CFD simulations of the reacting flow through an annular, small turbojet combustor with pre-filming air-blast atomizer were performed with two different spray modeling approaches: including wall film computations (film formation and break-up) and injecting fuel droplets directly downstream of the pre-filmer. In the former method, the whole multiphase phenomena, starting from primary break-up at the exit of the hollow cone simplex injector up to the evaporation of the droplets stripped or rebounded from the fuel film are simulated. In the latter method, which is widely used for practical purposes, droplets are injected at a location downstream of the air-blast atomizer with a presumed size and velocity distribution. Droplets are simulated within Lagrangian-Eulerian framework in both cases and flow of the wall film is computed on shell region. Counting for the film formation and breakup in the computations shows that, some of the droplets do not join the. fuel film, instead rebound from the pre-filmer wall directly into the combustor. This leads to larger droplet sizes inside the primary zone delaying the evaporation process and consequently the main chemical reaction zone is shifted in the downstream direction. Related to this circumstance, a decrease in the combustion efficiency by ～1% and a 30 % increase in the pattern factor were observed at the combustor exit in the pre-filming case.
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