Spray structure of a multi-slit type throttleable gas–liquid pintle injector

Pintle injectors are a type of coaxial injector for liquid propellant rocket engines, which have radial and axial flows impinging on each other for atomization and mixing. Previous studies have investigated the spray characteristics of pintle injectors, specifically the spray angle and droplet size. However, the macroscopic spray structure of pintle injectors has not been sufficiently observed. This study focuses on spray structures of a multi-slit type throttleable gas–liquid pintle injector using shadowgraphy and two-phase structured laser illumination planar imaging (2p-SLIPI). Cold flow experiments using air and water with pintle tips of various configurations under a throttling range of 20%–100% were conducted. Three-dimensional spray structures from a multi-slit type throttleable gas–liquid pintle injector were reconstructed by 2p-SLIPI tomography, and the tomographic uniformity index (UI) of each case was calculated from the Mie scattering intensity. Cross-sectional spray patterns of the pintle injector could be classified into three types. The experimental results showed that the spray angle is significantly related to the cross-sectional spray pattern and UI of the pintle injector. A recommended range of the spray angle from the perspective of the UI was proposed.