Preliminary Design and Assessment of a Waste Heat Recovery System for a Hybrid-Electric Heavy-Duty Vehicle

Heavy-duty vehicles (HDVs) are major contributors to greenhouse gas emissions and urban air pollution, particularly during cold-start and transient conditions where fuel efficiency and exhaust aftertreatment systems are less effective. This study proposes a novel waste heat recovery (WHR) architecture integrated into a hybrid HDV powertrain to address these challenges. The system combines an Organic Rankine Cycle (ORC) and a parallel hybrid electric powertrain. A quasi-static simulation model is developed, incorporating validated sub-models for the Internal Combustion Engine (ICE), electric propulsion system, battery, and WHR unit. The model is parameterized and preliminarily validated using a publicly available dataset from a 6-cylinder turbocharged Isuzu FTR 850 truck equipped with a Euro III 7.79-liter diesel engine, recorded under real-world driving conditions in South Africa across 28 trips and three payload configurations (0 kg, 1500 kg, and 3000 kg). The dataset includes key variables such as engine speed, exhaust temperature, fuel flow rate, and coolant temperature, enabling the assessment of cold-start dynamics and thermal recovery potential. The simulation examines energy fluxes from the exhaust and coolant circuits and explores the synergies between hybrid energy management and WHR. The results indicate that the proposed system can reduce fuel consumption and improve exhaust thermal profiles. Fuel consumption savings are strongly affected by energy management, ranging from 15% with a simplistic constant power strategy to 32% with the adoption of a fuzzy logic-based control strategy. These findings support the feasibility of WHR–TES hybrid integration in HDVs and offer promising directions for compliance with future emission standards such as Euro VII, EPA 2027, and China VII standards.