Microexplosion Investigation of Monomethylhydrazine Gelled Droplet with OH Planar Laser-Induced Fluorescence

Combustion of a nonmetallized organic gelled droplet was studied using high-speed (5 kHz) hydroxide planar laser induced fluorescence. Monomethylhydrazine was gelled with 3 and 6 wt % hydroxypropyl cellulose and burned in a pressure vessel with 35–414 kPa of ambient air. Fuel jetting is observed during the combustion of the gelled droplets. Three distinct types of jetting events were observed for the first time: 1) jets that distort the flame front, 2) jets that break the flame front, and 3) jets that form a fire ball outside of the flame front. The average jet speed was the highest for type 3 and the lowest for type 1. Speeds and locations of the fuel jets were quantified. It was observed that the radial jet velocity increases with increasing gellant concentration and decreases with increasing ambient pressure. Also, jets were observed to occur at the same location repeatedly. A possible explanation is that the initial jetting event weakens the shell, causing more jets to occur at the weakened location. Understanding the fuel jets of gelled droplet combustion is important because they are likely to influence the oxidizer–fuel ratio, chemical equilibrium, gas-phase mixing, and droplet trajectory in gel spray combustion.