A jet engine is designed for maximum thrust on a test stand (static thrust) of 53kN. The tests are conducted at 25°C and 1 atm ambient conditions. The engine has a inlet mass flow rate of 77 kg/s at designed static thrust. Assume that the nozzle is perfectly expanded to begin with and check if that assumption may have a problem. The fuel used in the engine is Kerosene, which produces 46 MJ/kg of fuel combusted. Assume the engine design is such that the maximum allowable turbine temperature of 1500K is reached. Required:
a. Assuming stoichiometric fuel-air ratio, compute the nozzle exit velocity.
b. The gases enter the turbine at relatively low velocity, and assume this is zero for this calculation. Assuming isentropic expansion across the turbine and nozzle, what is the exit temperature of the exhaust gases. The exhaust gases contain the mass fractions of CO2, H20 and N2 in the stoichiometric ratio (See class notes). Assume that the R for the exhaust gases is close to that of air and gamma is a constant.
c. What is the Mach No of the exhaust gases? What does this tell you about the assumption of pe=pa?
d. What is the temperature rise of the air due to the stoichiometric combustion of Kerosene? Is the stoichiometric burning of Kerosene viable? Why or why not?
e. Usually in real operation, engines are operated in a lean fuel-air mixture. Assuming a lean fuel-air mixture, with a fuel-air ratio of 0.02, what is the compressor pressure ratio and efficiency of the Brayton cycle for the engine?