Droplet combustion studies of nitromethane and its blends

An experimental study was conducted on droplet combustion of the monopropellant pure nitromethane (NM) as well as NM blended with methanol. Pure NM droplet combustion was conducted in a quiescent atmosphere of air with the droplets supported at the tip of quartz fibers under normal gravity. Additional experiments were conducted by varying the ambient oxygen mass fractions. The dependence of burning rate constant on initial droplet diameter was determined for pure NM, pure methanol, and NM-methanol blends and explained through a correlation dependent on the classical quasi-steady burning rate constant and the Grashof number associated with the droplet allowing for prediction of the burning rate constants of smaller droplets pertinent to spray combustion. The burning rate constants for commonly available nitromethane based fuel Rapicon-16 and NM-Dibutyl sebacate (DBS) blend with 90:10 ratio were also measured. The fuels were chosen to represent a range of cases from pure nitromethane to nitromethane-methanol blends typically utilized in practical applications. The nitromethane-DBS blend was formulated as a potential alternative to the conventional nitromethane-methanol-castor oil blends. The effectiveness of DBS as a desensitizer for nitromethane was established given that the burning rate constants for NM-DBS blends were found to be comparable to those of Rapicon-16 despite the higher concentration of nitromethane.