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In this paper the behavior of the internal flow under cavitating conditions and the influence of using different fuels is studied. For this purpose, a transparent nozzle (quartz plate) with a cylindrical orifice and four different fuels are used. The nozzle is installed in a pressurized rig with fuel in order to measure the mass flow and observe the flow inside the orifice using a special visualization technique with all fuels. Since the refractive index of the vapor bubbles of the fuel is different to de refractive index of the fuel in liquid state, the cavitation inside the nozzle can be appreciated. Pressure conditions at which the first bubbles inside the orifice appear are compared with the pressure conditions for mass flow collapse, showing that the beginning of the cavitation occurs before the mass flow collapse and that it depends both on the upstream and downstream pressure conditions and on the fluid viscosity used. Additionally it is observed that the mass flow collapse takes place once the cavitation is fully developed through the whole orifice and the presence of bubbles in the spray before the mass flow collapse indicating that the cavitation appears before the mentioned collapse. HIGHLIGHTS> Visualization of cavitation phenomenon in transparent diesel injection nozzles. > Influence of using different fuels in cavitation phenomenon. > Fuels with less viscosity tend to cavitate sooner. > Incipient cavitation occurs before the mass flow collapse. > The first bubbles in the spray appear before the mass flow collapse occurs.

Elsevier Payri, R.; Salvador Rubio, FJ.; Viera Sotillo, AA. (2016). Diesel ignition delay and lift-off length through different methodologies using a multi-hole injector. Applied Energy. 162:541-550. doi:10.1016Energy. 162:541-550. doi:10. /j.apenergy.2015 Raúl Payri, F.J. Salvador, Julien Manin, Alberto Viera; Diesel ignition delay and li -o length through di erent methodologies using a multi-hole injector. Applied Energy, 2015, 162, 541-550. Diesel ignition delay and li -o length through di erent methodologies using a multi-hole injector AbstractIn this paper, li -o length has been measured via both broadband luminosity and OH chemiluminescence. In addition, ignition delay has also been measured via broadband chemiluminescence and Schlieren imaging. A 3 ori ce injector from the Engine Combustion Network (ECN) set, referred to as Spray B, and a single component fuel (n-dodecane) was used. Experiments were carried out in a constant ow and pressure facility, that allowed to reproduce engine-like thermodynamic conditions, and enabled the study to be performed over a wide range of test conditions with a very high repetition rate. Data obtained was also compared with results from a single ori ce injector also from the Engine Combustion Network, with analog ori ce characteristics (90 micrometer outlet diameter and convergent shape) and technology as the injector used . Results showed that there is good correlation between the ignition delay measured through both methodologies, that oxygen concentration and injection pressure plays a minor role in the ignition delay, being ambient temperature and density the parameters with the highest in uence. Li -o length measurements showed signi cant di erences between methodologies. Minor deviation was observed between injectors with di erent nozzle geometry (seat inclination angle), due to temperature variations along the chamber, highlighting the importance of temperature distribution along combustion vessels. Empirical correlations for li -o and ignition delay were calculated, underlining the e ect of the conditions on the parameters studied. Coe cients of the correlations were compared with results for the single ori ce injector, this showed that variations of test conditions have the same impact on ignition delay and li -o length regardless the nozzle ori ce con guration.

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This article details a method for modelling the most critical parts of an injection system. It focuses on the most important component of the system, the injector itself. As a clear example of this methodology, the modelling of a first-generation common rail injection system is carried out using a commercial code. The proposed methodology for modelling the injection system is based on two types of characterization: a detailed dimensional characterization and a hydraulic characterization of the different internal parts of the injector. The dimensional characterization is based on the use of a fine detail measuring technique applied to all the constituents of the injector. These include the passages and internal lines of the injector, internal volumes, calibrated orifices, nozzle springs, clearances between moving sections of pistons, etc. The second type of characterization makes reference mainly to the hydraulic characterization of the nozzle and injector control orifices, which together with dimensional information makes it possible to determine the discharge coe cient. In this case, special emphasis is placed on the detection of critical cavitation conditions and repercussions of this on the flow. This is a typical phenomenon in control orifices and also in nozzles subject to strong pressure gradients. Once the model is obtained, it is tested and validated. Following this, the values of the experimental injected mass and rate of injection at different operating points are compared with the model results.