On the method of combustion instability mode determination in a cylindrical chamber and usage with experimental data

This research focused on determining the frequency, amplitude, and mode of pressure oscillations in a cylindrical atmospheric combustion chamber. The method developed for this analysis used theoretical pressure transducer traces as obtained through the solution to the dynamic pressure wave equation. Parameters obtained therein were compared to experimental pressure traces using digital signal processing and Fourier analysis techniques. Validation studies of the methodology conducted on both theoretical and historical data were in good agreement with theory. The accompanying experimental program used gaseous oxygen and methane with nitrogen diluent as oxidizer and fuel. The experimental program test matrix attempted to match full scale rocket test conditions. Open chamber acoustic mode matching results generally showed that a second tangential mode was present. Orifice plate testing showed other tangential modes present. These included the 1T, 3T and 5T modes with the 3T mode most common. Axial signal comparison results rarely matched acoustic modes.