Research on in-cylinder mixing uniformity of natural gas engines based on the rotating injector

To address the issue of poor in-cylinder mixing uniformity in direct-injection natural gas engines, a novel pneumatic self-rotating injector is presented in this paper. Unlike traditional nozzles that rely on straight jets, the proposed structure utilizes the interaction between the rotating natural gas jet and the in-cylinder air motion (including tumble and swirl) to improve mixing uniformity. Based on this rotary injector, a computational fluid dynamics (CFD) model of the direct injection and gas mixing processes within the engine cylinder was established. Through numerical simulations, the influences of injection pressure, jet rotation direction, and nozzle outlet inclination angle on the gas mixing uniformity are investigated systematically. Furthermore, by analyzing the characteristics of the in-cylinder flow field, the underlying mechanisms responsible for the differences in mixing efficiency under various injection methods are elucidated. The results indicate that, within the injection pressure range of 1.0–1.5 MPa, the proportion of the best mixture concentration range (BMCR) increases from 5.38% to 6.62%, and the mixing uniformity tends to increase. Backward rotation achieves a BMCR proportion of 9.26%, which is 39.9% higher than that of forward rotation (6.62%) at 1.5 MPa, and also outperforms conventional vertical injection (7.61%) by 22.2%. Increasing the nozzle outlet inclination angle from 30° to 45° further raises the BMCR proportion from 9.26% to 11.49%. The aim of this study is to investigate the mechanisms by which in-cylinder mixing uniformity is affected by rotary natural gas injectors, providing a theoretical basis and data to support the structural design.