Experience of operational development of starting characteristics of the APU combustion chamber

Abstract

The working process of a combustion chamber of the evaporative type used on most types of modern APUs is described in the paper. The combustion chamber discussed is characterized by a highly efficient working process with high combustion, low emissions of CO and NOx and low fuel-injection pressure in steady-state operation. However, the starting characteristics of the evaporative combustion chamber need to be improved. Ways of improving the starting characteristics of the auxiliary GTE with an evaporative type combustion chamber by optimizing the number and location of starting centrifugal injectors, the adjustment of the fuel feed law are discussed. Comparative computational and experimental data on the variations in combustion efficiency, partial operation of the turbine, gas temperature fields at the turbine inlet are given. Modeling of the startup process is performed by the developed nonlinear dynamic model of starting in which the combustion efficiency is represented as the product of two components: a known criterion of forcing Kv and a component approximated according to the thermal condition of the chamber evaporating pipe. Checking the engine starting with the activities for developing the combustion chamber at the high altitude-climatic test bench at the Central Institute of Aviation Motors has shown the necessity of adjusting the characteristics of fuel supply for high-altitude conditions N 4000m. It is shown that the maximum local gas temperature at the turbine inlet can be reduced by 50-60 C andthe range of reliable engine starting by fuel supply can be increased by the factor of 1.5-2.