Measurement of drop size distributions in a spray depends on the definition of the control volume for drop counting. For image-based techniques, this implies the definition of a depth-of-field (DOF) criterion. A sizing procedure based on an imaging model and associated with a calibration procedure is presented. Relations between image parameters and object properties are used to provide a measure of the size of the droplets, whatever the distance from the in-focus plane. A DOF criterion independent of the size of the drops and based on the determination of the width of the point spread function (PSF) is proposed. It allows to extend the measurement volume to defocused droplets and, due to the calibration of the PSF, to clearly define the depth of the measurement volume. Calibrated opaque discs, calibrated pinholes and an optical edge are used for this calibration. A comparison of the technique with a phase Doppler particle analyser and a laser diffraction granulometer is performed on an application to an industrial spray. Good agreement is found between the techniques when particular care is given to the sampling of droplets. The determination of the measurement volume is used to determine the drop concentration in the spray and the maximum drop concentration that imaging can support.

Combustion processes involved in internal combustion engines greatly depend on the characteristics of the spray. This study is focused on the comparison of three different techniques used for spray drop sizing. Laser diffraction (LDG), phase Doppler anemometry (PDA) and Image Analysis (IMA) have been used to characterize gasoline sprays produced by gasoline injectors of a direct injection type. Whereas studies comparing drop sizing techniques found in the literature are mainly dealing with steady flows, attention is paid here to the unsteady nature of the spray. The differences in the measurement volumes of the different techniques are also considered. As these diagnostics do not measure exactly the same kind of distribution, both PDA and IMA measurements were converted to spatial-averaged volume-weighted drop size distributions to be compared to LDG. The Sauter Mean Diameter D 32 and the mean diameter D 43 are used to characterize the spray for different time and position of the measurement volume in the spray. The comparison between the three techniques shows a good agreement. Greatest mean diameters are found on the leading edge of the spray and on the side of the spray facing stagnant air, so where the conditions are favourable to a fast evaporation of the smallest droplets. Velocity measurements done by PDA and drop shape morphology characterization are also discussed.

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Single shot hybrid fs/ps-CARS spectroscopy of N2 is demonstrated at repetition rate up to 5 kHz using an amplified probe delivering a constant energy per pulse between 1 and 5 kHz. We performed 5 kHz CARS thermometry in a laminar CH4/air flame and in ambient air, with a precision under 0.5% at typical flame temperature, which is 2 times more precise and 5 times faster than previous state of the art with this technique. Temperature was measured during long acquisition times up to 100 s, making the system suitable to record signals in the 0.01-2500 Hz spectral window; in our case 10 Hz temperature oscillations were probed.

This work presents the experimental investigation of heat fluxes through the walls of a reduced-scale rocket motor using hydrogen and oxygen as propellants. The engine is watercooled so that it can be run in steady state for up to 120 s. More than 100 thermocouples are used to retrieve wall temperature and derive heat fluxes. It is shown how the chamber pressure affects the overall heat-flux level, while the mixture ratio greatly influences its distribution. Direct visualisation of the flame provides an indication that the heat-flux distribution is correlated to the location of heat release given by OH* visualization.

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There is a need for experimental data in conditions representative injection in rocket engines to validate or initiate droplet formation models used in numerical simulations. A new cryogenic vessel was built upon the MASCOTTE test bench to study the atomization of a single oxygen liquid jet, under non-reactive conditions, with simultaneous optical diagnostics. A test plan was built to explore the fiber-type regime occurring in liquid rocket injection systems, with a fixed Reynolds number and a large range of Weber number and momentum flux ratio, compared to existing studies. High-speed images are used to describe qualitatively the fiber-type regime and to visualize were droplets are present, in order to prepare the drop-size measurements. A Phase Doppler Interferometer is used to measure the size and velocity of droplets produced by atomization of a liquid oxygen jet by a coflowing gas. Droplet size and velocity measurements were performed with a PDI close to the nozzle exit in order to provide data on droplets produced by the primary atomization process, which can be useful for numerical simulations initialisation. The radial evolutions of the axial velocity and of the drop size distribution show similar trends as observed in the literature. The axial velocity is investigated for different operating conditions with helium or nitrogen as atomizing gas, showing an increase on the side of the spray. The radial evolution of the droplet size shows a translation of the drop size distribution on the edge of the spray towards the smaller sizes, indicating that the biggest liquid elements stay close to the LOX jet.

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