Gas turbines – effect of regeneration on performance In a Brayton (gas turbine) cycle equipped with an ideal regenerator of effectiveness greater than zero, which performance metric is primarily improved (for given pressure ratio and turbine/compressor isentropic efficiencies)?

Introduction / Context:
A regenerator (recuperator) transfers heat from the hot turbine exhaust to the compressed air before combustion. This internal heat recovery reduces external fuel input for the same turbine inlet temperature, affecting key cycle metrics of Brayton engines and stationary gas turbines.

Given Data / Assumptions:

• Fixed pressure ratio, component efficiencies, and maximum temperature limit.
• Regenerator with nonzero effectiveness; pressure drops neglected for simplicity.
• Open or closed Brayton framework treated similarly for efficiency trends.

Concept / Approach:

By preheating the compressed air using exhaust heat, the required external heat addition in the combustor is reduced, increasing cycle thermal efficiency η_th = W_net / Q_in. The net work per unit mass flow (and thus work ratio) may change only slightly or even decrease when accounting for added pressure drops in real hardware, but the idealized primary benefit is higher thermal efficiency at moderate pressure ratios.

Step-by-Step Solution:

Verification / Alternative check:

Brayton-cycle T–s diagrams with regeneration show a shorter external heat-addition segment; computed η_th rises markedly at low to medium pressure ratios.

Why Other Options Are Wrong:

Work ratio improvement is not guaranteed and may decline with real pressure drops.Pollution avoidance is not an intrinsic function of regeneration.“None” or “specific thrust only” do not describe the principal thermodynamic effect.

Common Pitfalls:

Assuming regeneration raises turbine work output; it primarily reduces required heat input, thereby boosting efficiency, not necessarily net work.

Final Answer:

thermal efficiency