton cycle • • Working fluid – air Ideal gas High AFR – air as working fluid Complete combustion Temperature limits Thermal reservoirs Open or closed model Steady pressure heat exchange Brayton cycle Work in & work out Heat in & heat out Thermal efficiency Pressure ratio Back work ratio Brayton cycle Variable specific heat – isentropic processes of ideal gas Constant specific heats - k Cycles Otto – r Diesel – r & rc Brayton -rp Example The rate of heat addition to an airstandard Brayton cycle is 3.4X109 Btu/hr. The pressure ratio is 14; the minimum and maximum cycle temperatures are 520oR and 3000oR respectively. Find the thermal efficiency, mass flow rate, and net power. Example A gas turbine power plant opeating on an ideal Brayton Cycle has a pressure ratio of 8. Tha gas temperature is 300K at the compressor inlet and 1300K at the turbine inlet. Find the bwr and thermal efficiency of the cycle. Example Use the preceding data and modify for an compressor isentropic efficiency of 80% and a turbine isentropic efficiency of 85%. How is the thermal efficiency affected?