Integrating engine thermal management into waste heat recovery under steady-state design and dynamic off-design conditions

Integrating engine thermal management into waste heat recovery will increase the applicability of vehicular engine waste heat recovery systems (E-WHRS). Research gaps exist from steady-state design to dynamic operation. Here, we propose and verify the practicability of thermally managing recirculated exhaust gas and engine coolant by an organic Rankine cycle-based E-WHRS. Three levels of analysis are performed to bridge the gaps: configuration identification, dynamic response characterisation, and control strategy implementation. At the design level, a split-flow configuration is identified as the E-WHRS combining thermodynamic and thermal management merits. Split-flow compensates for the working fluid's unfavourable physical property, achieving successful thermal management and outperforming a single-loop E-WHRS by 54.8% in net power output. With a validated dynamic model, dynamic response analysis reveals the distinctive thermal management characteristic of heat sources against external fluctuations. It is concluded that heat sources interfere with each other, with recirculated gas being the more sensitive one. The positioning of heat source exchangers also influences thermal management, with the upstream exerting major impacts on the downstream. Finally, proper control enables the E-WHRS to achieve successful thermal management under off-design engine conditions. The control increases thermal management efficiency by 67.7% compared with the open-loop operation.