A. Dokhan

Bio: A. Dokhan is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Propellant & Particle size. The author has an hindex of 3, co-authored 3 publications receiving 186 citations.

The effects of bimodal aluminum with ultrafine aluminum on the burning rates of solid propellants

Abstract: Burning rates were measured for aluminized composite propellants with different aluminum (Al) sizes(monomodal distribution) and with bimodal Al distributions containing various amounts of ultrafine Al (UFAl). Enhanced rates were found for fine Al, with the enhancement increases for reduced Al size. The fine Al also burned in an intense region very close to the propellant surface, suggesting improved heat feedback in the form of radiation and conduction. Major modification of the burning rate could be achieved with moderate amounts of UFAl. Results obtained with various fine oxidizer particle sizes and mass fractions suggest that the degree of burning-rate modification depends on the ability to ignite the UFAl, for example, with leading-edge flames, as well as the availability of oxidizer near the Al-containing regions of the propellant.

The Effects of Al Particle Size on the Burning Rate and Residual Oxide in Aluminized Propellants

Abstract: The effect was examined of aluminum particle size and of bimodal Al particle size on the burning rate of propellants and the particle size distribution of residual product Al2O3. It is shown that major modification of the burning rate and product size can be achieved by replacement of 20% of the conventional Al by 0.1µm Al. These effects result from the presence of an intense near surface Al flame when 0.1µm fine Al is present.

The ignition of ultra-fine aluminum in ammonium perchlorate solid propellant flames

Abstract: A preliminary experimental investigation was carried out to investigate the ignition of ultrafine aluminum (UFAl) compared to conventional sized aluminum (CSAl) particles in ammonium perchlorate (AP)-polybutadiene acrylonitrile acrylic acid (PBAN) solid propellants. To evaluate the temperature criteria for igniting UFAl, matrix samples (binder, fine AP and Al only) were prepared with various loadings of 10μm fine AP (fAP) as a means of varying the AP-binder flame temperature, and with Al coarse-to-fine ratio of 0(30μm)/20(UFAl) and 80(30μm)/20(UFAl). Preliminary results showed that UFAl sized particles ignite at lower gasphase flame temperatures than CSAl particles and that the UFAl particles tend to affect the combustion processes close to the propellant surface depending upon the availability of oxidizer. * Senior Combustion/Propulsion Engineer. AIAA Member. E mail: allandokhan@hotmail.com † ‡ Regent Professor Emeritus. Fellow Member. Associate Professor. Senior Member. E mail: jerry.seitzman@ae.gatech.edu Senior Research Engineer. INTRODUCTION In recent studies of ultra-fine aluminum (UFAl~0.1μm) in ammonium perchlorate (AP) solid propellants with bimodal AP (10μm:400μm and 82.5μm:400μm) and bimodal aluminum (Al) distribution (30μm:UFAl), the burning of UFAl was found to create a very dense aluminum burning region (ABR) directly above and some distance beyond the propellant surface (~3000-4000μm) compared to the burning of conventional sized aluminum (CSAl~12-100μm). The density of the ABR was found to be the product of the number of burning Al particles/droplets/agglomerates leaving the propellant surface per unit area (one 30μm Al particle is the mass equivalent of 10 UFAl particles), which is very dependent upon the propellant microstructure (see later). The combustion of fine Al (~3μm) and UFAl particles occur much closer behind the AP-binder flame because of their near equilibrium state with the gas flow (temperature & velocity) compared to CSAl. As a result, they ignite quickly as they pass through the flame surface and burn close behind the convoluted flame canopy. This dense luminous bright ABR was found to be responsible for a significant amount of heat feedback to the propellant surface and to the AP-binder flame array in the form of either radiation and/or conduction, which resulted in high burning rate propellants. Copyright© 2003 A. Dokhan, E. W. Price, J. M. Seitzman and R. K. Sigman. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission 1

Combustion of Nano Aluminum Particles (Review)

Abstract: Nano aluminum particles have received considerable attention in the combustion community; their physicochemical properties are quite favorable as compared with those of their micron-sized counterparts. The present work provides a comprehensive review of recent advances in the field of combustion of nano aluminum particles. The effect of the Knudsen number on heat and mass transfer properties of particles is first examined. Deficiencies of the currently available continuum models for combustion of nano aluminum particles are highlighted. Key physicochemical processes of particle combustion are identified and their respective time scales are compared to determine the combustion mechanisms for different particle sizes and pressures. Experimental data from several sources are gathered to elucidate the effect of the particle size on the flame temperature of aluminum particles. The flame structure and the combustion modes of aluminum particles are examined for wide ranges of pressures, particle sizes, and oxidizers. Key mechanisms that dictate the combustion behaviors are discussed. Measured burning times of nano aluminum particles are surveyed. The effects of the pressure, temperature, particle size, and type and concentration of the oxidizer on the burning time are discussed. A new correlation for the burning time of nano aluminum particles is established. Major outstanding issues to be addressed in the future work are identified.