Configurations selection maps of CO2-based transcritical Rankine cycle (CTRC) for thermal energy management of engine waste heat

CO2-based transcritical Rankine cycle (CTRC) can be used for the waste heat recovery due to its safety and environment-friendly characteristics, and also fits for the high temperature of exhaust gas and satisfy the miniaturization demand of recovery systems. It can provide a reasonable pathway toward thermal energy management of engine. This work proposes novel configurations selection maps of four CTRC configurations for waste heat recovery of engines. Except for considering a regenerator added to traditional CTRC (basic CTRC) recovering exhaust waste heat, a preheater driven by engine coolant will be also taken into account in this paper. Thus, the four configurations include the basic CTRC (B-CTRC), the CTRC with a preheater (P-CTRC), the CTRC with a regenerator (R-CTRC) and the CTRC with both of the preheater and the regenerator (PR-CTRC). As different CTRC configurations have advantage of performance indicators under different conditions, and the focused indicators may also be various with applications, this paper focuses on proposing a kind of selection maps, which is used for the selection of the four CTRC configurations in the field of engine waste heat recovery. Comprehensive performance comparison are researched in this paper from three aspects, net power output based on the first law of thermodynamics, exergy efficiency based on the second law of thermodynamics and electricity production cost (EPC) as an indicator of the economic performance. After the comparative analysis, three selection maps separately based on the three performance indicators are proposed to give the selection reference of the CTRC configurations under different design conditions, which refer to turbine inlet pressure and temperature in this paper. It is meaningful for the design and operating of the CTRC configuration used for waste heat recovery of engines. Besides, it can also be a new method that can be expanded to other recovery system selection (e.g. ORCs) in engine field or other fields (e.g. solar, geothermal).