Chambers of turboreactors with variable geometry: A response to the matrix of pollution in cycles at high temperature, high pressure [LES FOYERS DE TURBOREACTEURS A GEOMETRIE VARIABLE:UNE REPONSE A LA MAITRISE DE LA POLLUTION DM45 DES CYCLES AHAUTE TEMPERATURE, HAUTE PRESSION]

The pollutants emissions decrease doesn't seem easily achievable, particularly with advanced engines cycles conditions with high pressure, temperature, and fuel to air ratio. For a given fuel and air split, the combustor size can't be reduced without leading to relight altitude, combustion stability, and emissions concerns. In addition, the liners areas to be cooled remain considerable, the cooling airflow increase leads to higher fuel to air ratio in the primary zone and finally to unacceptable Nox emissions levels due to higher flame temperatures. In order to satisfy the trade off in between the combustor performance at low and high engine ratings, several combustor concepts are in development. Among them, the use of variable geometries to modulate the primary zone airflow seems promotive. Indeed, this concept allows to satisfy the compromise between the different ratings taking into account the decrease of the combustor panels areas to be cooled. That is the reason why this variable geometry concept is particularly suitable to high pressure and temperature engines cycles. In this paper, test results recorded on a five-cups sector fitted with a variable geometry injection system, and some measured performance on a full annular combustor are commented. It appeared that acceptable performance in term of combustion stability can be met with a low volume combustor. The cooling airflow reduction and the primary zone fuel to air ratio control allow to meet quite good and homogeneous combustor exit temperature profiles whatever the engine rating.