Droplet combustion studies of hydrocarbon-monopropellant blends

An experimental investigation was conducted to characterize the monopropellant droplet combustion of pure and blended isopropyl nitrate (IPN), suspended on quartz fibers in a quiescent atmosphere. The blends were prepared by mixing varying percentages by weight of IPN with less viscous n-heptane, as well as highly viscous desensitizer dibutyl sebacate (DBS). Ignition was achieved by using a heated 60 μm Nichrome wire. The dependence of the burning rate constant of pure IPN on initial droplet diameter was investigated in the droplet size range of 0.79-1.97 mm. The blended IPN studies were carried out with initial droplet diameters of 2 and 1.5 mm for IPN-n-heptane and IPN-DBS blends respectively, to characterize the effect of gravimetric composition. The experiments revealed a strong dependence of IPN burning rate on droplet size. The IPN-DBS blends were characterized by severe micro-explosions, further atomizing the droplet, governed by the preferential evaporation of IPN over DBS. However, micro-explosions were conspicuously absent in case of IPN-n-heptane blends due to simultaneous gasification of both components.