Engine efficiency at maximum power, entropy production and equilibrium thermodynamics

TL;DR

This paper explores the efficiency of heat engines at maximum power, connecting thermodynamic principles with entropy production and equilibrium concepts, and introduces simplified formulas and intermediate-reservoir effects.

Contribution

It presents two classical thermodynamics routes to derive engine efficiency at maximum power and highlights the effectiveness of a simplified efficiency approximation.

Findings

Simplified efficiency formula outperforms traditional bounds

Intermediate-temperature reservoirs influence engine efficiency

Maximum power principles align with classical thermodynamics approaches

Abstract

The Carnot engine sets an upper limit to the efficiency of a practical heat engine. An arbitrary irreversible engine is sometimes believed to behave closely as the Curzon-Ahlborn engine. Efficiency of the latter is obtained commonly by invoking the maximum power principle in a non-equilibrium framework. We outline here two plausible routes within the domain of classical thermodynamics to arrive at the same expression. Further studies on the performances of available practical engines reveal that a simpler approximate formula works much better in respect of bounds to the efficiency. Putting an intermediate-temperature reservoir between the actual source and the sink leads to a few interesting extra observations.