Elsevier Payri, R.; Gimeno, J.; Viera, JP.; Plazas Torres, AH. (2013). Needle lift profile influence on the vapor phase penetration for a prototype diesel direct acting piezoelectric injector. Fuel. 113:257-265. doi:10.1016Fuel. 113:257-265. doi:10. /j.fuel.2013 and not injection pressure. Ambient temperature alone seems not to have and important effect on vapor penetration. Finally, the effects of the needle lift profile in the instant injection rate and vapor penetration are presented, confirming the strong relation between these three parameters, and confirming also that the needle lift plays a determinant role in the spray development, especially at the early stages of the injection process. Both boot and ramp shaped injections proved the ability to strongly influence the vapor penetration rate. In comparison to the square shaped injection, the effect of the ramp shaped injection delays the vapor penetration right from the start of injection while the effect of the boot shaped injection takes considerably longer to become noticeable. From the results, the needle lift control feature has proven to be a very versatile tool for engine designers to control the injection process as desired, opening a new path with a plenty of room for improvement.

h i g h l i g h t sTwo single hole nozzle (cylindrical and convergent) are used. A complete hydraulic characterization is done along with spray visualization. A fast pulsed light source is synchronized to a fast camera working at 160 kHz. The effect of nozzle geometry is analyzed for three different fuels. A large set of experimental data was obtained, which could be used for model validation. a b s t r a c tThe influence of internal nozzle flow characteristics over macroscopic spray development is studied experimentally for two different nozzle geometries and three fuels. The measurements include a complete hydraulic characterization consisting of instantaneous injection rate and spray momentum flux measurements, followed by a high-speed visualization of isothermal liquid spray in combination with cylindrical and conical nozzle configurations. Two of the fuels are pure components-n-heptane and ndodecane-while the third fuel consists of a three-component surrogate to better represent the physical and chemical properties of diesel fuel. The cylindrical nozzle with 8.6% larger diameter, in spite of higher mass flow rate and momentum flux, shows slower spray tip penetration when compared to the conical nozzle. The spreading angle is found to be inversely proportional to the spray tip penetration. The spreading angle is largely influenced by the nozzle geometry and the ambient density. Rail pressure was found to have weak influence on the near-field spreading angle and no influence on the standard deviation of the spreading angle. n-Heptane spray shows slowest penetration rates while n-dodecane and the surrogate fuel mixture show very similar spray behavior for variations in injection pressure and back pressure. However, the surrogate fuel mixture shows higher penetration than n-dodecane when using the conical nozzle and lower penetration than n-dodecane when using cylindrical nozzle.

Elsevier Payri, R.; Viera Sotillo, JP.; Pei, Y.; Som, S. (2015). Experimental and numerical study of liftoff length and ignition delay of a two-component diesel surrogate. AbstractUnderstanding and controlling mixing and combustion processes is fundamental for the ever more demanding pollutant regulations and fuel consumption standards of direct injection diesel engines. The fundamentals of these processes haven been long studied from both experimental and numerical perspectives. As numerical models become more advanced, the need for adequate experimental data increases. Hence, experimental methodologies and scientific databases need to be enhanced with more quantitative, accurate, consistent, and reliable information in order to evaluate the models in a robust fashion. The present study seeks to enhance the current state-of-the-art by further evaluating the combustion performance of a two-

Measurements of droplet size in optically-thick, non-evaporating, shear-driven sprays have been made using ultra-small angle x-ray scattering (USAXS). The sprays are produced by orifice-type nozzles coupled to diesel injectors, with measurements conducted from 1-24 mm from the orifice, spanning from the optically-dense near-nozzle region to more dilute regions where optical diagnostics are feasible. The influence of nozzle diameter, liquid injection pressure, and ambient density were examined. The USAXS measurements reveal few if any nanoscale droplets, in conflict with a popular computational model of diesel spray breakup. The average droplet diameter rapidly decreases with downstream distance from the nozzle until a plateau value is reached, after which only small changes are seen in droplet diameter. This plateau droplet size is consistent with the droplets being small enough to be stable with respect to further breakup. Liquid injection pressure and nozzle diameter have the biggest impact on droplet size, while ambient density has a smaller effect.

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Understanding and controlling mixing and combustion processes is fundamental in order to face the challenges set by the ever more demanding pollutant regulations and fuel consumption standards of direct injection diesel engines. The fundamentals of these processes haven been long studied by the diesel spray community from both experimental and numerical perspectives. However, certain topics, such as the influence of nozzle geometry over the spray atomization, mixing, and combustion process, are still not completely well understood and predicted by numerical models. The present study seeks to contribute to the current understanding of this subject, by performing state of the art optical diagnostics to liquid sprays injected through two singe-hole nozzles of different conicity. The experiments were carried out in a nitrogen-filled constantpressure-flow facility. Back pressures were set to produce the desired engine-like density conditions in the chamber, at room temperature. The experimental setup consists in a diffused back-illumination setup with a fast pulsed LED light source and a high-speed camera. The diagnostics focused on detecting the liquid spray contour and evaluating the influence of nozzle geometry over the time-resolved and quasi-steady response of the spray dispersion, at similar injection conditions. Results show a clear influence of nozzle geometry on spray contour fluctuations, where the cylindrical nozzle seems to produce larger dispersion in both time-resolved fluctuations and quasi-steady values, when compared to the conical nozzle. This evidences that the turbulence and radial velocity profiles originated at the cylindrical nozzle geometry are able to affect not only the microscopic scales inside the nozzle, but also macroscopic scales, such as the steady spray. Observations from this study indicate that the effects of the flow characteristics within the nozzle are carried on to the first millimeters of the spray, in which the rest of the spray formation downstream is pre-defined.

the instantaneous ROI and to provide experimental data with parametric variations useful for numerical model validations. Results show a strong relationship between the steady partial needle lift and the ROI. The effect is non-linear, and also strongly dependent on the injection pressure. The steady lift value at which the needle ceases to influence the ROI increases with the injection pressure. Finally, a transient analysis is presented, showing that the needle velocity may considerably affect the instantaneous ROI, because of the volume displaced inside the nozzle. Results presented in this study show that at constant injection pressure and energizing time, this injector has the potential to control many aspects of the ROI and thus, the heat release rate. Also, data presented are useful for numerical model validations, which would provide detailed insight into the physical processes that drive these observations, and potentially, to the effects of these features on combustion performance.

Making quantitative measurements of the vapor distribution in a cavitating nozzle is difficult, owing to the strong scattering of visible light at gas-liquid boundaries and wall boundaries, and the small length and time scales involved. The transparent models required for optical experiments are also limited in terms of maximum pressure and operating life. Over the past few years, xray radiography experiments at Argonne's Advanced Photon Source have demonstrated the ability to perform quantitative measurements of the line of sight projected vapor fraction in submerged, cavitating plastic nozzles. In this paper, we present the results of new radiography experiments performed on a submerged beryllium nozzle 520 microns in diameter, with a length/diameter ratio of 6. Beryllium is a light, hard metal that is very transparent to x-rays due to its low atomic number. We present quantitative measurements of cavitation vapor distribution conducted over a range of non-dimensional cavitation and Reynolds numbers, up to values typical of gasoline and diesel fuel injectors. A novel aspect of this work is the ability to quantitatively measure the area contraction along the nozzle with high spatial resolution. Analysis of the vapor distribution, area contraction and discharge coefficients are made between the beryllium nozzle, and plastic nozzles of the same nominal geometry. When gas is dissolved in the fuel, the vapor distribution can be quite different from that found in plastic nozzles of the same dimensions, although the discharge coefficients are unaffected. In the beryllium nozzle, there were substantially fewer machining defects to act as nucleation sites for the precipitation of bubbles from dissolved gases in the fuel, and as such its effect on the vapor distribution was greatly reduced.