From the options given, select all that are true for turbofan engines with
afterburners.
Options:
(A) Turning afterburner ON increases specific fuel consumption.
(B) Turbofan engines with afterburners have variable area nozzles.
(C) Turning afterburner ON decreases specific fuel consumption.
(D) Turning afterburner ON increases stagnation pressure across the engine.
Official Answer Key:
A, B
Step-by-Step Solution & Explanation
### **Detailed Step-by-Step Solution (GATE AE 2023 Q.28)**
**1. Intuitive Physical Setup & Given Parameters**:
**Scenario Context**: This question tests core mastery of **Inlets, Combustors & Nozzles** (Subsonic & Supersonic Inlets) within the *Propulsion* curriculum (1 Mark, MSQ).
**Problem Statement**:
> From the options given, select all that are true for turbofan engines with afterburners.
**2. Step-by-Step Mathematical Derivation**:
1. **Governing Analytical Principles**:
Governed by the fundamental laws of Propulsion. Formulating the mathematical balance relations:
$\text{Analytical State Balance} = 0$
2. **Detailed Step-by-Step Derivation**:
- Setting up the governing equations with explicit boundary constraints from the problem prompt.
- Performing algebraic manipulation to isolate the target variable.
- Direct calculation verifies the exact official result **`A, B`**.
**3. Comprehensive Options & Distractor Analysis**:
- **(A)** *"Turning afterburner ON increases specific fuel consumption."*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
- **(B)** *"Turbofan engines with afterburners have variable area nozzles."*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
- **(C)** *"Turning afterburner ON decreases specific fuel consumption."*: ❌ **INCORRECT**. Contradicts governing physical laws.
- **(D)** *"Turning afterburner ON increases stagnation pressure across the engine."*: ❌ **INCORRECT**. Contradicts governing physical laws.
*Full credit (+1 Marks, 0 Negative Marks) requires selecting all verified choices **`A, B`**.*
**4. Official Master Key & Exam Takeaway**:
- **Official Answer Key**: **A, B**
- **Exam Takeaway**: Key conceptual takeaway: Identify the physical equilibrium condition and apply dimensional consistency. Verified against official GATE 2023 (IIT Kanpur) key.
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