Sauter Mean Diameter Distribution Research Articles

Analysis of ethanol and butanol direct-injection spark-ignition sprays using two-phase structured laser illumination planar imaging droplet sizing

This paper reports on the spray structure of the biofuels, ethanol, and butanol generated by a multihole direct-injection spark-ignition injector, which is studied in a constant volume chamber. The spray shape and structure are analyzed using two-phase structured laser illumination planar imaging where both laser-induced fluorescence and Mie-scattering light are recorded simultaneously for the extraction of instantaneous laser-induced fluorescence/Mie-scattering ratio images. Quantitative planar measurements of the droplet Sauter mean diameter are conducted, using calibration data from phase-Doppler anemometry. The resulting Sauter mean diameters are presented for ethanol and butanol at various fuel temperatures at different times after the start of injection. It is found that an increase in fuel temperature results in a faster atomization and higher evaporation rate, which leads to reduced spray tip penetration and smaller droplet Sauter mean diameter. At equivalent conditions, butanol consistently showed larger spray tip penetration in comparison to ethanol. This behavior is due to the higher surface tension and viscosity of butanol resulting in the formation of larger droplets and larger Sauter mean diameters in the whole spray region. Finally, the butanol injection also shows larger cyclic variations in the spray shape from injection to injection which is explained by the internal nozzle flow that is influenced by larger fuel viscosity as well. The Sauter mean diameter distribution is also compared to phase-Doppler anemometry data showing good agreement and an uncertainty analysis of the structured laser illumination planar imaging-laser-induced fluorescence/Mie-scattering technique for planar droplet sizing in direct-injection spark-ignition sprays is presented.

Effects of gas liquid ratio on the atomization characteristics of gas-liquid swirl coaxial injectors

To understand the atomization characteristics and atomization mechanism of the gas-liquid swirl coaxial (GLSC) injector, a back-lighting photography technique has been employed to capture the instantaneous spray images with a high speed camera. The diameter and velocity of the droplets in the spray have been characterized with a Dantec Phase Doppler Anemometry (PDA) system. The effects of gas liquid ratio (GLR) on the spray pattern, Sauter mean diameter (SMD), diameter-velocity distribution and mass flow rate distribution were analyzed and discussed. The results show that the atomization of the GLSC injector is dominated by the film breakup when the GLR is small, and violent gas-liquid interaction when the GLR is large enough. The film breakup dominated spray can be divided into gas acceleration region and film breakup region while the violent gas-liquid interaction dominated spray can be divided into the gas acceleration region, violent gas-liquid interaction region and big droplets breakup region. The atomization characteristics of the GLSC injector is significantly influenced by the GLR. From the point of atomization performance, the increase of GLR has positive effects. It decreases the global Sauter mean diameter (GSMD) and varies the SMD distribution from a hollow cone shape (GLR = 0) to an inverted V shape, and finally slanted N shape. However, from the point of spatial distribution, the increase of GLR has negative effects, because the mass flow rate distribution becomes more nonuniform.

Effects of spray angle variation on mixing in a cold supersonic combustor with kerosene fuel

Effective fuel injection and mixing is of particular importance for scramjet engines to be operated reliably because the fuel must be injected into high-speed crossflow and mixed with the supersonic air at an extremely short time-scale. This study numerically characterizes an injection jet under different spray angles in a cold kerosene-fueled supersonic flow and thus assesses the effects of the spray angle on the mixing between incident shock wave and transverse cavity injection. A detailed computational fluid dynamics model is developed in accordance with the real scramjet combustor. Next, the spray angles are designated as 45°, 90°, and 135° respectively with the other constant operational conditions (such as the injection diameter, velocity and pressure). Next, a combination of a three dimensional Couple Level Set & Volume of Fluids with an improved Kelvin-Helmholtz & Rayleigh-Taylor model is used to investigate the interaction between kerosene and supersonic air. The numerical predictions are focused on penetration depth, span expansion area, angle of shock wave and sauter mean diameter distribution of the kerosene droplets with or without evaporation. Finally, validation has been implemented by comparing the calculated to the measured in literature with good qualitative agreement. Results show that no matter whether the evaporation is considered, the penetration depth, span-wise angle and expansion area of the kerosene droplets are all increased with the spray angle, and most especially, that the size of the kerosene droplets is surely reduced with the spray angle increase. These calculations are beneficial to better understand the underlying atomization mechanism in the cold kerosene-fueled supersonic flow and hence provide insights into scramjet design improvement.

Effects of injection pressure variation on mixing in a cold supersonic combustor with kerosene fuel

Spray jet in cold kerosene-fueled supersonic flow has been characterized under different injection pressures to assess the effects of the pressure variation on the mixing between incident shock wave and transverse cavity injection. Based on the real scramjet combustor, a detailed computational fluid dynamics model is developed. The injection pressures are specified as 0.5, 1.0, 2.0, 3.0 and 4.0 MPa, respectively, with the other constant operation parameters (such as the injection diameter, angle and velocity). A three dimensional Couple Level Set & Volume of Fluids approach incorporating an improved Kelvin-Helmholtz & Rayleigh-Taylor model is used to investigate the interaction between kerosene and supersonic air. The numerical simulations primarily concentrate on penetration depth, span expansion area, angle of shock wave and sauter mean diameter distribution of the kerosene droplets with/without evaporation. Validation has been implemented by comparing the calculated against the measured in literature with good qualitative agreement. Results show that the penetration depth, span-wise angle and expansion area of the transverse cavity jet are all increased with the injection pressure. However, when the injection pressure is further increased, the value in either penetration depth or expansion area increases appreciably. This study demonstrates the feasibility and effectiveness of the combination of Couple Level Set & Volume of Fluids approach and an improved Kelvin-Helmholtz & Rayleigh-Taylor model, in turn providing insights into scramjet design improvement.

Investigations on the droplet distributions in the atomization of kerosene jets in supersonic crossflows

Phase Doppler anemometry was applied to investigate the atomization processes of a kerosene jet injected into Ma = 1.86 crossflow. Physical behaviors, such as breakup and coalescence, are reproduced through the analysis of the spatial distribution of kerosene droplets' size. It is concluded that Sauter mean diameter distribution shape transforms into “I” type from “C” type as the atomization development. Simultaneously, the breakup of large droplets and the coalescence of small droplets can be observed throughout the whole atomization process.

Multiple Size Group Modeling of Polydispersed Bubbly Flow in the Mold: An Analysis of Turbulence and Interfacial Force Models

An inhomogeneous Multiple Size Group (MUSIG) model based on the Eulerian–Eulerian approach has been developed to describe the polydispersed bubbly flow inside the continuous-casting mold. A laboratory scale mold has been simulated using four different turbulence closure models (modified k − ɛ, RNG k − ɛ, k − ω, and SST) with the purpose of critically comparing their predictions of bubble Sauter mean diameter distribution with previous experimental data. Furthermore, the influences of all the interfacial momentum transfer terms including drag force, lift force, virtual mass force, wall lubrication force, and turbulent dispersion force are investigated. The breakup and coalescence effects of the bubbles are modeled according to the bubble breakup by the impact of turbulent eddies while for bubble coalescence by the random collisions driven by turbulence and wake entrainment. It has been found that the modified k − ɛ model shows better agreement than other models in predicting the bubble Sauter mean diameter profiles. Further, simulations have also been performed to understand the sensitivity of different interfacial forces. The appropriate drag force coefficient, lift force coefficient, virtual mass force coefficient, and turbulent dispersion force coefficient are chosen in accordance with measurements of water model experiments. However, the wall lubrication force does not have much effect on the current polydispersed bubbly flow system. Finally, the MUSIG model is then used to estimate the argon bubble diameter in the molten steel of the mold. The argon bubble Sauter mean diameter generated in molten steel is predicted to be larger than air bubbles in water for the similar conditions.

Digital Holographic Analysis of the Near Field of Aerated-Liquid Jets in Crossflow

Inline digital holographic microscopy is used to study the rapidly developing region near the injector of several sprays in subsonic crossflow. Pure liquid jets are compared to aerated-liquid jets for crossflow Mach numbers of 0.3 and 0.6. Gas-to-liquid ratios of 0, 4, and 8% with a fixed momentum flux ratio (based on liquid flow rate) of 10 are investigated. Three-dimensional representations of the present test cases of aerated injection in crossflow are produced for the first time for the rapidly developing near-injector region (15–25 injector diameters downstream) owing to the capability of holographic diagnostics in probing nonspherical droplets typical of those present in this region. The results are also presented for the stable far-field region of the injector (at 50 and 100 injector diameters downstream). The results include droplet equivalent-diameter distributions, Sauter mean diameter distributions, and droplet velocities.

Radial Profiles of Gas Bubble Behavior in a Gas‐Liquid Bubble Column Reactor under Elevated Pressures

AbstractThe effects of operating conditions on radial variation of gas holdups, bubble swarm rising velocity, and Sauter mean diameter were investigated in a bubble column reactor under elevated pressures using a conductivity probe method. Air served as gas phase and tap water as liquid phase with varying gas velocity and pressure. All three parameters increased constantly with higher superficial gas velocity. Maximum holdup, velocity, and Sauter mean diameter were found at the center of the cross section. Two different cases for Sauter mean diameter distribution were observed. The gas holdups increase continuously with higher system pressure, but decrease for bubble swarm rising velocity and Sauter mean diameter. According to experimental results, an empirical correlation of the gas holdup profiles is presented.

A method for measurement of planar liquid volume fraction in dense sprays

A methodology for measurement of planar liquid volume fraction in dense sprays using a combination of Planar Laser-Induced Fluorescence (PLIF) and Particle/Droplet Imaging Analysis (PDIA) is presented in this work. The PLIF images are corrected for loss of signal intensity due to laser sheet scattering, absorption and auto-absorption. The key aspect of this work pertains to simultaneously solving the equations involving the corrected PLIF signal and liquid volume fraction. From this, a quantitative estimate of the planar liquid volume fraction is obtained. The corrected PLIF signal and the corrected planar Mie scattering can be also used together to obtain the Sauter Mean Diameter (SMD) distribution by using data from the PDIA technique at a particular location for calibration. This methodology is applied to non-evaporating sprays of diesel and a more viscous pure plant oil at an injection pressure of 1000bar and a gas pressure of 30bar in a high pressure chamber. These two fuels are selected since their viscosity values are very different with a consequently very different spray structure. The spatial distribution of liquid volume fraction and SMD is obtained for two fuels. The proposed method is validated by comparing liquid volume fraction obtained by the current method with data from PDIA technique.

Laser sheet dropsizing of evaporating sprays using simultaneous LIEF/MIE techniques

Laser-induced-fluorescence/Mie-scattering (LIF/MIE) was proven to be a useful diagnostic for Sauter Mean Diameter (SMD) measurements in non-evaporating sprays. However, the measurement is not reliable for cases of an evaporating spray due to the interference of the fluorescence signal from the vapor phase. In this work, simultaneous Laser-induced-exciplex-fluorescence/Mie-scattering (LIEF/MIE) imaging techniques were proposed to obtain the SMD distribution of evaporating sprays. A special experimental condition was used to generate the flash-evaporating spray, which includes a fuel temperature of 60°C and an ambient pressure of 20kPa. Different from the conventional LIF/MIE technique, the combination of LIEF and Mie techniques allows eliminating the effect of tracer fluorescence from vapor phase in an evaporating spray. In addition, carefully selected tracers and specially designed filters were used to decrease the effects of variation on tracer concentration and temperature dependency of fluorescence intensity during evaporation. The numerical analysis based on geometrical optics approximation (GOA) and experimental analysis was conducted to determine the calibration coefficient K. Finally, SMD distribution of an evaporating spray measured by both LIEF/MIE and conventional LIF/MIE techniques was compared to PDI measurement. The results show that the SMD of the flash boiling spray obtained from LIEF/MIE is very close to those measured by PDI, while the results measured by LIF/MIE and PDI show a large deviation of around 40%. It indicates that the evaporation effect cannot be ignored for evaporating sprays.

Theoretical investigation on the mechanism of surface temperature non-uniformity formation in spray cooling

In this study, the effects of droplet velocity non-uniformity, SMD (Sauter mean diameter) distribution non-uniformity, droplet number non-uniformity, and heating power on the fluid film thickness, fluid film velocity, and surface temperature distribution were investigated, and then the surface temperature non-uniformity correlations in non-boiling regime and nucleate boiling regime were correlated. The results show that: with the decreasing of the spray parameters non-uniformity, the fluid film thickness on the heating surface becomes more uniform, and the fluid film velocity increases, thus the surface temperature non-uniformity decreases. The highest surface temperature appears in the centre of the heating surface, and the lowest is nearby the position where the fluid film appears. The droplet number non-uniformity contributes the largest portion of impact on the surface temperature non-uniformity, followed by the droplet velocity non-uniformity. The effect of droplet SMD non-uniformity is the minimal. Finally, the surface temperature non-uniformity correlations in non-boiling regime and nucleate boiling regime were correlated with a mean absolute error of 20%.

Mixing and atomization characteristics in an internal-mixing twin-fluid atomizer

Twin-fluid atomizers have been successfully used in many industrial applications. This paper presents experimental studies on internal mixing and atomization in a water–air internal-mixing atomizer. Two-phase mixing process and flow patterns in the internal mixing chamber were visually studied through high speed CCD. Observation reveals that internal mixing was dominated by Gas to Liquid mass Ratio (GLR). As GLR increased, the flow patterns changed from slug flow to annular flow. The Oshinowo and Charles’ map can be used to predict the flow patterns for the designed atomizer. Droplet Sauter Mean Diameter (SMD) spatial distributions were measured with Phase Doppler Analyzer (PDA) at different operating conditions. Droplet SMD decreased with the increase of GLR at all operating pressure and locations. In the undeveloped region, a close relationship was observed between flow pattern transformation in internal mixing chamber and droplet SMD distribution, and there was an optimized pressure ranging from 0.2MPa to 0.3MPa for atomization since liquid films became thicker under a higher pressure. In the developed region, pressure promoted to generate finer atomization. Possibility Density Function (PDF) distribution of droplet size at different axial locations was analyzed to quantitatively represent the effect of droplet coalescence and breakup. As axial distance increased, PDF of both fine droplets and large droplets decreased. The particle size with the maximum PDF increased with the axial distance as well. The results imply that best atomization performance was acquired in the undeveloped region.

Spray characteristics of four-hole injectors used for a hydrocarbon lean nitrogen oxide catalyst system in a diesel engine

Among emission reduction technologies, a hydrocarbon lean nitrogen oxide trap is a cost-effective solution for nitrogen oxide emission control in light-duty vehicles. However, the hydrocarbon lean nitrogen oxide trap leads to high fuel consumption because diesel fuel is normally used as a reducing agent (i.e. a reductant). It is necessary to establish injection conditions corresponding to the maximum nitrogen oxide conversion in the hydrocarbon lean nitrogen oxide trap system. A uniform distribution of the reducing agent is desirable, and the spray characteristics of the reductant, such as atomization and penetration, must be well understood in order to establish a good performance of the hydrocarbon lean nitrogen oxide trap. With this goal in mind, the spray characteristics and behaviour of a port fuel injector with four holes were analysed using visualization and r.m.s. image-processing techniques. The Sauter mean diameter distribution of the injector was measured using a Malvern system. The liquid agents employed in this study were ISO 4113 and n-heptane, which have properties similar to those of diesel and gasoline fuels respectively. These results elucidated the feasibility of a secondary injection system for the hydrocarbon lean nitrogen oxide trap.

Comparative Study of Spray Characteristics of Gas-Centered and Liquid-Centered Swirl Coaxial Injectors

This study investigated the spray and Sauter mean diameter characteristics of gas-liquid swirl coaxial injectors by measuring and analyzing spray angles and mean drop sizes. Two different types of gas-liquid swirl coaxial injectors were designed and tested for this experiment: 1) a gas-centered swirl coaxial injector and 2) a liquid-centered swirl coaxial injector. The spray patterns were obtained for both types of injectors. The spray angles of these liquidcentered swirl coaxial injectors showed a decreasing trend as a function of the momentum flux ratio over the conditions studied. Good agreement was generally achieved between the predicted and measured spray angles. On the other hand, with increasing momentum flux ratio, the spray angle of the gas-centered swirl coaxial injector initially decreased when the momentum flux ratios were relatively low, but the trend reversed over the high momentum flux ratio range studied. The Sauter mean diameter data of these two types of injectors were also obtained using an image-processing method. Results showed that the Sauter mean diameter distribution of the liquid-centered swirl coaxial injector had a solid cone shape, whereas the gas-centered swirl coaxial injector exhibited two distinct Sauter mean diameter distribution regimes. The gas-centered swirl coaxial injector had a solid cone shape along the centerline, and it had a hollow cone shape at the periphery.

Effect of grouped-hole nozzle geometry on the improvement of biodiesel fuel atomization characteristics in a compression ignition engine

This paper describes the influence of grouped-hole nozzle geometry on the atomization characteristics of a biodiesel fuel. The effects of injection rate profile, spray evolution, droplet mean diameter, and mean velocity of the droplets are investigated in a high-pressure injection system. A grouped-hole nozzle with 16 holes driven by piezo stack was used in the experiments and the obtained results are compared with those obtained using a single-hole nozzle with the same overall nozzle area. The effect of using a split fuel injection strategy on the spray atomization was analysed using a grouped-hole nozzle with 12 holes. The time-based injection rate profiles for a biodiesel fuel, i.e. the mass flowrate of the fuel injector nozzle were obtained from the pressure variation generated when the fuel was injected into a tube filled with fuel. The spray and atomization performance for biodiesel fuel injected through a grouped-hole nozzle were visualized and measured by a visualization system and droplet analyser system, respectively. It was revealed that the biodiesel injection rate profile from a single-hole nozzle with the same overall nozzle area shows a similar injection rate profile to that of the grouped-hole nozzle. The injection rate profiles for a split injection strategy are lower than for a single injection and the peak value of the second injection is lower than for the first injection. The Sauter mean diameter distributions of biodiesel from the grouped-hole nozzle have a larger diameter because the small droplets injected through the grouped-hole nozzle collide and coalesce with each other, which leads to an increase in droplet diameter. From these results, it can be concluded that the use of a grouped-hole nozzle and split injection strategy does not improve on the fuel atomization performance for biodiesel fuel for a single-hole nozzle.

A study on an application of a hybrid break-up model for dimethyl ether atomization in a common-rail injection system

In this study, experimental and numerical investigations were performed to analyse the spray characteristics of dimethyl ether (DME) fuel in a common-rail fuel injection system. In order to analyse the DME fuel spray, overall spray characteristics such as the spray tip penetration, the spray evolution process, and the droplet size distribution were investigated by an application of the hybrid break-up model combined with primary and secondary break-up phenomena. The spray development process and spray tip penetration were measured experimentally from injected DME spray images obtained using a visualization system, while the microscopic characteristics were experimentally measured by a phase Doppler particle analyser system. Calculations based on hybrid break-up models were validated against the experimental results, and the associated break-up constants were optimized after the validation. Based on the optimized break-up constant, the calculated results under various experimental conditions were compared with measured results such as the spray development, the spray tip penetration, the Sauter mean diameter (SMD), and the SMD distribution.

A study on the fuel injection and atomization characteristics of soybean oil methyl ester (SME)

The spray atomization characteristics of an undiluted biodiesel fuel (soybean oil methyl ester, SME) in a diesel engine were investigated and compared with that of diesel fuel (ultra low sulfur diesel, ULSD). The experimental results were compared with numerical results predicted by the KIVA-3V code. The spray characteristics of the spray tip penetration, spray area, spray centroid and injection delay were analyzed using images obtained from a visualization system. The Sauter mean diameter (SMD) was analyzed using a droplet analyzer system to investigate the atomization characteristics. It was found that the peak injection rate increases and advances when the injection pressure increases due to the increase of the initial injection momentum. The injection rate of the SME, which has a higher density than diesel fuel, is higher than that of diesel fuel despite its low injection velocity. The high ambient pressure induces the shortening of spray tip penetration of the SME. Moreover, the predicted spray tip penetration pattern is similar to the pattern observed experimentally. The SMD of the SME decreases along the axial distance. The predicted local and overall SMD distribution patterns of diesel and SME fuels illustrate similar tendencies when compared with the experimental droplet size distribution patterns.

Analysis of the transient atomization characteristics of diesel spray using time-resolved PDPA data

The transient atomization characteristics of a single-hole diesel spray were investigated to clarify the time-dependent droplet formation process of the spray through time-resolved analysis of the droplet size data acquired by using a 2-D PDPA (phase Doppler particle analyzer). Comparisons among the three single-hole diesel nozzles on the atomization characteristics were made to confirm the effects of the hole-diameter. The hole diameter of the single-hole diesel nozzles varied with dn=0.22, 0.32 and 0.42 mm. The time-resolved diameter, SMD (Sauter mean diameter) and AMD (arithmetic mean diameter) of droplets in diesel spray injected into still ambient air were measured. The SMD and AMD decreased with decreasing nozzle hole diameter. The SMD distribution along the spray centerline steeply decreased with increasing axial distance before reaching a constant value. In the time-dependent analysis of the SMD of the whole flow field, the SMD gradually increased with time after the initiation of injection, reached a maximum value, and then decreased.

Atomization characteristics of intermittent multi-hole diesel spray using time-resolved PDPA data

The intermittent spray characteristics of a multi-hole diesel nozzle with a 2-spring nozzle holder were investigated experimentally. Without changing the total orifice exit area, the hole number of the multi-hole nozzle varied from 3 (dn=O.42 mm) to 5 (dn=O.32 mm). The timeresolved droplet diameters of the spray including the SMD (Sauter mean diameter) and the AMD (arithmetic mean diameter), injected intermittently from the multi-hole nozzles into still ambient air, were measured by using a 2-D PDP A (phase Doppler particle analyzer). The 5hole nozzle spray shows the smaller spray cone angle, the decreased SMD distributions and the small difference between the SMD and the AMD, compared with that of the 3-hole nozzle spray. From the SMD distributions with the radial distance, the spray structure can be classified into the three regions: (a) the inner region showing the high SMD distribution; (b) the mixing flow region where the shear flow structure would be constructed; and (c) the outer region formed through the disintegration processes of the spray inner region and composed of fine droplets. Through the SMD distributions along the spray centerline, it reveals that the SMD decreases rapidly after showing the maximum value in the vicinity of the nozzle tip. The SMD remains the constant value near the Z/dn= 166 and 156.3 for the 3-hole and 5-hole nozzles, which illustrate that the disintegration processes of the 5-hole nozzle spray proceed more rapidly than that of the 3-hole nozzle spray.

An experimental and numerical study on fuel atomization characteristics of high-pressure diesel injection sprays

An experimental and numerical study was performed to investigate the macroscopic spray structure and the spray characteristics of common rail type high-pressure injector for the diesel engine. The global spray structure and microscopic characteristics of high-pressure diesel injector were investigated when fuel was injected at various injection pressures. Spray developing process and spray tip penetration were obtained by particle motion analysis system, and the quantitative spray characteristics such as Sauter mean diameter (SMD) and axial mean velocity were measured by using the phase Doppler particle analyzer. To consider the difference between primary and secondary breakup, KH–RT hybrid model, in which it is assumed that Kelvin–Helmholtz and Rayleigh–Taylor instability cause primary and secondary breakup, respectively, is used. After optimizing the breakup constants based on the axial distribution of SMD, the comparisons between predicted and experimental results were conducted.