LARGE-EDDY SIMULATION OF SPRAY COMBUTION IN A SECTOR COMBUSTOR FOR REGIONAL JET AIRCRAFT ENGINE - EFFECT OF DOUBLE-WALL LINER ON NOx FORMATION -

Abstract

Large-eddy simulation (LES) is applied to a turbulent spray combustion field in a sector combustor for a regional jet aircraft engine under development, and the effects of liner-cooling air flow outlet location (i.e., effect of single/double wall liners) on the combustion behaviour and NOx emission are investigated. The combustor is designed based on RQL (Rich burn, Quick quench, Lean burn) concept to reduce NOx emission. In the LES, Jet-A1 is used as liquid fuel, and individual droplet motion is tracked in a Lagrangian manner with a parcel model. As the turbulent combustion model, an extended flamelet/progress-variable approach, in which heat transfer between droplets and ambient gas including radiation and heat loss from walls can be taken into account, is employed. A detailed chemistry mechanism of Jet-A1 with 1537 reactions and 274 chemical species is used. The radiative heat transfer is computed by the discrete ordinate (DO) method. The LES results show general agreement with the experimental data, and the double wall liner design seems desirable for low NOx RQL combustor. INTRODUCTION Due to increasing environmental awareness worldwide, aircraft emission (NOx, CO, PM, etc.) control have become more stringent in recent years. The aircraft exhaust gas amount is severely limited by the regulations adopted by CAEP (Committee on Aviation Environmental Protection). By CAEP/6 regulations which came into effect in 2008, NOx emission is reduced by 12% and by CAEP/8 regulations which will come into effect in 2014 NOx will be reduced by further 15%. NOx regulation is expected to be more stringent in the future steadily (Moriai and Miyake, 2008). With this background, the low NOx combustor technology is very important in the development of the latest aircraft engines. However, the precise predictions of emission from the combustor including combustion characteristics are so difficult that the development cycles including hardware design, fabricating and evaluation tests are generally repeated many times to meet specification requirements and end up with huge cost and time. Therefore, if many hardware tests are substituted with numerical simulations, significant development cost reduction is possible. Because the internal flow of the combustor is composed of complex phenomena, including spray atomization, turbulent mixing, and chemical reactions, numerical simulation is very difficult. In recent years, LES (Large-eddy simulation) that can simulate unsteady turbulent flow well attracts attention. The purpose of this study is, therefore, to apply the LES to a turbulent spray combustion field in a sector combustor for a regional jet aircraft engine under development, and to predict the spray combustion behaviour and emissions such as NOx and soot. Special attentions are focused on the effect of liner-cooling air flow outlet location (i.e., effect of single/double wall liner designs) on the NOx emission. NUMERICAL METHODS Large-Eddy Simulation In this work, the compressible reacting flow equations with two-way coupling between the continuous phase (gas phase) and dispersed phase (fuel droplets) were solved using an unstructured large-eddy simulation (LES) solver: FrontFlow/Red as extended by Kyoto University, CRIEPI and NuFD (Numerical Flow Designing, Co., Ltd.), referred to as FFR-Comb. The numerical methods used here are basically the same as those written in our previous paper (Morial et al., 2013), but the compressible scheme in Demirdžić et al. (1993) is newly employed (Tachibana et al., 2015). As turbulent combustion model, a flamelet/progress-variable approach which is originally 1 June 30 July 3, 2015 Melbourne, Australia 9 2C-2