PHOTOCHEMICAL IGNITION OF PREMIXED HYDROGEN OXYGEN MIXTURES WITH ARF LASER/

The current work seeks to determine the feasibility of using radicals to improve the combustion of propulsion systems fueled by hydrogen. An ArF excimer laser (193 nn) with focused optics was used to photodisso ciate molecular oxygen in hydrogen/oxygen mixtures, producing ground-s tate atomic oxygen, O(P-3). In these experiments, the laser penetrated more than 20 cm into the mixture, there producing a maximum atomic ox ygen concentration which leads to pure photochemical ignition. The min imum laser pulse energy required for ignition has been determined over a range of equivalence ratios (0.2 to 2.0) and initial temperatures ( 400 to 520 degrees C) at a baseline pressure of 0.5 atm. Based on thes e values, the atomic oxygen concentration produced in the focal volume has been calculated. For these conditions, both the minimum Laser ene rgy and atomic oxygen concentration decrease strikingly as the initial mixture temperature increases. Results from a simplified ignition mod el agree with the experimental data. Both show only a weak dependence of the atomic oxygen concentration required for ignition on the equiva lence ratio of the mixture over the ranges studied.