Frederick L. Dryer
Department of Mechanical and Aerospace Engineering
Princeton University
Princeton, NJ 08544
Multi-Component Droplet Combustion Modeling
Anthony J. Marchese, Associate Professor
Department of Mechanical Engineering
College of Engineering
Rowan University
201 Mullica Hill Road
Glassboro, NJ 08028-1701
and
Department of Mechanical and Aerospace Engineering
Princeton University
Princeton, NJ 08544
Research Summary
A time-dependent, moving finite element model has been developed to simulate the combustion of liquid droplets in microgravity. The modeling approach, which was originally developed at Princeton University by Dr. S. Y. Cho, has been expanded to solve the problem of multi-component droplet combustion. To date, the microgravity combustion of pure heptane, pure methanol, methanol/water mixtures, and heptane/hexadecane mixtures have been successfully simulated. The calculations compare favorably with experiments in terms of droplet burning rates and flame positions.
OH* Chemiluminescence Model
A procedure has been developed to use hydroxyl (OH) radical chemiluminescence measurements along with numerical modeling to determine flame position and gain further insight into the structure of microgravity droplet flames. To validate this procedure, microgravity n-heptane and methanol droplet combustion experiments have been conducted. The spontaneous emission from electronically-excited hydroxyl radicals (OH*) within the envelope diffusion flame was measured using a UV-sensitive video camera. Chemical reactions describing the production, emission, and quenching of OH* were incorporated into the droplet combustion model. The modeling and experimental results indicate differences in the route of OH* production between n-heptane and methanol flames. In both cases, the location of maximum OH* emission intensity is very near the location of maximum flame temperature suggesting that OH* imaging is a good approach to measure the flame position and structure.
Non-Luminous Thermal Radiation Model
The effect of radiative heat loss from isolated droplet flames is usually assumed to be negligible. For the small droplet sizes studied in most isolated droplet combustion experiments conducted to date (< 1.0 mm), this assumption has been shown to be reasonable. For example, by neglecting radiation, a detailed numerical model accurately predicts the burning rate, flame position and extinction diameter for 1 millimeter-sized methanol/water droplets. However, recent space-based 3 to 5 millimeter methanol/water droplet combustion data show an increase in extinction diameter and a decrease in burning rate with increasing initial diameter. These results suggest that, at larger initial droplet diameters, the effect of radiative heat loss cannot be neglected. By including a radiation sub-model, the modified numerical model predicts that at droplet diameters greater than about 1 mm the effect of radiation results in a decrease in burning rate and a non-linear increase in extinction diameter with increasing initial diameter. At very large initial diameters (> 6 mm in atmospheric air), the model predicts that the droplet flame will ignite, but quickly self-extinguish due to excessive radiative heat loss.Microgravity Combustion Links
Droplet Combustion Modeling Papers
Marchese, A.J. and Dryer, F.L. "Radiative Effects in Space-Based Methanol/Water Droplet Combustion Experiments", Presented at the Eastern States Sectional Meeting of the Combustion Institute, Hilton Head, SC, December 1996.
Lee, J.C., Marchese, A.J., Tomboulides, A.G., Yetter, R.A., and Dryer, F.L. "Droplet Combusiton in a Low Reynolds Number Environment", Presented at the Eastern States Sectional Meeting of the Combustion Institute, Hilton Head, SC, December 1996.
Marchese, A. J. and Dryer, F. L., "The Effect of Thermal Radiation on Non-Luminous Droplet Combustion in Microgravity" , Combustion Science and Technology, In press, 1997.
Marchese, A. J. and Dryer, F. L., "The Effect of Non-Luminous Gas Phase Radiation on the Combustion of Large Droplets in Microgravity" , Presented at the Work-In-Progress Poster Session, Twenty-Sixth Symposium (International) on Combustion, Naples, Italy, July, 1996.
Marchese, A. J., Dryer, F. L., Vedha-Nayagam, M., and Colantonio, R., "Microgravity Combustion of Methanol and Methanol/Water Droplets: Drop Tower Experiments and Numerical Modeling", Twenty-Sixth Symposium (International) on Combustion, Pittsburgh, PA, 1996, p. 1209.
Marchese, A. J., Dryer, F. L., Vedha-Nayagam, M., and Colantonio, R., "Hydroxyl Radical Chemiluminescence Imaging and the Structure of Microgravity Droplet Flames", Twenty-Sixth Symposium (International) on Combustion, Pittsburgh, PA , 1996, p. 1219.
Marchese, A. J. and Dryer, F. L., "The Effect of Liquid Mass Transport on the Combustion and Extinction of BiComponent Liquid Droplets of Methanol and Water", Combustion and Flame, 105:104-122 (1996).
Marchese, A. J., Lee, J. C., Held, T.J. and Dryer, F. L., "The Effect of Detailed Chemistry and Transport on Microgravity Droplet Combustion", Third International Microgravity Combustion Workshop, Cleveland, OH, April 1995.
Marchese, A.J., and Dryer, F. L., "Transient Numerical Modeling of the Microgravity Combustion of Bi-Component Liquid Droplets: Heptane/ Hexadecane Mixtures", Western States/Central States/Mexican National Sectional Meeting of the Combustion Institute, San Antonio, TX, April 1995.
Marchese, A.J., and Dryer, F. L., "Transient Numerical Modeling of the Microgravity Combustion of Bi-Component Liquid Droplets: Methanol/ Water Mixtures", Eastern States Sectional Meeting of the Combustion Institute, Clearwater, FL, December 1994.
Marchese, A.J., and Dryer, F. L., "Computational Modeling of Methanol Droplet Vaporization", Eastern States Sectional Meeting of the Combustion Institute, Princeton, NJ, October, 1993.