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Development of a Laser Igniter for Direct Fired sCO2 Combustor


 The combustor of a typical Allam-Fetvedt cycle has pressures ranging up to 300 bar and CO2 dilution levels up to 90% by volume, which present a rather challenging environment to ensure reliable ignition. Laser igniters offer improved performance under such adverse conditions, i.e., extend ignitability to a wider range of pressures, equivalence ratios and dilution levels. Additionally, unlike hypergolic igniters laser igniters can be used for ignition multiple times. Additionally, the capability of laser igniters to ignite at higher pressures reduces the relight operation in a power plant from several hours to less than a second. In this paper we report our efforts to design and develop a laser igniter for such combustors. First, high-fidelity CFD modeling was performed for a combustor geometry fueled by coal-derived syngas. Based on the predicted flow field, a laser igniter having a capability to place the ignition kernel at the optimal location was designed and developed. Finally, the performance of the laser igniter was evaluated using several bench-scale tests using premixed mixtures of coal-derived syngas and oxidizers. These bench-scale tests showed that laser ignition was possible over a wide range of equivalence ratios, ϕ = 0.7 to 1.6, and initial pressures up to 50 bar. These tests also showed that multiple ignition kernels form at the focal point along the laser line of sight. Both volumetric ignition and use of multiple ignition pulses (i.e., burst mode) significantly improve ignitability of the fuel-oxidizer mixtures.