M. Orain

Experimental Study of Strut Injectors in a Supersonic Combustor Using OH-PLIF

The present experimental study, carried out in the framework of ONERA-JAXA cooperation, deals with the ignition and hydrogen flame development in a supersonic air flow at Mach 2.5, with stagnation conditions of 0.6 MPa and 1620 K. Different types of struts for hydrogen injection (equivalence ratio of 0.45) have been investigated. Some (Alternating-Wedge struts) are specially designed to enhance fuel-air mixing by the creation of streamwise vortices. The principal aim of this study is to obtain information on the flow structures in the supersonic combusting mixing layer, and the location of ignition and combustion zones. Instantaneous maps of the OH radical by means of the OH-PLIF technique in two planes downstream of the strut injector and conventional observations of the flame by video camera have been obtained. These visualizations are completed by global measurements of the ignition delays and heat release by means of wall pressure measurements. The efficiency of the different strategies of fuel injections are then compared and discussed.

Fluorescence Spectroscopy of Kerosene Vapour: Application to Gas Turbines

Progress to develop Planar Laser-induced Fluorescence on kerosene vapour is reported. Experiments were carried out in a heated test cell operating between 400 K and 700 K, at pressures between 0.1 MPa and 0.7 MPa. For a wavelength excitation of 266 nm, the fluorescence spectrum of kerosene vapour presents two separated fluorescence bands respectively in the 270-310 nm and in the 310-420 nm spectral regions which have different temperature, pressure and oxygen molar fraction dependence. Attribution of these spectral bands was achieved by comparison with reference spectra of several pure species which were analysed separately. Four species were identified, belonging to singlering aromatics and two-ring aromatics, as being primarily responsible for kerosene fluorescence. Temperature, pressure and mixture composition dependence of kerosene vapour absorption and fluorescence provides useful guidance for kerosene PLIF allowing quantitative imaging of local equivalence ratio and temperature. Illustrative results of visualisation of mixing layer between a jet and the surrounding air and measurement of local equivalence ratio are examined for a subsonic turbulent preheated kerosene/air jet exiting in air.

LOCAL EQUIVALENCE RATIO AND DEGREE OF PREMIXEDNESS OF REACTING MIXTURE IN SWIRL-STABILISED NATURAL GAS FUELLED BURNERS *

Local, time-dependent measurements of equivalence ratio of the reacting mixture and degree of non-stoichiometric (premixed) reaction were obtained in a swirl-stabilised natural gas-fuelled, nonpremixed burner using the intensity of Chemiluminescence from flame radicals. The measurements quantified the mean, rms of fluctuations and probability density functions of local equivalence ratio, heat release and probability of premixed, lean or rich, versus stoichiometric reaction at the stabilisation region of the flame. The burner was operated over a range of air flow Reynolds numbers from 18970 till 57600, overall equivalence ratio of 0.32 and imposed oscillations on the air flow to the burner at the resonance frequency of 350 Hz. The results show that the local mean equivalence ratio at the flame base was stoichiometric, but with large fluctuations to suggest that around 80% of the reaction was premixed either lean or rich. The degree of premixed reaction increased with axial distance from the burner exit and Reynolds number and the lean premixed reaction dominated. Imposed air flow oscillations lifted the flame and led to nearly fully premixed reaction.