A theoretical study of multi-particle ignition uses a hot spot model which calculates the temperature evolution of individual hot spots in an energetic material. It indicated that ultra-fine hot particles would be very effective in igniting energetic materials if impinging and penetrating the solid propellant. Igniting mixtures were prepared containing ultra-fine Ti particles which react fastest compared with coarse particle mixtures, standard B/KNO3 and black powder. The ultra-fine particles, however, are obviously oxidized or gasified too fast as to reach the energetic material to be initiated and longer ignition delays are found mainly compared with coarse particle mixtures. An optimized mixture of coarse and ultra-fine particles would give an improvement of ignition delay times.