Researchers propose Atkinson cycle engine optimization strategy to improve fuel economy

According to foreign media reports, the research and development team of Beijing Institute of Technology and Beiqi Foton Motor has proposed a strategy to optimize the performance of Atkinson cycle gasoline engines. Compared with traditional Otto cycle engines, this engine is more fuel-efficient and plays a key role in the development of hybrid electric vehicles .

Under partial load conditions, traditional gasoline engines have disadvantages such as large pumping losses and poor fuel economy, which cannot meet the economic and emission requirements of hybrid vehicles. With its many advantages, the Atkinson cycle engine has become the main choice for the development of hybrid vehicles. According to relevant research, 20%-30% of the fuel economy of hybrid vehicles is attributed to the development and application of the Atkinson cycle engine. At present, it is generally believed that the Atkinson cycle engine is an ideal hybrid vehicle engine.

In this study, researchers explored in detail the fuel-saving mechanism of the Atkinson cycle engine under low-speed and partial-load conditions. The team focused on the compression ratio range based on the cycle efficiency under small pressure rise ratio, and optimized the high pressure ratio and delayed intake valve closing (LIVC) under the compression pressure constraint.

At all pressure rise ratios, the Atkinson cycle has a clear advantage in cycle efficiency, especially at high pressure rise ratios. The ratio of pressure rise ratio/expansion ratio to effective compression ratio has a great influence on the Atkinson cycle. At a certain pressure rise ratio, the efficiency of the Atkinson cycle will first rise to the highest value, and then decrease as εe /εc increases.

Through thermodynamic analysis, the researchers preliminarily determined the compression ratio range based on the Atkinson cycle efficiency under small pressure rise ratio. Under the compression pressure constraint, the intake valve closing (IVC) under the compression ratio was optimized, and the compression ratio and valve timing were optimized through one-dimensional simulation.

Key findings include:

The team achieved significant improvements in pumping losses and fuel economy, verifying the effectiveness of the optimization strategy. The improvement in mechanical efficiency due to reduced pumping losses is the main reason for the improved fuel economy at low and medium loads, while the improvement in indicated thermal efficiency is the main reason for the improved fuel economy at high loads.

At 2000 rpm@2 bar and 3000 rpm@3 bar, the Atkinson cycle engine's BSFC increased by 9% and 8% respectively. The increase in intake pressure is the main reason for the decrease in pumping losses. The constant volume combustion process of the Atkinson cycle engine is more obvious, greatly improving the combustion quality.

The researchers said that they will explore the working process of the multi-cylinder Atkinson cycle engine and conduct in-depth research on the engine's power performance, emission performance, and how to effectively utilize the intake reflow effect.