Phase Doppler Anemometry Measurements Research Articles

Experiments investigation on atomization characteristics of a liquid jet in a supersonic combustor

The atomization characteristics of a liquid jet in a supersonic combustor were studied experimentally for the first time. A phase doppler anemometry (PDA) system was utilized for the measurement of droplets properties along the cross-sectional area of spray plumes inside the cavity. The results were obtained under the inflow conditions of Ma = 2.0 supersonic crossflow with a stagnation pressure of 0.55 MPa and a stagnation temperature of 300 K. The size and velocity distribution of droplet inside the cavity are obtained based on the PDA measurements. It was found that the Sauter Mean Diameter (SMD) distribution of droplets inside the cavity ranged from 30 to 55 μm. The average streamwise velocity ranged from −20 to 150 m/s and the average vertical velocity ranged from −20 to 30 m/s. Large droplets distribute in the central area of the cavity. Small droplets spread around the central area of the bottom and sidewall areas of the cavity. The area near the sidewall may be an ideal ignition location due to the lower SMD and velocity of droplets. The time-averaged motion trend of droplets in the cavity is proposed experimentally based on the streamwise and spanwise velocity distribution profiles of droplets. The presence of a recirculation zone within the cavity is confirmed. The recirculation area inside the cavity is mainly distributed in the front half of the cavity. The droplets in the cavity show a good tracking performance. With the effect of the airflow, the droplets in the top area of the cavity move toward the bottom and rear wall of the cavity. In addition, the droplets in the middle and bottom area of the cavity move toward the front wall of the cavity especially for droplets near the sidewall. These universal curves can potentially be used for the modeling of a liquid jet in a supersonic combustor.

Analysis of product properties in counter-current spray drying with two nozzles system

Results of the experiments on drying of skin-forming material sprayed with two nozzles in counter-current pilot spray dryer are presented in the article. Phase Doppler Anemometry (PDA) measurements were conducted above, between, and below two nozzles spraying upward and downward which allowed us to track changes of particle size distribution (PSD) and particle velocities in the tower for different nozzle configurations. The analysis of PSD shows that for two nozzles pointing downwards, the drying zone was observed under the lower nozzle whereas the agglomeration zone develops between nozzles. For the upward orientation of the lower nozzle, a zone of simultaneous drying and agglomeration forms between the nozzles. Analysis of product moisture content, PSD, and bulk density showed the effect of nozzle configuration on product properties.

Novel atomizer concept for CCS applications: Impinging effervescent atomizer

The concept design, testing of spray characteristics, and performance comparison of an original type of atomizer, the impinging effervescent atomizer (IEA), are introduced in this study. The liquid impinging is beneficially deployed in plain-orifice and external mixing twin fluid atomizers. IEA uses a collision of two or more effervescent liquid streams to improve the atomization and alter the spray characteristics. The Phase Doppler Anemometry (PDA) measurement technique and high-speed visualization of the liquid discharge and spray structure were used. The discharge coefficient (Cd), atomization efficiency (ηa), spray characteristics as a spray cone angle (SCA), integral Sauter mean diameter (ISMD), integral relative span factor (IRSF), and droplet size and velocity distribution inside the spray were investigated. The correlations for Cd, SCA, ISMD and IRSF are provided for a fast and reliable atomizer design to fit any application and operating conditions. The IEA provides a controllable SCA governed mainly by the exit orifice geometry. The ISMD is primarily controlled by the gas to liquid ratio (GLR) and the inlet pressure (pin). The impinging angle (β) has little effect on ISMD. A narrower droplet size distribution, mass redistribution within the spray, and a more uniform droplet size spatial distribution were observed for the IEA in comparison to other tested atomizers. The IEA spray covers 116% more area than single-orifice effervescent sprays, and the area coverage can be controlled by β. This coverage increases by 177% if β changes from 15 to 45°. Spray eccentricity (e) decreases with the increase of the number of the exit orifices (No) resulting in a more uniform droplet spatial distribution. The β, GLR and pin have no effect on e. The ηa of the IEA is equivalent to other internally mixing twin-fluid atomizers; the atomization air contains more than 90% of the delivered energy. The favourable IEA spray characteristics, such as IRSF, ISMD, spray coverage, SCA and ηa, enable the potential use of IEA in mass-transfer related processes and especially in CO2 capture columns.

EFFECT OF NON-AXISYMMETRIC INLET PORTS AND OPERATING CONDITIONS ON DROP DYNAMICS OF AN INTERNAL MIXING ATOMIZER

The effect of a non-axisymmetric inlet ports configuration of an internal-mixing twin-fluid atomizer on the spray characteristics is experimentally investigated. Inside the atomizer, two water jets are impinged on each other and are further disrupted by a central gas stream coming from the top. The operating conditions consider the variation of the gas mass flow rate at Reynolds and Weber numbers in the order of 10<sup>4</sup>-10<sup>5</sup>. Phase Doppler anemometry (PDA) measurements at four radial, four axial, and two perpendicular azimuthal positions are combined with a patternator device to obtain droplet size, axial velocity, and mass flux distributions. An approach for evaluating the overall spray asymmetry based on the mass flux distributions is proposed, which enabled the detection of slight asymmetries throughout the azimuthal direction, where especially differences in droplet sizes and velocities measured between the two azimuthal positions are observed. Higher Sauter mean diameters (SMDs) and lower velocities in regions of the spray with higher liquid mass flux are observed when compared to the azimuthal position perpendicular to it. In general, the liquid is considerably faster in the spray center than at the boundaries, where the fluctuating component of the velocity is higher due to the interaction of small droplets with the surrounding air. Overall, an increase in the gas flow rate reduces the droplet sizes and increases the velocity across the spray.

Liquid Pattern And Velocity Field On A Surface During Spray Impingement

The process of fuel injection and the associated wall impact is critical for the quality of combustion in engines. Secondary droplets and wall deposits are strongly related to incomplete combustion and soot emissions. To reduce harmful emissions and optimise the combustion, further investigations of the processes of spray impingement, secondary droplet formation and wall film formation are of central importance. In order to obtain a more comprehensive picture of the interaction between spray and wall, light sheet visualizations and particle image velocimetry (PIV) measurements were performed on an impinging gasoline spray within a conditioned pressure vessel. For this purpose, measurements were conducted both perpendicular to the jet axis and parallel to the wall. The focus here is on the conditions in a modern, homogeneously operated gasoline engine with a high-pressure injection valve with a well-known spray. The spray under investigation has already been studied using high-speed shadowgraphs and phase doppler anemometry measurements. The combination of the data allows validation and a better understanding of the present measurements. The injection pressure was 150 bar, the vessel temperature 80°C, and the nozzle-to-wall distance 35 mm. The vessel pressure was varied from 0.4 bar to 6 bar, which represents typical charge conditions in an engine. The measured data allowed the analysis of the internal structure of the spray and the quantification of the flow movements before and after the spray impact. The results obtained provided detailed new insights into the relevant sub-processes.

Effect of MDI Actuation Timing on Inhalation Dosimetry in a Human Respiratory Tract Model.

Accurate knowledge of the delivery of locally acting drug products, such as metered-dose inhaler (MDI) formulations, to large and small airways is essential to develop reliable in vitro/in vivo correlations (IVIVCs). However, challenges exist in modeling MDI delivery, due to the highly transient multiscale spray formation, the large variability in actuation–inhalation coordination, and the complex lung networks. The objective of this study was to develop/validate a computational MDI-releasing-delivery model and to evaluate the device actuation effects on the dose distribution with the newly developed model. An integrated MDI–mouth–lung (G9) geometry was developed. An albuterol MDI with the chlorofluorocarbon propellant was simulated with polydisperse aerosol size distribution measured by laser light scatter and aerosol discharge velocity derived from measurements taken while using a phase Doppler anemometry. The highly transient, multiscale airflow and droplet dynamics were simulated by using large eddy simulation (LES) and Lagrangian tracking with sufficiently fine computation mesh. A high-speed camera imaging of the MDI plume formation was conducted and compared with LES predictions. The aerosol discharge velocity at the MDI orifice was reversely determined to be 40 m/s based on the phase Doppler anemometry (PDA) measurements at two different locations from the mouthpiece. The LES-predicted instantaneous vortex structures and corresponding spray clouds resembled each other. There are three phases of the MDI plume evolution (discharging, dispersion, and dispensing), each with distinct features regardless of the actuation time. Good agreement was achieved between the predicted and measured doses in both the device, mouth–throat, and lung. Concerning the device–patient coordination, delayed MDI actuation increased drug deposition in the mouth and reduced drug delivery to the lung. Firing MDI before inhalation was found to increase drug loss in the device; however, it also reduced mouth–throat loss and increased lung doses in both the central and peripheral regions.

Effects of fuel properties and aerodynamic breakup on spray under flash boiling conditions

• Sprays of four single component fuels under flash boiling conditions were studied. • Spray collapses at R p of 0.28 for isooctane, hexane and ethanol, and 0.18 for pentane. • Ethanol has relatively larger near-field angle, far-field angle and SMD. • Aerodynamic breakup still plays an important role under low flash boiling conditions. • Isooctane, hexane and pentane under R p of 0.28 show a similar SMD value of 10 µm. The main purpose of this work is to conduct detailed comparisons of spray behavior among four important components of gasoline and to investigate the effects of fuel properties and aerodynamic breakup on spray behavior under flash boiling conditions. Isooctane, hexane, pentane, and ethanol were used as test fuels. Pressure ratio ( R p ) was used as an indicator for the superheated degree and varied from 0.14 to 1.1 by adjusting the ambient pressure. Both Diffused Backlight Imaging (DBI) and Phase Doppler Anemometry (PDA) measurements were used to obtain macroscopic and microscopic characteristics of sprays. Four dimensionless numbers were used to evaluate the aerodynamic breakup processes. The results showed that as the reduction of R p , the flash boiling intensity increased, leading to dramatic spray morphology changes and smaller droplet size, regardless of fuel type. Spray plumes merged into the spray center when lowering R p from 1.0. Spray collapsed at an R p of 0.28 for isooctane, hexane, and ethanol, and at an R p of 0.18 for pentane. Fuel properties also had significant effects on spray behaviors. Spray with pentane had the smallest penetration length, and a dramatic far-field angle reduction was observed at R p between 0.2 and 0.4, due to its higher vapor pressure and lower latent heat of vaporization. Under the same R p , ethanol sprays had relatively larger near-field angles, far-field angles, and Sauter mean diameter (SMD), due to its high latent heat of vaporization. All the dimensionless numbers showed that the spray with pentane had the largest aerodynamic breakup intensity, followed by hexane and isooctane, while ethanol had the lowest aerodynamic breakup intensity under the tested conditions. Aerodynamic breakup still played an important role under low flash boiling intensity conditions ( R p over 0.8). Microscopic results showed that SMD of isooctane, hexane, and pentane under an R p of 0.28 had a similar value of 10 µm.

Application of SLIPI-Based Techniques for Droplet Size, Concentration, and Liquid Volume Fraction Mapping in Sprays

Structured laser illumination planar imaging (SLIPI)-based techniques have been employed during the past decade for addressing multiple light scattering issues in spray imaging. In this article, SLIPI droplet sizing based on the intensity ratio of laser-induced fluorescence (LIF) over Mie scattering (SLIPI-LIF/Mie) and SLIPI-Scan for extinction-coefficient (µe) mapping are applied simultaneously. In addition, phase Doppler anemometry (PDA) and numerical calculations based on the Lorenz–Mie theory are also employed in order to extract the droplets Sauter mean diameter (SMD), the droplets number density (N), and the liquid volume fraction (LVF) in a steady asymmetric hollow cone water spray. The SLIPI-LIF/Mie ratio is converted to droplets SMD by means of a calibration procedure based on PDA measurements. The droplet SMD for the investigated spray varies from 20 µm to 60 µm, the N values range from 5 to 60 droplets per mm3, and the LVF varies between 0.05 × 10−4 and 5.5 × 10−4 within the probed region of the spray. To generate a series of two-dimensional images at different planes, the spray scanning procedure is operated in a “bread slicing” manner by moving the spray perpendicularly to the light sheet axis. From the resulting series of images, the procedure described here shows the possibility of obtaining three-dimensional reconstructions of each scalar quantity, allowing a more complete characterization of droplet clouds forming the spray region.

DROP DYNAMICS IN HETEROGENEOUS SPRAY FLAMES FOR NANOPARTICLE SYNTHESIS

In flame spray pyrolysis (FSP), the understanding of the atomization and spray formation of the coaxial atomizer is a key step to control the mixing of reactants, and precursor release, as well as nanoparticle formation and growth mechanisms. The drop size and drop dynamics of fuel/precursor mixtures are relevant parameters to control the particle synthesis via gas-to-particle conversion for tailoring the nanoparticle. The investigation of the multiphase flow structures, especially in the dense spray region using sophisticated nonintrusive laser diagnostics, such as phase Doppler anemometry (PDA), enables a characterization of the burner with multiscale spatial and temporal resolution. In the present work, the evolution of drop size and velocity under varying iron nitrate (FNT) concentration of the precursor is investigated allowing for an estimation of precursor release and evaporation via detailed PDA measurements. The drop size distributions of pure ethanol, and ethanol + 2-ethylhexanoic acid, as well as for FNT-based spray flames, were studied in order to reveal the influence of metal precursors on the combustion. Drop size/velocity correlations were determined in order to resolve the size class averaged evolution of drop velocities. The evolution of the drop size distribution along the axial centerline revealed a variation of the evaporation rate in space and increased evaporation rates for FNT containing spray flames. Furthermore, bimodal drop size distributions were observed for heights above the burner larger than 40 mm in FNT precursor spray flames, indicating the occurrence of possible μ-explosions of drops, that have been reported in the literature for similar systems but only in single-droplet experiments so far.

A Low-power Liquid-fuelled Burner Using a Novel Atomization Concept

ABSTRACTThe design of and experimental results for a low-power heating oil burner, operating between 1.25 and 5.1 kW with exhaust gas emissions within the normative regulations for domestic usage, are presented. In contrast to common domestic heating oil burners, the atomization and combustion sections are spatially separated to allow the implementation of a novel atomization concept for low-power liquid-fuelled burners proposed in a previous study. The main working principle for spray generation is the secondary atomization of a droplet chain impinging on a pin downstream. Through pulse-width modulation (PWM) of the droplet generator, modulation of the spray flowrate over a wide range with constant spray quality was achieved. Phase-Doppler anemometry measurements under non-reacting conditions were performed to obtain the droplet size distribution of the spray. Three model liquids were used to determine the influence of liquid properties on the droplet size distribution. The Sauter mean diameter (SMD) values obtained for all liquids and operation parameters studied are in the range of 10% of the primary droplet diameter, which is 30 µm for the setup in this study.

Experimental study on the electrospray and combustion characteristics of biodiesel-ethanol blends in a meso-scale combustor

The spray and combustion characteristics of biodiesel-ethanol blends were experimentally investigated by using electrospray atomization in a meso-scale combustor. Phase Doppler anemometry measurements were employed to obtain droplet size distribution. Optical measurements were carried out to quantify the electrospray structures. With the addition of ethanol, the spray angle increased and the droplet size decreased from 128 μm to 12 μm. The polydisperse spray of the biodiesel-ethanol blends with a low ethanol blending ratio yielded the bimodal distribution in droplet size due to Coulomb fission. Relative standard deviation of monodisperse droplets is below 15%. The combustion of the blends was performed in a meso-scale combustor with a 12 mm inner diameter. The flame can be stabilized near the mesh in the combustor without any external heating. It was found that the spray structures have a direct effect on the flame structures in spray combustion. 40% ethanol addition (BE40) has the best combustion performance compared to other blends. The results show that the flame of BE40 has a broader stabilization limit both in flow velocity and equivalence ratio. The reduction of the droplet size for the blends with high ethanol blending ratio results in the decrease of CO emission.

Impact of gasoline direct injection fuel injector hole geometry on spray characteristics under flash boiling and ambient conditions

The effect of injector nozzle design on the Gasoline Direct Injection (GDI) fuel spray characteristics under atmospheric and flash boiling conditions was investigated using Phase Doppler Anemometry (PDA) measurements. To understand the impact of hole diameter and conicity, experiments were conducted on two bespoke 3-hole injectors in a pressure and temperature controlled constant volume chamber and in the open air. The measurements were taken radially outward from the injector axis to the outer extent of the plume at distances of 15 mm, 25 mm and 40 mm from the injector tip.Observations of the influence of surrounding gas and temperature conditions and hole design on the injector spray performance were made. Under non-flash boiling conditions, it was found that the injection pressure dictates the length of the spray penetration before collapse occurs, with an increase in pressure resulting in an increase in this length. Comparison of mean velocity and droplet diameter data are also made to understand the performance under flash boiling conditions. Results show that, under flash boiling conditions, the droplet velocity significantly increases while the droplet size reduces. More importantly, it is found that the impact of the flash boiling environment on sprays of different hole geometries is different. Some hole designs offer more resistance against spray collapse. It was found that the mid-sized of the three hole diameters tested here was found to produce a spray that more readily collapsed than that of the smaller or larger hole diameters. In addition, it was found that under flash boiling conditions, the convergent hole had a greater propensity to exhibit spray collapse.

Methodology for Phase Doppler Anemometry Measurements on a Multi-Hole Diesel Injector

In this paper, a methodology for Phase Doppler Anemometry (PDPA) measurements on a multi-hole diesel injector is developed. Several key considerations were taken into account in this methodology: The windows for PDPA optical access must be clean, since fuel impregnated in these could preclude the droplets velocity acquisition. Some parts, including a device for spray isolation, were designed and manufactured to fulfill this goal. Taking into account that only one spray is measured, the isolation device captures all except three of the sprays (including the spray of interest). The two plumes accompanying the main spray were thought to conserve the actual air entrainment and thus the spray behavior. The spray of interest was aligned horizontally to ease the way that the PDPA measurements are carried out. The plume was lined up by means of the MIE-Scattering macroscopic optical technique. Images were acquired for several injection events and spray contours were detected and processed with a purpose-built Matlab tool. At each time step a spray axis inclination was estimated using the centroids from instantaneous contours. Also, preliminary droplet velocity measurements were made to check the effectiveness of the alignment and spray isolation strategies. Both geometrical characterization and spray alignment had very low measurement error. Radial velocity profiles show that PDPA measurements with this set-up configuration preserved the spray behavior.

Experimental study of local flame structures and fuel droplet properties of a spray jet flame

An n-heptane spray jet flame is characterised through quantitative measurements using laser-based techniques. The experimental set-up is composed of an annular non-swirled air co-flow that surrounds a central hollow-cone spray injector, leading to a stable flame with well- defined boundary conditions. Phase Doppler anemometry (PDA) measurements contribute to this investigation through the analysis of air and droplet aerodynamics and OH-PLIF images describe the two dimensional flame structure. The polydisperse spray distribution yields small droplets along the centreline axis while the majority of the mass is situated as big droplets along the spray borders. The flame structure presents a classical shape, with an inner wrinkled partially premixed flame front and an outer diffusion flame front. In addition Global Rainbow Refractometry Technique (GRT) has been used to measure droplet temperature in the different regions of the spray jet flame. This technique was first applied with a continuous laser (C-GRT) to get temporally averaged values of fuel droplet temperature according to the methodology developed initially by Letty et al. [1]. This technique has been extended to measure instantaneous and local fuel droplet temperature by using a pulsed laser. Therefore, conditional averaged measurements of fuel droplet temperature according to the distance of flame front are reported for the first time by coupling instantaneous GRT (I-GRT) with OH-PLIF. New insights on the thermal droplet behaviour in a spray flame are discussed.

Modelling on the dynamics of droplet impingement and bubble boiling in spray cooling

A spray cooling model incorporating a spray characteristics submodel and a heat transfer submodel to simulate the dynamics of spray characteristics, droplet impingement, and bubble boiling is presented. The spray characteristics submodel based on a Monte Carlo algorithm simulates the droplet diameter, velocity and spatial droplet flux distributions in actual spray conditions. The heat transfer submodel considers the spray cooling process as film flow boiling to include the processes of droplet impingement forced convection and thin film bubble boiling. Phase Doppler anemometry measurements are used as validation in the spray characteristics submodel, and as boundary conditions in the heat transfer submodel. Reasonable comparison is observed between the experiments and simulations. Parametric effects on the heat transfer performance and bubble dynamics are investigated. The simulation shows that increasing heat flux tends to increase the bubble growing frequency thereby causes the higher bubble collapsing flux and bubble puncturing flux. By fixing the droplet impinging velocity and flow rate, the surface temperature non-uniformity is found to be influenced by droplet diameter. A smaller impinging droplet diameter with a higher impinging droplet flux is favourable to bubble boiling due to more secondary nuclei and larger fractions of bubbles punctured at bigger diameters.

The influence of spill-line geometry on a spray generated by a pressure-swirl atomizer

An experimental investigation of characteristics of spray generated by a pressure-swirl atomizer (spill-return type) was performed using shadowgraphy and Phase-Doppler Anemometry (PDA). Several different geometries of the spill-return orifice were tested in terms of a spray stability and quality on a cold test bench. PDA measurement yields a drop-size distribution and velocity data while the shadowgraphy unveils a break-up process in detail. Performed measurements reveal significant differences in spray characteristics as well as differences in spray stability. The results suggest that the air core, formed inside the swirl chamber, passes through the spill orifice, which causes instability of the inner flow. These instabilities lead to a chaotic state of sheet breakup resulting in shortening of breakup distance. Obtained findings are used to propose possible changes in the atomizer design for improvement of its performance.

Concept for a cyclonic spray scrubber as a fission product removal system for filtered containment venting

The application of a cyclonic spray scrubber as a technology for filtered containment venting is proposed in this paper. This study has paired a mechanistic model for the kinetic particle coagulation of with Euler–Lagrange discrete particle simulations in order to predict particle decontamination factors. The continuous phase behavior has been investigated using computational fluid dynamics simulations together with phase Doppler anemometry measurements. Calculations show that spray scrubbing of radionuclide-bearing aerosols could be very effective, and predict that decontamination factors can be in excess of 106 for micron sized particles and excess of 103 for submicron particles. In the wake of the accident at the Fukushima Daiichi Nuclear Power Plant, filtered containment venting is being viewed as an increasingly important severe accident mitigation technology. Cyclonic spray scrubbing could be implemented as a passive technology for decontaminating containment gases in an emergency prior to their discharge to the atmosphere, and is a novel approach for this application.

An experimental and theoretical investigation of spray characteristics of impinging jets in impact wave regime

The current study focuses on experimentally and theoretically improving the characterization of the drop size and drop velocity for like-on-like doublet impinging jets. The experimental measurements were made using phase Doppler anemometry (PDA) at jet Weber numbers We j corresponding to the impact wave regime of impinging jet atomization. A more suitable dynamic range was used for PDA measurements compared to the literature, resulting in more accurate experimental measurements for drop diameters and velocities. There is some disagreement in the literature regarding the ability of linear stability analysis to accurately predict drop diameters in the impact wave regime. This work seeks to provide some clarity. It was discovered that the assumed uniform jet velocity profile was a contributing factor for deviation between diameter predictions based on models in the literature and experimental measurements. Analytical expressions that depend on parameters based on the assumed jet velocity profile are presented in this work. Predictions based on the parabolic and 1/7th power law turbulent profiles were considered and show better agreement with the experimental measurements compared to predictions based on the previous models. Experimental mean drop velocity measurements were compared with predictions from a force balance analysis, and it was observed that the assumed jet velocity profile also influences the predicted velocities, with the turbulent profile agreeing best with the experimental mean velocity. It is concluded that the assumed jet velocity profile has a predominant effect on drop diameter and velocity predictions.

Investigation and comparison of spray characteristics of pressure-swirl atomizers for a small-sized aircraft turbine engine

Abstract The quality of liquid fuel atomization highly affects the formation of gaseous pollutants and particulate matter emissions from combustion processes. Spray characteristics of two geometrically different pressure-swirl atomizers for a turbojet engine in light aircraft were measured on a cold test bench. A spill-return atomizer and its intended replacement simplex atomizer were investigated using Particle Image Velocimetry (PIV) and Phase-Doppler Anemometry (PDA). Single-camera and stereoscopic PIV measurements yielded velocity distributions in the axial cross-section of the spray cone. PDA measurements provided drop-size distribution and axial velocity data. Acquired results reveal significant differences in spray characteristics of the nozzles investigated at the same fuel injection pressures. The simplex nozzle produced spray with Sauter mean diameters lower by 5–20 μm depending on the regime, its spray was more stable but its shape greatly varied with fuel injection pressure. These differences are discussed in detail, their analysis indicate a potential for spray improvement provided by the novel atomizer design and elucidates the possible impact of the nozzle replacement on the combustion process.

Droplet characteristics and local equivalence ratio of reacting mixture in spray counterflow flames

Spray combustion was studied by injecting monodisperse 125 or 200μm ethanol droplets in a premixed natural gas fuel flame flowing against an opposed heated air jet. Phase Doppler anemometry and chemiluminescence measurements allowed to characterise both droplet parameters and the local reacting mixture. Both types of droplets crossed the flow stagnation plane and entered the opposite jet. However, 125μm droplets reversed their motion and oscillated around the stagnation plane, leading to increased droplet residence time in hot regions. The fuel vapour released by droplets close to the stagnation plane, mixed with the surrounding air and led to the ignition of a second fuel vapour flame below the natural gas flame. For 125μm droplets, mean local equivalence ratio of the fuel vapour flame was about 0.8, suggesting lean-premixed combustion; whereas 200μm droplets led to stoichiometric combustion. “Group Combustion” number was estimated from measurements and suggested that 125μm and 200μm droplets burned in different “Group Combustion” regimes.