The Measurement of Performance of Combustors Using Passive Acoustic Methods: Additional Results

Abstract

§This paper presents results obtained as part of a “proof of concept” program being carried out at the University of Nevada, Reno and the NASA Glenn Research Center. The purpose of this program is to determine the feasibility of using passive acoustic methods to determine the performance of jet engines and/or turbines. Data were recorded from six (6) acoustic transducers (microphones) mounted on a combustor ring and installed on a High Pressure Burner Rig (HPBR) located at the NASA Glenn Research Center. The HPBR was operated over several hours using a prescribed “duty cycle” of different fuel/air mixtures. Time frequency signal processing of the data showed that passive acoustic methods could be used to determine fuel/air ratios. These results have been reported in a previous paper. This paper presents additional results obtained by applying other signal processing techniques to the same data set. Correlation techniques and a multiple signal classification (MUSIC) algorithm were applied to the data from each of the microphones. The MUSIC algorithm provided pseudospectrum estimates of the signals by performing eigenspace analysis of the signal’s correlation matrix. The MUSIC algorithm was particularly suited to this data since it is narrow band and has dominant frequencies. Preliminary results presented in this paper indicate that this approach may lead to the ability to generate isothermal maps of a crosssection of a combustor.