3D mapping of droplet Sauter mean diameter in sprays

International Journal of Technology, 2021

Injection characteristics play an important role in the emission and overall thermal efficiency of an engine. Several methods have been proposed for analyzing different fuel injection characteristics. This study focused on the interferometric laser imaging for droplet sizing (ILIDS) technique to investigate the effects of droplet size and velocity under different conditions of waterglycerin mixtures. These effects were evaluated using intermittent spray flows in both ambient and pressurized constant volume spray chamber conditions. The initial results were compared to those reported by previous studies and used to determine the Sauter mean diameter (SMD), arithmetic mean diameter (AMD), droplet velocity, and probability density function of the spray droplet size. SMD and AMD tended to decrease as the plate temperature, injection pressure, and viscosity were increased at specific observation areas. The average velocity of the droplet increased with higher plate temperature and injection pressure at specific observation areas. The distribution of the smaller droplet increased with higher plate temperature and injection pressure. For the waterglycerin mixture, as the glycerin ratio increased, more viscous droplets were created. This was followed in higher nozzle shear force at the outlet of the fuel injector, which decreased the particle size and generated more atomized fuel sprays. This result can enable the reduction in hydrocarbon and carbon monoxide emissions from internal combustion engines.

2016

In this work, Phase Doppler Anemometry (PDA) measurements are used to test the hypothesis that the mean droplet size in Direct Injection Spark Ignition (DISI) engine fuel spray increases with distance from the injector due to the evaporation of the smaller droplets. In order to understand the role of evaporation, two velocity components and drop size PDA measurements were performed for one plume of a DISI injector using two fuels with widely differing vapour pressures. The measurements were taken along the plume centreline at four different vertical distances from the injector tip between 20 to 50 mm. on the plume centreline to evaluate the development of droplet size distributions along the plume. Measurements are also made across the plume (perpendicular to the plume centreline) at the 30 and 50 mm locations. Measurements using PDA closer to the injector are more difficult due to the high spray density (particularly apparent at 20mm or closer to the injector). A data fitting proce...

Particle & Particle Systems Characterization, 2000

An image analysis technique has been developed in order to determine the drop size distributions of sprays produced by low-velocity plain cylindrical jets. The particle sizing method is based on incoherent backlight images. Each drop is analyzed individually in the image. The two-dimensional image resulting from the projection of the three-dimensional object shape (the drop) on a screen (the video sensor surface) is modeled. The model, based on the point spread function formulation, has been developed to derive a relation between contrast and relative width of individual drops. This relation is used to extend the domain of validity of drop size in terms of size range, out of focus and image resolution. The shape parameter is determined for each drop image through morphological analysis. Spherical and non-spherical droplets are then sorted on the basis of this parameter. Non-spherical drops are regarded as non-fully atomized liquid bulks or coalesced drops. Finally, the droplet size distribution of true spherical droplets is established for a low-velocity plain cylindrical liquid jet.

2006

A spatial technique providing global size and velocity data over a two-dimensional region of a spray is often preferred for rapid optical characterization of sprays. The Generalized Scattering Imaging (GSI) approach for droplet sizing, based on both the Lorenz-Mie theory and the Finely Stratified Sphere Scattering Model can be applied to both homogenous droplets and inhomogeneous and/or absorbing droplets. A new system has been developed using the GSI approach, with the capability to measure the velocity and size of droplets with non-uniform and/or varying refractive index, even in regions of high particle number density. A windowed FFT based approach was used to identify the presence and location of a droplet oscillation pattern, and an optimized frequency-based algorithm was used to extract the droplet size. A two-frame tracking algorithm was devised to measure the velocity of droplets from the two consecutive image frames. The size range and droplet concentration limits were inve...

International Journal of Spray and Combustion Dynamics, 2010

In the present work, detailed laser-based diagnostic experiments were conducted to characterise the spray from low pressure 2-hole and 4-hole Port Fuel Injection (PFI) injectors. The main objective of the work included obtaining quantitative information of the spatio-temporal spray structure of such low-pressure gasoline sprays. A novel approach involving a combination of techniques such as Mie scattering, Granulometry, and Laser Sheet Dropsizing (LSD) was used to study the spray structure. The droplet sizes, distributions with time, Sauter Mean Diameters (SMD), droplet velocities, cone angles and spray tip penetrations of the sprays from the injectors were determined. The spray from these injectors is found to be ‘pencil like’ and not dispersed as in high pressure sprays. The application of the above mentioned techniques provides two-dimensional SMD contours of the entire spray at different instants of time, with reasonable accuracy.

Optics Express, 2018

Planar droplet sizing (PDS) is a technique relying on the assumption that laserinduced fluorescence (LIF) and Mie scattering optical signals from spherical droplets depend on their volume and surface area, respectively. In this article, we verify the validity of this assumption by experimentally analyzing the light intensity of the LIF and Mie optical signals from micrometric droplets as a function of their diameter. The size of the droplets is controlled using a new flow-focusing monodisperse droplet generator capable of producing droplets of the desired size in the range of 21 µm to 60 µm. Ethanol droplets doped with eosin dye and excited at 532 nm are considered in this study, and the individual droplets were imaged simultaneously at microscopic and macroscopic scale. The effects of laser power, dye concentration, and temperature variation are systematically studied as a function of LIF/Mie ratio in the whole range of droplet sizes. Finally, a calibration curve at tracer concentration of 0.5 vol% is deduced and used to extract the droplet Sauter mean diameter (SMD) from instantaneous images of a transient ethanol spray. This droplet size mapping is done using structured laser illumination planar imaging (SLIPI), in order to suppress the artifacts induced by multiple light scattering.

2016

3D droplet sizing and 2D optical depth measurements in sprays using SLIPI based techniques. In 18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics (pp. 01). Article 04.7_3_172 Lisbon Symposium.

The morphological composition of a typical modern Diesel spray is known to include complex structures such as ligaments and amorphous droplets, but most laser dropsizing techniques cannot diagnose drops that deviate from the spherical shape. Whilst direct imaging has potential for resolving arbitrary shapes, challenges remain to measure microscopic droplets in dense sprays. To this end, progress made with ongoing experimental investigations of the atomisation of diesel and biodiesel fuels is reported for the near-nozzle region using a long working distance microscope. The light source and imaging optics were optimised to produce blur-free shadowgraphic images of sprays with a viewing region of 593x784 µm. A number of image processing techniques were explored and described to identify both small and large liquid structures. A discrete wavelet transform was found to improve the detection of droplets smaller than 10 µm, and contrast-limited adaptive histogram equalisation provided the best detection of medium droplets and large ligaments. The measured diameters were compensated based on an analysis of the droplets’ local contrast and size. Droplet size distributions were measured for a non-additised diesel fuel and rape-methyl ester. The image processing algorithm was found to successfully discriminate between the two fuels.

Experiments in Fluids, 2005

Up to now, measurement of drop size remains difficult in dense sprays such as those encountered in Diesel applications. Commonly used diagnostics are often limited due to multi-scattering effects, high drop velocity and concentration and also nonspherical shapes. The advantage of image-based techniques on the others is its ability to describe the shape of liquid particles that are not fully atomized or relaxed. In the present study, a model is developed to correct the main drawbacks of imaging. It permits to define criteria for the correction of the apparent size of an unfocused drop and to determine a measurement volume independent of the drop size. This considerably reduces the over-estimation of large drops in the drop size distribution. Drop shapes are also characterized by four morphological parameters. The image-based granulometer is satisfactorily compared to a PDPA and a diffraction-based granulometer for measurements on an ultrasonic spray. Then, the new granulometer is applied to a diesel spray. One of the results of the analysis is that even if mean drop size distributions are stable 30 mm downstream from the nozzle outlet, the shape of the drops is still evolving towards the spherical shape. The atomization process is thus not totally established at this position in opposition to what can be deduced from the drop size distribution alone.

In this work, we report an original experimental approach for measuring the two-dimensional distribution of the droplets Sauter Mean Diameter (SMD) using the SLIPI-LIF/MIE technique. A hollow-cone spray is formed by continuously injecting water mixed with a non-toxic fluorescing dye at 20 bars injection pressure. The spray is illuminated using a continuous wave laser. The illumination wavelength (here, 447 nm) is carefully chosen to excite the injected dye/water mixture, which generates a significant Laser Induced Fluorescence (LIF) signal peaking at 514 nm. The LIF and Mie signals are simultaneously recorded using two CCD cameras and their intensity ratio is used to extract a two-dimensional distribution of the droplets SMD. In this article, we show that even for the case of a dilute hollow-cone spray, where single scattering events are in majority, the LIF/Mie measurement of droplets SMD still remains strongly affected by multiple light scattering. We demonstrate, then, that the use of SLIPI is unavoidable to obtain trustable SMD measurements based on the LIF/Mie ratio, even for optically dilute sprays.