Spontaneous ignition properties of metal alkyls

Abstract

Ignition in a supersonic flow requires an extremely reactive material. Various investigators at NACA (now NASA) and elsewhere have identified a number of metal compounds which are spontaneously flammable at room temperature and can be used for initiating combustion in a supersonic stream. The present work utilizes the technique of programmed ignition in blends of hydrocarbon and metal compounds which makes the blended fuel easier to handle. Depending upon the blend and the surrounding flow field, these can be made flammable at a desired distance from the point of injection. A parametric theoretical study of aluminum borohydride, triethyl boron, trimethyl aluminum and pentaborane as ignition promoting additives and hydrocarbon solvents such as JP-5, propane, butane and hexane has been performed. Mixture droplets of three different diameters and three different compositions were assumed to be injected in a 2000 m/s gas stream. Three ambient temperatures (500, 700 and 900 K.) were studied.