Fuel Spray Characteristics Research Articles

Experimental Study on the Spray Characteristics of Diesel and Hydrotreated Vegetable Oil (HVO) Fuels under Different Injection Pressures

This investigation employed the diffused back-illumination (DBI) technique to analyze the spray characteristics of hydrotreated vegetable oil (HVO) fuel at three injection pressures and compared them with conventional diesel fuel. The results showed that as the injection pressure increased, the peak injection rates of both the HVO and diesel increased. At injection pressures above 120 MPa, the injection rates of both fuels were nearly identical, though differences were observed at lower pressures. Increasing the injection pressure reduced the injection delay. The HVO fuel exhibited a shorter spray tip penetration, lower equivalence ratio, larger spray angle, and spray volume, but its spray angle stability was lower than that of diesel. The ambient gas entrainment rate primarily occurred in two stages, significantly influenced by the spray breakup development stage. For diesel sprays, the injection pressure mainly affected the equivalence ratio near the nozzle with minimal downstream impact. Dent’s model provided better predictions of the penetration distance for diesel, while Hiroyasu’s model was more accurate in predicting the penetration distance of the HVO at 120 MPa and 180 MPa. Inagaki’s model performed better in predicting the spray angle for diesel, whereas Hiroyasu’s model was more accurate for the HVO spray angle predictions. Through this research, a better understanding of the spray characteristics of green fuels will be achieved, providing a reference for the design and optimization of new generation engines.

Advancing Fuel Spray Characterization: A Machine Learning Approach for Directly Injected Gasoline Fuel Sprays

Compression ignition engines when operated on gasoline fuels cause significant reduction in NOx and particulate emissions. In such advanced combustion strategy, the fuel-oxidiser mixing process, intensified by the prolonged ignition delays of gasoline fuels, directly affects the stability and efficiency of combustion. Thus, optimising fuel spray characteristics leads to optimisation of injector design, engine performance and subsequent decrease in emissions. Since spray development is a complex process that involves wide range of length and time scales, computationally expensive modelling techniques can be replaced with machine learning (ML) models. These ML models are employed to predict spray characteristics utilizing datasets generated from comprehensive spray studies. In this work, a dataset of about 5400 instances taken from non-evaporating gasoline fuel spray imaging experiments under Gasoline Compression Injection (GCI) engine conditions is used to train various ML models with data split of 70 % and 30 % for training and testing, respectively, with five-folds cross-validation performed within the training. The fuel injection pressure (60 – 150 MPa), chamber pressure (0.1 – 2 MPa), nozzle diameter, nozzle hole conicity and injection duration are used as input features to the models for predicting the spray tip penetration and spray angle. The performance of four ML models was evaluated and compared under default and tuned hyperparameters against experimental data and available physics-based correlations in the literature. The models include random forest, extreme gradient boosting, multilayer perceptron, and elastic-net. The results show that the hyperparameter-tuned extreme gradient boosting model performs best in predicting the spray parameters. The overall model performance was evaluated using the coefficient of determination (R2), mean absolute error (MAE), and root mean squared error (RMSE), resulting in values of 0.884, 0.651, and 1.571, respectively. This study presents compelling evidence demonstrating the effectiveness of ML as a powerful tool for isolating non-linear behaviors from physical processes. By effectively decoupling these behaviors, ML enhances the accuracy of predicting spray characteristics while significantly reducing computational costs. The application of ML in fuel injector design has the potential to revolutionize engine performance and contribute to substantial reductions in emissions.

Investigating Spray Characteristics of Synthetic Fuels: Comparative Analysis with Gasoline

Article Investigating Spray Characteristics of Synthetic Fuels: Comparative Analysis with Gasoline Weidi Huang 1,2, Mitsuharu Oguma 2, Koichi Kinoshita 2, * , Yohko Abe 2, and Kotaro Tanaka 1,3 1 Carbon Recycling Energy Research Centre, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi 316-8511, Japan 2 Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology, Namiki 1-2-1, Tsukuba 305-8564, Japan 3 Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi 316-8511, Japan * Correspondence: koichi-kinoshita@aist.go.jp Received: 13 March 2024; Revised: 22 May 2024; Accepted: 31 May 2024; Published: 5 June 2024 Abstract: Studying synthetic fuels is imperative due to their potential to offer sustainable alternatives to conventional fossil fuels, thereby addressing environmental concerns, enhancing energy security, and facilitating the transition to cleaner and more efficient transportation systems. This study presents an experiment analysis concentrating on spray characteristics of five types of synthetic fuels (bio-naphtha, EtG, G40, bio-ethanol, and DMC) in a comparison with gasoline. The experiment was conducted ranging from non-evaporated conditions to evaporated conditions, to thoroughly assess the spray behavior of the tested fuels. Results showed that EtG and G40 share similar properties with conventional gasoline. The discharge coefficient (Cd) was found to increase closely linearly with the square root of fuel density. Under non-evaporated condition (Ta = 25 °C), except for DMC, the spray tip penetration of other fuels deviates within ±5% compared to gasoline. Under evaporated condition (Ta = 200 °C), EtG maintains a spray tip penetration within ±5% of gasoline, while bio-naphtha, G40, and DMC fall within ±10% of gasoline. Notably, bio-ethanol shows a 12% higher penetration compared to gasoline, likely due to its slower evaporation and higher latent heat of vaporization.

Investigation of Diesel Spray Characteristics in Low-temperature and Low-pressure Conditions

This study investigates the influence of altitude and injection pressure on diesel fuel spray characteristics, aiming to optimize diesel usage in high-altitude conditions. Experiments were conducted at three altitude levels (plains, 1670 m, and 2400 m) with corresponding atmospheric pressures and temperatures, alongside six injection pressures ranging from 50 MPa to 100 MPa. The investigation focused on key spray parameters: equivalence ratio, spray penetration velocity, turbulence kinetic energy, evaporation rate, spray penetration distance, and Sauter Mean Diameter (SMD). Findings indicate that increased injection pressure enhances spray penetration velocity, evaporation rate, and turbulence kinetic energy, while reducing SMD, irrespective of altitude. Conversely, higher altitudes were associated with increased spray penetration speed, larger SMD, decreased evaporation rate, increased turbulence, and a higher equivalence ratio. The study concludes that both altitude and injection pressure significantly impact diesel spray characteristics, providing essential theoretical support for the application and optimization of diesel fuels in varied altitude conditions.

Study of RP-3/n-butanol fuel spray characteristics and ANN prediction of spray tip penetration

The blending of aviation fuel with biomass is currently an effective way to meet the demand for sustainable aviation fuel. This study tested the physical parameters of fuel blends of 0∼30 % volume fraction n-butanol with RP-3 aviation kerosene, and the macroscopic characteristics of the spray penetration tip (STP), spray cone angle (SCA), and spray area (SA) of the blends were investigated by computational fluid dynamics at different injection pressures (100–160 MPa) and ambient pressures (0.8–1.5 MPa). A model using artificial neural networks (ANN) was built to forecast the STP of the fuel. The findings indicate that the blending of n-butanol has little impact on the spray characteristics of the fuel. The STP and SA of the blended fuel rise but have a small effect on the SCA as injection pressure increases. The STP and SA of the fuel gradually decrease, while the SCA becomes larger as ambient pressure increases. NET9 which has 6 input layers, 9 hidden layers and 1 output layer with the best performance (RMSE: 0.46213, R2: 0.99969) was selected and the prediction error of NET9 was less than 3 %. This indicates that the model has the best prediction ability and can be used in subsequent research.

Study on spray characteristics of biodiesel alternative fuels for in-cylinder environment of diesel engine

This paper presents an experimental study of spray characterization of MD-NH (a blend of methyl decanoate and n-heptane in a molar ratio of 1:1 to characterize biodiesel) in an in-cylinder environment of diesel engines to provide a reference for the experimental study of engines in advanced combustion mode. Based on the Peng-Robinson state equation, the thermodynamic model of real fluid was established, and the influence law of ambient temperature and pressure on the diffusion characteristics of fuel flow was analyzed. Based on the constant volume combustion bomb experiments, the variations of spray penetration distance, spray cone angle, spray projection area, spray air entrainment mass, and spray fragmentation forms in different critical environment conditions were studied. The results show that the transport properties of the fuel change abruptly within the critical point neighborhood of the fuel. As the ambient temperature increases, near the critical temperature, the thermal conductivity of biodiesel decreases and then increases; density and kinematic viscosity decrease at an accelerated rate; and surface tension increases to a maximum and then disappears sharply. The diffusion coefficient decreases sharply when the ambient pressure reaches the critical pressure. The spray characteristics of biodiesel in sub/supercritical conditions were different. Compared with the subcritical environment, the biodiesel spray penetration distance decreases, the spray cone angle increases, the spray projection area decreases, and the air entrainment mass increases in the supercritical atmosphere, which induces a gas-liquid interface mixing layer and promotes the mixing of biodiesel with the atmosphere gas. The experimental data in this paper fill the gap in the study of biodiesel spray characteristics in supercritical environments and provide a basis for high-fidelity numerical simulation of the spray model.

Experimental Investigation on Gasoline—Water Mixture Fuel Impingement Preparation Method and Spray Characteristics with High Injection Temperatures and Pressures

Gasoline–water mixed injections are of great interest because of their advantages for reduced manufacturing costs and improved atomization, with the potential to alleviate engine detonation and reduce emissions. In this work, based on the principle of impinging flow, a real-time gasoline–water mixture preparation system for internal combustion engines was designed and the preparation system performance was compared with the standard swirl mixing technique. An image processing method was established to quantify the uniformity of the prepared mixture. Based on the flash-boiling spray flash-boiling spray experiment, the spray characteristics of different gasoline–water mixtures were analyzed under different injection temperatures (30–160 °C) and pressures (5–15 MPa). The experiments showed that the impinging pressure was the main factor affecting the emulsification performance of the real-time gasoline–water mixture, and that the proposed real-time mixing system could produce a stable gasoline–water emulsion. For temperatures in the 30–160 °C range, the flash-boiling spray flash-boiling spray experiments showed that the spray penetration distance first decreases and then increases with the injection temperature, while the spray angle shows an opposite trend. The turning point corresponded to the flash-boiling point of each gasoline–water mixture.

Review of physicochemical properties and spray characteristics of biodiesel.

The United Nations Sustainable Development Goals by 2030 deal with seventeen goals for the planet's sustainability. The present review focuses on affordable and clean energy through the effective combustion of fuels with minimal pollution. Effective fuel spray characteristics are essential for combustion among various parameters and fuel properties. The inherent nature of the fuel has a functional relationship with the injection and injectors' conditions. Therefore, the study of fuels' physicochemical properties is essential. This review deals with the spray characteristics of biodiesel. Biodiesels in its purest form and blended with diesel, di-n-butyl ether, dimethyl ether, diethyl ether, ethanol, and butanol are considered for the study. The physicochemical properties of biodiesels, injection conditions, and injector constraints are analyzed to understand the spray process. The atomization features such as spray tip penetration, Sauter mean diameter, spray cone angle, spray area, and spray volume are analyzed. The chemical properties of biodiesel are utilized to describe the spray's transient behavior. In addition, supporting systems for spray diagnostics and models are also discussed. The highlighted significant spray challenges features and future research direction benefit the fuel and combustion community.

A comprehensive review on the atomization and spray characteristics of renewable biofuels

Due to sustainability, rising energy demands, environmental concerns and energy security issues, scientists and researchers around the world are studying renewable biofuels as an alternative to fossil fuels. Biofuels or alternative fuels such as biodiesel, pure plant oil, DME (dimethyl ether) and alcohols which are derived from different renewable biomass sources were investigated by the scientific community as a substitute fuel for diesel engines. The spray process plays the main role in the proper combustion of fuel in engines, leading to a decrease in tailpipe emissions and an increase in engine efficiency. Development in the understanding of biofuel spray characteristics results in low emissions compared to fossil fuels and thus making biofuels a sustainable option for the future. Since, fuel properties have a significant impact on spray development, hence numerous experimental and computational studies were conducted. This article critically examines the atomization and spray characteristics of various alternative fuels utilized for diesel engines. In addition, recent advances and progress in numerical modeling and simulation of the biodiesel spray process are also discussed. To meet renewable fuels viability in CI (compression ignition) engines as a substitute to diesel fuel, various associated challenges and their probable solutions are also discussed.

Atomization characteristics of different water/heavy fuel oil emulsions in a pressure-swirl injector

In the present study, different water in heavy fuel oil (HFO) emulsion fuels containing 5, 10, 15% water content have been prepared under ultrasound irradiation without surfactant. The stability of the prepared emulsion fuels has been investigated. The best stability was observed for the emulsion fuel containing 5% water (E5) due to its more uniform water droplet size distribution. Then, the atomization behavior and spray characteristics of the emulsion fuels have been investigated in a pressure-swirl injector using a high speed camera. The examined ranges for temperature and pressure were (60–110 °C), and (10–25 bar), respectively. The breakup length for each fuel sample in each operating condition was calculated through the image processing analysis. It was found that the micro explosion phenomena associated with the evaporation of the water droplets in the fuels has the most impact on the emulsion fuel spray characteristics. The best atomization performance was observed for E5 considering all examined fuel samples. A 68% decrease in the breakup length was observed for E5 compared to the neat HFO at 90 °C and 15 bar.

Spray characterization of boron-loaded slurry fuels using high-speed imaging technique

The characterization of atomized spray in terms of its structure, break-up, and droplet morphology is crucial to analyze an engine's performance. Therefore, in this study, the spray characteristics of boron-laden slurry fuels have been evaluated experimentally through a high-speed imaging technique. The rheological properties of the boron-loaded slurry fuels have been measured and their impact on the atomization behavior has been qualitatively analyzed. The spray cone angle, penetration length, sheet break-up length, ligament length, ligament diameter, and droplet diameter distribution are obtained by processing the time-sequences images. The experiments were performed at three atomizing air-to-liquid ratios (ALR). Spray characteristics of the fuel samples with various particle loadings (10%, 20%, and 30%) have been analyzed and compared with that of the pure Jet A-1. The obtained results were qualitatively analyzed with different non-dimensional parameters, such as Momentum flux ratio, Weber number, Ohensorge number, and Reynolds number. The results show that an increase in viscosity due to particle loading significantly affects the spray characteristics. However, a better atomization behavior of boron slurry fuel at higher ALR than low ALR, even with higher particle loading, has been observed. This is possibly due to the change in momentum flux ratio at higher atomizing air velocity.

Study of fuel spray characteristics using a high-pressure common rail diesel injection system by the method of Schlieren

The supercritical atmosphere created by the increase in temperature and pressure in the diesel engine cylinder is the key factor that causes changes in the fuel atomization process. In this study, the differences in spray morphology of n-heptane under different ambient temperature and pressure conditions were investigated using a constant volume combustion bomb combined with the Schlieren method. Based on the Peng-Robinson equation of state (PR equation), several transport characteristics models are constructed to predict the transport characteristics of n-heptane under different operating conditions. During the experiment, the injection pressure and fuel temperature were kept constant (80 MPa, 300 K), the ambient pressure was varied from 2 to 5 MPa, and the fuel temperature was changed from 400 to 800 K, spanning from subcritical to supercritical state. Three different spray regions have been identified based on the fuel temperature and spray geometry: liquid phase region, gas-liquid interface mixing layer, gas phase region. The results show that in a subcritical environment (400 K, 2 MPa), the fuel injection and atomization process is dominated by evaporation. The degree of heat exchange between the fuel and the medium gas is very low, while a small amount of phase change occurs. When the fuel is in low (600 K, 3 MPa) and medium supercritical (600 K, 4 MPa) ambient atmosphere, turbulence becomes the dominant factor in the fuel atomization process. The mixing layer at the gas-liquid interface at the edge of the liquid jet increases significantly. When the fuel is in a high supercritical (700 K, 4 MPa; 800 K, 5 MPa) atmosphere, the jet takes on a shape similar to that of a gas jet, and the mixing layer at the gas-liquid interface becomes the main part of the spray projection area.

ORIFICE WALL CAVITATION AND SINGLE STRING CAVITATION IN FUEL INJECTORS

It has been pointed out that cavitation inside a fuel injector plays an important role in the fuel spray characteristics, which affects the thermal efficiency and exhaust gas emissions. Recently, it was pointed out that when needle lift is low, not only orifice wall cavitation but also single string cav-itation may occur in the mini-sac and valve-covered orifice (VCO) nozzles, which increases largely the spray cone angle. However, the mechanism and condition of the appearance of single string cav-itation have not been clarified yet. In this study we carry out high-speed visualization of orifice wall cavitation and single string cavitation in various transparent injectors with a single orifice and a simple rectangular sac, whose gap <i>Z</i>, sac width <i>W</i>, orifice diameter <i>D</i>, liquid kinematic viscosity ν, and mean liquid velocity <i>V</i> in the orifice are varied, to investigate the governing dimensionless parameters and to examine whether we can quantitatively predict the formation criteria of single string cavitation or not. Moreover, particle image velocimetry (PIV) analysis is conducted to measure the velocity distribution, to clarify the flow structure, and to quantify the circulation in the sac. As a result, we conclude that regardless of the shape and size of the fuel injectors, the length of cavitation in an orifice can be predicted by using the modified cavitation number σ<sub>c</sub>. The appearance of single string cavitation and circulation in the sac are possible to be predicted quantitatively by using a dimensionless Re<sub>1</sub> proposed in this study, which is the ratio among the inertial and viscous forces.

Wall Adhesion Characteristics of Fuel Spray under Flow Conditions in Intake Port Fuel Injection Spark Ignition Engines

Wall Adhesion Characteristics of Fuel Spray under Flow Conditions in Intake Port Fuel Injection Spark Ignition Engines

Spray Characteristics of RP-3 Jet Fuel at Non-Evaporating and Evaporating Environments

Spray Characteristics of RP-3 Jet Fuel at Non-Evaporating and Evaporating Environments

Effect of Fuel Physicochemical Properties on Spray and Particulate Emissions.

To investigate the effect of fuel physicochemical properties on spray and particulate emissions, fuel spray characteristics were tested on a constant volume chamber (CVC) test rig using a high-speed camera method to investigate the effect of different injection and ambient pressures on spray characteristics. In the engine bench tests, the effects of particulate emissions from five different diesel fuels with different physicochemical properties were analyzed under low-, medium-, and high-load steady-state conditions and 5 s transient loading conditions. The test results showed that the spray tip penetration of different CNs results from the combined effect of the fuel properties. The spray cone angle of the five fuels increased with the increase of injection and ambient pressure, and the impact of ambient pressure on the spray cone angle was more prominent. Spray tip penetration and spray projection area increase with increased injection pressure and decrease with increased ambient pressure; compared with spray tip penetration, the spray cone angle has more influence on spray projection area, especially near-field spray cone angle as the primary influence factor. Fuels with different ignition characteristics have other effects on particulates at different loads. At low loads, choosing CN = 55.3 fuel improved the number and mass of particulates; at medium and high loads, choosing CN = 51 fuel reduced the number of particulate emissions. Fuels with different volatilities have different effects on particulates at other loads. At low loads, CN = 54.9 fuel was chosen with moderate volatility and aromatic content. At medium and high loads, the volatility of the fuel had a lower weight on particulates, and the aromatic content had a higher weight. Under the transient loading condition of 5 s, using fuel with a higher CN, good volatility, and lower aromatic content can appropriately reduce the number of particulate emissions.

Effects of Low Pressure Injection on Fuel Atomization and Mixture Formation for Heavy Fuel Engines

The application of direct injection (DI) technology can effectively improve the atomization effect of heavy fuel to reduce the fuel loss of heavy fuel engines (HFE). The fuel spray characteristics directly affect the combustion performance of the engine. To investigate the atomization process and evaporation characteristics of heavy fuel in-cylinder for an air-assisted direct injection (AADI) engine, a simulation calculation model of AADI HFE was established with the use of a computational fluid dynamics tool. The air-assisted injector model and the one-dimensional performance calculation model were verified by test data. The influences of injection timing and injection pressure on the spray characteristics and mixture formation in the engine cylinder were discussed. The results show that the mixture concentration distribution is uniform after the injection timing is advanced, and the mass fraction of the fuel evaporation increases. The earlier injection timing can provide the fuel with sufficient time to evaporate, while the later injection timing will result in increasing the Sauter mean diameter (SMD) of the fuel droplets, and the unevaporated heavy fuel in the combustion chamber tends to become concentrated. With the increase in air injection pressure, the distribution of the mixed gas in the cylinder becomes uniform, and the SMD of the fuel droplets in the cylinder decreases. When the injection pressure is 0.65 MPa and 0.75 MPa, the difference between the SMD of the fuel droplets in-cylinder decreases, and a favorable fuel atomization effect can be maintained.

Numerical and Experimental Spray Analysis of Castor and Jatropha Biodiesel under Non-Evaporating Conditions

Fuel spray characteristics influence combustion, which in turn has a direct impact on engine performance and emissions. Recently, there has been an increasing interest in novel castor oil biodiesel. However, few investigations have been performed that combine both numerical and experimental biodiesel spray analyses. Hence, in this paper, we aim to explore the spray behavior of castor and jatropha biodiesel by employing numerical and experimental methods under non-evaporating, varying injection, and ambient conditions. The experimental study was carried out in a control volume vessel (CVV) at high injection and ambient pressures. The fuel atomization was modelled in ANSYS Fluent using a Lagrangian/Eulerian multiphase formulation. The results revealed that the Kelvin–Helmholtz and Rayleigh–Taylor (KHRT) model coupled with the Taylor Analogy Breakup (TAB) model provide a better estimation of the penetration length (PL) and spray cone angle (SCA) compared to the KH and TAB models. On average, Jatropha biodiesel (JB-20) and castor biodiesel (CB-20) showed a 10% to 22% longer PL, 8% to 10.6% narrower spray cone angles, and 3% to 6% less spray area, respectively, compared to diesel. The numerical predictions showed that JB-20 and CB-20 had an around 24.7–48.3% larger Sauter mean diameter (SMD) and a 38.6–73.3% average mean diameter (AMD).

Research on fuel spray characteristics of coal-made Fisch-Tropsch process diesel/methanol

ABSTRACT Fuel spray characteristics have a big influence on the combustion process and pollutants of diesel engines. The physical characteristics of fuel such as latent heat of vaporization, density and viscosity are also changed when methanol is added to the fuel, resulting in changes in fuel transport characteristics and spray characteristics, which affect the combustion process. A high-pressure common rail spray characteristics visualization platform was built to assess the spray characteristics of diesel, Fischer-Tropsch process diesel and Fischer-Tropsch process diesel mixed with 5%, 10% and 15% methanol. The spray penetration distance, spray projection area and spray cone angle of the five fuels were measured under various injection pressures and back pressure conditions. In addition, the influence of the physical characteristics of the fuels on the spray characteristics was analyzed. The results showed that the spray penetration distance of Fischer-Tropsch diesel/methanol blends changed by about 2%, the spray cone angle elevated by 1%-5%, and the spray projected area increased by 10%-23% when the back pressure ranged from 120 to 160 MPa. When the back pressure was constant and the injection pressure was increased from 120 to 160 MPa, the spray penetration distance of Fischer-Tropsch process diesel/methanol blends increased by about 13%, the spray cone angle increased by about 4%, and the spray area increased by 9% to 33%. Our results provide a basis for the application of Fischer-Tropsch process diesel/methanol blends in diesel engines.

Spray cyclic variations of multicomponent fuels under subcooled, transitional, and superheated conditions

The superheated spray has attracted attention due to itsenhanced atomization in gasoline direct injection (GDI) engines. Even though spray characteristics of multicomponent fuels under superheated conditions have been studied before, the connection between plume-to-plume interaction and spray cyclic variation (SCV) has not been adequately addressed. Moreover, the lack of physical understanding of SCV for multicomponent fuels hampers effort to reduce GDI engine cyclic variations. Thus, this work investigates the SCV of binary and ternary multicomponent fuel blends under superheated conditions. Three pure components of n-pentane, isooctane, and n-decane were analyzed and compared to their twelve binary and ternary blends. The experiments were conducted using the laser Mie-scattering technique in a spray chamber at a fuel temperature of 70 °C and ambient pressure of 50 kPa. This test condition facilitated the occurrence of subcooled, transitional, and superheated sprays for all 15 fuel blends. Five spray plume-to-plume interaction levels are defined to reveal the relationship between the SCV and plume-to-plume interaction. The results show that the spray structure is constrained by the blending ratio of n-pentane (high volatility component). The transitional spray exhibited higher plume-to-plume interaction with larger SCV on the variations of partially connected plumes. Both the non-collapsed spray (no plumes interaction) and totally collapsed spray (wholly merged plumes) showed less SCV. However, the total collapsed spray showed higher SCV compared to non-collapsed spray.