Energy harvesting in diesel engines to avoid cold start-up using phase change materials

Abstract

In diesel engines, a significant amount of energy is wasted to the environment by the exhaust gases and coolants. In this study, a new design of the exhaust waste heat recovery (WHR) heat exchanger is proposed to preheat the intake air before supplying it into a diesel engine at the cold start-up conditions. The heat exchanger is designed of ribbed plates containing paraffin wax phase change material (PCM). This PCM is used to store the thermal energy coming out from the engine during the operation for later use in cold start-up conditions. A numerical model is developed and validated with the experimental results in the literature. The effect of different design conditions along with various operating conditions is evaluated. The influences of ribs height and spacing, engine rotational speed, and intake air temperature on the thermal energy storage were evaluated. Based on the results, it can be concluded that the highest thermal performance was obtained at a rib gap of 90 mm and a rib height of 7.5 mm. Through the warming-up process, in less than 1 min, the cold intake air temperature can be increased from 273 to 302.2 and from 283 K to 300.7 K. This results in overcoming the cold start-up difficulties, specifically in icy weather, and delivers preheated air to the engine after 1 min.