Performance of neat and gelled monomethylhydrazine and red fuming nitric acid in an unlike-doublet combustor

Ignition and combustion characteristics of neat and gelled monomethylhydrazine (MMH) and red fuming nitric acid (RFNA) were investigated through the use of an unlike doublet injector. MMH gelled with either hydroxypropylcellulose or fumed silica was tested with RFNA gelled with fumed silica. High-speed video results showed that the type of gelling agent has a major impact on the ignition and combustion of the hypergolic propellants. Mismatched rheological properties hinder rapid and repeatable ignition events. Gels with matched rheological properties produce repeatable ignition delays similar to those observed with neat propellants. An elevated pressure combustion chamber was developed to allow direct comparison of combustion efficiency between neat and gelled propellants. Experimental combustion efficiencies were 83% for neat propellants compared to 68% for fumed silica gelled propellants. The results indicate that gelled propellants can operate with acceptable ignition delays but suffer from reduced combustion efficiency and stability when compared to neat propellants.