Experimental characterization of self-excited combustion pulsation in a thermoacoustic combustor

•A new method for depicting the self-excited combustion pulsation was proposed.•Harmonic and coupling analysis of heat release, temperature and pressure was conducted.•Self-excited thermo-acoustic instability can be deepened by the new information. Combustion in a pulse combustor was commonly regarded as a quasi-regular pulsation process, or even a sinusoidal pulsation. However, how to precisely describe the pulsation process is still under investigation. This paper proposed a new method for depicting the thermo-acoustic coupling process in a Helmholtz pulse combustor based on three thermo-acoustic-related parameters including heat release, temperature, and pressure. We attempted to quantitatively characterize the combustion pulsation through meticulous depiction, harmonic analysis and coupling analysis of the three parameters. The transient temperature was measured by a tunable diode laser absorption spectroscopy (TDLAS) sensor, while the heat release and pressure signals were measured by a CH*-selected photomultiplier tube and a pressure transducer, respectively. The ensemble average-based data processing method was then utilized to obtain the variations of heat release, temperature and pressure with time within a pulsation period. To analyze the dynamic behaviors and coupling relationships quantitatively, the ensemble-averaged signals were further decomposed into the fundamental, second and third harmonic components. The phases and amplitudes of the three harmonics under different operation conditions were obtained and compared. Results indicate that the three parameters interact and couple with each other, which influences the generation and progression of the self-excited pulsation process. Coupling of the three parameters shows different characteristics under different operation conditions. In addition, the intake mode of the pulse combustor and the transportation and mixing behaviors of fuel and oxidant also influence the thermal and acoustic parameters. Addition of the temperature parameter to the thermo-acoustic coupling in combustion provides not only new and valuable information on the fundamental features of the self-excited thermo-acoustic instability, but also a new reference for in-depth understanding of pulse combustion, and hence for the design of high-performance combustor.