Effect of cavitation on velocity in the near-field of a diesel nozzle

The entire process of atomization of the fuel in an internal combustion engine plays a very important role in determining the overall efficiency of these engines. A good atomization process could help the fuel to mix with the air properly leading to its efficient combustion, thereby reducing the emitted pollutants as well. The recent trend followed by the engineers focused on designing fuel injectors for more efficient atomization is to increase the atomization pressure while decreasing the nozzle orifice diameter. A consequence of this is the development of cavitation (formation of vapor cavities or bubbles in the liquid) inside the injector close to the nozzle. The main reason behind this is the sudden changes in the pressure inside the injector and these cavities or bubbles are usually formed where the pressure is relatively low.This work mainly focuses on studying the formation of cavitation and its effect on the velocity of the spray in the near nozzle region using asymmetrical transparent nozzle equipped with a needle lift sensor with nozzle diameter of 0.35 mm at 300 bar of injection pressure. The experiment consists in recording of several image-pairs, which are separated by about 300 ns, capturing the dynamics of the spray, a few millimeters from the nozzle in the direction of the flow. These image-pairs are then used to compute the velocity from the displacement of the liquid structures and ligaments by correlating the first image with the second. About 200 of such velocity graphs are then averaged to obtain a velocity map and is compared with the similar average velocity maps obtained at different times from the start of the injection. The angular spread of the spray from each of these images is calculated as well. The images showing cavitation inside the injector are also recorded at these same instants of time so as to understand the effects of cavitation on the velocity and angular spread of the spray close to the nozzle.Comment: 13th International Conference on Liquid Atomization and Spray Systems, Aug 2015, Tainan, Taiwan. 2015, https://iclass2015.tw

Velocity measurements in a cavitating micro-channel flow

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Experimental investigation of cavitating flow in 2D and 3D transparent diesel nozzle models

International audienceThe paper describes two experimental setup dedicated to the study of cavitation in diesel injectors. The two experimental setup are described and preliminary results are presented. The first approach consists of flow characterization in 3D and real-size transparent injector. A second approach deals with a 2D injector and is dedicated to the specific study of surface roughness effect on cavitation processes

Optical investigation of a cavitating flow in a 2D nozzle

International audienceIn heat engines (vehicle), cavitation plays an important role in fuel atomization mechanisms. The physics of cavitation as well as its impact on spray formation and injector efficiency are not well documented yet. Experimental investigations are required. The complexity of modern injectors and the extreme conditions of injection do not facilitate experimental investigations. In this paper, experiments are conducted in a simplified geometry. The model nozzle consists of a transparent 2D micro-channel supplied with a test-oil (ISO 4113). Velocity fields are obtained by means of a shadowgraph-like imaging arrangement using PIV components (double pulsed laser and double-frame camera). Pressure fields are obtained by interferometry coupled with a Schlieren technique

PIV measurements using refraction at a solid/fluid interface

Laser light sheet refraction at the fluid flow/window interface is proposed to proceed fluorescent PIV measurements, in particular for cases for which optical access limits the possibilities of illuminating a flow with a planar collimated light sheet. The study of the laser sheet propagation for the present measurement method is led with ray tracing to quantify the illumination intensity. To describe the limitations of this developed PIV version (the R-PIV), we proposed a cross-correlation model (CCM) for analysing image pairs and that is an extension of the ones used in the cases of $\mu$-PIV or P-PIV techniques. This cross-correlation model accounts for the R-PIV optical constraints as 1) in-depth and longitudinal inhomogeneities of the light sheet refraction at the location of the object plane or 2) integration in depth of the fluorescence from seeding particles. This refracted PIV (R-PIV) and the P-PIV techniques are further compared in the case of an academic pipe flow whose analytic solution is known. Our extended cross-correlation model function is finally applied, knowing the theoretical flow velocity, the flow illumination and the seeding flow parameters, to analyse some error levels in determining the real flow velocity field.Comment: 40 pages, 27 figures. This is the version of the article before peer review or editing, as submitted by an author to Measurement Science and Technology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Simultaneous high-speed internal and external flow measurements for a high-pressure diesel nozzle

We present an extensive experimental study focused on understanding the impact of cavitation in a high-pressure diesel nozzle on the macroscopic properties of fuel spray. Several high-speed videos of the liquid flow through a transparent, asymmetric cylindrical nozzle with a single orifice (phi = 0.35 mm) are recorded along with the videos of the resulting spray in the near-nozzle region, issued with an injection pressure of 300 bar at a frame-rate of 75 kHz. The high-repetition images of the internal flow are then used to estimate the onset of cavitation inside the transparent nozzle and the probability of development of cavitation in different regions of the nozzle with an average estimate of the amount of cavitation with time. On the other hand, recorded spray images are used to study spray penetration, cone-angles and velocity from the start of fuel injection. A novel approach is proposed for the measurement of perturbations that occur in form of big liquid structures along the spray boundary.Comment: in 27th European Conference on Liquid Atomization and Spray Systems, Sep 2016, Brighton, United Kingdom. 201

Caractérisation spatio-temporelle des tourbillons générés proches de la soupape d'un moteur à combustion interne

L'aérodynamique des moteurs à combustion interne est soumise à de larges fluctuations cycle à cycle qui rentrent dans le bilan des émissions polluantes. Le développement des outils de diagnostiques optiques permet désormais de mesurer et d'étudier ces fluctuations, notamment dans des géométries réelles de moteur. Dans le cadre d'une analyse de ces fluctuations dans la phase d'admission, phase durant laquelle se structure l'écoulement, nous étudions la dynamique d'un jet de soupape sur un banc d'essai stationnaire avec une différence de pression constante aux bornes du montage et une levée de soupape fixe. Des mesures de vitesses résolues temporellement ont été réalisées par PIV à une cadence de 7,5 kHz. Une analyse de type POD (Décomposition Orthogonale en Modes Propres) des champs instantanés de vorticité permet de caractériser l'évolution spatio-temporelle des tourbillons présents dans les couches de cisaillement du jet, et d'analyser certains aspects de la dynamique de l'écoulement à la soupape

Contrôle d'écoulement autour d'un corps non profilé bidimensionnel en interaction avec le sol

L'objectif de cette contribution reposant sur une étude expérimentale est d'illustrer l’implémentation du contrôle d'écoulement sur un corps non profilé bidimensionnel et son effet sur la force de traînée associée. La stratégie de contrôle consiste à associer sur cette maquette à culot droit un volet d’angle 20° et un dispositif de soufflage par jets pulsés pour une injection périodique d’air à proximité de l’arête du volet. Une attention particulière est portée à l’effet de la distance entre cette maquette et la paroi inférieure de la veine d’essais sur le gain apporté par le contrôle, tout comme à celui de la vitesse de soubassement. Le nombre de Reynolds associé à cette étude est 175000 en prenant comme dimension de référence la hauteur de la maquette. L’évaluation de l’effet du contrôle sur la traînée est effectuée de manière indirecte par la mesure de la distribution de pression pariétale au culot de la maquette. On montre que la fréquence d’actionnement est un paramètre déterminant pour l’augmentation de pression au culot. Des mesures de vitesse par vélocimétrie par images de particules à haute fréquence d’acquisition ont été complétées de mesures par anémométrie à fil chaud. En plus de l’approche statistique s’appuyant sur la décomposition de Reynolds, une analyse de l’écoulement de sillage par une description sous forme de moyennes de phase, la référence de phase étant donnée par le signal de commande de l’actionneur, est menée. La fréquence d’acquisition élevée des champs de vitesse permet enfin la détermination de corrélations spatio-temporelles dans le sillage indiquant les échelles des structures cohérentes s’y développant sous l’effet du contrôle

Arterial pressure-based cardiac output monitoring: a multicenter validation of the third-generation software in septic patients

Second-generation FloTrac software has been shown to reliably measure cardiac output (CO) in cardiac surgical patients. However, concerns have been raised regarding its accuracy in vasoplegic states. The aim of the present multicenter study was to investigate the accuracy of the third-generation software in patients with sepsis, particularly when total systemic vascular resistance (TSVR) is low.Journal ArticleMulticenter StudyValidation StudiesSCOPUS: ar.jinfo:eu-repo/semantics/publishe