PROPANOL DROPLET FLAMMABILITY AND COMBUSTION IN AIR-DILUENT ENVIRONMENTS UNDER NORMAL AND REDUCED GRAVITY

Abstract

Reduced gravity and normal gravity combustion experiments were performed with individual fiber-supported propanol droplets with initial diameters that were typically in the 1.2 to 1.3 mm range. The environment was composed of an air-inert mixture at 0.1 MPa and about 298 K, where helium, carbon dioxide and xenon were separately used as inerts. In the experiments, the amount of inert gas in the environment was progressively increased until droplets could no longer be ignited. Droplet ignitability depended on the gravitational level as well as the inert gas in the environment. In general, the amount of inert gas required to suppress combustion was higher in reduced gravity than normal gravity. Use of xenon required significantly higher mole fractions for suppression of combustion relative to helium or carbon dioxide. Increasing the amount of inert gas generally decreased burning rates and increased flame standoff ratios. The data indicate that ambient gas transport properties play an important role in determining flammability and combustion behaviors of droplets.

Keywords:

• Flammability limits
• Liquid droplets
• Microgravity flame phenomena

This research was supported by the NASA Microgravity Combustion Program. The Technical Monitor was D. L. Dietrich. Gratitude is also expressed to E. Baumann, A. G. Birchenough, G. C. Blank, M. Camargo, L. A. Casco, D. L. Dietrich, C. Hampton, D. Kralj, S. Rogers, J. C. Owens, M. McMillan, L. Ross and J. Wessel for their assistance at the NASA Glenn Research Center at Lewis Field, to R. Lie and H. Tran for their efforts with the thermocouple measurement system and to V. Tam for his assistance with image analyses.

Notes

The table entries are based on thermocouple data.

µg refers to reduced gravity and 1-g refers to normal gravity.

µg refers to reduced gravity and 1-g refers to normal gravity.

µg refers to reduced gravity and 1-g refers to normal gravity.