JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III AEROSPACE PROPULSION I Previous Question Paper (March - 2021 - R13/R15)

For air as an ideal gas, γ = 1.4 and c_p = 1.005 kJ/kgK. Given P₁ = 0.2 MPa, T₁ = 303 K, r_p = 6, T₃ = 1173 K, η_c = 0.9, η_t = 0.9, and ε = 0.8.

1. Compressor work: T_2s = T₁(r_p)^(γ-1)/γ = 303(6)^0.286 = 506.6 K. T₂ = T₁ + (T_2s - T₁)/η_c = 303 + (506.6 - 303)/0.9 = 529.2 K. W_c = c_p(T₂ - T₁) = 227.3 kJ/kg.

2. Turbine work: T_4s = T₃/(r_p)^(γ-1)/γ = 1173/(6)^0.286 = 701.7 K. T₄ = T₃ - η_t(T₃ - T_4s) = 1173 - 0.9(1173 - 701.7) = 748.8 K. W_t = c_p(T₃ - T₄) = 426.3 kJ/kg.

3. Cycle efficiency without regeneration: η = (W_t - W_c) / (c_p(T₃ - T₂)) = (426.3 - 227.3) / (1.005(1173 - 529.2)) = 0.308 or 30.8%.

4. With regeneration: T₅ = T₂ + ε(T₄ - T₂) = 529.2 + 0.8(748.8 - 529.2) = 704.9 K. Heat added Q_in = c_p(T₃ - T₅) = 1.005(1173 - 704.9) = 470.6 kJ/kg. η_reg = (W_t - W_c) / Q_in = 199 / 470.6 = 0.423 or 42.3%.

5. Percentage increase = ((0.423 - 0.308) / 0.308) × 100 = 37.3%.

The operating principle of a gas turbine engine is based on the Brayton Cycle, which involves continuous flow compression, combustion, and expansion. The process follows these stages:

1. Compression: Atmospheric air is drawn into the compressor, where its pressure and temperature are significantly increased.
2. Combustion: The high-pressure air enters the combustion chamber where fuel is injected and burned at constant pressure, resulting in a high-temperature, high-energy gas stream.
3. Expansion: The hot, high-pressure gases expand through the turbine, extracting work to drive the compressor and the load (or producing thrust in jet engines).
4. Exhaust: The remaining energy is discharged as exhaust gases.

Diagram description: The system consists of a rotary compressor, a combustion chamber, and a turbine mounted on a common shaft. Air enters the compressor, flows to the combustor, expands through the turbine, and exits. The turbine provides the mechanical power to sustain the compressor operation.