Chiara Manfletti

Laser ignition of a cryogenic thruster using a miniaturised Nd:YAG laser

An experimental study has been conducted to assess the feasibility of implementing laser ignition in cryogenic reaction and control and orbital manouvering thrusters. A experimental thruster with a single-coaxial injector element combustion chamber for testing with liquid oxygen/gaseous hydrogen and liquid oxygen/gaseous methane was designed for this purpose. Mapping tests conducted using a standard table top laser revealed that the minimum incident energies required for 100% reliable laser plasma and laser ablation ignition of liquid oxygen/gaseous hydrogen are 72 mJ and 14.5 mJ respectively. In addition, the miniaturised HIPoLas® laser was mounted directly on the thruster and used as ignition system. This paper reports locations of energy deposition, levels of delivered energy and associated ignition probabilities obtained. The results indicate the feasibility of using a laser system for the direct ignition of reaction and control and orbital manouvering thrusters and highlight further investigations and developments necessary for the implementation of miniaturised laser systems for vacuum igntion of cryogenic propellants.

Ignition Overpressure in Laser Ignited Reaction and Control Thrusters

Advanced ignition systems have been subject of great interest due to the need of developing a new generation of ignition systems for alternative propellant combinations for reaction and control system (RCS) and orbital and manoeuvring system (OMS) thrusters which move away from the classic but toxic hypergolic propellants monomethylhydrazine (MMH) and dinitrogen tetroxide (NTO). Laser ignition is one of a number of advanced ignition methods which are currently under investigation for use on reaction and control thrusters using green propellants. An investigation examining the laser ignition energies required to successfully ignited an experimental RCS chamber fed with liquid oxygen/gaseous hydrogen (LOx/GH2) and with liquid oxygen/gaseous methane (LOx/GCH4) revealed that all successfully induced ignitions using on a single-point energy deposition were hard igntions associated with a signficant ignition overpressure. The investigation of laser ignition of a single injector RCS thruster has shown that the ignition delay, defined as the time elapsed from valve opening to ignition of the combustion chamber, and which is frequently used to explain observed overpressures, is not the only parameter which impacts on the ignition overpressure. Patterns of flame growth have been identified and qualitative relationships have been established between flame growth behavious and the observed ignition overpressure.

Temperature Field in a Cryogenic LOX/CH4 Spray Flame

To prepare for the application of CARS thermometry to LOX/methane spray ames CARS spectra have been recorded in a O2/CH4-burner at pressure up to 11 bar. Based on the experience obtained, potential probe molecules have been selected for the application of CARS to a LOX/CH4 spray ame. A CARS system allowing simultaneously the thermometry of the two probe molecules H2 and H2O was then used to map the temperature eld in a cryogenic rocket model combustor. The suitability of H 2-CARS thermometry in a LOX/CH4 ame is demonstrated and the results provide a quantitative data base for the validation of simulation tools.