Droplet size and morphology characterization for diesel sprays under atmospheric operating conditions

The shape of microscopic fuel droplets may differ from the perfect sphere, affecting their external surface area and thus the heat transfer with the surrounding gas. Hence there is a need for the characterization of droplet shapes, and the estimation of external surface area, in order to enable the development of physically accurate mathematical models for the heating and evaporation of diesel fuel sprays. We present ongoing work to automat-ically identify and reconstruct the morphology of fuel droplets, primarily focusing in this study on irregularly-shaped, partially-deformed and oscillating droplets under atmospheric conditions. We used direct imaging tech-niques based on long-working distance microscopy and ultra-high-speed video to conduct a detailed temporal investigation of droplet morphology. We applied purpose-built algorithms to extract droplet size, velocity, vol-ume and external surface area from the microscopic ultra-high-speed video frames. High resolution images of oscillating droplets and a formation of a droplet form ligament, sphericity factors, volume as well as external surface area are presented for 500 bar injection pressure in the near nozzle region (up to 0.7 mm from nozzle exit) under atmospheric conditions. We observed a range of different liquid structures, including perfectly spher-ical, non-spherical droplets and stretched ligaments. We found that large droplets and ligaments exceeding the size of the nozzle hole could be found at the end of injection. In order to estimate droplet volume and external surface area from two-dimensional droplet information, a discrete revolution of the droplet silhouette about its major centroidal axis was used. Special attention was paid to the estimation of actual errors in the prediction of volume and surface characteristics from a droplet silhouette. In addition to the estimation of droplet volume and external surface area, the actual shape reconstruction in 3D coordinates from a droplet silhouette was performed in order to enable future numerical modelling studies of real droplets

Comprehensive Organic Analysis of Antartic Micrometeorites

Introduction: Micrometeorites (MMs) are thought to be significant contributors of organic material to the early Earth [1], and a variety of techniques have been employed to identify their organic composition [2-6]. These include the identification of key organic groups using combinations of infrared, energy dispersive Xray, electron energy loss and Raman spectroscopy and scanning transmission X-ray microscopy [2-4], highlighting similarities between that of MMs and carbonaceous chondrites. Few studies, however, have focused on the characterisation of individual micrometeoritic organic components. Microscopic L2MS has been used to identify up to C5 polycyclic aromatic hydrocarbons and their alkyl derivatives [5]. A combination of ionexchange chromatography and fluorimetric detection has also been successful in identifying a number of protein amino acids including glycine and alanine [6]. We have previously reported a method to analyse ?g-sized quantities of extraterrestrial materials, with prior application to assessing organic volatile release from MM atmospheric entry heating simulations [7]. In this study we utilise this technique to characterise the organic composition of Antarctic terrestrial particles and MMs collected in 1994 from Cap-Prudhomme [8]

Collisionless heating in capacitive discharges enhanced by dual-frequency excitation

We discuss collisionless electron heating in capacitive discharges excited by a combination of two disparate frequencies. By developing an analytical model, we find, contrary to expectation, that the net heating in this case is much larger than the sum of the effects occurring when the two frequencies act separately. This prediction is substantiated by kinetic simulations, which are also in excellent general quantitative agreement with the model for discharge parameters that are typical of recent experiments

Augmented Sustainability Measures for Scotland

We estimate and compare two empirical measures of the weak sustainability of an economy for the first time: the change in augmented green net national product (GNNP), and the interest on augmented genuine savings (GS). Yearly calculations are given for each measure for Scotland during 1992-99. Augmentation means including, using projections to 2020, changed production possibilities enabled by exogenous technical progress or changing oil prices. The change in augmented GNNP and interest on augmented GS are both always positive, showing no sustainability problem for Scotland then, according to the assumptions underlying our weak sustainability calculations. However, the former greatly exceeds the latter, a mismatch which poses an unresolved problem with the theory. Resolving it may require respecifying the utility functions used in mainstream growth theory.sustainability, Scotland, genuine savings, green NNP, augmentation

The effect of operating conditions on post-injection fuel discharge in an optical engine

After the end of injection, the needle closes and residual fuel present inside the injector sac and orifices is discharged due to the high fluid inertia. This so-called post-injection fuel discharge can present several problems. The excess fuel can undergo incomplete combustion due to its large, slow moving and often surface-bound nature. Not only does this have a negative effect on emissions and performance, but it has been speculated that the by-products of incomplete combustion are implicated in the growth of carbonaceous deposits on the tips of fuel injectors. Accumulation of these deposits is known to lead to premature fuel injector failure that can lead to re-ductions in power output and engine lifetime. Seeing as modern multiple-injection strategies give rise to an in-creased number of transient injection phases, post-injection discharges are an increasingly common occurrence during normal operating conditions. In order to develop a phenomenological model for the fluid dynamics after the end of injection, there is a need to characterise the causes of this discharge and how they might be influenced by engine operating conditions. In this study we present ongoing analysis into results from the first visualisation of post injection fuel discharge at the microscopic level under engine-like operating conditions. We observed the process of fuel discharge for multi-hole injectors, using a high-speed camera fitted with a long-distance micro-scope and a high-speed laser illumination source. We related the effect of a variety of operating conditions on the severity of this process, including injection pressure and in-cylinder pressure along with a characterisation of the dynamics of the various modes by which these undesired liquid structures are produced. We present the different modes by which this process occurs and we conclude that the extent of post-injection discharge depends on both the in-cylinder and injection pressures

Reddenings of FGK supergiants and classical Cepheids from spectroscopic data

Accurate and homogeneous atmospheric parameters (Teff, log (g), Vt, [Fe/H]) are derived for 74 FGK non-variable supergiants from high-resolution, high signal-to-noise ratio, echelle spectra. Extremely high precision for the inferred effective temperatures (10-40 K) is achieved by using the line-depth ratio method. The new data are combined with atmospheric values for 164 classical Cepheids, observed at 675 different pulsation phases, taken from our previously published studies. The derived values are correlated with unreddened B-V colours compiled from the literature for the investigated stars in order to obtain an empirical relationship of the form: (B-V)o = 57.984 - 10.3587(log Teff)^2 + 1.67572(log Teff)^3 - 3.356(log (g)) + 0.0321(Vt) + 0.2615[Fe/H] + 0.8833((log (g))(log Teff)). The expression is used to estimate colour excesses E(B-V) for individual supergiants and classical Cepheids, with a precision of +-0.05 mag. for supergiants and Cepheids with n=1-2 spectra, reaching +-0.025 mag. for Cepheids with n>2 spectra, matching uncertainties for the most sophisticated photometric techniques. The reddening scale is also a close match to the system of space reddenings for Cepheids. The application range is for spectral types F0--K0 and luminosity classes I and II.Comment: accepted for publication (MNRAS

Augmented Sustainability Measures for Scotland

We estimate and compare two empirical measures of the weak sustainability of an economy for the first time: the change in augmented green net national product (GNNP), and the interest on augmented genuine savings (GS). Yearly calculations are given for each measure for Scotland during 1992-99. Augmentation means including, using projections to 2020, production possibilities enabled by exogenous technical progress or changing terms of trade. In passing, we clarify the treatment of environmental expenditures in green accounting. The change in augmented GNNP and interest on augmented GS are both always positive, showing no sustainability problem for Scotland; but the former greatly exceeds the latter, showing an unresolved problem with the theorysustainability, Scotland, genuine savings, green NNP, augmentation