Hollow Cone Spray Research Articles

Droplet size, spray structure and droplet velocity mapping in hollow cone sprays using SLIPI-based techniques

The Structured Laser Illumination Planar Imaging (SLIPI) technique received significant attention in recent years due to notable improvements in the measurement of droplet size and the visualization of internal structure in both dilute and dense sprays. However, despite the improvements, the technique remains limited to these microscopic characteristics of the spray, primarily due to the complexity of the optical setup and image acquisition process. In this article, the capabilities of the SLIPI application are exploited, specifically employing the 3p-SLIPI-LIF/Mie (SLSD), and combined application of 1p-SLIPI-LIF & PIV (1p-SLIPI-PIV) for mapping of both Sauter Mean Diameter (SMD) and mean droplet velocity in combination with detailed spray structure analysis. The measurements were carried out in hollow cone sprays operated at the range of injection pressures from 25 to 107 bar. The results obtained using the SLIPI techniques were compared with the Phase Doppler Anemometry (PDA) measurements showing good agreement for both the SMD and mean droplet velocity. The significant improvements in the important microscopic characteristics (droplet size & velocity) and visualization of the internal structure in a wider flow field of hollow cone sprays allowed detailed analysis and understanding of the dispersed phase flow owing to the suppression of diffused light resulting from the multiple scattering effects.

Taxa de aplicação e pontas associados à eletrificação de gotas afetam a qualidade da pulverização em feijoeiro

ABSTRACT The objective of this work was to evaluate the application efficiency of different nozzle tips associated with increasing application rates. A field experiment was conducted in a factorial 3 × 4 randomized block design with four replicates. The first factor consisted of three types of nozzle tips (simple flat fan, hollow cone, and hollow cone with the electrification of the drops), and the second factor constituted the four application rates (50, 100, 200, and 250 L ha-1). Electrostatic technology and a hollow cone tip increased the deposited volume on leaves on the upper and medium strata of the common bean plant, regardless of the application rate used. The increase in the application rate increased the volume of spray solution captured in the upper, medium, and lower strata, the drop density, the volumetric median diameter (VMD), and the percentage of foliar coverage, regardless of the spray tip evaluated. The percentage of leaf coverage on the adaxial and abaxial leaf was not influenced by the simple fan or hollow cone spray tips, with or without the association of electrostatic technology.

Use of Unmanned Aerial Vehicle for Pesticide Application in Soybean Crop

The use of unmanned aerial vehicles (UAVs) for pesticide application has increased substantially. However, there is a lack of technical information regarding the optimal operational parameters. The aim of this study was to evaluate the quality of pesticide application on a soybean crop using a UAV employing different spray nozzles. The experiments were conducted using a completely randomized design with four treatments and eight repetitions. The trial was conducted in a soybean growing area during the soybean reproductive stage (1.1 m tall). The treatments included aerial application (rate: 10 L hm−2) using an Agras MG1-P UAV with XR 11001 (flat fan), AirMix 11001 (air-induction flat fan), and COAP 9001 (hollow cone spray) nozzles; for comparison, ground application (rate of 100 L hm−2) using a constant pressure knapsack sprayer with an XR 110015 (flat fan) nozzle was performed. The deposition was evaluated by quantifying a tracer (brilliant blue) using spectrophotometry and analyzing the droplet spectrum using water-sensitive paper. Furthermore, the application quality was investigated using statistical process control methodology. The best deposition performance was exhibited by the application via UAV using the COAP 9001 and AirMix 11001 nozzles. For all the treatments, the process remained under statistical control, indicating commendable adherence to quality standards. The aerial application provided greater penetration of the spray into the crop canopy. With the use of the UAV, the coverage on the water-sensitive paper was <1%; moreover, the AirMix 11001 and XR 110015 nozzles had the lowest drift potential.

Impact of Transverse Acoustic Excitation and Air Swirl on a Confined Hollow Cone Sheet

Abstract This study investigates the effect of imposing symmetric transverse acoustic excitation and counter-rotating air swirl flow on a confined hollow cone spray sheet. We study the impact of these forcing conditions on two unstable modes—sheet flapping and sinuous wave growth modes—and their phasic relationship. We used the shadowgraphy technique, and only the sheet edges were analyzed using the method of snapshot proper orthogonal decomposition (POD). In this study, we used postprocessing techniques to estimate the nondimensional breakup length, phase averaged cone angle, and continuous wavelet transform (CWT) frequency. Results show that imposing acoustic excitation alone causes the sheet edges to flap, axisymmetrically, at the pressure antinode, while at the pressure node and base flow condition, the asymmetric sinuous wave mode is dominant. At the pressure intermediary, we find the possible dominance of both modes. While the dominant effect of air swirl alone was difficult to ascertain, results from CWT analysis show that POD mode 1 and mode 3 have very similar spectral content, with mode 3 showing a flapping mode. Finally, air swirl flow has a more dominant effect than acoustics in causing sheet breakup.

Deposition of spray droplets by four spray nozzles and two working pressures

The deposition of spray droplets on the target can be influenced by the type spray nozzle used, as well as the employed working pressure. Thus, with the commercial availability of new spray nozzles, performance studies with the new models become necessary. This study was carried out to evaluate ground deposition of spray droplets by four models of spray nozzles, at two working pressures. The experiment was conducted in Dourados/MS, in September 2020, with strip design and 4x2 factorial scheme, with five repetitions. Four spray nozzles were used (single flat fan, ST-IA 02 model; angle flat fan MUG 02; hollow cone MGA 02; and double flat fan ST-IA/D 02), working at 30 and 50 psi pressures. The distance between each nozzle was 50 cm, 60 cm above the ground. Water-sensitive paper was used and, immediately after application, the paper was scanned using the DropScan® tool. Subsequently, the number of droplets, coverage, amplitude, dispersion, Volume Median Diameter (VMD), Number Median Diameter (NMD), DV09, and DV01 were evaluated. The hollow cone spray nozzle provided a higher number of droplets and greater coverage compared to the other nozzles for the studied weather conditions.

Experimental Study on Breakup Characteristics of Hollow Cone Spray in Gas Crossflow

Hollow cone spray with a medium spray half-cone angle (in the range of 36°–45°) exposed to a gaseous crossflow is a situation that has been extensively investigated experimentally. In this experiment, flow visualization techniques are employed to examine the initial liquid sheet thickness at the nozzle orifice exit and the sheet breakup process. The dynamics of the primary breakup of the sheet is analyzed based on the observations of the sheet breakup in the near-nozzle region. The experimental results show that the breakup mechanism of the liquid sheet varies greatly depending on liquid centrifugal momentum and aerodynamic force. Four distinct breakup modes are observed, and the breakup regimes are mapped in the parametric space based on the liquid Weber number (84–2175) and the liquid-to-air momentum ratio (22–8455). It is observed that the leeward side of the sheet is dominated by shear oscillation breakup within the range of the liquid-to-air momentum ratio less than 600. The influences of the aerodynamic Weber number on breakup frequency and the number of surface waves observed on the leeward side sheet are discussed by analyzing the spray images. The breakup-regime transition criteria for hollow cone spray in crossflow and the trajectory of spray in crossflow are proposed by employing a multivariable regression method.

Using Inpyrfluxam to Control Peanut (Arachis hypogaea L.) Foliar and Soil-Borne Diseases

Aims: To determine peanut disease control and yield response to inpyrfluxam applied at various timings during the growing season.
 Study Design: Randomized complete block design with 4 reps.
 Place and Duration of Study: Field studies were conducted from 2016 through 2020 in the south Texas peanut growing region near Yoakum (29.276o N, 97.123o W).
 Methodology: Fungicides were applied with a CO2-propellant sprayer. The spray boom was equipped with three D2-23 hollow-cone spray nozzles per row with the middle nozzle centered over each plant in the row and another nozzle located as such to spray on each side of the plant to provide thorough coverage with a spray volume was 187 L ha-1. Some studies included a non-treated control while other studies included chlorothalonil only at 1.26 kg ha-1 as the comparison treatment. Each plot consisted of four rows spaced 97 cm apart and 7.9 m long.
 Results: Inpyrfluxam applied twice in a 4 to 5 fungicide spray program in combination with chlorothalonil provided early leaf spot control as good as or better than the standards of chlorothalonil plus either azoxystrobin alone or azoxystrobin plus benzovindiflupyr applied 2 times. Control of Rhizoctonia pod rot, caused by Rhizoctonia solani Kuhn, with inpyrfluxam at 0.04, 0.05. 0.075, or 0.1 kg ai ha-1 applied 2 times during the growing season was comparable to two applications of azoxystrobin at 0.22 kg ai ha-1. Control of southern blight, caused by Sclerotium rolfsii Sacc., with one to two applications of inpyrfluxam at 0.05 to 0.1 kg ha-1 was comparable to azoxystrobin plus benzovindiflupyr. Peanut yield response was influenced by the level of soilborne and foliar disease control exhibited with each fungicide program, as those programs which provided the best control also produced the highest yield.
 Conclusion: These studies show the ability of inpyrfluxam to provide control of multiple diseases found in southwest peanut production.

Droplet breakup and coalescence characteristics of hollow cone spray in crossflow

Droplet breakup and coalescence characteristics of hollow cone spray in crossflow

AXIAL ACOUSTIC VELOCITY INTERACTION WITH HOLLOW CONE LIQUID SHEET IN A SWIRLING FLOW FIELD

This experimental investigation concerns the effect of imposed axial acoustic velocity fluctuations on the primary atomization of a hollow cone liquid sheet in the presence of a strong air swirl. The atomization dynamics are elucidated by positioning the spray at an acoustic velocity node, antinode, and a mixed point in the standing wave field generated due to the imposed axial acoustic excitation. High-speed shadowgraph images acquired in-sync with dynamic pressure measurements are processed to clarify the unstable behavior observed in the spray dynamics; this was achieved by extracting key parameters such as breakup length, spatial growth rates, phase differences, and by employing Proper Orthogonal Decomposition (POD). A novel method to obtain the breakup length of a hollow cone spray from the position of maximum wave amplitude is presented. The breakup length is the smallest for the mixed point. The phase difference between the left and right half-angle fluctuations shows that the flapping motion of the spray is predominantly observed at the mixed point for different air-to-liquid ratios. Another novel approach is adopted to identify the physical mechanisms corresponding to each POD spatial mode by comparing POD spatial modes obtained from experiments to those generated artificially.

Flashback-induced flame shape transition in a two-stage LPP aeronautical combustor

Large-Eddy Simulations were performed to study the flashback-induced flame shape transition of a lean premixed M flame in a staged liquid-fuelled aeronautical lean-burner, as observed experimentally. The BIMER combustor is a Lean Premixed Prevapourised (LPP) burner composed of two stages, each with its own injector and swirler: the main outer stage, called multipoint, uses jet-in-crossflow injection to achieve the LPP regime, while the central stage, called pilot, uses a pressure swirl injector to create a hollow cone spray to stabilise the flame. During LPP operation, this M flame presents a strong acoustic activity, promoting a periodic flashback of its leading edge. When, aiming to stabilise the flame, the pilot injection is increased and the multipoint injection decreased, the oscillating leading edge (due to the longitudinal acoustic perturbations) attaches to the pilot spray, changing the flame into a Tulip shape. Two phenomena were identified as being the most relevant causes of this flame shape transition. First, the leading edge position and the thermoacoustic instability amplitude are directly linked to the combustion chamber final temperature. The higher the temperature in the chamber, the more upstream the leading edge stabilises, and the higher the acoustic oscillation amplitude, both increasing the risk of a successful flashback. Second, the injection regime with high pilot injection allows the leading edge to attach to the pilot spray, as the flame only transitions when the pilot spray is sufficiently high. The higher the pilot fuel flow, the higher the amount of fuel sprayed in the critical region where the flame might attach for a transition to the Tulip shape. Therefore, as the change in injection regime is the main mechanism lean staged burners use to reduce emissions while increasing operability, this works shows that an M flame is unsuitable to such burners with similar aerodynamic topology and properties.

VALIDATION OF Σ−YLIQ ATOMIZATION MODEL IN PRESSURE SWIRL ATOMIZER

In many combustion and agricultural applications atomizers are used to increase the surface area of the liquid to ensure high rates of mixing and improve evaporation. The most common, simple, and reliable atomizer is the pressure swirl atomizer. This atomizer is said to have quality and effective atomization compared to others and induces swirling motion to the liquid and gives a hollow cone spray with air core as it emerges from the exit orifice. To enhance the understanding and prediction of the atomizing characteristics various atomization models are used and need to be investigated experimentally. This paper presents a validation of the Σ−Yliq atomization model of two-phase flow in a pressure swirl atomizer using commercial CFD star-cd code and laser-diffraction based drop measurements. To obtain the best results for the droplet mean diameter between the prediction and the experiment in terms of turbulence different k-e models were evaluated. The results show that the computational predictions of Sauter Mean Diameter (SMD) for the model have a good agreement with most of the experimental measurements in the radial positions when standard k-ɛ turbulence was used. However, more divergence was observed between the predictions and the experimental measurements when the RNG and Realizable k-ɛ turbulence models were used in the predictions. It was also observed that the model has good agreement with the mean droplet measurements on the spray centreline and radial axis with a percentage error of less than five percent.

Computational fluid dynamics characterization of the hollow-cone atomization: Newtonian and non-Newtonian spray comparison

Disintegration of liquid masses in a free-surface flow is still an open question in the field of small-scale spray applications such as dispensing of detergents or sanitizing products. In this context, the pressure-swirl atomizer is widely investigated. It allows to improve several spray characteristics through the formation and breakup of a conical liquid sheet that results in the well-known hollow-cone atomization. From this perspective, the characterization of a small-scale pressure-swirl spray under laminar flow conditions is the focus of this work. The configuration of the device and the physical properties of the discharged liquid are the key parameters that modify the attributes of such multiscale flow. In this regard, the entire picture of the fragmentation process is structured into multiple stages: internal nozzle flow, outer displacement of the liquid–gas interface, droplet spread into the atmosphere, and droplet-wall interactions on a collection surface. Through the computational fluid dynamics, we analyze the influence of the main fluid/packaging parameters on the hollow-cone spray properties, and on the whole atomization process. Reynolds and Ohnesorge numbers are coupled with the Sauter mean diameter to distinguish different breakup mechanisms and spray performances. The solution of the entire spray system is performed by implementing the volume-of-fluid-to-discrete-phase-model, which allows to capture the liquid–gas interface displacement and track the droplets produced downstream the primary atomization, simultaneously. With this Eulerian–Lagrangian hybrid model, we link key features of the hollow-cone spray process to spray pattern and droplet size distribution for both Newtonian and non-Newtonian fluid properties.

Use of different spray volumes and hydraulic nozzles in air-assisted electrostatic insecticide application technologies to control coffee berry borer (Hypothenemus hampei) populations

Chemical control is essential for efficient pest management in coffee crops. Application technologies should safely deliver insecticides to the target whilst protecting the environment, insecticide applicators, and consumers. To achieve these goals, application volumes, hydraulic nozzles, and application techniques should be evaluated. This study assessed the biological efficiency of different spray volumes and spray nozzles used to apply insecticides to control coffee berry borer (Hypothenemus hampei) populations. We applied insecticides using a hydropneumatic sprayer with and without an electrostatic spraying system. The experiment followed a randomized block factorial design (2 × 2 + 1) and included two types of spray nozzles [a hollow cone spray nozzle (JA1) and a hollow cone spray nozzle with air induction (TVI)], two spray volumes (200 and 400 L ha-1), one additional treatment (SPE2 nozzle with a 200 system 200 L ha-1), and six replicates. We assessed the control efficiency of the different application methods by evaluating the percentage of fruits damaged 20 and 40 days after the date of application. The spray volume did not affect the biological efficiency of pest control, and the lower spray volume (200 L ha-1) was effective in the control of coffee berry borers. Application of insecticides using coarse droplets was more efficient than the application using very fine and fine droplets. The TVI hydraulic spray nozzle effectively controlled coffee berry borers at 200 and 400 L ha-1. The electrostatic application system performed similarly to the conventional system in terms of the control of the coffee berry borers, and was less efficient than the conventional system under some operational conditions.

Experimental investigation of the lift-off height and soot formation of a spray flame for different co-flow conditions and fuels

Since the combustion process in spray flames is a highly complex multi-phase phenomenon, which involves several simultaneous processes such as atomization, vaporization, and chemical kinetics, it is still not fully understood. In the present work, an experimental investigation has been performed for three different hydrocarbon fuels (n-Heptane, n-Decane, n-Dodecane), in order to understand the effect of varying co-flow conditions, fuel mass flow rate, and fuel type on both the flame lift-off height and soot formation. The fuels were injected through a hollow-cone spray injector, with a nominal spray cone angle of 80∘ and orifice diameter of 120μm in an annular non-swirled preheated air co-flow. The flame lift-off height was determined by recording the OH* chemiluminescence, whereas soot formation has been determined through the color diffused back-illumination extinction technique. From the results, it has been observed for a certain fuel that the flame lift-off height is mainly controlled by the co-flow velocity and air co-flow temperature. The results also show that the fuel that yields largest droplet size and that possesses the lowest volatility exhibits the highest flame lift-off height. Furthermore, the results evidence a strong influence of the co-flow velocity on the soot formation. With an increase in co-flow velocity, the flame lift-off height is increased and so the amount of air entrainment, leading to a less rich reaction zone just downstream of the lift-off height, which in turn results in less soot formation. Finally, the comparison among different fuels shows that their differences in soot formation are likely related to fuel sooting tendency. This property, in turn, depends on the fuel molecular structure playing an important role on its determination.

Effect of acoustic velocity on the primary atomization of a hollow cone spray in a swirling flow field

Effect of acoustic velocity on the primary atomization of a hollow cone spray in a swirling flow field

Spray nozzle selection contributes to improved postemergence herbicide crabgrass control in turfgrass

For optimum postemergence crabgrass (Digitaria spp.) control, a single quinclorac herbicide application could be properly timed and delivered with spray nozzles that produce spray droplets ranging from very coarse (401-500 μm) to medium (226-325 μm) in size to maximize target coverage and minimize the potential for drift. Crabgrass is an invasive annual grass weed of cool-season turfgrass maintain as lawns, golf courses, and sports pitches. Postemergence herbicide applications for crabgrass control in turfgrass swards often rely on repeated applications for effective control. Optimizing postemergence crabgrass applications can reduce pesticide inputs and contribute to sustainable turfgrass management practices. Two field studies evaluating crabgrass control were conducted in 2020 in a mixed stand of Kentucky bluegrass (Poa pratensis L.) with perennial ryegrass (Lolium perenne L.) in Ohio (USA) and in perennial ryegrass in Pennsylvania (USA). Both sites have histories of natural crabgrass [Digitaria sanguinalis (L.) Scop.] infestation. A postemergence herbicide, quinclorac, was applied at the product label rate and tank-mixed with methylated seed oil at the crabgrass plant stage of three-leaf to one tiller. Different spray nozzles were selected to deliver the following spray droplet classifications and sizes at 275 kPa: Delavan Raindrop 1/4, ultra coarse (>650 μm); TurfJet 1/4TTJO4, extremely coarse (501-650 μm); Air Induction AA8004 or XRTeeJet 8015, very coarse (401-500 μm); XR TeeJet 8008 or GreenLeaf TDAD04, coarse (326-400 μm); XR TeeJet 8004, medium (226-325 μm); and XRTeeJet 8003 fine (145-225 μm). Crabgrass pressure was low in Ohio, and herbicide efficacy at 60 days after treatment was considered acceptable when applied from all spray nozzles that produced spray droplet sizes ranging from ultra coarse to fine. Crabgrass pressure was severe in Pennsylvania, and herbicide efficacy at 60 DAT was considered marginally acceptable when applied from spray nozzles that produced spray droplet sizes ranging from very coarse to medium. Future research should consider cultural practices that would be complementary to postemergence herbicide applications with the goal to reduce pesticide use further and minimize any potential environmental impacts related to spray drift. Highlights - In turfgrass sites with low crabgrass pressure, one postemergence application of quinclorac herbicide could potentially achieve acceptable control with spray nozzles that produce spray droplets ranging from ultra coarse (>650 μm) to fine (145-225 μm). - In turfgrass sites with heavy crabgrass population and pressure, one postemergence application of quinclorac herbicide is best optimized with spray nozzles that produce spray droplets ranging from very coarse (401-500 μm) to medium (226-325 μm). - Overall, turfgrass management practitioners should avoid using spray nozzles that produce a hollow cone spray pattern with ultra coarse (>650 μm) spray droplets which can result in poor or irregular herbicide coverage, or fine (145-225 μm) spray droplets which are subject to potential drift and possible negative off-target effects. - Overall, in an effort to reduce herbicide use for postemergence crabgrass control, a single quinclorac herbicide application could be properly timed and optimized with nozzles that produce spray droplets ranging from very coarse (401-500 μm) to medium (226-325 μm) in size, however, future research should consider cultural practices that would further optimize and also reduce herbicide applications.

Three-dimensional computational fluid dynamics simulation of the hollow-cone spray process: The stability of the conical liquid sheet

The characterization of atomization in small-scale applications, such as those typical of the consumer goods industry, is not widely investigated, despite its enormous interest as in the case of sanitation. In this field, the features of the atomizer are selected to achieve a wide spray pattern. This is the case of the pressure-swirl atomizer, where the swirl flow leads the liquid sheet to exhibit a distinctive hollow-cone shape. The configuration of the atomizer and the properties of the multiphase system (liquid–gas) affect the spray morphology and the droplets/ligaments distribution. The aim of the work is to investigate through computational fluid dynamics the stability of the gas–liquid interface produced by a swirling liquid injection. By implementing the volume-of-fluid method, we show transient simulations, in which the liquid–gas interactions take place within and outside the nozzle simultaneously. Depending on the different liquid properties and geometric features, we examine the hollow-cone spray performance in terms of cone angle and liquid sheet morphology. A stability analysis allows to determine whether spraying or jetting conditions are attained depending on Reynolds and Ohnesorge numbers, as the hollow-cone shape can degenerate into a straight jet under specific operating conditions. Viscosity is known to be a relevant parameter in fluid formulation, which impacts on both relevant dimensionless parameters. Newtonian and non-Newtonian rheologies are here considered for their ubiquitous presence in detergent or sanitation fluids. In both cases, we find a critical condition that marks the switch from the spraying to the jetting regime.

Numerical Study on Flow Structures of a Hollow Cone Spray in Crossflow

In this paper, numerical investigation on the flow field structure of a hollow cone spray injected transversely into a confined crossflow is presented. The unsteady turbulent flow is predicted by adopting the Scale-Adaptive Simulation approach and the atomization of the spray is predicted by using the linear instability analysis and Taylor analogy breakup theory. The interactions between the hollow cone sprays (with two different spray angles of 80° and 40°) and the crossflow inside a rectangular duct (95 mm × 95 mm in cross-section) at ambient temperature and pressure are simulated. The results show that there exist six large-scale vortex structures in the mixing flow field, namely the Counter-rotating Vortex Pair (CVP), the horseshoe vortex, the shear layer vortex, the hairpin vortex, the wake vortex, and the upright vortex. The formation mechanisms of these vortices are analyzed. The CVP and the hairpin vortex dominate the flow field and exert significant influences on droplet dispersion in span-wise and stream-wise directions respectively. The influence of the spray angle on the vorticity of the CVP is small, but a smaller spray angle can lead to larger depths of the spray and the CVP and a smaller distance between both CVP cores.

An Improved Prediction of Pre-Combustion Processes, Using the Discrete Multicomponent Model

An improved heating and evaporation model of fuel droplets is implemented into the commercial Computational Fluid Dynamics (CFD) software CONVERGE for the simulation of sprays. The analytical solutions to the heat conduction and species diffusion equations in the liquid phase for each time step are coded via user-defined functions (UDF) into the software. The customized version of CONVERGE is validated against measurements for a single droplet of n-heptane and n-decane mixture. It is shown that the new heating and evaporation model better agrees with the experimental data than those predicted by the built-in heating and evaporation model, which does not consider the effects of temperature gradient and assumes infinitely fast species diffusion inside droplets. The simulation of a hollow-cone spray of primary reference fuel (PRF65) is performed and validated against experimental data taken from the literature. Finally, the newly implemented model is tested by running full-cycle engine simulations, representing partially premixed compression ignition (PPCI) using PRF65 as the fuel. These simulations are successfully performed for two start of injection timings, 20 and 25 crank angle (CA) before top-dead-centre (BTDC). The results show good agreement with experimental data where the effect of heating and evaporation of droplets on combustion phasing is investigated. The results highlight the importance of the accurate modelling of physical processes during droplet heating and evaporation for the prediction of the PPCI engine performance.

Effect of Different Fuels on Combustion Instabilities in an Annular Combustor

Abstract Combustion instability in annular combustors of jet engines is a recurring issue. In this study, the characteristics of instabilities for different fuels are investigated by combining the instability maps obtained in a laboratory-scale annular combustor equipped with multiple swirling spray injectors (MICCA-spray) and flame describing functions (FDFs) from a single sector configuration (SICCA-spray). Two types of liquid fuels are injected as hollow cone sprays: heptane, which is fairly volatile, and dodecane, which is less volatile. Experiments are also conducted with gaseous propane, perfectly premixed with air, which serves as a reference. An instability map is systematically drawn by varying the global equivalence ratio and thermal power. The data indicate that the amplitude and frequency of instabilities depend, for the same operating point, on the fuel injection conditions (premixed or spray) and fuel type. Overall trends show that premixed propane is unstable in a broad operating domain. Injection of liquid fuels induces changes in flame time lag that modifies the unstable regions. For heptane, the instability map is closer to the propane reference map, whereas dodecane exhibits wider stable regions. An attempt is made to understand these features by examining the FDF, which gives the ratio of relative fluctuations in heat release rate to the relative fluctuations in velocity. The FDFs measured in a single sector configuration give access to gain and phase information that can be used to determine unstable bands and calculate an instability index guiding the interpretation of the differences in instabilities of the three fuels.