Dilute Spray Research Articles

Direct Numerical Simulation of Vortex Breakdown in Evaporating Dilute Sprays

AbstractThe effects of different vortex breakdown states on the evaporation process characterizing air-acetone vapor swirling jets laden with liquid acetone droplets in the dilute regime are discussed based on results provided by direct numerical simulations. Adopting the point-droplet approximation, the carrier phase is solved using an Eulerian framework, whereas a Lagrangian tracking of the dispersed phase is used. Three test cases are investigated: one with fully-turbulent pipe inflow conditions and two with a laminar Maxworthy velocity profile at different swirl rates. Consequently, turbulent, bubble-type, and regular conical vortex breakdown states are established. Following phenomenological and statistical analyses of both phases, a significant enhancement of the overall droplet evaporation process due to the onset of the conical vortex breakdown is observed due to the strongest centrifugal forces driving the entire liquid drops towards the low-saturation mixing layer of the jet. The effects of droplet inertia on evaporation are isolated through an additional set of simulations where liquid droplets are treated as Lagrangian tracers. While it is found that inertial effects contribute to enhanced vaporization near the mixing layer under bubble vortex breakdown conditions, droplet inertia plays a secondary role under both turbulent and conical vortex breakdown due to intense turbulent mixing and high centrifugal forces, respectively.

Multiscale numerical modeling of a complete spray evolution including breakup of liquid jet injection in gaseous cross flow

A direct coupling of the Volume of Fluid method (VOF) and the Lagrangian Particle Tracking (LPT) technique within a Large Eddy Simulation (LES) framework is revisited and assessed by numerically investigating a liquid jet injection into a cross-flowing air (JICF). To close the subgrid scale (SGS) terms appropriate SGS models are considered. In particular, an interfacial SGS term is included into the VOF scalar transport equation in order to achieve a suitable LES and to describe properly the liquid column and the break-up processes (primary and secondary). The dilute spray region including the droplets resulting from the secondary breakup is solved using the LPT approach. Since the latter allows the cell size to be multiple times larger than the droplet diameter, this reduces the computational expenses significantly making it possible to handle the simulation of the whole spray evolution including the complete liquid atomization without complex tunable atomization models. For this purpose, two operating conditions of a JICF existing in the literature are considered. The achieved results are first presented in terms of mesh sensitivity, required computational costs and impact of the interfacial SGS term. Next, comparisons between pure VOF/LES and VOF/LPT/LES for both qualitative features and quantitative properties are provided and discussed. In overall, a good agreement with experiments for the quantitative properties is reported. It is especially found that both the Rosin–Rammler and Gaussian distributions offer nearly a more accurate fit to the particle size distribution except for the range from 0 to 10 μm. Together with the detailed characteristics of vortices evolving and an extended breakup regime map, the spray characteristics including the spray structure are well captured. Finally, even though the interfacial SGS term has an evident influence on the jet and atomization dynamics, its impact on quantitative properties is not so prominent under these operating conditions.

A physics-driven Σ-Y atomization model for heavy-duty engine simulations

The atomization of a liquid jet is a multi-scale and multi-physics problem of interest for many engineering applications. Particularly, it drives the fuel-oxidizer mixing and dictates the efficiency of combustion engines. High-fidelity multi-phase simulations remain challenging due to the excessive computational cost required to capture all the atomization scales. Thus, atomization models are necessary to represent sub-grid liquid structures. In this work, a modified Σ-Y model in the context of Eulerian-Lagrangian Spray Atomization (ELSA) is used to transport the surface area density of the spray. The model's predictive performance is assessed under various operating conditions relevant to heavy-duty engines using the Engine Combustion Network (ECN) Spray C and Spray D research-grade injectors. The classic droplet collision formulation of the Σ-Y model alone does not replicate the response of the measured spray surface area to changes in injector, ambient pressure, and injection pressure, requiring individual tuning of the model's parameters. Instead, a transition between dense and dilute spray breakup mechanisms is proposed in terms of the average droplet spacing. The collision breakup mechanism represents the dilute spray, whereas the droplet size in the dense spray is driven by a competition between the integral scale of turbulence and the balance between the turbulent kinetic energy and the surface energy of the droplets. Such an approach minimizes the requirements for model tuning. Moreover, the role of the constants of a compressible standard k-ε RANS model is assessed in the injector's internal flow and external spray simulation framework, and an updated set is proposed. The results are validated against x-ray radiography and Ultra-Small Angle X-ray Scattering (USAXS) data and highlight the predictive capabilities of the proposed physics-driven Σ-Y model, which is compatible with engine simulation turnaround times.

Optimization of planar LIF/Mie imaging for droplet sizing characterization of dilute sprays

Optimization of planar LIF/Mie imaging for droplet sizing characterization of dilute sprays

Droplet sizing in atomizing sprays using polarization ratio with structured laser illumination planar imaging.

Previous research has shown that the polarization ratio technique allows the characterization of the surface mean diameter, D21, of droplets forming dilute sprays. However, its application to optically dense sprays has posed significant challenges due to the presence of multiple light scattering. Additionally, errors in measurement can arise from the angular dependence of the signal. In this Letter, we present a novel, to the best of our knowledge, method that addresses these challenges. Our approach combines the use of a telecentric objective with structured laser illumination, to both optimize light detection and suppress the unwanted intensity from multiple scattering. This approach enables the utilization of the polarization ratio technique for measuring the droplet size of challenging atomizing sprays. The method offers a promising solution for accurate and comprehensive spray characterization. It is applied, here, to a hollow-cone water spray running at 30, 50, and 70 bar injection pressure, reaching an optical depth up to three.

Effects of hydrogen addition on laminar dilute n-dodecane spray flames

With the increasing demand for carbon–neutral propulsion technology, hydrogen addition appears to be a viable short-to-medium-term solution. This study investigates the dynamics of overall lean, laminar dilute n-dodecane spray flames in premixed hydrogen/air mixture by simulating one-dimensional dilute spray flames over a wide range of hydrogen addition and n-dodecane droplet diameter. The characteristic residence time and evaporation time are analyzed to reveal the pre-evaporation mode, and examine the distinct evaporation characteristics throughout the flames. The flame structure and flame propagation speed are then examined, with the impact of subtle fuel chemistry coupling at low-temperature-chemistry regime being revealed. At atmospheric pressure conditions, the flame speed monotonically increases with hydrogen addition due to the enhanced reactivity. However, it has a nonmonotonic trend with initial droplet diameter due to the subtle coupling of evaporation and chemical kinetics. More interestingly, at engine-relevant conditions, the flame propagation speeds firstly decrease and then increase with hydrogen addition, this is because small hydrogen addition inhibits the low-temperature reaction pathway that could offset the effects of enhanced high-temperature reactivity on flame propagation. In addition, the flame propagation speeds are less sensitive to the droplet diameter unless the droplets are sufficiently large and the long evaporation process reduces the effective local equivalence ratio of the overall fuel-lean mixtures.

One dimensional model of electrospray neutralization

An Eulerian one-dimensional model is proposed and used to analyze the discharge of a dilute spray of electrically charged droplets by a corona discharge of polarity opposite to that of the droplets in the gap between two parallel electrodes charged at different potentials. The effects on the neutralization process of the flux of droplets, the ions current, and the voltage applied between the electrodes are discussed. The results show that there is a minimum voltage, dependent on other parameters, below which the problem does not have a solution. Conditions required to prevent fly-back of the droplets are also discussed.

Modeling and LES of high-pressure liquid injection under evaporating and non-evaporating conditions by a real fluid model and surface density approach

Numerical modeling of high-pressure liquid fuel injection remains a challenge in various applications. Indeed, experimental observations have shown that injected liquid fuel jet undergoes a continuous change of state from classical two-phase atomization and spray droplets evaporation to a dense-fluid mixing phenomenon depending on the ambient pressure, temperature, and fuel properties. Accordingly, a predictive and efficient computational fluid dynamics (CFD) model that can represent the possible coexistence of subcritical and supercritical regimes during the fuel injection event is required. The widely used Lagrangian Discrete Droplet Method (DDM) requires parameter tuning of model constants and cannot model the dense near-nozzle region. Meanwhile, the high computational cost of Interface Capturing Methods (ICM) has prohibited their application to industrial cases. Thus, another alternative is an Eulerian Diffuse Interface Model (DIM), where the unresolved interface features are modeled instead of being tracked. Accordingly, the current work proposes a fully compressible multi-component two-phase real-fluid model (RFM) with a diffused interface and closed by a thermodynamic equilibrium tabulation method based on a real-fluid equation of state. The RFM model is complemented with a postulated surface density equation for fuel atomization modeling within the Large Eddy Simulation (LES) framework. The Engine Combustion Network (ECN) Spray A injector non-evaporating and nominal evaporating conditions are used as a reference for the proposed model validation. Simulations are performed using the proposed RFM model that has been implemented in the CONVERGE CFD solver. Under the non-evaporating condition, the RFM model can capture well the fuel mass distribution in the near-nozzle field, but also the interfacial surface area. Besides, the predicted drop size from simulations falls within the experimental data range. On the other hand, under the evaporating condition, spray liquid and vapor penetrations and fuel mixture fraction distribution are also accurately predicted. The vaporization effect on the surface area density is revealed to enhance surface generation in the dense spray region while reducing the surface density in the dilute spray region. The mean droplet size is also relatively reduced under the evaporating condition in the diluted spray region. Overall, the accuracy and computationally efficiency of the proposed RFM model coupled with the surface density equation for high-pressure fuel injection modeling are confirmed, allowing its use for high pressure industrial configurations in future studies.

The effect of fuel droplets on the burning velocity of strained laminar acetone/air flames

The effect of fuel droplets on the burning velocity of strained laminar premixed flames is investigated via experimentation and simulation. The twin counterflow configuration was used to obtain reference flame speeds as a function of strain rate for a prevaporized flame and a dilute spray flame simultaneously, both composed of acetone and air. The mixtures were varied with respect to nominal equivalence ratio (0.8–1.4) and strain rate (200–600 s−1). Gas velocities were measured using particle image velocimetry. Droplet size, velocity, and concentration were measured using phase Doppler anemometry: non-reacting flow measurements were taken at a position upstream of the stagnation plane; reacting flow measurements were taken along the stagnation streamline. The droplet Sauter mean diameter ranged between 65–75 μm, and the estimated fuel liquid fraction varied between 6–22%, increasing with nominal equivalence ratio. The results show that the reference flame speed of the spray flame decreases slightly relative to that of the prevaporized flame in the case of lean mixtures, but appears unchanged in the case of stoichiometric and rich mixtures. Gas velocity profiles and droplet measurements along the stagnation streamline suggest that the spray flame vaporization is incomplete, such that the reference flame speed corresponds to that of a lower equivalence ratio. Conversely, the opposing flame is affected by the fraction of droplets that do not vaporize in the spray flame and either penetrate the flame front, causing fuel enrichment, or evaporate near the stagnation plane, reducing the adiabatic flame temperature. The effect appears primarily for rich mixtures with higher liquid fraction, as evidenced by the lower reference flame speed and lower axial velocity rise across the flame. This study provides a systematic framework to examine the influence of fuel droplets on laminar flame propagation using a single-component fuel in the counterflow configuration.

LES Study of stabilization mechanism in lifted ethanol spray flames

This work presents a detailed numerical investigation of dilute spray lifted flames experimentally studied by O’Loughlin and Masri at the University of Sydney (O’Loughlin and Masri, Combust. Flame 2011), with a focus on understanding the mechanism that governs flame stabilization under the influence of sprays. Two ethanol flames with varied spray mass loading and degree of partial-premixing at the inlet are simulated by large eddy simulation (LES) combined with the dynamically thickened flame (DTF) model with finite-rate chemistry. Chemical explosive mode analysis (CEMA) is employed which helps identify the prominent role of an entrainment-based ignition process along the shear layer; this process dominates the flame anchoring of the downstream partially-premixed reaction zone. Thus, a higher spray loading can intensify the entrainment, leading to a faster formation of ignition kernels. Furthermore, in present flames, the stabilization point appears to be sustained in a purely gaseous zone with the most reactive mixture fraction and low scalar dissipation rate. Results show that the premixed flamelet can adequately represent flame structures at the leading-edge that are primarily controlled by the inlet partial-premixing, whereas the upstream evolving pre-ignition mixtures are fit for the diffusion flamelet. Moreover, both flamelet configurations fail in capturing downstream structures with a direct spray - flame interaction because the larger droplets produce a less homogeneous mixture with a higher scalar dissipation rate. This is more evident in the lean spray flame.

Assessment of subgrid dispersion models for large-eddy simulations of turbulent jet flows with dilute spray droplets

High-fidelity simulations for polydispersed sprays in the Eulerian–Lagrangian framework need to incorporate subgrid-scale effects in the particle evolution equations. Although the quasi-linear evaporation rate formulation captures evaporating droplet statistics, further improvement is required when subgrid-scale velocity effects become essential. The subgrid dispersion model strongly affects droplets spatial distribution, and subsequently net evaporation rate, depending on how rapidly they are dispersed into the dry air region. The main original contribution of this study is to assess the performances of a number of commonly used dispersion models in a consistent manner, against a reference direct simulation results. The models considered are (i) discrete random walk, (ii) approximate deconvolution method, (iii) stochastic model based on the Langevin equation, and (iv) combined approximate deconvolution method with the Langevin equation. Mass and enthalpy transfer source terms together with droplet diameters and particle distributions were compared against corresponding direct numerical and large-eddy simulations without a model as reference cases. Numerical results at low Stokes and moderate Reynolds numbers indicate that the dispersion model choice does not affect Eulerian field averages or fluctuations. However, proper dispersion models are essential to capture droplet distributions in the far-field region after jet breakup for Stokes number smaller than unity. The unclosed Lagrangian momentum equation without any dispersion model most accurately reproduces direct numerical simulation in the near field.

Using tank-mix adjuvant improves the physicochemical properties and dosage delivery to reduce the use of pesticides in unmanned aerial vehicles for plant protection in wheat.

Unmanned aerial vehicles (UAVs) are widely used to improve the efficiency of pesticide applications. Low-volume spraying operations require more efficient deposition of droplets on the target surface. Therefore, pesticide deposition and retention on plant surfaces is a serious challenge for modern precision agriculture. Tank-mix adjuvants have been used to improve spray dilutions performance; however, their effects on the physicochemical properties of spray dilutions, dosage delivery, and pesticide dosage are unclear. Tank-mix adjuvant 8860 significantly improved the physicochemical properties of spray dilutions, inhibited spray droplets rebound, improved the wetting and spreading performance of spray dilutions on wheat leaves, and increased the effective deposition of tebuconazole on wheat leaves. Even when its dosage was reduced by one-third, the spray solution still showed excellent disease control and effective deposition of the active ingredient on wheat leaves. The use of appropriate tank-mix adjuvants in UAV-based plant protection for wheat can significantly improve the performance of spray dilutions, increase the efficiency of pesticide dosage delivery, and improve disease control. These adjuvants can also help reduce the pesticide use while ensuring their effectiveness. © 2022 Society of Chemical Industry.

Evaluation of trans-critical transition of single- and multi-component sprays under diesel engine-like conditions

• The discrepancies in trans-critical transition of different sprays are unraveled. • Droplets in dilute sprays cannot represent the thermodynamic state of dense sprays. • Diesel sprays are more prone to transition to supercritical than n-dodecane sprays. The trans-critical transition of multi-component sprays under the ECN Spray-A conditions has attracted extensive interest. However, the drastic change of critical points of multi-components makes this controversial. In this study, the trans-critical transition of sprays before and after the end of injection is evaluated by numerical methods, and new findings have been obtained. First, the robust and accurate thermodynamic equilibrium solver and multi-component droplet evaporation model were developed and implemented into the OpenFOAM. These models have been validated against the measured phase change diagram and isolated droplet evaporation rate. Then, the mixture critical temperatures of n-dodecane/nitrogen and multi-component diesel/nitrogen were calculated under a wide range of pressures based on the thermodynamic equilibrium solver. The mixture critical temperature decreases almost linearly with the increase of the pressure. Following that, extensive sprays of n-dodecane and multi-component diesel under high temperature and pressure conditions were simulated, and the predicted spray liquid penetrations were validated against the experimental data. The results found that the dilute sprays after the end of injection are more prone to transition to the supercritical mixing regime, while the trans-critical possibility of dense sprays before the end of spray decreases due to the cooling effect of extensive evaporation. Finally, the trans-critical transitions of multi-component diesel sprays before and after the end of injection were evaluated and compared with those of n-dodecane sprays. Due to the low mixture critical temperature and evaporation rate of diesel, its sprays are more likely to transition to the supercritical regime. Therefore, it can conclude that the dilute sprays after the end of injection cannot represent the thermodynamic state of dense sprays. Moreover, the multi-component diesel and n-dodecane sprays follow a different trans-critical transition pathway.

Effects of tank-mix adjuvants on physicochemical properties and dosage delivery at low dilution ratios for unmanned aerial vehicle application in paddy fields.

Unmanned aerial vehicles (UAVs) have been developed to improve the efficiency of pesticide applications, and they are now widely utilized in Asia. The deposition and retention periods of pesticides on plant surfaces present serious challenges for modern precision agriculture, as these factors directly affect pesticide bioavailability, efficacy, and loss. Tank-mix adjuvants have been utilized to improve pesticide performance, but their effects on physicochemical properties and dosage delivery at low dilutions are not well understood. We found that different tank-mix adjuvants affected droplet impact behavior, the wetting and spreading of spray dilutions, and pesticide deposition on rice leaves by changing the physicochemical properties of spray dilutions. The adjuvant methyl oxirane polymer with oxirane, mono (3,5,5-trimethylhexyl) ether (adjuvant c) significantly reduced the dynamic surface tension of the spray dilution and inhibited the rebound of large droplets (D0 =2 ± 0.2 mm) and spray droplets (0.2MPa with a LU-01 nozzle) on rice leaves, and improved the wetting and spreading performance of the spray dilution on rice leaves. Field tests showed that adjuvant c could significantly increase the deposition of chlorantraniliprole on rice leaves. Overall, the use of appropriate tank-mix adjuvants at low dilution ratios for UAV application in paddy fields can improve the performance of spray dilutions, increase the effective deposition and wetting spread of pesticides on rice leaves, further reduce the dosage of pesticide products and improve pesticide utilization. © 2022 Society of Chemical Industry.

Assessment of Finite-Rate Chemistry Effects in a Turbulent Dilute Ethanol Spray Flame

Simulations of a benchmark ethanol dilute spray flame are performed with four combustion models at different levels of closure for turbulence–chemistry interaction (TCI) to provide a head-to-head comparative analysis on the closure effects of TCI. The evaluation is performed in the context of Reynolds-averaged Navier–Stokes simulations taking advantage of the simple jet configuration, together with a Lagrangian discrete phase model for tracking the spray droplets. Two well-validated ethanol mechanisms consisting of 40 and 50 species, respectively, are employed to describe the chemical kinetics and reveal the impact of chemistry. Results are compared against measurement, including gas-phase velocity, temperature, and droplet velocity, demonstrating the improvement with the increasing accuracy in TCI modeling from characteristic time scale model, laminar finite rate model, eddy dissipation concept model, and transported probability density function (PDF) model. Effects of micromixing in PDF simulation are further investigated considering different model formulations and mechanical-to-scalar timescale ratios (). The Euclidean minimum spanning tree model with yields the best prediction of the mean temperature. The analysis on flame structure suggests that the flame exhibits a mixed mode of combustion, i.e., a stratified premixed flame in the upstream and a typical non-premixed flame in the downstream.

Oxidation phenomena of diesel post fuel in the expansion stroke

Post fuel is injected to avoid plugging of diesel particulate filters (DPF). However, at advanced post fuel injection timings, the post fuel is partially oxidized in the cylinder under the high temperature conditions and the hydrocarbon supplied to DOC is not sufficient to regenerate the DPF. In this paper, partial oxidation phenomena at advanced post fuel injection timings were investigated with an engine and a high pressure-temperature optical constant volume chamber. In the engine experiments, the oxidation ratio of the post fuel was calculated from the exhaust gas composition. When the post fuel is injected at 30 CA ATDC, 83% of the post fuel is oxidized, however when the injection timing is 60 CA ATDC, the oxidation ratio of the post fuel becomes 2.2% and there is a 40.9% fuel loss mostly due to oil dilution. The reaction speed, in-cylinder temperature, and oxygen concentration (mol/m3) at the post fuel injection timing are related to the partial oxidation ratio of the post fuel. In the experiments with the constant volume chamber, the spray behaviors at the post fuel injections were observed. The ignition delay becomes longer with lower in-cylinder temperature and lower oxygen concentration, and the spray dilution of the post fuel during the ignition delays affects the heat release and the location where the partial oxidation in the chamber occurs. Based on the experimental data of engine speed, oxygen concentration, and in-cylinder temperature at the start of post fuel injection, an experimental formula for the post fuel oxidation ratio based on the Arrhenius equation was suggested by multiple regression analysis of the engine test data.

Quantification of coflow effects on primary atomization of pressure swirl atomizers

Extension of high momentum jet stabilised combustors towards liquid fuel operation has shown significant injector shape and injection strategy impact on the fuel air mixing behaviour, the flame position and stability and ultimately pollutants. This can be attributed to the lack of optimised injection concepts as well as fundamental understanding of turbulence–spray interactions that dictate atomization and fuel placement in high turbulence gas flow conditions. The current work uses a canonical flow channel to investigate the bilateral interactions between a highly turbulent coaxial air flow and the primary atomization process of a liquid spray generated by pressure-swirl atomizers. A novel two-phase particle image velocimetry (PIV) method with phosphor-particles is developed to enable flow field measurements near the gas–liquid interface as well as in the dilute spray region. In addition, a shadowgraphy technique is applied to detect the disturbances on the sheet surface. Liquid fuel is replaced by deionised water due to safety concerns and the coaxial air flow velocity is varied from 0 to 80 m/s. The results show a significant influence of the aerodynamic forces on the growth rate of sheet disturbances with increasing coflow velocities. This induces an advanced breakup of comparable thick liquid sheets at large Weber numbers. The novel PIV method enabled the quantification of the turbulent kinetic energy transfer between the phases that is strongly dependent on the slip velocity at the gas–liquid interface. These findings assist the ongoing development of liquid fuel injection systems for high momentum jet based combustors and provide validation data for numerical simulations of primary atomization.

Dilute spray flames of ethanol and [formula omitted]-heptane in the transition to mild combustion

The structure and stabilisation mechanisms of ethanol and n-heptane spray flames are investigated in this study. The burner configuration involves a dilute spray of dispersed droplets which is produced and transported via a carrier gas stream of air to the reaction zone, where the flames are stabilised by a hot coflow of combustion products. A range of coflow conditions were implemented for the different flame cases, allowing the effects of the coflow oxygen (O2) concentration and temperature to be examined independently. The resulting flames were analysed using three simultaneous laser diagnostic techniques, enabling the combined planar imaging of the hydroxyl (OH) and formaldehyde (CH2O) radicals, along with the location of droplets. For both fuel types, a noticeable shift in stabilisation behaviour was observed with a variation in the coflow O2 concentration from 11% to 3%, while the coflow temperature was not seen to have a significant impact. These flames also show an interesting departure from the typical behaviour observed for gaseous and prevaporised flames in a similar configuration, particularly for coflow conditions that are typically associated with the transition to the mild combustion regime.

A flamelet LES of turbulent dense spray flame using a detailed high-resolution VOF simulation of liquid fuel atomization

A numerical framework used to model dense spray flames is proposed. In this framework, the liquid fuel (acetone) atomization is solved by a detailed high-resolution VOF simulation, and the Eulerian components of liquid droplets are transformed into Lagrangian droplets, which are stored in a database at a certain downstream cross-section. Then, the combustion process is solved by a LES/FPV (flamelet progress variable) adopting the pre-stored database of Lagrangian droplets (i.e., the position, size, and velocity of each droplet) as the inlet boundary conditions. This framework is a one-way coupling between a VOF simulation and a combustion simulation. The validity of this approach is investigated by comparing the computations with the experiments of the Sydney Piloted Needle Spray Burner. The VOF simulation shows that the volume flux of the droplets at the nozzle exit fluctuates both temporally and spatially and the larger droplets tend to be located away from the center axis compared to the small droplets. The computed breakup length is in good agreement with the empirical correlation. In the database of the Lagrangian droplets for the LES/FPV of spray flames, the location of the sampling cross-section, the sampling time, and the threshold value for Eulerian–Lagrangian (E-L) transformation strongly affect the properties of the Lagrangian droplets, and are critical for the successful use of the LES/FPV. Two spray flames with different recess distances are computed using their optimal pre-stored droplets databases and both show generally good agreement with the experiments in terms of the gas temperature and droplet size distributions. The spray flame with a longer recess distance, which is more representative of a dilute spray, is considered to have a longer and wider premixed core than that with a shorter recess distance representing a dense spray. The discrepancy in the prediction of denser spray flames becomes more evident leading to over-predictions of gas temperature further downstream. Reasons for this behavior are discussed in the text.

The role of formulation co-ingredients in skin and glove barrier protection against organophosphate insecticides.

Commercially formulated pesticide products are complex mixtures of one or more active ingredients and several co-ingredients. However, the modifying effect of co-ingredients on skin uptake and glove barrier protection has been poorly studied. The aim of this study was to understand the role of formulation co-ingredients in skin and glove barrier protection performance against organophosphate insecticides. We adapted standard in vitro diffusion cell methods to test permeation kinetics of two commonly used organophosphate insecticides: dimethoate and omethoate. For spray dilutions, dimethoate and omethoate did not reach breakthrough glove permeation rate (1μg·cm-2 ·min-1 ) and no or little skin permeation was observed for up to 8h, regardless of formulation. For exposure conditions involving highly concentrated products, significant differences in glove permeation were observed between different formulations of dimethoate (about 1.5-fold, P < 0.05) and of omethoate (184-fold, P < 0.001). In contrast, no difference (P > 0.05) was observed between formulations in terms of skin permeation. These results suggest that co-ingredients play a critical role in glove barrier protection against undiluted organophosphate insecticides, whereas their influence on skin uptake was insignificant within the exposure time tested. This implies that dermal exposure risk may vary between handling different formulated products of the same active ingredient hence recommending a common glove material for different formulations of the same chemical without careful consideration of co-ingredients and their permeation properties may not necessarily be appropriate. © 2021 Society of Chemical Industry.