Dual split transcritical carbon dioxide cycle based on all engine operating conditions with high thermal adaptability

Abstract

To achieve carbon peaking and carbon neutrality goals, the CO2 transcritical power cycle is regarded as a promising technology for waste heat recovery. Variations in the working conditions of the engine can lead to significant fluctuations in waste heat. Therefore, to enhance adaptability to changes in heat sources, this study focuses on natural gas engines and proposes a dual split flow system for the CO2 transcritical power cycle based on heat capacity matching. This system features two diversion designs that can actively adjust the mass flow rate of carbon dioxide through different heat sources, thereby actively adjusting the equivalent heat capacity of the working fluid and matching the changes in heat sources under varying operating conditions. Based on actual road conditions, this study establishes a dynamic model of system and proposes a flow adaptive allocation control strategy for achieving heat capacity matching. The study conducted simulations of the dynamic system of the waste heat recovery system under all engine operating conditions, and interesting results showed that CO2 transcritical power cycle achieved positive net power output under all engine operating conditions, with over 91 % of engine operating conditions achieving a cylinder liner water utilization rate greater than 99 %, under the studied engine operating conditions, the flue gas utilization rate was greater than 92.2 %, and the engine BTE increased by 2.96 −7.04 %.