JNTU B.Tech III AIRCRAFT PROPULSION Previous Question Paper (September - 2021 - R18)

Given parameters: Mach number M = 0.8, Altitude = 10 km, Thrust F = 50,000 N, Air mass flow rate m_a = 45 kg/s, Fuel mass flow rate m_f = 2.65 kg/s, Fuel heating value h_PR = 42,800 kJ/kg.

1. Specific Thrust (F_s):

2. Thrust Specific Fuel Consumption (TSFC):

3. Exit Velocity (V_e):

Using the thrust equation F = m_a(V_e - V_a) + (m_a + m_f)(V_e - V_a) is generally simplified as F = m_a(V_e - V_a) for basic calculations, or more accurately F = (m_a + m_f)V_e - m_aV_a. At 10 km altitude, the speed of sound a is approximately 299.5 m/s. Thus, flight velocity V_a = M × a = 0.8 × 299.5 = 239.6 m/s. Assuming negligible pressure thrust:

An afterburner (or reheat) is a component added to a turbojet or turbofan engine located between the turbine and the exhaust nozzle. It injects additional fuel directly into the high-velocity exhaust gases, where it burns, significantly increasing the gas temperature and pressure before expansion through the nozzle. This provides a substantial boost in thrust for short periods.

Advantages of an afterburning turbojet engine include:

• Provides a significant increase in thrust (often 30% to 50% or more) for short-duration maneuvers, such as takeoff, climb, or combat acceleration.
• Allows for supersonic flight capabilities in aircraft that might otherwise be limited by the thrust-to-weight ratio of a dry engine.
• Offers a high thrust-to-weight ratio compared to increasing engine size or adding more engines, as the additional hardware is relatively lightweight.
• Provides rapid response for emergency power requirements.