An overview of PCM-driven heat recovery systems for sustainable energy applications

Abstract

The transition toward sustainable and energy-efficient energy systems requires advanced strategies to recover and reutilize waste heat from internal combustion engines (ICEs), where more than half of the fuel energy is typically rejected through exhaust gases and coolant streams. Phase change material (PCM)–based waste heat recovery (WHR) systems have attracted increasing attention due to their high latent heat storage density, near-isothermal operation, and suitability for transient engine conditions. This review critically synthesizes recent advances in PCM-based WHR systems for engine applications, with emphasis on system configuration, operating conditions, performance enhancement techniques, durability, and sustainability. The methodology is based on a comprehensive review of experimental, numerical, and techno-economic studies addressing single-stage and cascaded PCM thermal energy storage systems, PCM material selection, heat exchanger integration, and enhancement strategies such as nanoparticle additives and structural modifications. The reviewed literature consistently shows that cascaded PCM systems achieve higher heat recovery rates and improved energy and exergy efficiency, with reported gains of approximately 10–30% depending on design and operating conditions. Engine load strongly influences system performance, as higher loads increase PCM charging efficiency and reduce charging time. To overcome the inherently low thermal conductivity of PCMs, nano-enhanced PCMs and structural modifications have been widely adopted, yielding thermal conductivity enhancements of 30–150% and heat transfer improvements of .20–35%. Long-term studies indicate that composite and form-stable PCMs maintain thermal stability over extended cycling. While PCM-based systems demonstrate economic and environmental benefits in building applications, comparable techno-economic and life-cycle assessments for engine WHR remain limited. The novel contribution of this review lies in its integrated evaluation of thermodynamic performance, configuration strategies, enhancement methods, and sustainability aspects, identifying the gaps and providing an integrated framework to guide future research toward efficient, durable, and sustainable PCM-based engine WHR systems.