Thermodynamic analysis and high-dimensional evolutionary many-objective optimization of dual loop organic Rankine cycle (DORC) for CNG engine waste heat recovery

Abstract

The complex and changeable working conditions of compressed natural gas (CNG) engines have brought great challenges to the efficient recovery of waste heat energy. The dual loop organic Rankine cycle (DORC) system can effectively recover and utilize CNG engine waste heat due to its structural advantages. Determining the nonlinear variations between operating parameters and thermodynamic performance serves as the basis for obtaining the thermodynamic performance limits of the DORC system. However, traditional analysis methods have obvious limitations in this area. Based on the bilinear interpolation algorithm, this paper comprehensively analyzes and evaluates the nonlinear and strong coupling characteristics between operating parameters and net power output, thermal efficiency, and exergy destruction. In addition, the comprehensive thermodynamic performance limits of the DORC system have a critical effect on its engineering application yet have not been thoroughly and comprehensively optimized. Therefore, this paper proposes an equilibrium-based thermodynamic high-dimensional evolutionary many-objective optimization (EMO) method for the DORC system. The optimal thermal efficiency, net power output, and total exergy destruction of the DORC system reached 37.11 kW, 14.27%, and 104.58 kW, respectively. Based on the optimization results under equilibrium and unequilibrium weight, the dominant relationship between the different thermodynamic performances of the DORC system is then analyzed. This research can provide a direct reference for analyzing and optimizing the comprehensive thermodynamic performance of the DORC system.