Conceptual and experimental study of an Atkinson cycle engine of a Series-Parallel hybrid ‎electric vehicle

The Atkinson cycle engine plays a crucial role in advancing Hybrid Electric Vehicles (HEVs) due to its superior fuel efficiency compared to the Otto cycle engine. Thermodynamic analysis highlights the Atkinson cycle’s significant advantage in cycle efficiency, with factors such as the expansion ratio and effective compression ratio, influencing overall efficiency. This investigation focuses on converting an Otto cycle engine to an Atkinson cycle engine by implementing late intake valve closing and increasing the compression ratio. The optimization of the high geometric compression ratio from 10.7 to 12.4 aims to overcome the Atkinson cycle’s drawback, where combustion performance deteriorates due to a reduction in the effective compression ratio. GT-Power software is used to simulate engine performance under various operating points, and comprehensive experiments are conducted to determine the performance, fuel consumption, and combustion characteristics of the developed Atkinson engine. Experimental results show that the Atkinson cycle engine exhibits substantially lower overall fuel consumption compared to the Otto cycle engine, with an improvement in maximum thermal efficiency from 34% to 34.6%. Additionally, the fuel-efficient range of the Atkinson cycle engine surpasses that of the Otto cycle engine, with the minimum fuel consumption area now occurring at low-medium speed and medium-high-load operational conditions.