Dr.-Ing. Paris A. Fokaides
As a research associate at Karlsruhe University, I designed and commissioned test facilities which mimic the conditions in jet engines combustion chambers, under atmospheric and elevated pressure conditions (20 bar). In particular, during my employment at Engler-Bunte Institute of Karlsruhe University, I designed and/or commissioned three combustion chamber units, of which I present the main concept of operation.
The test facility which was used for the implementation of my thesis was a two segment combustion chamber. It was designed to operate against corrosion in heat-resistant stainless steel (1.4841). The combustion chamber was divided into four different segments, which fulfill different requirements. The LDA segment had the function to enable laser-optical access to the flow field in the combustion chamber. In addition, in the LDA segment, radial sockets were installed, both for further application of probe measurement techniques and for ignition of the flame. The measuring windows, made of brass, were arranged at an angle of θ = 150 ° with respect to each other and were positioned far outwards, to minimize fouling effects due to the deposition of tracer particles on the quartz glass windows. A second segment with radial sockets, allowed access to the probe measurement techniques. The burnout segment and the annular combustor outlet geometry, with central hub lock, was designed in such a way to prevent the central backflow zone propagation over long axial distances beyond the top of the combustor due to the principle of two-dimensional constraint, which may result in ambient air mixing within the combustor.
The blue color of the lower three combustion chamber segments indicates that they were water cooled. The insulation of the combustion chamber against heat loss took place through two layers. The first layer, seen from the inside, was a ceramic high-temperature resistant fiber product based on aluminum-silicate fibers. The consistency and machinability of this material is comparable to soft wood. It has a high temperature resistance up to T = 1700K. The purpose of this insulation with ceramic was to minimize the heat loss of cooling water and the environment and to protect the metallic combustion chamber material from high temperatures. The second layer was a flexible mat of ceramic fibers sandwiched between the ceramic cylinder and the metallic inner wall.
The burner of the test arrangement consisted of the nozzle assembly and the nozzle. The burner mounted on the front had an outer diameter of 99mm and could thus be retracted over a length of l = 100mm in the experimental combustion chamber. Gas or liquid fuel was added via a central lance in the nozzle, which was located on the back of the burner. Due to the fact that the entire construction was designed to prevent corrosion, the fuel lance was made of heat-resistant stainless steel (1.4541), which has a relatively high thermal expansion coefficient, occur especially at high Luftvorwärmtemperaturen TL, before length changes, which were taken into account by constructive measures , The upper end of the burner head plate is not flat, but rises from outside to inside at an angle of φ = 3 °, so that the combustion chamber has a frusto-conical geometry. The entry of the nozzle block into the chamber was achieved with a radial seal and thus the penetration of ambient air into the combustion chamber by the ring vortex in the lower combustion chamber corners was prevented.
Since the measurement of the flow field within the combustion chamber by means of the Laser Doppler Anemometry LDA requires tracing, tracer particles were added to the two combustion streams by means of tubes in the feed nozzle. In order to obtain the best possible homogeneous mixing of the tracer particles, the baffle plates in the feed nozzle were of great importance. Both air flow rates could be pre-heated up to 450 ° C with the help of electrically operated air preheaters. There was the possibility of separate adjustment of primary and secondary air, depending on the requirements of the experiment. Volumetric flows supplied to the burner were measured by variable area flowmeters and could be converted into mass flows by the simultaneous measurement of pressure and temperature of the respective gas flows.