A premixed hydrogen/oxygen catalytic igniter

An experimental program was conducted at the NASA Lewis Research Center to study the catalytic ignition of hydrogen and oxygen propellants using a premixing hydrogen/oxygen injector. The premixed injector was designed to eliminate problems associated with catalytic ignition caused by poor propellant mixing in the catalyst bed. Mixture ratio, mass flow rate, and propellant inlet temperature were varied parametrically in testing, and a pulse mode life test of the igniter was conducted. The results of the tests showed that the premixed injector eliminated flame flashback in the reactor and increased the life of the igniter significantly. The results of the experimental program and a comparison with data collected in a previous program are given. Future reusable rocket engines will require ignition systems that are safe, reliable, lightweight, and low cost to insure mission success. The use of a catalyst to initiate propellant ignition in a reusable hydrogen/oxygen engine is a simple concept that has several potential advantages when compared with other ignition techniques. Catalytic igniters are passive in operation, require no external energy source, and they present no radio interference problems. Catalytic igniters for the decomposition of monopropellant hydrazine have flown in space for periods over eight years, and the use of catalysts for the ignition of hydrogen and oxygen propellants has been studied in the past. This report presents the results of an experimental program conducted to study the performance of a catalytic igniter utilizing a premixing hydrogen/ oxygen injector. J C The concept of using catalysts to ignite the hydrogen/oxygen propellant combination was studied in the 1960's and early 1 9 7 0 ' ~ , ~ , ~ and an experimental data base was created. This early research identified flashback, which is the propagation of the flame from the catalyst bed back to the injector face, as one of the key problems associated with catalytic ignition. Flashback often resulted in the destruction of the catalyst and reactor hardware, and different approaches were attempted in an effort to characterize, if not alleviate, the problem. Localized propellant streaks and mixture ratio transients were identified as one source of flashback, caused by poorly mixed propellants entering the catalyst bed. Mixing zones and inert diffusion beds were both incorporated in an attempt to arrest flashback by allowing the propellants to mix thoroughly before entering the catalyst bed. Additional research, which preceded this study, also showed that the injector was the critical component in the design of an effective catalytic igniter. This study also showed that if the propellants were not well mixed when they enter the catalyst bed, localized hot spots in the bed and flashback could occur.3 Since mixing zones or diffusion beds had not been shown to eliminate flashback in catalytic igniters, an injector was needed that would introduce a uniform hydrogen/oxygen mixture into the catalyst bed. The goals of the present experimental program were to enhance and characterize the performance of a gaseous hydrogen/oxygen catalytic igniter which employed a premixed injector design and to add to the experimental data base for hydrogen/oxygen catalytic ignition. This report details the hardware, facility, and test procedures used for this experiment. The results of testing at