z. h. chen

An uneven mixing of hydrogen-blended natural gas will lead to hydrogen embrittlement in distribution pipelines, thereby affecting the quality of terminal gas, and thus highlighting the importance of ensuring the uniformity of hydrogen and natural gas mixing. In this study, FLUENT software was used to simulate three different hydrogen filling modes, namely, T-tube, bending-tube, and static mixer, and the mechanisms underlying the mixing of hydrogen and natural gas under different filling modes were analyzed. In addition, we assessed the influences of gas velocity, hydrogen blending ratio, and mixer length and blade angle on the mixing effects of a static mixer. The results revealed that among the three mixing methods assessed, the static mixer has the best overall mixing effect. Increasing gas velocity was found to have no significant effect on the mixing of hydrogen and natural gas. With an increase of hydrogen blending ratio, the mixing uniformity of hydrogen and natural gas increased from 99.49% to 99.95%, whereas there was an increase from 84.12% to 99.05% when the length of static mixer was increased, and an increase from 59.53% to 99.78% in response to an increase in blade angle. Our findings in this study can provide a methodological reference for increasing the mixing uniformity of hydrogen and natural gas in hydrogen-blended natural gas pipeline networks, and thereby contribute to the safe and rapid development of the hydrogen energy industry.

The hollow projectile is a new type of projectile that has complex water entry hydrodynamics characteristics and has attracted significant attention in recent years. As such, it is important to investigate the effects of different entry velocities and aperture diameters on the cavity morphology, cavitation, dynamics, and motion characteristics of hollow projectiles when entering water at high speeds. In this study, four stages of an open cavity, cavity stretching, cavity closure, and cavity contraction in the water entry processes of a hollow projectile at 50–200 m/s and four aperture diameter projectiles at 100 m/s were studied using the volume of fluid (VOF), realizable k-ε turbulence, and Schnerr-Sauer cavitation model. With an increase in the speed, the depth of the cavity closure increases, thereby advancing the closure time. The timing of the surface closure at 50 m/s is clearly different from that at 100–200 m/s. Cavitation is not obvious and is near the cavity wall at 50 m/s, although the entire cavity is almost filled with vapor at 100–200 m/s. The friction resistance has two step points when impacting the water surface and entering the water completely. As the velocity increases or the aperture ratio reduces, the splash is higher, the cavity volume is larger, the cavitation phenomenon is more obvious, the cavity closure time is delayed, and the frictional resistance of the projectile is greater. The results of this study can guide the production and application of hollow projectiles in the future.

For diesel engines equipped with a combined spiral/tangential inlet, the main object of the valve structure and valve lift dissimilitude strategies is the valve, the changes of both will alter the motion state of the in-cylinder airflow, which has an important impact on the formation and combustion of the mixture. In order to investigate the flow performance of valve structure and valve lift dissimilitude, this paper used computational fluid dynamics (CFD) numerical simulation and multi-parameter regression methods to optimize the dual intake valve structure and obtained three valve structures with better intake performance first. Then, the optimized intake valve structure models were combined with the valve lift dissimilitude schemes to conduct steady-flow tests for the intake port. Through the reasonable combining of the two, the intake performance of the original engine was further improved. The results show that the valve structure has a relatively small influence on the intake mass, while it has a greater effect on the formation of the swirl in the cylinder, increasing the swirl ratio by 8.0%. The optimized valve structure model was combined with the valve lift dissimilitude scheme. It was found that the valve structure with optimal intake mass combined with the dissimilitude scheme of the largest valve lift of the spiral inlet could increase the flow coefficient by a maximum of 1.9%. The valve structure of the optimal swirl ratio combined with the dissimilitude scheme of the largest valve lift of the tangential inlet could increase the swirl ratio by a maximum of 9.7%. This study can guide diesel engines with combined intakes to increase the intake mass and improve the intake performance.