Magnetic Resonance Imaging measurements inside and in the near-nozzle regions

Magnetic Resonance Imaging (MRI) is a non-invasive, three-dimensional imaging technique capable of measuring optically opaque media. Its signal can be sensitized to many parameters (velocity, diffusion/mechanical dispersion, air-liquid boundaries, etc). It is most sensitive where the sample’s density is the highest, i.e., inside the spray nozzle and in the near-nozzle regions; these are also regions which represent a significant challenge for the most common methods used in spray characterization [1]. In this study, results are presented using MRI 1H measurements of near-nozzle and inside the nozzle regions of a water spray generated by a ceramic flat-fan hydraulic atomization nozzle. High flow speeds and the medium heterogeneity required the use of short encoding times (0.1-0.5 ms) and the use of MRI techniques originally developed for materials science applications. Water flow inside the nozzle was well-characterized by proton density and velocity maps which demonstrated the flow acceleration, with rotation developing towards the orifice. The signal from the near-nozzle region showed the expected flat-fan pattern up to 4 mm away from the orifice, with steady signal loss with distance, as the liquid atomized into droplets. The results demonstrate the potential of MRI for measuring spray characteristics in these regions, and measurement challenges are discussed. Corresponding author: [email protected] Introduction: basics of MRI Magnetic Resonance Imaging (MRI) is a non-invasive 3D imaging technique that uses Nuclear Magnetic Resonance (NMR). Atomic nuclei with a non-zero spin have a magnetic moment that will orient itself along the lines of the external magnetic field B0 (similar to how a compass needle is aligned along the direction of the Earth field). The orientation time is characterized by a constant T1 that depends on how quickly the energy is transferred between the nuclei and the environment. After several T1 periods, the sample is fully polarized, and the macroscopic nuclear magnetization is formed. If an orthogonal magnetic field B1 oscillating at the resonant oscillation frequency