Ways to temporarily increase jet-engine thrust: Which method reliably boosts thrust in a turbojet/turbofan power unit?

Introduction / Context:
Aircraft engines sometimes require short-term thrust augmentation for takeoff or combat. Several techniques are discussed in propulsion courses, but not all are standard or broadly effective. This item separates proven practices from distractors.

Given Data / Assumptions:

• Conventional turbojet/turbofan with turbine exit stream available for tailpipe reheat.
• No fundamental hardware redesign beyond accepted augmentation systems.
• Safety, operability, and certification considerations matter.

Concept / Approach:

Afterburning (reheat) injects fuel in the exhaust duct and ignites it, significantly increasing jet temperature and exit velocity for a marked thrust rise, albeit with high specific fuel consumption. Water or water–methanol injection at the compressor inlet has historically increased mass flow and limited compressor temperature for some engines, but it is not generally used on modern turbofans due to performance and maintenance penalties. Direct ammonia injection into the main combustor is not a standard certified thrust-boost practice for aviation gas turbines.

Step-by-Step Solution:

Verification / Alternative check:

Military jet specs and propulsion texts document afterburner thrust increases on the order of 50–70% or more, confirming its effectiveness.

Why Other Options Are Wrong:

Water injection is conditional and dated; ammonia injection is atypical and problematic for combustion and materials; “all of the above” incorrectly groups them as equally valid.

Common Pitfalls:

Assuming any injected fluid increases thrust safely; overlooking turbine temperature limits and compressor surge margins.

Final Answer:

Burning additional fuel downstream of the turbine (afterburning/ reheat in the tailpipe)