Thermal energy storage system for efficient diesel exhaust aftertreatment at low temperatures

To reduce cold-start emissions, a thermal energy storage (TES) system can be used in conjunction with the exhaust aftertreatment system. Phase change materials (PCM) can be used in the TES system to absorb the exhaust gas thermal energy, thus liquefying and storing it as latent heat. This allows storage of the exhaust gas thermal energy during the engine's high-load conditions and gradually releases the thermal energy back to the catalyst substrate during the engine-off period. Based on the results, implementing a TES system into the diesel aftertreatment system has shown great potential in reducing a vehicle's emissions, particularly for hybrid vehicles. This approach can assist the catalyst to activate the emissions’ conversion reactions straight after the cold-start. However, its effectiveness largely depends on the duration of the engine-off periods between the driving cycles. In this study, it was found that facilitating the heat transfer between the PCM and the catalyst can significantly improve the emissions’ reduction performance by avoiding the catalyst to light-out after the cold-start. A substantial improvement in the system's thermal behaviour was observed by using PCM additives and metallic catalyst substrates to increase the system's thermal conductivity. Although a TES system increases the aftertreatment cost and complexity, it can result in substantial emissions’ reduction over the vehicle's operating life. This can also translate into reduced vehicle fuel consumption and CO2 emissions, as the emissions-related fuel penalty will be minimized.