Some effects of gravity on the behavior of premixed flames

This paper reports how, in ground-level tests on Bunsen-type premixed flames, a vertical fixed-frequency pumping effect can be observed at the tip of the flame, provided the latter is tall enough and the flow is laminar at the burner outlet. The effect vanishes completely under the microgravity conditions prevailing during parabolic flight tests, when natural convection no longer exists; in contrast, pumping frequency becomes higher as the acceleration of gravity increases. In a recent parabolic flight program, the frequency increase was measured while the aircraft was climbing at 1.8 g acceleration. Flight tests were supplemented by ground testing to derive the law of the frequency change as a function of pressure, equivalence ratio and flow velocity