Spray Shape Research Articles

Calibration strategy of diesel-fuel spray atomization models using a design of experiment method

The Reitz and Diwakar and the KHRT atomization models are widely used for high-pressure diesel-fuel spray. The constants in both models must be calibrated to correctly predict the injection process based on the nozzle geometry, injection conditions, and fuel. Calibration can be significantly time-consuming given the four constants in both models. This paper suggests a strategy to assess the impact of models’ constants on spray tip penetration and mean droplet-diameter predictions on a reference case, with an injection pressure of 700 bar, to characterize the influence of the atomization model’s calibration. The assessment used a design of experiment method (DOE), which demonstrated the important interaction between constants on the results. Obtained calibrations were used for comparing the models’ performances qualitatively and quantitatively by accounting for spray and air-entrainment characteristics. Both models gave similar results, but the KHRT model yielded a better spray shape. Finally, based on DOE results, a method is proposed to modify the model’s constants for higher pressures (900 and 1300 bar).

Influence of intake geometry variations on in-cylinder flow and flow–spray interactions in a stratified direct-injection spark-ignition engine captured by time-resolved particle image velocimetry

Time-resolved particle image velocimetry and Mie-scattering of fuel droplets at 16 kHz were used to capture simultaneously the temporal evolution of the in-cylinder flow field and spray formation within a direct-injection spark-ignition engine. The engine was operated in stratified combustion mode, with stratified mixtures created by a triple injection late in the compression stroke. The impact of geometric variation of the intake port on in-cylinder flow and flow–spray interactions was investigated, focusing on the second injection, since it provides ignitable mixtures at the time of ignition and is subject to strong fluctuations, rather than the first injection, which is very reproducible. Flow field statistics conditioned on the spray shape of the second injection revealed regions with macroscopic cycle-to-cycle flow variations, which correlated with the spray for all recorded cycles. The flow–spray interaction was traced back to before the first injection using correlation analysis, which revealed that cycle-to-cycle fluctuations of the large-scale tumble vortex had a big impact on the spray shape of the second injection, while the first injection was unaffected. This indicates that the origin of the spray fluctuations may be during intake. Despite significant flow modifications due to the intake port geometry variation, fluctuation levels of the second injection were the same for both geometries, that is, spray fluctuations were not sensitive to the geometric change.

Evolution of liquid and gas phases in multi-plume spray injection

In this study, the unsteady development of multi-plume sprays has been investigated by large eddy simulations with Eulerian–Lagrangian multiphase approach for both global spray characteristics and local flow features. Multi-plume sprays are injected at the injection pressures of 10 MPa and 15 MPa, and the temperature of Ts = 297.65 K into the ambient air at the atmospheric pressure and temperature of Ta = 293.15 K. Experimentally obtained global multi-plume spray characteristics in terms of spray shape and penetration are used to validate the present numerical simulations. The present numerical predictions for Sauter mean diameter and its temporal variation agree well with the empirical correlations. The predicted droplet size distribution evolves temporally and spatially, and exhibits bimodal distribution, until eventually the mode for small droplet sizes dominates. The spray plumes are found to have limited interaction due to the relatively large orientation angles between the plumes. Because of the momentum transfer from the liquid to gas phase, spray-induced air jets appear in the multi-plume sprays. Using vorticity, pressure, and λ2 − criterion fields, it is shown that the spray-induced air jets form similar vortical structures as single phase jets. Similarities between the spray-induced air jets and single phase jets in terms of the shear layer vortical structures such as hairpin-like vortices improves our understanding of the entrainment and mixing processes in multi-plume sprays. Copyright © 2016 John Wiley & Sons, Ltd.

Biodiesel production from Cynara cardunculus L. and Brassica carinata A. Braun seeds and their suitability as fuels in compression ignition engines

The development of energy crops can provide environmental benefits and may represent an opportunity to improve agriculture in areas considered at low productivity. In this work, we studied the energy potential of two species (Brassica carinata A. Braun and Cynara cardunculus L.) and their seed oil productivity under different growth conditions. Furthermore, the biodiesel from the oil extracted from the seeds of these species was produced and analysed in term of utilisation as fuels in compression ignition engines. In particular, the spray penetration and shape ratio were measured in a constant-volume chamber and compared with the results obtained with a standard diesel fuel. These results were obtained using a standard common rail injection system at different injection pressure, injection duration, and constant-volume chamber pressure.

Probing into the Effects of Fuel Injection Pressure and Nozzle Hole Diameter on Spray Characteristics under Ultra-high Injection Pressures Using Advanced Breakup Model

In this article, non-evaporating and non-reacting diesel spray is modeled under ultra-high injection pressure using an Eulerian-Lagrangian scheme. This is accomplished in order to probe into the effects of injection pressure, nozzle diameter, and ambient density on spray characteristics. An advanced hybrid breakup model that takes into consideration the transient processes during spray injection has been added to the open source code OpenFOAM. Reynolds-Average Navier-Stokes (RANS) equations are solved using standard turbulence model and fuel droplet is tracked by a Lagrangian scheme. Published experimental data have been used for validation of spray characteristics at 15 kg/m3 ambient density and injection pressures of 100, 200 and 300MPa. Also, three nozzle diameters of 0.08, 0.12 and 0.16mm have been implemented for investigating the effect of this parameter on spray formation. Computed spray shape, jet penetration, spray volume, equivalent ratio along the injector axis and Sauter Mean Diameter (SMD) illustrate good agreement with experimental data of single hole nozzle and symmetric spray. The effects of fuel injection pressure, nozzle hole diameter and ambient density on main spray parameters are presented. It is concluded that numerical model presented here is quite suitable for accurately predicting diesel spray shapes under ultra-high injection pressures.

Definition of a CFD Multiphase Simulation Strategy to Allow a First Evaluation of the Cavitation Erosion Risk Inside High-Pressure Injector

Diesel engine performance is strictly correlated to the fluid dynamic characteristics of the injection system. Actual Diesel engines employ injector characterized by injection pressure till 200MPa that, associated to micro-orifice design, result in critical flow conditions inside injector holes.One of the most remarkable consequence of the critical flow conditions inside injector holes is the cavitation phenomenon. The cavitation inside the injector tip and holes can be correlated to two main effects. The first one is on the spray shape and on the atomization process. The second one is on the physical erosion generated on the injector internal walls by the vapour bubble collapse.About the cavitation erosion risk, it is necessary to quantitatively predict the cavitation aggressiveness and the most probable location of cavitation erosion: they are complex problems that cannot be solved by the application of experimental techniques. For this reason, the application of fully transient CFD multiphase simulation (i.e. the needle motion is reproduced during the simulation) can be considered as a very useful approach to evaluate the multiphase flow behaviour inside real size injector holes.The present work addresses two main issues: numerical simulation of cavitating flows inside injector holes and an assessment of the cavitation erosion risk in terms of both 3D map and magnitude. All the analysis are performed by adopting a 3D-CFD multiphase simulation strategy validated against experimental data.

커먼레일을 이용한 디젤과 BD20 연료가 인젝터에 미치는 영향에 관한 연구

The characteristics of diesel and biodiesel are similar like as cetane number and auto-ignition temperature. High cetane number of diesel and BD could make possible to compression ignition. but BD showed different atomization from diesel due to component like density, viscosity and iodine value etc. Because of this, the biodiesel requires validation. This study using diesel and BD20 investigated effect to durability injector. Durability test were used common rail and bosch solenoid type 5-hole injector. Total test was 672hr but actual running time was 200hr. Spray experiments for spray characteristics were carried out using constant volume combustion chamber. Spray characteristics of diesel and BD showed different result up to durability test time. After 100hr, diesel showed spray shapes were stable but BD was not. After 200hr, difference of diesel and BD spray shapes were grow serious.

Experimental analysis on spray development of 2-methylfuran–gasoline blends using multi-hole DI injector

Confronting the situation of environment pollution and energy shortage, direct injection (DI) system has been commonly used in gasoline engines for its good performance in fuel economy, combustion efficiency, emissions and cold-start. Currently, 2-methylfuran (MF) has already been a more attractive biomass fuel in spark ignition (SI) engine, however, there is little knowledge about its spray behaviors in DI injector, especially when it is used as a gasoline additive. In this study, the spray characteristics of MF–gasoline blends M20 (20% volume fraction MF–gasoline blend fuel), M40 and pure gasoline from 6-hole DI injector are investigated under various ambient pressures and fuel temperatures using high-speed schlieren photography. The experimental results show that two different spray shapes, flash boiling and non-flash boiling, can be observed from experiment images. When flash boiling occurs at low ambient pressure, the level of flash boiling intensifies with the increase of MF mixing ratio which can make spray front collapse intensely. The spray area increases with the MF mixing ratio rising and it has a negative correlation with the fuel temperature at low ambient pressures. As for no flash boiling case, the spray penetration decreases with the increase of MF mixing ratio. Under the ambient pressure of 0.6MPa and 0.85MPa, the spray cone angle for same fuel increases with the increase in fuel temperature. On the other hand, at the same fuel temperature, spray area increases slightly with the increase of mixing ratio of MF blended in gasoline.

A study on diesel spray tip penetration and radial expansion under reacting conditions

The shape of Diesel spray was investigated at real engine conditions in a constant pressure combustion chamber. Schlieren imaging technique was used to make quantitative measurements of spray tip penetration and radial width stressing the impact that the fuel combustion and heat release have on the spray shape. The heat-release region and the Lift-off length were identified measuring OH* chemiluminescence. The fuel (n-dodecane) as well as the operating conditions and the injector used (single axially-oriented hole, 89 μm-diameter) were chosen following the guidelines of the Engine Combustion Network. The effects of different operating parameters on the axial and radial expansion were also investigated. According to the results the reacting spray can be divided into three parts: an inert part, a transient one, and a quasi-steady one that lays between the two other regions. A new method for evaluating this radial expansion of reacting spray was developed, which was evaluated under the different operating conditions. Results show that the radial expansion increases with increasing injection pressure and decreasing ambient temperature and ambient density. The oxygen concentration has no obvious effect on the radial expansion.

Modeling the atomization of high-pressure fuel spray by using a new breakup model

The main objective of this research is to develop a new breakup model and investigate the influence of cavitation, turbulence on processes of high-pressure diesel sprays. The model distinguishes between jet primary atomization and droplet secondary atomization. The primary atomization was simulated based on a modified turbulence induced atomization model taken into account the coupling effects of the relaxation of the velocity profile, cavitation and turbulent fluctuation based on the principle of conservation of energy. The growth time scale of surface waves was provided by Kelvin–Helmholtz (K–H) instability theory on an infinite length cylinder for an inviscid liquid jet. The time scale of initial surface waves based on K–H instability theory on an infinite plane jet is much larger than that based on infinite length cylindrical jet. Based on the present modified model, the weighting coefficients of turbulence and cavitation on the overall atomization can be distinguished clearly. There was remarkable variation in simulated spray shape with present models. It could be seen that the original turbulence induced atomization model results in a shorter spray penetration and smaller drops near the spray core than the modified model. When applying the turbulent weighting coefficient Ct in the determination of the spray angle, the resultant value of spray angle gradually drops due to the reduction of Ct. However, the spray angle increases with increasing the cavitation weighting coefficient Ccav. Comparing the experimental results (such as spray angle, tip penetration and spray shape) with the theoretical ones for different injection pressure, gives a reasonable agreement.

On large eddy simulation of diesel spray for internal combustion engines

Large eddy simulation of diesel spray in a constant volume vessel as well as in an internal combustion engine has been performed. Spray is modeled using Eulerian–Lagrangian approach. The modeling involves primary and secondary break-up, the spray-induced turbulence (SIT) and the stochastic turbulence dispersion (STD) of parcels. Including SIT, based on Baharawaj et al. (2009), in coarse grids, e.g., Δx = 0.5mm, hardly affects the results. With finer grids, e.g., Δx = 0.25mm and Δx = 0.125mm, the local mixture fraction in the downstream flow field slightly decreases whereas the prediction of the spray tips and air entrainment dose not respond to the inclusion of SIT.In the constant volume vessel configuration, including STD in the model is shown to be crucial in obtaining predictive results. It is shown that a simulation excluding STD leads to an unrealistic prediction of the spray shape, over-prediction of the liquid and vapor lengths and erroneous distribution of the mixture fraction and air entrainment.Further investigation on the SIT and STD effects is carried out in practical internal combustion engine operating under a partially premixed charge (PPC) compression ignition condition where the PPC condition is obtained by employing a triple-injection strategy during the late engine compression stroke. It is found that when STD is not included, the fuel spray wall-wetting as well as the fuel spray parcels residing in the cylinder wall vicinity are increased. Furthermore, an unrealistic distribution of mixture fraction in the in-cylinder gases is observed. The results suggest that it is necessary to consider models for particle dispersion when LES of internal combustion engines is performed, in order to properly capture the combustion phasing. The significance of STD is found to increase when the ambient air density is low.

Transient characteristics of diesel sprays from a deposit rich injector

The transients of the early stage evolution of high pressure diesel sprays from a clean and a deposit rich injector were explored using high speed imaging at 24.4kiloframes per second (kfps). Fuel was injected into a liquid that offered high density ambient conditions and, for comparison, fuel was also injected into air at less dense ambient conditions. By comparison of the evolving fuel spray from a new fuel injector to those of an injector rich in carbonaceous deposits at/in the nozzle, anomalous spray behaviour resulting from the presence of deposits becomes apparent. The fuel spray cone angle from a deposit rich injector increased by 10–140% compared to the fuel spray cone angle from a new injector. The accompanying spread in the measured angle was from 100% to 200% greater for the deposit rich case. The presence of deposits significantly affected the early stages of spray evolution, the reproducibility of the spray shape from a deposit rich injector being very low. The observed occurrence of transient radial bulging has the potential to reduce the axial momentum and reduce the combustion performance in diesel engines.

Development of High-Speed Image Acquisition Systems for Spray Characterization Based on Single-Droplet Experiments

Abstract. Accurate spray and droplet characterization is important for increased understanding of the pesticide spray application process. The goal of this study was to develop two image acquisition systems based on single-droplet experiments using a piezoelectric single-droplet generator and a high-speed imaging technique, which will be used in a later stage of this study to evaluate micro and macro spray characteristics and droplet impact behavior. Experiments with different camera settings, lenses, diffusers, and light sources and the resulting image quality parameters showed the necessity of having a good image acquisition and processing system. The image analysis results contributed to selecting the optimal setup for measuring droplet size and velocity, which consisted of a high-speed camera with 6 I¼s exposure time, a microscope lens at a working distance of 430 mm resulting in a field of view of 10.5 mm A— 8.4 mm, and a xenon backlight without a diffuser. The high-speed camera with a macro video zoom lens at a working distance of 143 mm with a larger field of view (88 mm A— 110 mm) in combination with a halogen spotlight with a diffuser was found to have the best potential for measuring macro spray characteristics, such as the droplet trajectory, spray angle, and spray shape.

Large eddy simulation of spray and combustion characteristics with realistic chemistry and high-order numerical scheme under diesel engine-like conditions

The accuracy of large eddy simulation (LES) for turbulent combustion depends on suitably implemented numerical schemes and chemical mechanisms. In the original KIVA3V code, finite difference schemes such as QSOU (Quasi-second-order upwind) and PDC (Partial Donor Cell Differencing) cannot achieve good results or even computational stability when using coarse grids due to large numerical diffusion. In this paper, the MUSCL (Monotone Upstream-centered Schemes for Conservation Laws) differencing scheme is implemented into KIVA3V-LES code to calculate the convective term. In the meantime, Lu’s n-heptane reduced 58-species mechanisms (Lu, 2011) is used to calculate chemistry with a parallel algorithm. Finally, improved models for spray injection are also employed. With these improvements, the KIVA3V-LES code is renamed as KIVALES-CP (Chemistry with Parallel algorithm) in this study. The resulting code was used to study the gas–liquid two phase jet and combustion under various diesel engine-like conditions in a constant volume vessel. The results show that using the MUSCL scheme can accurately capture the spray shape and fuel vapor penetration using even a coarse grid, in comparison with the Sandia experimental data. Similarly good results are obtained for three single-component fuels, i-Octane (C8H18), n-Dodecanese (C12H26), and n-Hexadecane (C16H34) with very different physical properties. Meanwhile the improved methodology is able to accurately predict ignition delay and flame lift-off length (LOL) under different oxygen concentrations from 10% to 21% with ambient density increasing from 14.8kg/m3 to 30.0kg/m3 and ambient temperatures from 850K to 1300K in a constant volume combustion chamber. With increasing oxygen concentration, the ignition delay time and consequently the flame LOL decrease, as the flame moves upstream as expected. On the other hand, reduction in the ambient temperature from 1000K to 900K retards the auto-ignition time and moves the burning location downstream under different oxygen concentrations.

Development of CFDMethod for Spray Shape Estimation

Development of CFDMethod for Spray Shape Estimation

GDI spray structure analysis by polycapillary X-ray [formula omitted]-tomography

A X-ray μ-tomography technique, using a Cu Kα source at 8.048keV coupled with both polycapillary optics and CCD detector, has been developed to reconstruct the composition of a transient gasoline spray generated by a high-pressure GDI injector for automotive applications. The polycapillary elements enable shaping the divergent beams and getting high-contrast images due to the suppression of radiation multiple scattering. A pressure-tight device permits the 360° rotation of a six-hole nozzle, with a step of 0.1°, at injection pressures up to 20MPa, while the spray plume develops in a vented Plexiglas chamber at the atmospheric backpressure. The entire system is configured as a table-top experiment. The extinction images acquired along the X-ray source-spray-detector line-of-sight have permitted the reconstruction of a 3D structure together with a morphology of the jets within a 3mm region downstream the nozzle. The spray shape as well as the propagation direction can be clearly identified in the tomographic reconstruction for all the six jets. Quantitative measurements of the fuel mass density in the near nozzle region have been performed. Typical Gaussian-shape distribution of the intensities appears for the cross sections revealing the more dense jet regions in the core, while slight longitudinal asymmetries indicate an interaction between the jet plumes.

Experimental research on flash boiling spray of dimethyl ether

The high-speed digital imaging technique is applied to observe the developing process of flash boiling spray of dimethyl ether at low ambient pressure, and the effects of nozzle opening pressure and nozzle hole diameter on the spray shape, spray tip penetration and spray angle during the injection are investigated. The experimental results show that the time when the vortex ring structure of flash boiling spray forms and its developing process are determined by the combined action of the bubble growth and breakup in the spray and the air drag on the leading end of spray; with the enhancement of nozzle opening pressure, the spray tip penetration increases and the spray angle decreases. The influence of nozzle hole diameter on the spray tip penetration is relatively complicated, the spray tip penetration is longer with a smaller nozzle hole diameter at the early stage of injection, while the situation is just opposite at the later stage of injection. This paper establishes that the variation of spray angle is consistent with that of nozzle hole diameter.

Experimental study of spray characteristics of biodiesel derived from waste cooking oil

In this study, the fuel spray characteristics and air-fuel mixing process of waste cooking oil biodiesel (B100) and its blend with diesel (B20) were investigated and compared with diesel fuel. Spray characteristics such as spray tip penetration, spray angle, spray velocity and spray morphology were investigated under high injection and ambient pressure conditions using a constant volume spray chamber. The air-fuel mixing process was analysed using empirical relations like fuel volume, mass of air entrained within the spray and equivalence ratio. The results shows that B100 has higher spray tip penetration and velocity but narrow spray angles due to high viscosity and large momentum possessed by B100 compared to B20 and diesel fuels. The deviation in spray tip penetration reduces under high ambient pressure. The spray angle shows no change under various injection pressures; however it increases significantly under high ambient pressure. The spray shape is affected by the cavitation inside the injector nozzle holes. The fuel volume and amount of air entrainment within the spray showed that B100 exhibits poor air-fuel mixing compared to B20 and diesel fuels. Nevertheless, the equivalence ratio along the axial direction of spray reveals that the B100 has lean equivalence ratio compared to B20 and diesel fuel due to the presence of inherent oxygen content in its structure. A numerical simulation was conducted using new hybrid spray model implemented in KIVA4 and found that the results obtained from the simulation were in good agreement with the empirical results calculated from the experiments.

Spray structure as generated under homogeneous flash boiling nucleation regime

We show the effect of the initial pressure and temperature on the spatial distribution of droplets size and their velocity profile inside a spray cloud that is generated by a flash boiling mechanism under homogeneous nucleation regime. We used TSI's Phase Doppler Particle Analyzer (PDPA) to characterize the spray. We conclude that the homogeneous nucleation process is strongly affected by the initial liquid temperature while the initial pressure has only a minor effect. The spray shape is not affected by temperature or pressure under homogeneous nucleation regime. We noted that the only visible effect is in the spray opacity. Finally, homogeneous nucleation may be easily achieved by using a simple atomizer construction, and thus is potentially suitable for fuel injection systems in combustors and engines.

A study on the spray and engine combustion characteristics of diesel–dimethyl ether fuel blends

The purpose of this study was to compare the spray characteristics, the combustion characteristics and the emissions (nitrogen oxides, carbon monoxide, hydrocarbon and smoke) of typical fuels (100% diesel and 100% dimethyl ether) and diesel–dimethyl ether fuel blends in a constant-volume chamber and a single-cylinder direct-injection diesel engine. The spray characteristics were investigated by varying the ambient pressure and the fuel injection pressure using a common-rail fuel injection system with various fuel mixture ratios. The spray characteristic research parameters were the spray shape, the penetration length and the spray angle at the seven-hole injector. Common types of injector were used (Bosch). Two types of fuel blended by mass fraction were employed. Typical fuels (100% diesel and 100% dimethyl ether) and fuel blends with diesel:dimethyl ether mixture ratios of 95:5 and 90:10 were used. The injection pressure was fixed at 70 MPa while the ambient pressure was varied (0 MPa, 2.5 MPa and 5 MPa). The combustion experiments were conducted in a single-cylinder engine equipped with a common rail. The injection pressure was 700 bar at 1200 r/min. The amount of injected fuel was adjusted to obtain a fixed input calorific value of 972.2 J/cycle in order to make a comparison between the fuel types. The results showed that the injection quantity was greater with diesel fuel but not for dimethyl ether fuel and for the fuel blend with the higher mixing ratio. The spray penetration length increased with increasing ambient pressure for diesel but decreased for dimethyl ether with a larger spray angle. The ignition delay and the heat release rate decreased with increasing dimethyl ether which led to a higher indicated mean effective pressure and higher thermal efficiency because there was less negative work in the expansion. The total hydrocarbon emissions and the carbon monoxide emissions decreased with increasing dimethyl ether, but the nitrogen oxide emissions generated were greater owing to the increased combustion temperature.