Accelerated Computed Tomography for Spray Characterization

Computed tomography (CT) is a valuable diagnostic technique for visualizing plume direction and assessing mixture quality within combustion chambers under engine-relevant conditions. High-speed extinction imaging followed by tomographic reconstruction enables temporally and spatially resolved measurements of liquid volume fraction and plume evolution in multi-jet sprays. Traditionally, tomographic reconstruction requires capturing multiple angular views by rotating the injector and averaging over numerous injections to ensure statistical convergence. This process is time-intensive, particularly due to the large volume of data acquisition and the corresponding delays in data saving, often requiring dozens of injections per view angle. In this study, we investigate the minimum number of injections required to achieve sufficient CT image quality, thereby significantly reducing experimental time. Two injectors are evaluated: a symmetric 8-hole Spray M injector from the Engine Combustion Network (ECN), and an asymmetric 6-hole injector designed for lateral mounting in the cylinder. Methanol is injected at ambient temperature (20°C) and a backpressure of 0.5 bar, with an injection pressure of 200 bar. We analyze how the number of averaged injections influences the convergence of optical thickness and the resulting CT image quality. Key metrics include optical density distribution, spray penetration, plume angle, and centerline profiles. By comparing these parameters across both injector configurations, we identify an optimized injection count for rapid tomographic imaging. Our results demonstrate that using a two-injection strategy can reduce the total acquisition time by over 90% compared to the previous 27-injection averaging approach for symmetric injector, without significant loss in image fidelity. These findings highlight the potential for broader and more accessible application of fast CT techniques in spray characterization, without the need for excessive experimental resources.