Dynamics of Post-Injection Fuel Flow in Mini-Sac Diesel Injectors Part 1: Admission of 1 External Gases and Implications for Deposit Formation

Samples of unadditized, middle distillate diesel fuel were injected through real-size optically accessible mini-sac diesel injectors into ambient air at common rail pressures of 250 bar and 350 bar respectively. High-resolution images of white light scattered from the internal mini-sac and nozzle flow were captured on a high-speed monochrome video camera. Following the end of each injection, the momentum-driven evacuation of fuel liquid from the mini-sac and nozzle holes resulted in the formation of a vapour cloud and bubbles in the mini-sac, and vapour capsules in the nozzle holes. This permitted external gas to gain entrance to the nozzle holes. The diesel fuel in the mini-sac was observed to rotate with large initial vorticity, which decayed until the fuel became stationary. The diesel fuel remaining in the nozzle holes was observed to move inwards towards the mini-sac or outwards towards the nozzle exit in concert with the rotational flow in the mini-sac. The mini-sac bubbles’ internal pressure differences revealed that the bubbles must have contained previously dissolved oxygen and nitrogen. Under diesel engine operating conditions, this multi-phase mixture would be highly reactive and could initiate local pyrolysis and/or oxidation reactions. Finally, the dynamical behaviour of the diesel fuel in the nozzle holes would support the admission of external hot combustion gases into the nozzle holes, establishing the conditions for oxidation/pyrolysis reactions with surrounding liquid fuel films

An experimental investigation into the effect of hydrodynamic cavitation on diesel

Samples of commercial diesel were subjected to forty hours of intense cavitation flow across a diesel injector in a specially designed high-pressure recirculation flow rig. Changes to the optical absorption and scattering properties of the diesel over time were identified by the continuous measurement of spectral extinction coefficients at 405 nm by means of a simple optical arrangement. Identical diesel samples were maintained at 70 oC for forty hours in a heated water bath, in order to distinguish the effects of hydrodynamic cavitation and temperature on the cavitated diesel samples. The commercial diesel samples subjected to high pressure cavitation flow and water bath heating revealed a response to the flow and temperature history that was identified by an increase in the optical extinction coefficients of the cavitated and heated samples. The contribution of cavitation flow and temperature to the variation in spectral extinction coefficient was identified. It was concluded that the increases observed in the spectral extinction coefficients of the cavitated commercial diesels were caused by the cavitation affecting the aromatics in the commercial diesel samples

Chemical Association via Exact Thermodynamic Formulations

It can be fruitful to view two-component physical systems of attractive monomers, A and B, ``chemically'' in terms of a reaction A + B C, where C = AB is an associated pair or complex. We show how to construct free energies in the three-component or chemical picture which, under mass-action equilibration, exactly reproduce any given two-component or ``physical'' thermodynamics. Order-by-order matching conditions and closed-form chemical representations reveal the freedom available to modify the A-C, B-C, and C-C interactions and to adjust the association constant. The theory (in the simpler one-component, i.e., A = B, case) is illustrated by treating a van der Waals fluid.Comment: 15 double-spaced pages (RevTeX), including 1 eps figur

An Optical Characterization of Atomization in Non-Evaporating Diesel Sprays

High-speed planar laser Mie scattering and Laser Induced Fluorescence (PLIF) was employed for the determination of Sauter Mean Diameter (SMD) distribution in non-evaporating diesel sprays. The effect of rail pressure, distillation profile, and consequent fuel viscosity on the drop size distribution developing during primary and secondary atomization was investigated. Samples of conventional crude-oil derived middle-distillate diesel and light distillate kerosene were delivered into an optically accessible mini-sac injector, using a customized high-pressure common rail diesel fuel injection system. Two optical channels were employed to capture images of elastic Mie and inelastic LIF scattering simultaneously on a high-speed video camera at 10 kHz. Results are presented for sprays obtained at maximum needle lift during the injection. These reveal that the emergent sprays exhibit axial asymmetry and vorticity. An increase in the rail pressure was observed to lead to finer atomization, with larger droplets observable in the neighbourhood of the central axis of the spray, decreasing with radius towards the spray boundaries. Finally, the light kerosene was observed to produce smaller droplets (as measured by Sauter mean diameter), relative to the conventional diesel, suggesting a correlation between distillation profile and viscosity, and mean spray droplet size

OH 1720 MHz Masers in Supernova Remnants --- C-Shock Indicators

Recent observations show that the OH 1720 MHz maser is a powerful probe of the shocked region where a supernova remnant strikes a molecular cloud. We perform a thorough study of the pumping of this maser and find tight constraints on the physical conditions needed for its production. The presence of the maser implies moderate temperatures (50 -- 125 K) and densities ($\sim 10^5 cm^{-3}$), and OH column densities of order $10^{16} cm^{-2}$. We show that these conditions can exist only if the shocks are of C-type. J-shocks fail by such a wide margin that the presence of this maser could become the most powerful indicator of C-shocks. These conditions also mean that the 1720 MHz maser will be inherently weak compared to the other ground state OH masers. All the model predictions are in good agreement with the observations.Comment: 16 pages, 5 Postscript figures (included), uses aaspp4.sty. To appear in the Astrophysical Journa

Why Do European Venture Capital Companies Syndicate?

Financial theory, resource-based theory and access to deal flow are used to explain syndication practices among European venture capital (VC) firms. The desire to share risk and increase portfolio diversification is a more important motive for syndication than the desire to access additional intangible resources or deal flow. Access to resources is, however, more important for non-lead than for lead investors. When resource-based motives are more important, the propensity to syndicate increases. Syndication intensity is higher for young VC firms and for VC firms, specialised in a specific investment stage. Finally, syndication strategies are similar across European countries, but differ from North American strategies

Analyzing Forensic Evidence Based on Density with Magnetic Levitation

This paper describes a method for determining the density of contact trace objects with magnetic levitation (MagLev). MagLev measurements accurately determine the density (±0.0002 g/cm3) of a diamagnetic object and are compatible with objects that are nonuniform in shape and size. The MagLev device (composed of two permanent magnets with like poles facing) and the method described provide a means of accurately determining the density of trace objects. This method is inexpensive, rapid, and verifiable and provides numerical values—independent of the specific apparatus or analyst—that correspond to the absolute density of the sample that may be entered into a searchable database. We discuss the feasibility of MagLev as a possible means of characterizing forensic-related evidence and demonstrate the ability of MagLev to (i) determine the density of samples of glitter and gunpowder, (ii) separate glitter particles of different densities, and (iii) determine the density of a glitter sample that was removed from a complex sample matrix.Chemistry and Chemical Biolog

The effect of cavitation on atomization in non-evaporating diesel sprays

The determination of the distribution of the local liquid volume fraction (LVF) in non-evaporating diesel sprays was achieved using Laser Induced Fluorescence (LIF). The LVF distribution developing during the primary and secondary atomisation was investigated as a function of rail pressure, physical properties and needle lift. Samples of conventional diesel and light kerosene were injected through an optically accessible mini-sac type injector, employing a custom diesel fuel injection system. The optical arrangement facilitated the acquisition of images with an image resolution of 28μm/pixel using a high speed camera operating at 10 kHz. The analysis is focused on images obtained at different injection stages (1.8ms, 3.7ms, 5.6ms after start of injection (SoI)). The results revealed that the diesel spray developed an asymmetric structure, especially at the intermediate and later stages of the injection. The LVF decreases with increasing axial distance and the primary atomisation occurs immediately after the spray enters the surrounding gas. Lastly, the findings of the phenomenological analysis suggests that conventional diesel shows a later primary and secondary atomisation than light kerosene, due to their difference in the physical properties

The characterisation of diesel nozzle flow using high speed imaging of elastic light scattering

Two identical, conventional six-hole, valve-covered orifice (VCO) diesel injectors have been modified in order to provide optical access to the region below the needle, and the nozzle-flow passages. This has been achieved through the removal of the metal tips, and their replacement with transparent acrylic tips of identical geometry. These two identical injectors were employed in order to offer comparability between the measurements. One of them had a dark, anodised inner surface at the base, while the other had a silvered inner surface at the base. Elastic scattering of incident white light from the internal cavitating flow inside the nozzle holes of the optically accessible diesel injector tips was captured on a high-speed electronic camera. The optical image data was obtained for three injector rail pressures ranging from 200 bar to 400 bar, and for five diesel fuels of varying density, viscosity, and distillation profile, in order to identify variations in cavitation flow behaviour inside the nozzle hole passages. A set of mean time-resolved diesel fuel flow images were obtained from 30 successive fuel injection pulses, for each operating condition, for each injector. The mean cavitation image occurring in the nozzle holes was converted to the mean proportion of nozzle hole area producing cavitation-induced optical scattering. The mean normalised area images were then analysed, and were able to demonstrate the anticipated inverse relationship between injected fuel mass and cavitation volume fraction (indicated by mean normalised area), and the effect of fuel viscosity and distillation profile on cavitation volume fraction (again indicated by mean normalised area)

Thermoelastic Damping in Micro- and Nano-Mechanical Systems

The importance of thermoelastic damping as a fundamental dissipation mechanism for small-scale mechanical resonators is evaluated in light of recent efforts to design high-Q micrometer- and nanometer-scale electro-mechanical systems (MEMS and NEMS). The equations of linear thermoelasticity are used to give a simple derivation for thermoelastic damping of small flexural vibrations in thin beams. It is shown that Zener's well-known approximation by a Lorentzian with a single thermal relaxation time slightly deviates from the exact expression.Comment: 10 pages. Submitted to Phys. Rev.