Research on the impacts of operating frequency at combustion process for opposed single-cylinder free piston generator under direct injection

The opposed single-cylinder free piston generator（OSFPG）has the characteristics of compact structure, variable compression ratio and low emission characteristics of common free piston generator, etc. More, it also has unique features such as high unit power, low vibration noise, and good motion stability, etc. So, in this research, a physical prototype platform based on OSFPG is built. For the key factors, both experiment and simulation have been combined to investigate the changes in OSFPG's work performance under different operating frequencies. It was found that operating frequency affected OSFPG's working characteristics through the entire combustion period. More, the combustion period of each combustion stage increased with the increase of the operating frequency, and the increase amplitude was gradually reduced with the advancing of the ignition advance angle, but the operating frequency affected the after burning period most. When the operating frequency changed from 15 Hz to 35 Hz, the after burning period was extended by at least 100 %. The important thing was that the indicated thermal efficiency of the OSFPG increased first and then decreased with the increase of operating frequency. When the operating frequency was 25 Hz, the OSFPG's indicated thermal efficiency could reach 40.4 %.