Experimental study on spray characteristics of aviation kerosene from a pressure-swirl nozzle in high-speed airflow with elevated temperatures

The combustor employed in small and medium-sized turboshaft engines is characterized by a small flame tube height and a large distance between adjacent burners, rendering it challenging to ignition. Moreover, the process of spray ignition exhibits complexity and needs further investigation. This study will delve into the performances of spray atomization and spark ignition within an annular combustor. Our objective is to thoroughly elucidate the interplay among atomization characteristics and flame propagation, seeking to shed some light on the fundamental mechanisms underlying flame dynamics from the perspective of timescales during the light-round processes. Planar Mie scattering and high-speed imaging technologies are employed to capture droplet distribution and time-resolved flame images, respectively. We have developed an algorithm capable of precisely tracking the flame front, enabling us to map out the trajectories of flame propagation. An analysis of transient flames reveals that the movement of leading points can be elucidated by the characteristics of the flow field and the distribution of the spray. It is demonstrated that the velocity of the flame front is affected by factors such as the pressure drop, equivalence ratio, and the distance between adjacent burners. Through an analysis of numerous spark events, this work identifies three distinctive flame propagation patterns: swirling-entrainment, archlike-entrainment, and another archlike-entrainment pattern. It is noted that these patterns exhibit variations by alterations in pressure drop and equivalence ratio.

Experimental investigation on dynamics of spray atomization, ignition, and flame propagation in an annular combustor

Zhu,

Hou,

et al. 2024

Investigation in the bag breakup of water droplet in airflow with different temperatures and densities

Zheng,

Gan

2024

This paper tries to clarify the respective significance of thermal effects and airflow density on the influence of bag breakup of water droplets in hot airflow. The bag breakup processes of water droplets in the airflow temperature range of 293 K (ρg=1.205 kg/m3) to 493 K (ρg=0.716 kg/m3) were investigated. Meanwhile, room-temperature gas mixtures with corresponding densities were prepared using room-temperature helium blended with room-temperature air to explore the bag breakup processes of water droplets. The results show that although the critical conventional Weber number (Wecon) of spherical droplets for bag breakup varies significantly in both streams, the critical initiation Weber number (Weini) of disk-shaped droplets for bag breakup remains almost consistent. Different deformation processes from Wecon to Weini result in different Wecon. In the gas mixtures with room temperature, the critical Wecon for bag breakup increases from 9.47 to 12.12 as the stream density decreases from 1.205 to 0.716 kg/m3. However, the critical Wecon for bag breakup decreases from 9.47 to 7.80 in the hot airflow at identical airflow density variations.

Influence of adjacent nozzles on flow and fuel atomization characteristics of the central nozzle in a triple-nozzle combustor

Wang,

Zhang,

et al. 2024

This paper examined the influence of adjacent nozzles on the flow and fuel atomization characteristics of the central nozzle in a triple-nozzle model combustor. High-frequency particle imaging velocimetry testing for airflow and phase Doppler particle analyzer testing for fuel particles were employed. Under the central nozzle air intake mode, the momentum exchange between the swirling flow and the surrounding stationary air leads to a seemingly shrinking flow field. While under the triple nozzles air intake mode, the low static pressure at the geometric center between adjacent nozzles attracts the swirling flows to converge, resulting in a larger expansion angle. Confinement has a complex impact on swirling flow. When the angle of the swirling airflow is small, it guides the flow to expand. However, when the angle becomes too large, it restricts further expansion. Observed Sauter mean diameter (SMD) peaks for the tested cases lie within a similar range, suggesting comparable spray angles. Nevertheless, the triple-nozzle air intake mode exhibits consistently higher SMD values and significantly greater spray core penetration depth. Instantaneous flow characteristics deepen the understanding of these differences in atomization results. The large range of airflow oscillation under the central nozzle air intake mode allows the airflow to directly interact with the droplets. While under the triple-nozzle air intake mode, the air flow path is too far away from the spray, resulting in that most droplets do not receive sufficient aerodynamic forces for atomization.