The asymmetric Otto engine: frictional effects on performance bounds and operational modes

TL;DR

This paper analyzes an asymmetric quantum Otto engine with a harmonic oscillator, deriving efficiency bounds, examining friction effects, and mapping operational modes including heat engine, refrigerator, and heater.

Contribution

It provides analytic efficiency bounds for asymmetric driving schemes and characterizes the cycle's operational modes and phase diagram.

Findings

Friction in expansion significantly reduces performance.

Engine cannot operate as a heat engine at low temperatures.

Optimal operation regimes depend on sudden or gradual strokes.

Abstract

We present a detailed study of an asymmetrically driven quantum Otto engine with a time-dependent harmonic oscillator as its working medium. We obtain analytic expressions for the upper bounds on the efficiency of the engine for two different driving schemes having asymmetry in the expansion and compression work strokes. We show that the Otto cycle under consideration cannot operate as a heat engine in the low-temperature regime. Then, we show that the friction in the expansion stroke is significantly more detrimental to the performance of the engine as compared to the friction in the compression stroke. Further, by comparing the performance of the engine with sudden expansion, sudden compression, and both sudden strokes, we uncover a pattern of connections between the operational points, and we indicate the optimal operation regime for each case. Finally, we analytically characterize the complete phase diagram of the Otto cycle for both driving schemes and highlight the different operational modes of the cycle as a heat engine, refrigerator, accelerator, and heater.