In the secondary chamber of ducted rocket, there exists a relative speed between boron particles and air stream. Hence, the ignition laws under static conditions cannot be simply applied to represent the actual ignition process of boron particles, and it is required to study the effect of forced convective on the ignition of boron particles. Preheating of boron particles in gas generator makes it possible to utilize the velocity difference between gas and particles in secondary chamber for removal of the liquid oxide layer with the aid of Stoke's forces. An ignition model of boron particles is formulated for the oxide layer removal by considering that it results from a boundary layer stripping mechanism. The shearing action exerted by the high-speed flow causes a boundary layer to be formed in the surface of the liquid oxide layer, and the stripping away of this layer accounts for the accelerated ignition of boron particles. Compared with the King model, as the ignition model of boron particles is formulated for the oxide layer removal by considering that it results from a boundary layer stripping mechanism, the oxide layer thickness thins at all times during the particle ignition and lower the ignition time. 1. Introduction Systematic advances in missile propulsion systems technology have provided large increases in missile performance capabilities. Replacement of much of solid propellant rocket oxidizer with free stream air, as in the ducted rocket concept, offers over 5 to 1 increase in missile range capability [1]. Boron has been considered for many years as a prime candidate used for increasing the ducted rocket capabilities based on its high potential energy release on both a volumetric and gravimetric basis coupled with a high energy of combustion, high combustion temperature, and low-molecular-weight products [2]. These properties make boron an attractive material for use in ducted rocket propellants [3]. In order for these advantages to be realized, however, the boron particles must ignite and burn completely within a very limited residence time. Since boron particles are generally initially coated with an oxide layer with inhibits combustion and since boron has an extremely high boiling point, which necessitates surface burning subsequent to oxide removal, this can become difficult, particularly under adverse operating conditions [4]. In previous work, two scenarios for boron ignition and combustion have been identified, which differ in the controlling element in the overall process mechanism [5]. Two controversial theories remain to be
References
[1]
R. S. Fry, “A century of ramjet propulsion technology evolution,” Journal of Propulsion and Power, vol. 20, no. 1, pp. 27–58, 2004.
[2]
B. Natan and A. Gany, “Ignition and combustion boron particles in the flow field of a solid fuel ramjet,” Journal of Propulsion and Power, vol. 7, no. 1, pp. 37–43, 1991.
[3]
C. L. Yeh and K. K. Kuo, “Ignition and combustion of boron particles,” Progress in Energy and Combustion Science, vol. 22, no. 6, pp. 511–541, 1996.
[4]
M. K. King, “Ignition and combustion of boron particles and clouds,” Journal of Spacecraft and Rockets, vol. 19, no. 4, pp. 294–306, 1982.
[5]
D. Meink？hn, “Boron particle ignition and the marangoni effect,” Combustion Science and Technology, vol. 176, no. 9, pp. 1493–1536, 2004.
[6]
G. Mohan and F. A. Williams, “Ignition and combustion of boron in O2/inert atmospheres,” AIAA Journal, vol. 10, no. 6, pp. 776–783, 1972.
[7]
S. C. Li and F. A. Williams, “Ignition and combustion of boron particles,” International Journal of Energetic Materials and Chemical Propulsion, vol. 2, no. 1–6, pp. 248–271, 1991.
[8]
A. Macek and J. M. Semple, “Combustion of boron particles at atmospheric pressure,” Combustion Science and Technology, vol. 1, no. 3, pp. 181–191, 1969.
[9]
W. Zhou, R. A. Yetter, F. L. Dryer, H. Rabitz, R. C. Brown, and C. E. Kolb, “Multi-phase model for ignition and combustion of boron particles,” Combustion and Flame, vol. 117, no. 1-2, pp. 227–243, 1999.
[10]
J. X. Hu, Z. X. Xia, and D. Q. Wang, “Study on burning rate of boron particles in secondary chamber of ducted rocket under forced convection conditions,” Journal of Solid Rocket Technology, vol. 30, no. 1, pp. 21–25, 2007.
[11]
R. O. Foelsche, R. L. Burton, and H. Krier, “Ignition and combustion of boron particles in hydrogen/oxygen explosion products,” AIAA 97-0127, 1997.
[12]
M. A. Gurevich, I. M. Kir'yanov, and E. S. Ozerov, “Combustion of individual boron particles,” Combustion, Explosion, and Shock Waves, vol. 5, no. 2, pp. 150–153, 1969.
[13]
D. Meink？hn, “Liquid oxide surface layers in metal combustion,” Combustion Theory and Modelling, vol. 8, no. 2, pp. 315–338, 2004.
[14]
D. Meink？hn, “The effect of particle size and ambient oxidizer concentration on metal particle ignition,” Combustion Science and Technology, vol. 181, no. 8, pp. 1007–1037, 2009.
[15]
A. Povitsky and Y. Goldman, “Boron particle ignition in high-speed flow,” in Proceedings of the 29th AIAA Joint Propulsion Conference, vol. 2202, AIAA paper 93, 1993.
[16]
A. A. Ranger and J. A. Nicholis, “Aerodynamic shattering of liquid drops,” AIAA Journal, vol. 7, no. 2, pp. 285–290, 1969.
[17]
M. Zhou and F. C. Zhuang, “Aerodynamic shattering of liquid drops using a boundary layer stripping mechanism,” Journal of National University of Defense Technology, vol. 13, no. 3, pp. 29–33, 1991.
[18]
M. K. King, “Boron particle ignition in hot gas stream,” Combustion Science and Technology, vol. 8, no. 5-6, pp. 254–273, 1974.
