Planar Laser Induced Fluorescence Measurements of CH\(_{2}\)O in Ozone Assisted Cool Flames

Abstract

Cool flames are necessary to understand for the future of internal combustion engines, ignition timing, engine knock, and burning limits. Formaldehyde is a key indicator of of cool flames and it gives cool flames their observable blue luminescent reaction front. The goal of this experiment was to measure varying formaldehyde species concentration present in ozone-assisted cool flames that are generated in a non-premixed counterflow burner using planar laser induced fluorescence. Planar laser induced fluorescence is a laser diagnostic imaging technique that was used for the species concentration measurement in this experiment. The PLIF technique generated a laser sheet that is passed through a window in the high pressure burner to generate fluorescence, that was then captured with an intensified CCD camera. The flames were ozone-assisted DME fuel flames with an equivalence ratio of 0.5, and the ozone concentration was varied throughout eight different runs. The CH\(_{2}\)O signal level as a function of ozone concentration addition was plotted and revealed a positive linear slope. Therefore, it was concluded that increased ozone concentration addition leads to stronger CH\(_{2}\)O signal in cool flames. An uncertainty analysis was also performed, in order to test the reliability of the laser pulse and the background noise of the camera. The standard error of the mean was calculated to be 1.256 u.a., the total uncertainty is 3.29 u.a. and the percent uncertainty is 0.6%, meaning the measurements are very reliable.