Using finite time thermodynamic theory, an irreversible steady-flow Lenoir cycle model is established, and expressions of power output and thermal efficiency for the model are derived. Through numerical calculations, with the different fixed total heat conductances ($U_T$) of two heat exchangers, the maximum powers ($P_{\max }$), the maximum thermal efficiencies (${\eta }_{\max }$), and the corresponding optimal heat conductance distribution ratios ($u_{L_P(opt)}$) and ($u_{L_{\eta }(opt)}$) are obtained. The effects of the internal irreversibility are analyzed. The results show that, when the heat conductances of the hot- and cold-side heat exchangers are constants, the corresponding power output and thermal efficiency are constant values. When the heat source temperature ratio ($\tau$) and the effectivenesses of the heat exchangers increase, the corresponding power output and thermal efficiency increase. When the heat conductance distributions are the optimal values, the characteristic relationships of $P-u_L$ and $\eta -u_L$ are parabolic-like ones. When $U_T$ is given, with the increase in $\tau$, the $P_{\max }$, ${\eta }_{\max }$, $u_{L_P(opt)}$, and $u_{L_{\eta }(opt)}$ increase. When $\tau$ is given, with the increase in $U_T$, $P_{\max }$ and ${\eta }_{\max }$ increase, while $u_{L_P(opt)}$ and $u_{L_{\eta }(opt)}$ decrease.

Applying finite-time thermodynamics theory, an irreversible steady flow Lenoir cycle model with variable-temperature heat reservoirs is established, the expressions of power ($P$) and efficiency ($\eta$) are derived. By numerical calculations, the characteristic relationships among $P$ and $\eta$ and the heat conductance distribution ($u_L$) of the heat exchangers, as well as the thermal capacity rate matching ($C_{wf1}/C_H$) between working fluid and heat source are studied. The results show that when the heat conductances of the hot- and cold-side heat exchangers ($U_H$, $U_L$) are constants, $P\text{-}\eta$ is a certain “point”, with the increase of heat reservoir inlet temperature ratio ($\tau$), $U_H$, $U_L$, and the irreversible expansion efficiency (${\eta }_e$), $P$ and $\eta$ increase. When $u_L$ can be optimized, $P$ and $\eta$ versus $u_L$ characteristics are parabolic-like ones, there are optimal values of heat conductance distributions ($u_{L_P(opt)}$, $u_{L_{\eta }(opt)}$) to make the cycle reach the maximum power and efficiency points ($P_{\max }$, ${\eta }_{\max }$). As $C_{wf1}/C_H$ increases, $P_{\max }\text{-}{C}_{wf1}/C_H$ shows a parabolic-like curve, that is, there is an optimal value of $C_{wf1}/C_H$ (${(C_{wf1}/C_H)}_{opt}$) to make the cycle reach double-maximum power point (${(P_{\max })}_{\max }$); as $C_L/C_H$, $U_T$, and ${\eta }_e$ increase, ${(P_{\max })}_{\max }$ and ${(C_{wf1}/C_H)}_{opt}$ increase; with the increase in $\tau$, ${(P_{\max })}_{\max }$ increases, and ${(C_{wf1}/C_H)}_{opt}$ is unchanged.