Applicability analysis of waste heat recovery technology and strategy exploration for hybrid electric vehicles under diverse road conditions

Abstract

Abstract The challenges of energy conservation and environmental protection are becoming severe. Therefore, hybrid electric vehicles (HEVs), owing to their low fuel consumption and low emissions, are being considered as the ideal transition models between conventional fuel vehicles and pure electric vehicles. The growing demand for increasing vehicle efficiency has motivated the introduction of waste heat recovery (WHR) technology in the automotive industry. The organic Rankine cycle (ORC), with its advantages of great flexibility, high safety, low cost, and low maintenance requirements, is considered to be a potential WHR method. Currently, only a few studies have been conducted on coupling the HEV with ORC-WHR systems, which focus on the exploration of hybrid powertrain strategies under a certain type of road condition, but lack the applicability analysis of WHR technology and strategy exploration for HEVs operating under diverse road conditions. To analyze whether the WHR system has considerable and valuable energy savings potential under various road conditions, an applicability analysis is conducted under nine types of standard driving cycles. Based on these, for better adaptability to the complex and changing road conditions, an optimization strategy for the HEV-WHR integrated system is proposed based on road condition recognition technology. The results reveal that the WHR system is not suitable for urban road conditions, but is well adapted to suburban and highway conditions. For example, under the NYCC (New York City Cycle) and the Artemis Urban Driving Cycle, the WHR system even increases energy consumption by 0.18% and 0.12%, respectively, while under suburban and highway road conditions, the overall impact of coupling the WHR system reduces energy consumption by 3.36%–10.60%. Meanwhile, in HEV-WHR system coupling with the above proposed optimization strategy, the state of charge (SOC) of the battery is more stable, the start and stop times of the WHR system decrease, the engine thermal efficiency and average motor efficiency are much higher than the efficiencies obtained without the optimization strategy, and the ultimate energy savings potentials are calculated as 3.19%, 3.59%, and 4.16% under the CLTC (China Light Vehicle Test Cycle), NEDC (New European Driving Cycle), and WLTC (Worldwide Light Vehicle Test Cycle) driving cycles.