Research on performance optimization and fuel-saving mechanism of an Atkinson cycle gasoline engine at low speed and part load

The Atkinson cycle engine plays a key role in the development of hybrid electronic vehicle (HEV) because of greater fuel economy than Otto cycle engine. The thermodynamic analysis shows Atkinson cycle has the significant advantage of cycle efficiency and the ratio of expansion ratio to effective compression ratio and pressure rise ratio have great influence on efficiency. A performance optimization strategy for the Atkinson cycle engine is proposed through analysis of compression ratio range according to cycle efficiency at small pressure rise ratio and optimization of the high compression ratio and the late intake valve closure (LIVC) under the compression pressure constraint. The experimental results show significant improvements in pumping losses and fuel economy are achieved, thus verifying verifies the effectiveness of the optimization strategy and brake specific fuel consumption (BSFC) of is improved by 9% at 2000 rpm@2 bar and 8% at 3000 rpm@3 bar, respectively. The fuel-saving mechanism is investigated in depth. The increase of mechanical efficiency due to the reduction in pumping mean effective pressure (PMEP) is the main reason for the fuel economy improvement at low and medium load, while the increase of indicated thermal efficiency is the main reason at high load. The increase in intake pressure is the main reason for the decrease in PMEP. The Atkinson cycle engine can achieve more obvious constant volume combustion and the combustion quality has been greatly improved. These findings can be used as guidelines for the development of new Atkinson cycle engines.