Effect of Diesel injection pressures up to 450MPa on in-nozzle flow using realistic multicomponent surrogates

Investigations with 300MPa injection pressures show significant soot reduction, but the effect of such extremepressures on the in-nozzle flow has not been closely examined. The study of the in-nozzle flow is important becauseit dominates primary break-up characteristics and therefore the combustion efficiency. Moreover, the characteristicpressure drops in Diesel injectors may cause the fuel to cavitate, which leads to enhancements in the nozzleoutlet velocity, the spray cone angle and the fuel atomisation. In this work, the fuel property database is modelledusing the molecular-based PC-SAFT EoS with an eight-components surrogate based on a grade no. 2 Dieselemissions-certification fuel. The composition for the surrogate is (in mole fration): 2.7% n-hexadecane, 20.2% n-octadecane, 29.2% heptamethylnonane, 5.1% n-butylcyclohexane, 5.5% trans-decalin, 7.5% trimethylbenzene and15.4% tetralin. Then, this surrogate is utilised in simulations for a common rail 5-hole tip injector tapered nozzle.The needle is assumed to be still at a lift of 100μm, which is representative of the lift reached during pilot injection.The injector operating pressures start from 180MPa and reach 450MPa. The collector back pressure is 5MPa. Thedensity of the bulk fluid is assumed to vary according to a barotropic-like scheme, following an isentropic expansion.Results show an increase in the mass flow rate, following the square root of the pressure difference law and alsoin the outlet velocity, both as expected. Surprisingly, the cavitation is significantly reduced as the injection pressureincreases. A focused study on this particular phenomenon shows a significant decrease in the Reynolds numberin the sac, therefore the flow is found to be more stable and the pressure drop along the nozzle is smaller. Thereason for the lower Reynolds number is found on the heavy nature of Diesel fuels. While the sac average velocityincreases 15% between an injection pressure of 180MPa and 450MPa, the kinematic viscosity increases close to a70%

On the effect of realistic multicomponent diesel surrogates on cavitation and in-nozzle flow

Cavitation and cavitation-induced erosion highly depends on the thermodynamic properties of the fluid, which in turn affect the in-nozzle flow. However, many predictive models used today rely on constant properties or very simplified diesel surrogates. In this work, the diesel properties are predicted using a realistic four-component diesel surrogate, named J1D, which is compared with the traditionally used n-dodecane and then additised with n-hexane in amounts of 1% and 10%, named 1C6 and 10C6 respectively. The fuel property variation as function of pressure is modelled using the PC-SAFT EoS. The fluids are then used in simulations for a common rail 5-hole tip injector nozzle. The needle is assumed to be still at a lift of 105µm, which is representative of the lift reached during pilot injection. The injector operating pressure is 180MPa and the collector back pressure is 5MPa. The density of the bulk fluid is assumed to vary according to a barotropic-like scheme, following an isentropic expansion. Regarding the results from the simulations, the value of mass flow rate was proportional to the liquid density of the fluids. From the results, it appears that for substances with similar viscosity and density, such as J1D, 1C6 and 10C6 the vapour pressure is dominant in the cavitation production, as the greater the vapour pressure the greater the cavitation obtained. However, when the vapour pressure is comparable, such as that for J1D and n-dodecane, the difference in density and viscosity of the fluids seems to provide the cause for a greater vaporisation the lighter the fluid is. Despite its exploratory nature, this study offers some insight into the use of complex EoS and surrogate mixtures and their effect on cavitation and preferential vaporisation in diesel

Ionization fraction and the enhanced sulfur chemistry in Barnard 1

Barnard B1b has revealed as one of the most interesting globules from the chemical and dynamical point of view. It presents a rich molecular chemistry characterized by large abundances of deuterated and complex molecules. Furthermore, it hosts an extremely young Class 0 object and one candidate to First Hydrostatic Core (FHSC). Our aim was to determine the cosmic ray ionization rate and the depletion factors in this extremely young star forming region. We carried out a spectral survey towards Barnard 1b as part of the IRAM Large program ASAI using the IRAM 30-m telescope at Pico Veleta (Spain). This provided a very complete inventory of neutral and ionic C-, N- and S- bearing species with, up to our knowledge, the first secure detections of the deuterated ions DCS+ and DOCO+. We used a state-of-the-art pseudo-time-dependent gas-phase chemical model to determine the value of the cosmic ray ionization rate and the depletion factors. The observational data were well fitted with $\zeta_{H_2}$ between 3E-17 s$^{-1}$ and 1E-16 s$^{-1}$. Elemental depletions were estimated to be ~10 for C and O, ~1 for N and ~25 for S. Barnard B1b presents similar depletions of C and O than those measured in pre-stellar cores. The depletion of sulfur is higher than that of C and O but not as extreme as in cold cores. In fact, it is similar to the values found in some bipolar outflows, hot cores and photon-dominated regions. Several scenarios are discussed to account for these peculiar abundances. We propose that it is the consequence of the initial conditions (important outflows and enhanced UV fields in the surroundings) and a rapid collapse (~0.1 Myr) that permits to maintain most S- and N-bearing species in gas phase to great optical depths. The interaction of the compact outflow associated with B1b-S with the surrounding material could enhance the abundances of S-bearing molecules, as well.Comment: Paper accepted in Astronomy and Astrophysics; 28 pags, 21 figure

Effect of realistic multicomponent diesel surrogates on predicted in-nozzle flow and cavitation

In-nozzle flow dominates primary break-up characteristics and therefore the combustion efficiency. However, predictive methods of the internal nozzle flow and its link with the spray characteristics have traditionally used constant fuel properties, which may lead to large inaccuracies. Surprisingly enough, neither the effects of using realistic surrogates have been closely examined. In this work, the fuel property variation as function of pressure and temperature of three diesel surrogates are modelled using the PC-SAFT state-of-the-art EoS; these include n-dodecane and two mixtures comprising four and eight components, named V0 and V1 respectively, based on a grade no. 2 diesel emissions-certification fuel. Then, the surrogates used in simulations for a common rail 5-hole tip injector. The needle is assumed to be still at a lift of 105µm, similar to that used for pilot injections. The injector operating pressure is 180MPa and the collector back pressure is 5MPa. Heat effects are omitted and no turbulence model is used. The bulk fluid is considered to be a single phase whose density varies according to a barotropic-like scheme, following an isentropic line. Results show that the mixture surrogates V0 and V1 have a greater vapour pressure than that of n-dodecane, although they are significantly heavier both in density and viscosity. Predicted cavitation clouds occupied a ∼14% larger volume for V1 than that for n-dodecane. Slight differences were observed on mass flux, where V1 gave an increase of ∼7% with respect to n-dodecane. Interestingly, the amount of vaporised components which appear simultaneously in the two mixtures were not the same, which may show that there exists an interaction between the components during the vaporisation process. Despite its exploratory nature, this study offers some insight for the first time into the use of complex EoS and surrogate mixtures, which may be worth to capture the particular properties of diesel fuel during high pressure injections

¿Qué hay de nuevo en la Rizartrosis?

La rizartrosis en el momento actual está en periodo de avance, ya que nuevos descubrimientos biomecánicos sobre que ligamento es más importante para la estabilidad, e histológicos con el hallazgo de mecanoreceptores en los ligamentos abren un nuevo abanico de posibilidades terapéuticas con el control neuromuscular. La clasificación de Eaton y Littler sigue vigente actualmente, aunque hay nuevas propuestas como el índice radiológico para la artrosis del pulgar. El tratamiento poco ha variado, ya que la trapecectomía sigue siendo una opción válida, pero numerosas técnicas han sido desarrolladas, sin tener ningún estudio que confirme la superioridad de alguna con las demás. Últimamente, nuevas técnicas como la artroscopia, o la utilización de dispositivos tipo Tightrope®, se empiezan a utilizar, sin tener todavía estudios a largo plazo que nos indiquen si son realmente eficaces.Nowadays, osteoarthritis of the thumb is breakthrough time. Thaks to the new biomechanical findings which ligament is more important for stability, and the histological finding of tha mechanoreceptors in the ligaments, that open up a new range of therapeutic possibilities with neuromuscular control. The classification of Eaton and Littler is still currently in force, although there are new proposals as the radiological index for osteoarthritis of the thumb. Treatment has changed little, the trapeziectomy remains as an option, but many techniques have been developed without any studies that confirm the superiority of one with the other ones. Recently, new techniques such as arthroscopy, or use Tightrope® type devices are beginning to use, without yet having longterm studies that tell us whether they are really effective

Supercritical and transcritical real-fluid mixing using the PC-SAFT EOS

A numerical framework has been developed to simulate the mixing of supercritical and transcritical fluids using an equation of state based on statistical associating fluid theory. In a Diesel engine the liquid fuel is injected into supercritical air. After the injection, the Diesel is heated over its critical temperature reaching a supercritical state. Modelling real-fluid effects is critical in order to properly characterize the air/fuel mixing in the combustion chamber. By using the PC-SAFT EoS (Perturbed Chain Statistical Association Fluid Theory Equation of State) real fluids effects can be taken into account in a CFD simulation. The PC-SAFT EoS shows best results than cubic EoS computing liquid density, compressibility, speed of sound, vapor pressures and density derivatives. Unlike cubic EoS, this model accounts for the shape and size of the molecules. Gas, liquid, supercritical and vapor-liquid equilibrium states can be simulated. PT FLASH (Isothermal Multiphase Flash Calculation) is applied to compute the phase diagram used by the code. Shock tube problems were conducted in a wide range of pressures and densities using n-dodecane to show the capability of the developed algorithm. The results were compared with the solution of an exact Riemann solver which has the PC-SAFT EoS implemented showing a high degree of agreement. In addition, a two-dimensional simulation of supercritical nitrogen jet mixing was carried out to check the multidimensional capability of the code

Electronic and vibrational predissociation in Ari2 photodissociation dynamics

A quantum dynamical study of the ArI2 predissociation where both vibrational and electronic processes can take place was performed. A set of 5 coupled diatomics-in-molecules (DIM) electronic potentials was used. Both perpendicular and linear initial ArI2(X) isomers were considered. Only the a′ state had non-negligible effect on photodissociation dynamics for the linear isomer. Decay rates oscillated as a function of the vibrational excitation of I2(B) but the intramolecular vibrational energy was the main source of energy which occurred in vibrational predissociation.This work has been supported by DGICYT @Ministerio de Educacio´n y Ciencia ~MEC!, Spain# under Grant No. PB95-0071, INTAS under Grant No. 97-31573, and the Spanish–French PICASSO Project No. HF1999-0132. A.A.B. also thanks MEC for sabbatical fellowship.Peer Reviewe

Quantum Zeno-based control mechanism for molecular fragmentation

A quantum control mechanism is proposed for molecular fragmentation processes within a scenario grounded on the quantum Zeno effect. In particular, we focus on the van der Waals Ne-Br$_2$ complex, which displays two competing dissociation channels via vibrational and electronic predissociation. Accordingly, realistic three dimensional wave packet simulations are carried out by using ab initio interaction potentials recently obtained to reproduce available experimental data. Two numerical models to simulate the repeated measurements are reported and analyzed. It is found that the otherwise fast vibrational predissociation is slowed down in favor of the slow electronic (double fragmentation) predissociation, which is enhanced by several orders of magnitude. Based on these theoretical predictions, some hints to experimentalists to confirm their validity are also proposed.Comment: 4 pages, 3 figure

Vibrational effects in the quantum dynamics of the H + D_2^+ charge transfer reaction

The H + D_2^+(v=0,1 and 2) charge transfer reaction is studied using an accurate wave packet method, using recently proposed coupled diabatic potential energy surfaces. The state-to-state cross section is obtained for three different channels: non-reactive charge transfer, reactive charge transfer, and exchange reaction. The three processes proceed via the electronic transition from the first excited to the ground electronic state. The cross section for the three processes increases with the initial vibrational excitation. The non-reactive charge transfer process is the dominant channel, whose branching ratio increases with collision energy, and it compares well with experimental measurements at collision energies around 0.5 eV. For lower energies the experimental cross section is considerably higher, suggesting that it corresponds to higher vibrational excitation of D_2^+(v) reactants. Further experimental studies of this reaction and isotopic variants are needed, where conditions are controlled to obtain a better analysis of the vibrational effects of the D_2^+ reagents.Comment: 15 pages, 7 figure