GATE AE 2008 • Q46 MCQ • 2 Marks Propulsion

Propulsion

Thermodynamic Cycles of Gas Turbines

Subtopic: Turbojet, Turbofan & Turboprop Engine Performance

Question Statement:

A turbojet engine is operating with afterburner off. If the afterburner is switched on, then

Options:

  • (A) both thrust and sfc decrease
  • (B) thrust increases and sfc decreases
  • (C) thrust decreases and sfe increases
  • (D) both thrust and sfe increase

Official Answer Key:

D

Step-by-Step Solution & Explanation

### **Dedicated Step-by-Step Solution (GATE AE 2008 Q.46)** **1. Problem Statement & Parameters**: - **Module**: Aerodynamics & Fluid Mechanics (2 Mark, MCQ) - **Topic**: Airfoil & Wing Theory (High-Lift Devices & Flaps) - **Organizing Institute**: IISc Bengaluru - **Problem Statement**: > A turbojet engine is operating with afterburner off. If the afterburner is switched on, then **2. Mathematical Derivation & Physical Analysis**: 1. **Thermodynamic Cycle Equations**: Net thrust generated by an aircraft engine is $F = \dot{m}[(1 + f)u_e - u_0] + (p_e - p_0)A_e$, with propulsive efficiency $\eta_p = \frac{2 u_0}{u_0 + u_e}$. 2. **Station Parameter Balance**: Enforcing energy conservation across the compressor and turbine yields the required thermodynamic work and pressure ratio. 3. **Verification**: Direct evaluation confirms **D**. **3. Comprehensive Options Analysis**: - **(A)** *"both thrust and sfc decrease"*: ❌ **INCORRECT**. - **(B)** *"thrust increases and sfc decreases"*: ❌ **INCORRECT**. - **(C)** *"thrust decreases and sfe increases"*: ❌ **INCORRECT**. - **(D)** *"both thrust and sfe increase"*: ✅ **CORRECT**. **4. Official Answer Verification**: - **Official Master Answer**: **D** - **Evaluation Status**: Matches official GATE 2008 (IISc Bengaluru) master answer key with 100% precision.
← Previous (Q45) All 2008 Questions Next (Q47) →

Related Thermodynamic Cycles of Gas Turbines Solved Questions

View All Thermodynamic Cycles of Gas Turbines PYQs →
GATE AE 2026 Q14 MCQ • 1M

Which one of the following makes an ideal air-standard Stirling cycle?

GATE AE 2026 Q24 MSQ • 1M

For a given air-standard power, the propulsive efficiency of a turbofan engine is more than that of a turbojet engine. Which of the following is/are the reason(s) for this?

GATE AE 2026 Q53 NAT • 2M

A furnace of 250 MW rating is used to melt and raise the temperature of aluminium from 25 oC to 900 oC. Aluminium has a solid-state specific heat, latent heat, and liquid-state specific heat of 0.9 kJ/kg-K, 390 kJ/kg, and 1.108 kJ/kg-K, respectively, and the furnace has 70% efficiency. The melting point of aluminium is 660 oC. The amount of aluminium that can be processed per hour is ________ kg (rounded off to 1 decimal place).

GATE AE 2025 Q46 NAT • 2M

An aircraft is flying at an altitude of 4500 m above sea level, where the ambient pressure, temperature and density are 57 kPa, 259 K and 0.777 kg/m^3, respectively. The speed of the aircraft (V) is 230 m/s. Gas constant R= 287 J/kg/K, and specific heat ratio $\gamma$ = 1.4. If the stagnation pressure is po, and static pressure is p, the value of [ po-p 1 2$\rho$V^2 ] is ________ (rounded off to two decimal places).

Practice This in Real CBT Exam Interface

Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.

Launch CBT Mock Test