An experimental study of partially premixed flame sound

The occurrence of oscillating combustion and combustion instability has led to resurgence of interest in the causes, mechanisms, suppression, and control of combustion noise. Noise generated by enclosed flames is of greater practical interest but is more complicated than that by open flames, which is not clearly understood. Studies have shown that different modes of combustion, premixed and non-premixed differ in their sound generation characteristics. However, there is lack of understanding of the region bridging these two combustion modes. Sound generation by partially premixed flames was studied. Starting from a non-premixed flame, air was gradually added to achieve partial premixing while maintaining the fuel flow rate constant. Methane, ethylene, and ethane partially premixed flames were examined with hydrogen added for flame stabilization. The sound pressure generated by methane partially premixed flames scales with M5 compared to M3 for turbulent non-premixed methane flames. The sound pressure generated by partially premixed flames of ethane and ethylene scales as M ∼ 4.5. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).