Phase change materials for waste heat recovery in internal combustion engines: A review

Since most of the energy consumed by an internal combustion engine (ICE) is wasted, heat recovery from the exhaust and coolant is considered as a promising technology for improving the engine efficiency. The systems that used for recovering wasted thermal energy are called waste heat recovery (WHR) systems. However, most WHR methods suffer from main drawbacks such as difficult implementation, low thermal controllability and poor thermal storability. These drawbacks could be overcome by integrating thermal energy storage (TES) systems with ICEs. TES relies on sensible heat, latent heat and thermochemical storage. Latent heat storage method with phase change materials (PCMs) is the most utilized in ICEs because of its good controllability and high storage capacity. Therefore, this review presents the applications of TES with PCMs for recovering waste energy in ICEs. The literature shows that PCMs could be incorporated into different ICEs systems including exhaust recovery systems, cooling recovery systems, catalytic converters, diesel generators, evaporator and pressure regulators, additional diesel heaters, and cylinder's body. The previous studies on these systems show the potential of TES with PCMs in storing and recovering waste heat. Moreover, it is shown that the recovered heat by PCMs is mainly used for purposes of engine pre-heating during cold-start, maintaining hot temperature of catalysts for better conversion efficiency, and heating domestic and industrial water. Finally, the problems of PCMs with ICEs such as bulky system problem, high initial cost, corrosion issues, and poor stability; are also discussed in this review.