The present study aims at contributing to the development of a methodology to predict and improve the ignition performances of aircraft combustors. A model has been developed to investigate the early growth of a spherical ignition kernel in a two-phase flow mixture. It has been combined with a multiphysic code through two different approaches. The ignition kernel model is used to build the ignition probability map of a combustor. The output of the model can also be introduced as an initial condition in an unsteady simulation to test the flame propagation in the combustor. To validate both methods, RANS and LES simulations have been performed on an experimental combustion chamber, reproducing one sector of an industrial combustor.
As part of the investigations of the ignition of jet-engines under altitude conditions, a detailed data base was built with the results of experiments on the two-phase flow produced by an actual swirl air/kerosene turbojet injection system. The injection system had a fairly simple geometry. It was used with liquid kerosene injected through a pressure-swirl fuel atomiser. In this case the measurements were carried out at atmospheric pressure in a windowed combustion chamber, with air at ambient temperature. The tested equivalence ratio was 0.95 which corresponds to an air mass flow rate of 0.035 kg/s. For this operating point, we obtained the velocity field of the gas phase under non-reactive conditions by LDA. The axial velocity component of the gas phase was also measured in the burning spray using an original method with a phase Doppler device. The data recorded with the PDA were also processed to obtain the kerosene droplet sizes and velocities under reactive conditions. The same phase Doppler device was used in non-reactive conditions to measure the size and velocity distributions of the kerosene droplets in a section close to the injection system exit in order to complete the data base with the boundary conditions for the liquid phase. In addition the flame was visualised qualitatively. The picture of the stabilized flame was processed with an Abel transform to compare the LDA/PDA measurements with the flame structure, obtained under the reactive conditions. Finally, unsteady pressure measurements were taken under non-reactive conditions and the LDA measurements processed, close to the injection system exit, to get the PVC (Precessing Vortex Core) frequency. The data were analysed to determine the influence of the spray combustion on the two-phase flow. The geometry of the whole experimental setup and the data base are available to other researchers for testing and validating spray combustion models and unsteady two-phase flow numerical simulations.
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