An investigation of the validity of a homogeneous equilibrium model for different diesel injector nozzles and flow conditions

In the present work, a methodology for modeling flow behavior inside the fuel injector holes is applied to a number of cases with different geometries and flow conditions. After assessment of the approach results through various experimental studies looking into the flows behavior inside the diesel nozzles, two series of analyses are defined. In the first study, the effect of inlet pressure is investigated by using a series of different rail pressures in both numerical and experimental tests in a single hole industrial injector. Results show a non-cavitating flow and an approximately linear increase of the velocity, turbulence kinetic energy, and turbulence dissipation energy with the increase of pressure difference and linear increase of the mass flow rate with the square root of the pressure difference in this nozzle. The second study is related to the effect of hole geometry on injector performance. The effects of entrance edge rounding and the tube conicity factor are investigated by changing these parameters in a series of geometries from an industrial diesel nozzle. Results show that cavitation occurs in the geometries with a sharper edge and low conicity. The role of the cavitation in emerging flow properties is emphasized in the values of the injector discharge factor and the turbulence properties. The results of this work can be used in the simulation of the primary breakup of fuel spray, and this approach is useful for design and optimization of the injectors for industrial sectors

A comparison of different measurement methods of mechanical properties of Al thin films

The paper compares two different methods for testing of metallic thin films: microcompression test and nanoindentation. Microcompression test is one possibility how to perform mechanical tests on a very small scale. This method requires preparation of a small cylindrical specimen (micropillar) of micrometric size by FIB and execution of a compression test using nanoindenter device equipped with a flat diamond punch. Stressstrain curves of the thin films were obtained from such tests. Nanoindentation tests were then conducted to compare the results on the same films. Two different metal thin films - AlCuW, AlCuSi with thickness 2 mu m and grain size 3.8 mu m in average were prepared by PVD method. In this paper, we announce the results of measurements, a comparison of the results obtained by each method and identify advantages and limitations of the methods

Wheel-rail profile condition monitoring

Increased railway patronage worldwide is putting pressure on rolling stock and infrastructure to operate at higher capacity and with improved punctuality. Condition monitoring is seen as a contributing factor in enabling this and is highlighted here in the context of rolling stock being procured with high capacity data buses, multiple sensors and centralised control. This therefore leaves scope for advanced computational diagnostic concepts. The rail vehicle bogie and associated wheelsets are one of the largest and most costly areas of maintenance on rolling stock and presented here is a potential method for real time estimation of wheel-rail contact wear to move this currently scheduled based assessment to condition based assessment. This technique utilises recursive ‘grey box’ least squares system identification, used in a piecewise linear manner, to capture the strongly discontinuous nonlinear nature of the wheel-rail geometry

Laser-Excited Elastic Guided Waves Reveal the Complex Mechanics of Nanoporous Silicon

Nanoporosity in silicon leads to completely new functionalities of this mainstream semiconductor. A difficult to assess mechanics has however significantly limited its application in fields ranging from nanofluidics and biosensorics to drug delivery, energy storage and photonics. Here, we present a study on laser-excited elastic guided waves detected contactless and non-destructively in dry and liquid-infused single-crystalline porous silicon. These experiments reveal that the self-organised formation of 100 billions of parallel nanopores per square centimetre cross section results in a nearly isotropic elasticity perpendicular to the pore axes and an 80% effective stiffness reduction, altogether leading to significant deviations from the cubic anisotropy observed in bulk silicon. Our thorough assessment of the wafer-scale mechanics of nanoporous silicon provides the base for predictive applications in robust on-chip devices and evidences that recent breakthroughs in laser ultrasonics open up entirely new frontiers for in-situ, non-destructive mechanical characterisation of dry and liquid-functionalised porous materials.Comment: 12 pages, 8 figures, Supplementary information available as ancillary file, in pres

Progettazione di un sistema stampo per la sinterizzazione e l'estrazione senza attrito di una micro ruota dentata in alluminio attraverso processo FAST - Field Assisted Sintering Technology

Lo scopo di questo progetto è stato sviluppare e progettare un sistema stampo innovativo per la riduzione della forza di estrazione pezzo dopo un processo di sinterizzazione interno allo stampo (FAST). Lo stampo è stato pretensionato durante la sinterizzazione. La fase sperimentale ha previsto la produzione di micro ruote dentate in alluminio, prodotte sia con che senza pretensionamento dello stampo. Le forze di estrazione risultanti mostrano una riduzione nella configurazione pretensionat

CFD Study of Needle Motion Influence on the Spray Conditions of Single-Hole Injectors

[EN] The spray characteristics and, consequently, the success of the Diesel combustion process is strongly affected by the manner in which fuel is introduced in the combustion chamber. This work consists in studying the effect of needle motion of typical single-hole sac-type injectors on nozzle exit conditions. Three-dimensional moving mesh simulations have been carried out to calculate the injection process using cylindrical and conical nozzle geometries. The CFD analysis includes a study of the effect of cavitation on kinetic turbulent energy and velocity profiles. Results show that the flow within the nozzle and at the exit varies depending on the nozzle geometry and needle position. The model predicts clouds of cavitation that grow and exit the nozzle at low needle lifts. A kind of hysteresis in the development of the flow has also been observed between needle opening and closing. The existing correlation between turbulence and cavitation at the nozzle hole exit during the needle motion has been quantifiedThis research has been funded by the Spanish Government in the frame of the Project "Caracterizacion experimental de la cavitacion en el flujo interno e influencia sobre modelos de chorro Diesel," Reference TRA2007-68006-C02-01. S.H. and P.F. were partially supported by the Universidad Politecnica de Valencia under the program "Primeros Proyectos de investigacion," in the frame of the project "Simulacion CFD de chorros Diesel en inyeccion directa: la atomizacion primaria," Reference PAID-2759 and by the Generalitat Valenciana under Contract No. GV/2010/039.Margot, XM.; Hoyas Calvo, S.; Fajardo, P.; Patouna, S. (2011). CFD Study of Needle Motion Influence on the Spray Conditions of Single-Hole Injectors. Atomization and Sprays. 21(1):31-40. doi:10.1615/AtomizSpr.v21.i1.30S314021

Discontinuity induced bifurcations of non-hyperbolic cycles in nonsmooth systems

We analyse three codimension-two bifurcations occurring in nonsmooth systems, when a non-hyperbolic cycle (fold, flip, and Neimark-Sacker cases, both in continuous- and discrete-time) interacts with one of the discontinuity boundaries characterising the system's dynamics. Rather than aiming at a complete unfolding of the three cases, which would require specific assumptions on both the class of nonsmooth system and the geometry of the involved boundary, we concentrate on the geometric features that are common to all scenarios. We show that, at a generic intersection between the smooth and discontinuity induced bifurcation curves, a third curve generically emanates tangentially to the former. This is the discontinuity induced bifurcation curve of the secondary invariant set (the other cycle, the double-period cycle, or the torus, respectively) involved in the smooth bifurcation. The result can be explained intuitively, but its validity is proven here rigorously under very general conditions. Three examples from different fields of science and engineering are also reported

Approaches for Detailed Investigations on Transient Flow and Spray Characteristics during High Pressure Fuel Injection

High pressure injection systems have essential roles in realizing highly controllable fuel injections in internal combustion engines. The primary atomization processes in the near field of the spray, and even inside the injector, determine the subsequent spray development with a considerable impact on the combustion and pollutant formation. Therefore, the processes should be understood as much as possible; for instance, to develop mathematical and numerical models. However, the experimental difficulties are extremely high, especially near the injector nozzle or inside the nozzle, due to the very small geometrical scales, the highly concentrated optical dense spray processes and the high speed and drastic transient nature of the spray. In this study, several unique and partly recently developed techniques are applied for detailed measurements on the flow inside the nozzle and the spray development very near the nozzle. As far as possible, the same three-hole injector for high pressure diesel injection is used to utilize and compare different measurement approaches. In a comprehensive section, the approach is taken to discuss the measurement results in comparison. It is possible to combine the observations within and outside the injector and to discuss the entire spray development processes for high pressure diesel sprays. This allows one to confirm theories and to provide detailed and, in parts, even quantitative data for the validation of numerical models