Afterburning in open-cycle turbojet engines (military use) In military turbojets, fuel is sometimes burned in the exhaust (after the turbine) using an afterburner. This practice primarily increases which performance metric?

Introduction / Context:
Afterburning (reheat) adds fuel downstream of the turbine to raise jet exhaust temperature before the nozzle. It is used in combat aircraft to achieve short bursts of very high thrust for takeoff, climb, or supersonic dash.

Given Data / Assumptions:

• Open-cycle turbojet with an afterburner located between the turbine exit and nozzle.
• No change to compressor/turbine work with afterburner “on”.
• Objective: understand primary performance effect.

Concept / Approach:
Thrust for a pure jet depends on mass flow and jet velocity relative to flight speed. Afterburning raises exhaust temperature and therefore increases nozzle exit velocity for the same mass flow, producing more thrust. However, it achieves this at very poor propulsive and thermal efficiencies, drastically increasing specific fuel consumption and reducing range/endurance.

Step-by-Step Solution:

Verification / Alternative check:
Flight manuals and engine data show dramatic increases in specific fuel consumption with afterburner engaged, confirming that efficiency and range decrease even as thrust rises steeply.

Why Other Options Are Wrong:

Thermal efficiency and range do not increase; they decrease in afterburning operation.“Specific fuel consumption only” decreasing is incorrect; SFC increases significantly.

Common Pitfalls:
Confusing afterburning with reheating inside the Brayton cycle between turbine stages (a different concept). Afterburners add energy after the turbine and do not help shaft work or cycle efficiency.

Final Answer:

thrust only