Article: Alam, FE; Liu, YC; Avedisian, CT; Dryer, FL; Farouk, TI; (2015) “n-Butanol Droplet Combustion: Numerical Modeling and Reduced Gravity Experiments”, Proceedings of the Combustion Institute, 35: 1693-1700
Abstract: Recent interest in alternative and bio-derived fuels has emphasized butanol over ethanol as a result of its higher energy density, lower vapor pressure and more favorable gasoline blending properties. Numerous efforts have examined the combustion of butanol from the perspective of low dimensional gas-phase transport configurations that facilitate modeling and validation of combustion kinetics. However, fewer studies have focused on multiphase butanol combustion, and none have appeared on isolated droplet combustion that couples experiments with robust modeling of the droplet burning process. This paper presents such an experimental/numerical modeling study of isolated droplet burning characteristics of n-butanol. The experiments are conducted in an environment that simplifies the transport process to one that is nearly one-dimensional as promoted by burning in a reduced gravity environment.
Measurements of the evolution of droplet diameter (D-o = 0.56-0.57 mm), flame standoff ratio (FSR equivalent to D-f/D) and burning rate (K) are made in the standard atmosphere under reduced gravity and the data are compared against numerical simulation. The detailed model is based on a comprehensive time-dependent, sphero-symmetric droplet combustion simulation that includes spectrally resolved radiative heat transfer, multi-component diffusive transport, full thermal property variations and detailed chemical kinetic. The simulations are carried out using both a large order kinetic mechanism (284 species, 1892 reactions) and a reduced order mechanism (44 species, 177 reactions). The results show that the predicted burning history and flame standoff ratios are in good agreement with the measurements for both the large and reduced order mechanisms. Additional simulations are conducted for varying oxygen concentration to determine the limiting oxygen index and to elucidate the kinetic processes that dictate the extinction of the flame at these low oxygen concentrations. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
Funding Acknowledgement:
National Aeronautics and Space Administration [NNX09AW 19A, NNX08AI51G]; University of South Carolina Startup Fund
Funding Text:
This work was supported by the National Aeronautics and Space Administration through grant numbers NNX09AW 19A (for FLD), NNX08AI51G (for YCL and CTA) and the University of South Carolina Startup Fund (for FEA and TIF). Special thanks to Mr. Michael Hicks, Dr. Daniel Dietrich of NASA for their interest and assistance throughout the course of this investigation. The authors are also thankful to Prof. Rolf Reitz of University of Wisconsin-Madison for sharing their kinetic database.