Light Transmission in Sprays Impacted by Multiple Light Scattering:Monte Carlo Simulation Assuming the ECN Spray G

In this study, Monte Carlo simulation of photon transport through sprays has been achieved using the online “Multi-Scattering” software. Such simulations were focused on evaluating the accuracy of light transmission measurement of four distinct methods using diffuse light illumination without filtering (1),collimated homogeneous laser beam without filtering (2), structured collimated laser beam with multiple scattering suppression (3), collimated laser beam with Fourier filtering prior to detection (4). The number of unwanted photons, which have been scattered multiple times in the forward direction, is deduced.This leads to deduce the wrong optical depths (OD) from the Beer-Lambert law. The simulation parameters used, are directly related to some previous experimental data (sprays from ECN Spray G injector imaged from 0.25 ms to 1.00 ms after liquid injection), enabling direct comparison and interpretation of the outcomes. Results indicate that method (4) effectively suppresses multiple and forward scattering,providing accurate measurement of OD. Method (3) delivers effective results but is partially compromised by depth-of-field issues and the detection of single light scattering. Method (2), which does not incorporate any filtration, has been shown to be reliable for OD < 1, due to the low probability of multiple scattering. Method (1) results in a substantial underestimation of the OD, even at low droplet densities,on account of the considerable influence of single scattering. Based on those simulations, a procedure is proposed, allowing for correction for such effects.