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.