Atomization characteristics of impinging-jet injectors in liquid rocket engines

Impinging liquid jet injectors are high efficiency injector types, which are typically used in liquid fuel rocket engines, with applicability, low cost and easy to manufacture. It allows the identical or different liquid jets to collide at a certain point at an angle, to form a liquid sheet as a result of the impact, and to break the layer into droplets due to instability in the formed sheet. Parameters such as the speed of jets, angle between jets, number of jets, and properties of the fluid passing through the jets directly affect the primary break-up process and thus the combustion stability and performance. In this work, like-on-like doublet, unlike doublet and triplet injectors were analyzed using computational fluid dynamics (CFD). Firstly, the analyzes were performed for a like-on-like doublet impinging injector and validated by an experimental study in the literature. Secondly, CFD analyzes of unlike doublet and triplet impinging injectors were carried out. In the first part, Large Eddy Simulation (LES) and Reynolds-averaged Navier Stokes ( RANS ) approaches were used for modelling the turbulence. Two different approaches were compared according to the experimental results in the literature and liquid sheet formation and droplet-size distribution at different jet velocities were examined. For this study, adaptive mesh refinement (AMR) method was applied by controlling the smallest grid size. The mesh independence was performed by examining the agreement of the different number of grids with the experiment, and therewith medium mesh was selected and subsequent studies continued over that computational mesh. In the second part, CFD analyzes of an unlike doublet injector are performed with liquid oxygen and liquid methane to investigate the atomization characteristics of a real oxidizer and fuel couple. After that, triplet impinging-jet injector analyzes were performed under the conditions used for the like-on-like doublet injector. Water was used for all three injectors and the differences in the sheet break-up length and droplet-size distribution were investigated. these two different studies were compared with the results of like-on-like injector studies accomplished in the first part. The medium computational grid was used for the analyzes in the second and third part. The analysis of like-on-like doublet impinging injector have a good agreement with Phase Doppler Particle Analyzer (PDPA) results for the droplet-size distributions. In general, droplet sizes decreased with increasing jet velocity. The reason for this is that turbulence is strengthened by increasing velocity. The stronger turbulence makes the greater instability and the stronger atomization.