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Laser-induced fluorescence spectroscopy of kerosene vapour was performed in a heated test cell operating between 450 and 900 K, at pressure from 0.1 to 3.0 MPa, for oxygen molar fraction between 0 and 21 %, with different laser excitation wavelengths (248, 266, 282 and 308 nm). Results show that, depending on the laser excitation scheme, kerosene fluorescence spectrum exhibits one or two fluorescence bands in the UV–visible range (attributed to aromatics naturally present in kerosene fuel). Fluorescence intensity of these bands decreases with increasing temperature, pressure and oxygen molar fraction. Different imaging strategies were derived from spectroscopic findings to simultaneously measure temperature and equivalence ratio fields in kerosene/air sprays, or flame structure and fuel spatial distribution in kerosene/air aeronautical combustors, by means of planar laser-induced fluorescence on kerosene vapour (K-PLIF).

Fluorescence of the S 1→S 0 transition of naphthalene vapour after laser excitation at 266 nm was studied in a heated cell. Experiments were carried out for temperature in the range 350–900 K, at pressure between 0.1 and 3.0 MPa and for oxygen molar fraction from 0 to 21%. The absorption cross section of naphthalene showed a non-monotonic dependence upon temperature, which may be attributed to the spectral structures present in the absorption spectrum of naphthalene. Under nitrogen atmosphere, naphthalene fluorescence bi-exponentially decreased by an order of magnitude as temperature increased, whereas it increased by about 10% with pressure. Strong influence of quenching by O2 on naphthalene fluorescence was observed and Stern–Volmer plots were found to be linear for temperatures between 450 and 750 K. The dependence of naphthalene fluorescence on oxygen concentration suggests one to use this molecule for fuel-concentration measurements in turbulent flows.

International audience; Planar laser-induced fluorescence on atomic iron is investigated in this paper, and a measurement strategy is proposed to monitor the fluorescence of iron atoms with good sensitivity. A model is proposed to fit the experimental fluorescence spectra, and good agreement is found between simulated and experimental spectra. Emission and laser-induced fluorescence measurements are performed in the flames of ammonium perchlorate composite propellants containing iron-based catalysts. A fluorescence signal from iron atoms after excitation at 248 nm is observed for the first time in propellant flames. Images of the spatial distribution of iron atoms are recorded in the flame in which turbulent structures are generated. Iron fluorescence is detected up to 1.0 MPa, which opens the way to application in propellant combustion.; L'imagerie de fluorescence induite par laser est appliquée aux atomes de fer et une stratégie pour leurs mesurer avec une bonne sensibilité est présentée dans cet article. Un modèle est développé pour calculer les spectres de fluorescence et un bon accord est trouvé entre les spectres calculés et expérimentaux. Les mesures en émission et en fluorescence induite par laser sont effectuées dans des flammes de propergols composites à base de perchlorate d'ammonium dopés avec des catalyseurs ferriques.Le signal de fluorescence induit par l'excitation laser à 248 nm des atomes de fer est observé pour la première fois dans les flammes de propergol. La répartition spatiale des atomes de fer est visualisée en flamme dont les structures turbulentes sont forcées. La fluorescence du fer est détectée jusqu'à 1,0 MPa, ce qui ouvre des perspectives de visualisation d'écoulements de gaz de combustion de propergols solides.

Local temporally-resolved measurements of chemiluminescent intensity from OH ∗ , CH ∗ and C ∗ 2 radicals were obtained in premixed counterflow flames operating with propane and prevaporised fuels (isooctane, ethanol and methanol), for different equivalence ratios and strain rates. The results quantified independently the effects of fuel type, strain rate and equivalence ratio on chemiluminescent emissions from flames. The ability of chemiluminescent intensity from OH ∗ , CH ∗ and C ∗ 2 radicals to indicate heat release rate depends strongly on fuel type. The intensity ratio OH ∗ /CH ∗ has a monotonic decrease with equivalence ratio for all fuels and can be used to measure equivalence ratio of the reacting mixture. For propane and isooctane, the OH ∗ /CH ∗ ratio remains independent of flame strain rate, whereas some dependence is observed for ethanol and methanol.

Fluorescence of the S1→S0 transition of 1,2,4-trimethylbenzene vapour after laser excitation at 266 nm was investigated in a heated cell. Experiments were performed for temperature between 350 and 900 K, at pressure between 0.1 and 3.0 MPa and for oxygen molar fraction between 0 and 21%. The absorption cross section was found to reduce by about 20% between 350 and 900 K. 1,2,4-trimethylbenzene fluorescence exponentially decreased by three orders of magnitude as temperature increased. A similar behaviour was observed with pressure, although fluorescence reduced only by a factor of 2.5 between 0.1 and 3.0 MPa. Additionally, Stern–Volmer plots were found to be linear for temperatures between 450 and 750 K. Using the dependence of 1,2,4-trimethylbenzene fluorescence on temperature, potential use of this molecule for temperature measurements in turbulent flows is suggested.

Combustion processes involved in cryogenic propellant LOX/H2 systems are very complex. In order to improve understanding and modeling of such processes, a test facility, called Mascotte, was developed by ONERA in the early 1990s. A research program involving teams from universities and ONERA has run for several years on the Mascotte bench and the purpose of this article is to summarize the results of systematic research obtained at ONERA. The first part of the article briefly describes the test facility and the related low and high-pressure combustors. In the second part, findings of both qualitative and quantitative measurements using high-speed photography, shadowgraphy, backlighting, and Coherent Anti-Stokes Raman Scattering are presented and discussed for different operating conditions. Differences of flame structure in sub- and supercritical regimes are emphasized. In particular, imaging techniques show evidence of the absence of ligaments and droplets around the LOX jet at supercritical pre...

Chemiluminescent emissions from OH⋅, CH⋅, and C⋅2 and continuous emissions from CO⋅2 have been measured in natural-gas-fuelled, premixed, counterflow flames operating with an equivalence ratio between 0.7 and 1.3 and strain rates between 80 and 400 s−1, achieved by varying the exit velocity of the jet between 1 and 5 m s−1. Cassegrain receiving optics coupled to a high-performance spectroscopic unit allowed local, temporally resolved measurements of intensity of chemiluminescence in flat flames, which were compared with measurements along a line of sight obtained from flame spectra. This study allowed independent evaluation of the effects of strain rate and equivalence ratio on intensity of chemiluminescence and the ability of intensity of chemiluminescence to indicate heat release rate. Results suggest that intensities of chemiluminescence from OH⋅ and CH⋅ and background intensity from CO⋅2 are good indicators of heat release rate, whereas that from C⋅2 is not. The study also evaluated the ability to measure equivalence ratio of the reacting mixture using intensity of chemiluminescence and found that the intensity ratio OH⋅/CH⋅ has a monotonic decrease with equivalence ratio for lean and stoichiometric mixtures, while remaining independent of flame strain rate. The results indicate that the intensity ratio OH⋅/CH⋅ can measure with uncertainties of 5% the equivalence ratio up to values of 1.1 and with uncertainties of 20% for richer mixtures due to the low sensitivity of the intensity ratio OH⋅/CH⋅ for rich mixtures. The intensity ratios of C⋅2/OH⋅ and C⋅2/CH⋅ have a non-monotonic dependence on equivalence ratio and a dependence on strain rate and are thus not suitable for measurements of equivalence ratio. An approach to measuring the time-dependent equivalence ratio of the reacting mixture is suggested and data processing methods and associated uncertainties are presented. The potential of the technique for local measurements in practical burners is discussed and further evaluation of the spatial resolution is required in such flames. However, suggestions have been provided on how the spatial resolution can be improved in practical flames.

This paper describes a Cassegrain optics-based chemiluminescence sensor (CS) for measurements in gas turbine combustors. The chemiluminescence sensor measures the equivalence ratio of reacting fuel and air mixtures, and can identify the flame location, in partially premixed flames. It has the potential for monitoring the degree of premixedness of reacting fuel and air in industrial gas turbine combustors, where operation with lean premixed mixtures is important for reduction of NO, emissions. The spatial resolution of the sensor is evaluated by comparing OH* chemiluminescence measurement from the CS with laser induced OH fluorescence, in the cone-shaped premixed flame of a Bunsen burner. The ability of the sensor to measure in a modified micro-gas turbine environment burning a methane/air, as well as, a methane/ water/air flame (humidified flame) is also demonstrated. (Less)

Assessing the feasibility of combustion in miniaturised combustors (volume less than 1 cm3 ) is a key point for the development of micro gas turbines. This paper presents the results obtained in a combustion chamber operating with a hydrogen-air mixture. A stable combustion was obtained with an output power between 100 and 1200 W, for air mass flow rate from 0.1 to 0.5 g/s, and equivalence ratio between 0.3 and 0.7. Experimental results were obtained using thermocouples to measure temperature of the burnt gases at the outlet of the combustor, and information on combustion efficiency and output power was derived. In addition, laser-based measurements were performed using spontaneous Raman spectroscopy and Rayleigh scattering to determine radial profiles of temperature and main species concentrations at the outlet of the combustor.

Planar laser-induced fluorescence measurements of fuel-vapor concentration around a monodisperse stream of acetone droplets is presented. Droplets were injected in a confinement at different temperatures and the influence of parameters such as droplet diameter, droplet spacing, and temperature of the surrounding gas on droplet evaporation were characterized. Radial and axial profiles of fuel-vapor concentration were obtained for different experimental conditions, and results indicate that the spatial distribution of fuel vapor around droplets depends on the aforementioned parameters. The halation phenomenon is identified as a potential bias for fuel-vapor measurements in the vicinity of droplets and a strategy is proposed to prevent its influence. The application of the technique for fuel-vapor measurements in real sprays is also discussed. Experiments were compared with different simplified theoretical droplet evaporation models. Numerical results show the necessity of including corrections for ...

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.