16th Int Symp on Applications of Laser Techniques to Fluid Mechanics Lisbon, Portugal, 09-12 July, 2012 - 1 - Two dimensional Laser Induced Plasma Spectroscopy for the measurements of local composition in gaseous flow and sprays Tapish Agarwal 1,2 , Laurent Zimmer 1,2,* 1: CNRS, UPR 288 "Laboratoire d’Energetique moleculaire et macroscopique, combustion" Grande Voie des Vignes, 92295 Chatenay-Malabry 2: Ecole Centrale Paris, Grande Voie des Vignes, 92295 Chatenay-Malabry, Laboratoire EM2C - CNRS UPR 288 - Ecole Centrale Paris * correspondent author: Laurent.zimmer@ecp.fr Abstract An extension of the Laser Induced Plasma Spectroscopy technique has been presented to achieve a very high spatial resolution. It is based on the simultaneous recording of the plasma with cameras equipped with different interferential filter centered on the main atomic emission wavelengths. Exact calibration procedure is explained and typical results obtained in a laminar burner using air and nitrogen are presented. This technique can be easily coupled to other planar images, like Particle Image Velocimetry to yield simultaneous velocity and scalar information. Typical uncertainties were quantified in a laminar burner and are lower than classic (0D) LIPS approaches. A procedure to obtain spatially resolved energy deposition has been proposed based both on the mixture fraction measurement and the absolute intensity of oxygen emission. An application in a combustor using liquid fuel has been shown and the spatial resolution of the technique could determine the influence of the droplets as creating multiple sparks. Furthermore, using the ratio between hydrogen and oxygen, it was shown that typical ignited sparks were those with high concentration of hydrogen localized in space. Using the approach proposed in the paper to estimate local energy, those regions were also regions in which the major part of the energy was deposited. Finally, it is possible to combine the data obtain by this new technique with time resolved PIV data to fully understand the dynamics of laser ignition in liquid fuelled combustor. 1. Introduction In many practical systems of combustion where the fuel is liquid, the exact local mixture fraction is hard to determine. The uniformity of the mixture fractions seems to be required to achieve current regulations. Therefore, one has to develop measurement techniques that are ready to be implemented without requiring the knowledge of the exact chemical composition, how would be required by a Laser Induced Fluorescence strategy ([Orain et al. 2009]). Chemiluminescence monitoring may be a good choice for temporal variations (see Guethe et al. 2012). However, this may suffer from exact spatial resolution. An important aspect of gas turbine, especially for aeronautically based engines, is the ignition procedure. At present, ignition is performed with an electric spark, located at the wall. It would be possibly beneficial to use Laser Ignition to deposit the initial energy in the center of the chamber, avoiding heat loss at the spark plug and high velocity regions. Furthermore, this may be combined with diagnostics to understand and possibly control ignition. Among laser diagnostics that do not require a perfect knowledge of the exact chemical composition of the fuel, Laser Induced Plasma Spectroscopy seems to be a possible solution. Recent calibration procedure, developed in Zimmer and Tachibana, 2007 enabled the absolute measurements of the local equivalence ratio, regardless of the source of the plasma. Reported single shot uncertainties were within less than 5%. It is possible to use the natural emission of the plasma when creating the spark required for ignition to know perform the measurements (Zimmer et al. 2007). The technique has been shown to work even under high pressure (Zimmer and Yoshida, 2012) and typical