Cooling of gas turbine combustion chambers

Abstract

From the pressure-volume diagram for the turbo-jet cycle (see figure 1) it could be seen that between the compression and expansion stages there is another stage in which the working fluid expands at constant pressure. This is brought about by burning large quantities of fuel with extensive volumes of air in combustion chambers. Heat is released in such a manner that the air is expanded and accelerated to give a smooth stream of uniformly heated gas required by the turbine. Also, the pressure-volume diagram indicates that the combustion process should be carried out with a minimum of pressure loss. Such a loss would represent a reduction in area of the diagram, implying a reduction in the avail able work. As in any flow system, the pressure loss in a combustion chamber is proportional to a "pressure loss factor" which depends upon the geometry of the system, and to the square of the velocity. In order to minimise on pressure loss it is necessary to operate at relatively low velocity which would then need a combustion system of large cross-sectional area together with a diffuser at its upstream end. In a combustion process there is, however, another argument for reducing the level. of velocity. Air from the engine compressor enters the combustion chamber (see figure 2) at a velocity in the region of 122 to 183 / meters per meters per second [...].