Simultaneous neutron radiography of metal nozzle geometry and near-field spray

Sprays are prominent in various aerospace propulsion systems, but in-nozzle and near-field flow characteristics are not fully understood. Therefore, various nonintrusive probes have been applied to the measurement of spray characteristics. Such probes include well-known X-ray techniques and, to some extent, less well-known neutron methods, which are particularly useful for the study of flows inside nozzles. Unlike X-rays, for which the penetration depth of heavy metals is limited, neutrons are able to penetrate deeply into some metals, including aluminum, lead, and steel. Neutron imaging also complements X-ray imaging in light element detection, especially hydrogen, due to the large incoherent scattering cross section (80 b, in which 1 b 10−²⁸ m²) with hydrogen. Thus, for dense near-field sprays, which combine metal nozzles and hydrogen-based liquids (e.g., hydrocarbon fuels), it is advantageous to use neutrons rather than X-rays for imaging measurements. In this work, proof-of-principle in situ neutron radiography measurements of metal spray nozzles and water sprays were conducted. The neutron results were compared with optical shadowgraph images of the sprays, which showed a good agreement. Additionally, imaging of the nozzle interior geometry and water inside the nozzle was demonstrated, and it was shown that neutron radiography can produce quantitative liquid concentration by two-dimensional snapshot and three-dimensional tomography scans.