Development of a fuel-air premixer for a sub-ppm NO_x burner

The concept of the cyclic periodical mixing combustion process, which had been presented earlier [1, 2], was implemented in a test combustor with external mixture preparation [3, 4]. As a major step towards the technical implementation of the process in gas turbines a low-pressure-drop fuel-air premixer on the basis of a vortex generator has been developed and implemented in the test rig. The premixer was optimized for preheat temperatures relevant for gas turbines, so that with high air preheat between 680 K and 780 K NO _x emissions below 1 ppm(v) and CO emissions below 8 ppm(v) (15% O₂, dry) were achieved in the tests for adiabatic flame temperatures between 1550 K at the blowout limit and an upper limit of 1630 K. As the measured emissions are almost identical with the data measured previously for the perfectly premixed case it can be concluded that the vortex mixer generates a spatially and temporally almost uniform mixture for properly selected fuel to air momentum flux ratios.