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We examine a quantum Otto engine using both Bose–Einstein condensation (BEC) and normal Bose gas as working medium trapped in generalized external potential. We treated the engine quasi-statically and endoreversibly. Since the expansion and compression in both quasi-static and endoreversible take place isentropic, the expression of efficiency is similar. However, the power output in the quasi-static cycle is zero due to infinite and long stroke time. In contrast, with an endoreversible cycle, thermalization with two reservoirs takes place at a finite time. We use Fourier's law of conduction to formulate the relation between temperature of medium and reservoir, making work depend on heating and cooling stroke time. Moreover, we maximized the power with respect to compression ratio κ to obtain efficiency at maximum power (EMP). We found that EMP is significantly higher when using BEC as a working medium; meanwhile, EMP with normal Bose gas is just Curzon–Ahlborn efficiency. We also investigate the effect of thermal contact time τ with hot (τ h) and cold (τ l) reservoir on EMP. We found that when complete thermalization, τ h = τ l , stroke time occurs, there are no significant differences. Nevertheless, while incomplete thermalization arises, adjusting various cooling and heating stroke time provides a significant result on EMP, which is much higher at τ h < τ l stroke time and lower at τ h > τ l stroke time. We conclude this incomplete thermalization leads to the condition where residual coherence emerges which enhances the EMP of the engine. [ABSTRACT FROM AUTHOR]

We consider optimizations of Lenoir engine within a quantum dynamical field consisting of N noninteracting fermions trapped in multilevel infinite potential square-well. Fermions play a role as working substance of the engine with each particle nested at different levels of energy. We optimized this quantum heat engine model by analysing the physical parameter and deriving the optimum properties of the engine model. The model we investigated consists of one high-energy heat bath and one low-energy sink bath. Heat leakage that occurs between these two baths as expected will degenerate the efficiency of quantum heat engine model. The degeneration increased as we raised the constant parameter of heat leakage. We also obtained loop curves in dimensionless power vs. efficiency of the engine, which efficiency is explicitly affected by heat leakage, but in contrast for the power output. From the curves, we assured that the efficiency of the engine would go back to zero as we raised compression ratio of engine with leakage. Lastly, we checked Clausius relations for each model with various levels of heat leakage. We found that models with leakage have a reversible process on specific compression ratios for each variation of heat leakage. Nevertheless, the compression ratio has limitations because of the ∮ d Q / E > 0 after the reversible point, i.e. violates the Clausius relation. [ABSTRACT FROM AUTHOR]