Heating and storage: A review on exhaust thermal management applications for a better trade-off between environment and economy in ICEs

Exhaust thermal management (ETM) plays a prime role in reducing pollutant emissions from internal combustion engines (ICEs), especially during cold-start and warm-up conditions. Under ever-stringent emissions and fuel-efficiency regulations, it is challenging to achieve a better trade-off between energy efficiency and emissions. This review paper is focused on the various ETM technologies and their applications, both engine-based and device-added. Furthermore, a comprehensive explanation and analysis of the various ETM technology principles, working characteristics, advantages, and limitations of their applications are provided to aid pertinent researchers in the choice and design of thermal management solutions. Engine-based ETM technologies cannot be used to their maximum potential because of additional fuel consumption or limited application range. Solutions integrating multiple technologies are becoming more prevalent to mitigate the fuel consumption and emissions penalties associated with engine-based ETM technologies. From an energy efficiency standpoint, closely coupled the ETM device, such as an electrically heated catalyst (EHC), with the controlled device is more efficient, due to the reduction of heat losses. In addition, ETM techniques based on waste heat recovery (WHR), especially thermodynamic cycles and thermal energy storage (TES) systems, are progressively gaining attention because of the demand to minimize CO2 emissions in the field of marine, locomotive and stationary power generators. However, the difficulty of miniaturization limits their development in the vehicle sector. Finally, the review concludes with suggested technological solutions and future work directions to address the challenges that ETM technologies confront in applications.