Extinction of Lifted Flames Under Normal and Micro-Gravity Conditions

Inert diluents are commonly used to suppress fires in both normal- and microgravity conditions. While previous work has elucidated the effects of introducing an inert diluent into a flow in which nonpremixed flames are established, little work has been done on the effect these diluents have on partially premixed flames (PPFs). PPFs are hybrid flames that have characteristics of both premixed and nonpremixed flames. Herein, experimental measurements and numerical simulations of PPF and nonpremixed flames diluted by CO$_2$ are conducted. Visual images are experimentally obtained in microgravity, while visual images, chemiluminescence, and radiation measurements are obtained in normal gravity . The resulting fluid dynamics and chemistry interactions are elucidated. PPFs and nonpremixed flames lift off as CO$_2$ is added to the flame prior to blowout. The quantity of CO$_2$ necessary for flame blowout decreases with increased partial premixing of the initial flow. The rich premixed reaction zone of a PPF is found to weaken as CO$_2$ is added to the flow.