Towards simplified monitoring of instantaneous fuel concentration in both liquid and gas fueled flames using a combustor injectable LIBS plug

In this study, instantaneous measurement of fuel concentration and flame diagnostics in both liquid and gas hydrocarbon fueled flame is presented using a simplified laser-induced breakdown spectroscopy (LIBS) approach. The newly developed device or hereinafter the “plug” receives specified lines from the plasma emission without resorting to the conventional LIBS system. Bandpass filters and photodiodes were mounted in the plug to capture hydrogen (656 nm) and oxygen (777 nm) atomic lines. Since H/O intensity ratio has a linear relationship with fuel concentration, the plug's calibration curve between equivalence ratio and H/O intensity ratio is constructed. Single phase and two-phase hydrocarbon fuel fields were measured with the device using gasoline (liquid) and LPG (gas). With the advantage of simplicity of the plug, multiple plasma points and plugs were simultaneously applied in the fuel field and showed possibility of using a single laser device to construct multi-points concentration mapping. Also, flame diagnostics scheme was proposed based on the observed difference of intensity duration between reactive and non-reactive fuel fields.