In a turbojet engine, subsequent to heat addition to compressed air, to get the power output, the working substance is expanded in
Option (A)
Turbine blades, which is essentially an isentropic process
Option (B)
Turbine blades, which is polytrophic process
Exit nozzle, which is essentially in isentropic process
Exist nozzle, which is a constant volume process
Correct Option:
Question Solution:
The surrounding air at velocity equal to the plane speed enters the inlet section which is designed as a diffuser. The air is slowed down and part of kinetic energy of the air dream is converted into the pressure. This type of compression is called ram compression further compression is achieved in a rotary compression, which usually an axial flow types. The pressurized air then flows into the combustion chamber where fuel is added. This raises temperature rapidly due to combustion chamber where fuel is added. This raises temperature rapidly due to combustion of fuel, which occurs at constant pressure. The hot combustion products then enter the gas turbine where they undergo a limited expansion through polytropic process. The turbine is designed to produce power, which is just sufficient to drive the compressor, fuel pump and other auxiliaries. The exhaust from the turbine is at considerably higher than the atmospheric pressure. These are then expanded in the exit nozzle and result in conversion of energy of hot gas unto kinetic energy. The gases emerge from the exit with a higher velocity. Due to increases in velocity i.e. momentum of gases flowing through the exit, a reaction or thrust in opposite direction is produced and this propels aircraft