In the turbine section of a pure turbojet engine, which changes occur to the gas as it passes through?

• A. Pressure increases, Velocity decreases, Temperature increases
• B. Pressure decreases, Velocity increases, Temperature decreases
• C. Pressure increases, Velocity increases, Temperature decreases
• D. Pressure decreases, Velocity decreases, Temperature increases

Answer: (B)

In the turbine section the hot gas is allowed to expand while it transfers energy to the turbine blades. This expansion reduces the gas’s pressure and temperature because its enthalpy is being converted into shaft work. As the gas expands through the turbine, it also accelerates, so its velocity increases as it passes the blades. Therefore, the gas exits the turbine with lower pressure and temperature but higher velocity than it had entering. This is why the best description is a decrease in pressure, an increase in velocity, and a decrease in temperature.