Single and multicomponent liquid droplet combustion: Detailed kinetic modeling and microgravity experiments

The time-dependent, spherically symmetric combustion of single and bicomponent alcohol and alkane droplets has been simulated using a moving finite element model. Newly (and independently) developed chemical kinetic mechanisms have been used to describe the gas phase chemistry. Semi-empirical vapor-liquid equilibrium models have been applied to accurately describe the phase change at the droplet surface. Spatially and temporally varying gas phase thermal and transport properties are included as are time-dependent mass and energy transfer in the liquid phase. A non-luminous gas phase radiation model has been developed to account for radiative loss from the flame and radiative gain at the droplet surface. To compare the calculated flame structure with experimental results, a hydroxyl radical chemiluminescence model has also been developed.; The results of methanol/water droplet combustion modeling have been compared with previously reported experimental data. Numerical results are consistent with experiments when it is speculated that sufficient internal liquid phase motion is present to reduce the effective liquid mass Peclet number to the order of one.; A new semi-empirical mechanism for n-heptane oxidation and pyrolysis has been developed and validated against several independent data sets, including new flow reactor experiments performed as part of this research.; The new n-heptane mechanism has been used to model the gas phase chemical kinetics in transient, spherically symmetric droplet combustion calculations. For combustion in air at 1 atm, the model predicts very small extinction diameters, which is consistent with the results of previous investigators who observed either "burn-out" (i.e. extinction diameter too small to measure) or extinction diameters of less than 100 microns. In addition to single component n-alkane calculations, bicomponent droplet combustion calculations of mixtures of n-heptane and n-hexadecane are also presented.; 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 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.; A series of microgravity methanol and methanol/water droplet combustion experiments were conducted using a 2.2 second drop tower. Analysis of the flame and droplet diameter data yielded burning rates and flame stand-off ratios for a wide array of methanol and methanol/water droplet combustion conditions.; In the drop tower experiments, the available test time was not, in general, sufficient to observe extinction of the droplet flame. In order to observe this phenomena, experiments have recently been conducted aboard the Space Shuttle in the Fiber-Supported Droplet Combustion Investigation (FSDC-1). In this experiment, methanol droplets of 3 to 5 mm were burned in air. The data show an increase in extinction diameter and a decrease in burning rate with increasing initial diameter. By including a radiation sub-model, the numerical model closely reproduces these phenomena. The model also predicts that, at very large initial diameters, the droplet flame will quickly self-extinguish due to excessive radiative heat loss. (Abstract shortened by UMI.)...