A quantum cascade laser based mid-infrared sensor for the detection of carbon monoxide and nitrous oxide in the jet of a microwave plasma preheated auto-ignition burner

Abstract

Auto-ignition (AI) processes play an enormous role in a multiplicity of technical applications e. g. in lean premixed prevaporized gas turbines, direct injection diesel engines or new combustion processes like compression auto-ignition. All these applications have in common that fuel is injected into hot turbulent flows. To study AI processes a new test-rig has been designed at the institute for Reactive Flows and Diagnostics (RSM) at TU Darmstadt. The aim of this research project is the investigation of AI from a fuel jet propagating into a preheated turbulent air co-flow under well known boundary conditions.The air co-flow is preheated by the plasma of a microwave plasma heater to temperatures between 500 °C and 1150 °C. First measurements with a commercial sensor showed an increased concentration of nitrogen oxide (NO x ) components to about 1% Vol. in the preheated air. Since especially nitrous oxide (N 2 O) can strongly influence the burning process, it is of great importance to determine its exact concentration. Towards an enhanced understanding of AI, it is also crucial to know the produced carbon monoxide (CO) amount directly in the flame. a) 600 700 800 900 1000 1100 4 6 8 10 12 14 16 N2O concentration / ppm Temperature / °C b) 85 90 95 100 105 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0 4.4 CO concentration / %vol distance to fuel lance / mm Fig. 2 a) Calculated detection limits of N2O in dependency of the air co-flow temperature. The minimum detectable intensity was determined from the standard deviation of the residual of a Voigt-fit to the absorption spectrum of a reference-cell with a fixed amount of N2O. b) Measured CO concentration in the methane flame. The concentration is slightly increasing with distance (in flame propagation) due to the increasing lack of oxygen. References[1] P. Werle, "A review of recent advances in semiconductor laser based gas monitors", Spectrochimica Acta Part A 54, 197-236 (1998) 978-1-4799-0594-2/13/$31.00 ©2013 IEEE