Experimentation with Porous Inert Material to Control Thermoacoustic Instabilities in Lean Direct Injection Combustion

Stringent environmental regulations require more efficient and cleaner jet engines for civil aviation applications. An interesting development has been the introduction of lean direct injection (LDI) combustion techniques. Previous research has proven that the LDI combustion yields lower nitrogen oxides and carbon monoxide emissions in gas-turbine jet engines. However, thermoacoustic instabilities remain an issue with LDI combustion. Previous research conducted at the University of Alabama has indicated that the insertion of a Porous Inert Material (PIM) can reduce such instabilities. Positioned on the dump plane, the PIM interferes with the flow field in the corner and central recirculation regions. In this study, a single LDI injector was tested without the PIM to ascertain the equivalence ratio at which a strong instability occurs and establish a baseline case. Then, experiments at several test conditions of interest are performed to determine the effect of the PIM. Measurements include acoustic probes to record the sound spectra and OH*- chemiluminescence imaging to characterize the reaction zone. PIM is shown to improve the acoustic performance although geometric optimization would be necessary to achieve the best results.