Experimental and Numerical Study of High-Altitude Ignition of a Turbojet Combustor

Abstract

This paper aims at contributing to the methodology used for the numerical prediction of ignition inside a combustion chamber. For this purpose, experiments are carried out in a model combustor with improved optical access. Laser tomography and high-speed video give a first insight into the unsteady airflow and the flame structure. Laser Doppler anemometry is used to measure the gas flow velocity field, and the nonreactive two-phase flow is studied in detail using particle Doppler analysis. The velocity field of the burning spray is measured using particle image velocimetry. Ignition tests are performed to evaluate the minimum global equivalence ratio. This in-depth database is used to validate RANS simulations conducted in parallel using the ONERA computational fluid dynamics (CFD) code CEDRE. The numerical model for transient, spherical kernel ignition, proposed in previous work, has been improved and fully implemented in CEDRE. A first parametric study has been conducted on a basic configuration consisting of three validation cases: a gaseous mixture, a monodisperse spray, and a polydisperse spray. These validation cases are inspired from previous studies found in the literature and give a better understanding of the basic phenomena involved in the first stages of flame propagation. This model is then used in combination with CEDRE to estimate the ignition probability of given spark-plug positions in a more realistic configuration: the MERCATO combustor.