Droplet size development in a DISI injector fuel spray (original) (raw)
Related papers
Drop-Size Measurement Techniques Applied to Gasoline Sprays
Atomization and Sprays, 2010
Combustion processes involved in internal combustion engines greatly depend on the characteristics of the spray. This study is focused on the comparison of three different techniques used for spray drop sizing. Laser diffraction (LDG), phase Doppler anemometry (PDA) and Image Analysis (IMA) have been used to characterize gasoline sprays produced by gasoline injectors of a direct injection type. Whereas studies comparing drop sizing techniques found in the literature are mainly dealing with steady flows, attention is paid here to the unsteady nature of the spray. The differences in the measurement volumes of the different techniques are also considered. As these diagnostics do not measure exactly the same kind of distribution, both PDA and IMA measurements were converted to spatial-averaged volume-weighted drop size distributions to be compared to LDG. The Sauter Mean Diameter D 32 and the mean diameter D 43 are used to characterize the spray for different time and position of the measurement volume in the spray. The comparison between the three techniques shows a good agreement. Greatest mean diameters are found on the leading edge of the spray and on the side of the spray facing stagnant air, so where the conditions are favourable to a fast evaporation of the smallest droplets. Velocity measurements done by PDA and drop shape morphology characterization are also discussed.
Characterization of the Spray of the DISI Multi-hole Injector by Means of Phase Doppler Anemometer
Journal of Thermal Science and Technology, 2010
The spray from a multi-hole injector applied to direct injection spark ignition (DISI) engine was investigated. In order to understand the detailed structure of the transient spray near the nozzle a combined LDA/PDA system was used. PDA system was optimized in order to detect relative smaller droplets. Size-classified technique was used to get deep information about the spray characterizations near nozzle. The experiments were performed at 7 MPa of injection pressure. At early stage of spray the droplet velocity distribution in the centre of the spray showed high value. Smaller droplets under 15 µm showing followability to air flow, while larger droplets over 20 µm will have drag due to momentum decay. Droplets of 15<D≤20 µm in diameter is criteria for follow/penetration near the nozzle. Near the nozzle, the atomization predominantly occurs at the centre region of the spray.
Droplet diameter measurement near a nozzle exit of a common-rail Diesel injector using PDA
International Conference on Liquid Atomization and Spray Systems (ICLASS), 2021
The purpose of this study is to measure the droplet diameter distribution very close to the nozzle hole of a common-rail Diesel injector using a phase Doppler anemometer (PDA). Experimental investigations of atomization process were restricted due to very high-speed and very dense spray region phenomena in the case of the spray from the common-rail injection. In this experiment, droplet diameter and axial velocity in spray formed by one hole of the common-rail Diesel injector were measured with HiDense PDA system to investigate atomization characteristics near the nozzle exit of the common-rail Diesel injector. HiDense PDA system permits accurate measurements in spray with extremely high particle concentrations, and it is the only PDA system available that provide high quality measurements in the core region of the spray cone. Optimization of optical setup and measurement condition of signal processor were carried out to measure the accurate droplet diameter distribution very close to the nozzle exit under higher injection pressure conditions. It is possible to measure the droplet diameter distribution at the 10mm from the nozzle exit under 100MPa as the injection pressure. Radial distributions of droplet velocity were measured using HiDense PDA system. At 10 mm from the nozzle exit, there are strong shear layer between the surround air and injected spray. Narrower droplet distribution can be seen at 10 mm from the nozzle exit.
Journal of Physics: Conference Series, 2007
Background: To evaluate the deposition efficiency of spray droplets in a nasal cavity produced from a spray device, it is important to determine droplet size distribution, velocity, and its dispersion during atomization. Due to the limiting geometric dimensions of the nasal cavity airway, the spray plume cannot develop to its full size inside the nasal vestibule to penetrate the nasal valve region for effective drug deposition. Methods: Particle/droplet image analysis was used to determine local mean droplet sizes at eight regions within the spray plume under different actuation pressures that represent typical hand operation from pediatric to adult patients. Results: The results showed that higher actuation pressure produces smaller droplets in the atomization. Stronger actuation pressure typical of adult users produces a longer period of the fully atomized spray stage, despite a shorter overall spray duration. This produces finer droplets when compared with the data obtained by weaker actuation pressure, typical of pediatric users. Conclusion: The experimental technique presented is able to capture a more complete representation of the droplet size distribution and the atomization process during an actuation. The measured droplet size distribution produced can be related to the empirically defined deposition efficiency curve of the nasal cavity, allowing a prediction of the likely deposition.
Droplet Size and Velocity Distributions of a Transient Hollow-Cone Spray for GDI Engines
Particle & Particle Systems Characterization, 2001
An experimental investigation of a gasoline direct injection (GDI) spray, emerging from an electronically controlled swirl-type injector, was carried out at an injection pressure and duration of 7.0 MPa and 3.0 ms, respectively, in an optically accessible vessel, at atmospheric pressure and ambient temperature. The temporal and spatial spray evolution was investigated in terms of global spray structure, interaction with the external gas, time-resolved droplet size and velocity distribution. The measurements were carried out with an AVL Engine Video System with a CCD camera, a frame grabber and a strobe flash triggered by the injection apparatus. Digital image processing software for the study of the global parameters of the spray was used. A particle Doppler analyzer (PDA) system was used to estimate the local droplet size and velocity as function of the radial coordinate and distance from the nozzle. A laser light extinction technique was applied to investigate the region close to the nozzle up to 5 mm.
PDA measurement of transient spray formed by a disi multi-hole injector
2006
The droplet characteristics of unsteady fuel spray formed by multi-hole injector used in direct injection gasoline engine was investigated. In order to understand the detail structure of transient spray, a phase Doppler anemometer was used. The traverse system of the vessel was designed to obtain two-dimensional structure of spray. The laser power at measurement volume was optimized in order to detect relative smaller droplets. It is necessary to evaluate the effect of laser power of measurement volume on detection limit of smaller droplets under 10 μm. Phase locking method was used to analyze ensemble mean value of axial/ radial droplet velocity, axial/ radial slip velocity, relative droplet Reynolds number, and droplet turbulent kinetic energy. As a result, smaller droplets under 10 μm can follow the entrainment vortex at the spray shell. On the other hand, larger droplets over 30 μm have larger velocity to penetrate the entrainment vortex. Intermediate droplets of 15<D≦ 20μm in diameter are criteria for follow/ penetration of vortex.
The role of droplet fragmentation in high-pressure evaporating diesel sprays
International Journal of Thermal Sciences, 2009
The relative importance of the physical processes taking place during the development of Diesel sprays is evaluated through use of a denseparticle Eulerian-Lagrangian model. The physical processes considered include the influence of the injection conditions, as determined by a nozzle cavitating flow model, liquid-core atomisation, droplet break-up, turbulent dispersion, droplet-to-droplet interactions and vaporisation. For the latter, different physical mechanisms are included, considering high pressure and temperature as well as multi-component effects. Droplet aerodynamically-induced break-up is the dominant mechanism determining the contact area between the droplets and the surrounding air during their fragmentation period. Furthermore, a new model is considered for the droplet deformation induced during the fragmentation processes of the moving droplets. That is found to increase substantially the interface area available for heat transfer and vaporisation and to reproduce the observed trend of liquid penetration being independent of injection pressure. Model predictions are successfully compared against a wide range of experimental data for the liquid and vapour penetration, spray CCD (Charge Coupled Device) images and PDA (Phase Doppler Anemometry) measurements for various injector nozzle geometries. The results are found to predict trends as well as actual values of the penetrating fuel plumes, as function of nozzle geometry, injection pressure and air thermodynamic conditions covering the range of conditions of modern supercharged DI Diesel engines. (M. Gavaises). of DI Diesel engines are strongly affected by the nozzle flow exit characteristics, which control the atomisation process of the injected fuel and the subsequent spray development . Under most operating conditions cavitation occurs inside the injector nozzle [2]; this is generally accepted as one of the most important parameters affecting fuel spray atomisation . Laser-based experimental techniques, for example , have been extensively applied as diagnostic tools in characterising the transient development of high-speed sprays. However, due to the very short time scales of the underlying processes and the very large number of droplets present, the link with the internal nozzle flow during the injection period remains still a grey area. Moreover, simultaneous imaging of the internal nozzle flow and the spray is very difficult; thus, up to now relevant information is mainly based on computational models.
Energy & Fuels, 2010
Mixture formation in spray-guided direct injection spark ignition engines (SG-DISI) with late injection timing is mainly controlled by spray atomization and evaporation and strongly depends on fuel properties. The influence of fuel composition on the liquid spray structure was determined for a 12-hole solenoid injector with integral and light sheet Mie scattering as well as phase Doppler anemometry (PDA). Late injection timing in a high pressure atmosphere was simulated in an injection chamber (1.5 MPa, 293 and 673 K) to characterize the spray propagation and evaporation of alkanes with high and low volatility (n-hexane, n-heptane, n-decane) and a 3-component mixture of these alkanes with similar fuel properties like gasoline fuel. Under high chamber pressure and low ambient temperature, the spray propagation and the resulting droplet sizes are similar for all fuels. However, for n-decane, the droplet size distribution is shifted to smaller droplets and the spray appeared to be less dense because of fuel-dependent internal nozzle flow which results in a reduced injected fuel mass. In contrast, under high ambient temperature conditions for more volatile fuel components, the liquid spray length is reduced and droplet size as well as droplet momenta are decreased. Small amounts of high boiling fractions delay the evaporation and support the overall spray stability also for multicomponent mixtures which is indicated by increased spray length as well as larger droplet sizes and momenta. Moreover, the droplet size distributions and the small liquid Peclet numbers (Pe L ≈ 1) of the 3-component fuel indicate a demixing of light and heavy boiling components in the 3-component fuel under conditions which are typical for DISI strategies with late injection. *Corresponding (1) Ipp, W.; Egermann, J.; Schmitz, I.; Wagner, V.; Leipertz, A.; Hartmann, M.; Schenk, M.
The influence of airflow on fuel spray characteristics from a slit injector
Fuel, 2007
Optimization of fuel spray, airflow, and their interaction with the cylinder and piston wall is crucial to achieve stable combustion of stratified charge with minimum emissions in direct-injection spark-ignition (DISI) engines. In this study, the interaction between air and fuel spray from slit injector was investigated in a steady airflow system generated by a wind tunnel under atmospheric conditions. Both Mie scattering images and phase Doppler anemometry (PDA) measurements of the spray were analyzed for different air velocities. Three-dimensional computational fluid dynamics (3-D CFD) have been employed to further explain the mutual interaction between air and spray. It was found that increasing the airflow velocity across the spray results in a significant change in the bottom part of the spray while a slight change was observed close to the nozzle exit. The variation in spray geometry, which is mainly attributed to an aerodynamic effect and to extracted droplets from the main spray by the airflow effect, was evaluated and presented for different air velocities. The spray droplet size redistribution within the spray plume was investigated, and regions with smaller and larger droplets were identified and discussed. The results indicate that the effect of airflow pattern on droplet size distribution within the spray is a considerable factor in the optimization of airflow and spray together. This could be considered in achieving a limited ignitable region without much diffusion of smaller droplets to the non burning zone during the part load operation of DISI engines.