21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-5.8.1

CHARACTERISTICS OF MOMENTUM-DOMINATED HYDROCARBON TURBULENT DIFFUSION FLAMES

Hegde U., Yuan Z. G., Stocker D. P.*, Bahadori M. Y.**
National Center for Microgravity Research, Cleveland, USA; *NASA Lewis Research Center, USA; **Science and Technology Develop. Corporation, Los Angeles, USA

Keywords: momentum-dominated, hydrocarbon, turbulent, diffusion, flames

This paper presents results obtained in a study of turbulent propane and methane gas-jet diffusion flames under momentum-dominated conditions in a microgravity environment. Experiments were conducted at the 2.2-Second Drop Tower and S.18-Second Zero Gravity Facility at NASA Lewis. These were supported by numerical modeling of the flame utilizing a k-E formalism. Although momentum-dominated flames are important in practical applications such as jet and rocket engines: ramjets and other combustors, there is lack of information on these flames because, under normal gravity conditions, the high Froude numbers required also result in high Reynolds numbers. For hydrocarbon flames, this requirement leads to large flame sizes and intense turbulent conditions which are not practical to resolve. In the microgravity studies described here, momentum-dominated turbulent flames are obtained at moderate Reynolds numbers below 10000. Experiments to date have studied flame sizes, and temperature and pressure fluctuations. Findings described include (i) the larger size of the microgravity flames compared with their buoyancy influenced normal-gravity counterparts, (ii) the presence of relatively higher frequency components in the normal gravity spectra compared to the microgravity case and (iii) computations which show that the axial velocity in the downstream regions of the normal-gravity flame can be more than twice those in the micro gravity flame due to buoyant acceleration. The implications of these findings regarding the turbulence characteristics of the flames are discussed.

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