Discrete multicomponent model for biodiesel spray combustion simulation

An important first step in spray combustion simulation is an accurate determination of the fuel properties which affects the modelling of spray formation and reaction. In a practical combustion simulation, the implementation of a multicomponent model is important in capturing the relative volatility of different fuel components. A Discrete Multicomponent (DM) model is deemed to be an appropriate candidate to model a composite fuel like biodiesel which consists of four components of fatty acid methyl esters (FAME). In this paper, the DM model is compared with the traditional Continuous Thermodynamics (CTM) model for both diesel and biodiesel. The CTM model is formulated based on mixing rules that incorporate the physical and thermophysical properties of pure components into a single continuous surrogate for the composite fuel. The models are implemented within the open-source CFD code OpenFOAM, and a semi-quantitative comparison is made between the predicted spray-combustion characteristics and optical measurements of a swirl-stabilised flame of diesel and biodiesel. The DM model performs better than the CTM model in predicting a higher magnitude of heat release rate in the top flame brush region of the biodiesel flame compared to that of the diesel flame. Using both the DM and CTM models, the simulation successfully reproduces the droplet size, volume flux, and droplet density profiles of diesel and biodiesel. The DM model predicts a longer spray penetration length for biodiesel compared to that of diesel, as seen in the experimental data. Also, the DM model reproduces a segregated biodiesel fuel vapour field and spray in which the most abundant FAME component has the longest vapour penetration. In the biodiesel flame, the relative abundance of each fuel component is found to dominate over the relative volatility in terms of the vapour species distribution and vice versa in the liquid species distribution. © 2014 Elsevier Ltd. All rights reserved.

Application of fast oxygen sensors for investigations into air-path dynamics and EGR distribution in a diesel engine

The control of NOX emissions by exhaust gas recirculation (EGR) is of widespread application. However, despite dramatic improvements in all aspects of engine control, the subtle mixing processes that determine the cylinder-to-cylinder distribution of the recirculated gas often results in a mal-distribution that is still an issue for the engine designer and calibrator. In this paper we demonstrate the application of a relatively straightforward technique for the measurement of the absolute and relative dilution quantity in both steady state and transient operation. This was achieved by the use of oxygen sensors based on standard UEGO (universal exhaust gas oxygen) sensors but packaged so as to give good frequency response (∼ 10 ms time constant) and be completely insensitivity to the sample pressure and temperature. Measurements can be made at almost any location of interest, for example exhaust and inlet manifolds as well as EGR path(s), with virtually no flow disturbance. At the same time, the measurements yield insights into air-path dynamics. We argue that "dilution", as indicated by the deviation of the oxygen concentration from that of air, is a more appropriate parameter than EGR rate in the context of NOX control, especially for diesel engines. Experimental results are presented for the EGR distribution in a current production light duty 4-cylinder diesel engine in which significant differences were found in the proportion of the recirculated gas that reached each cylinder. Even the individual inlet runners of the cylinders exhibited very different dilution rates - differences of nearly 50% were observed at some conditions. An application of such data may be in the improvement of calibration and validation of CFD and other modelling techniques. Copyright © 2014 SAE International.

Influence of turbulence-chemistry interaction for n-heptane spray combustion under diesel engine conditions with emphasis on soot formation and oxidation

The influence of the turbulence-chemistry interaction (TCI) for n-heptane sprays under diesel engine conditions has been investigated by means of computational fluid dynamics (CFD) simulations. The conditional moment closure approach, which has been previously validated thoroughly for such flows, and the homogeneous reactor (i.e. no turbulent combustion model) approach have been compared, in view of the recent resurgence of the latter approaches for diesel engine CFD. Experimental data available from a constant-volume combustion chamber have been used for model validation purposes for a broad range of conditions including variations in ambient oxygen (8-21% by vol.), ambient temperature (900 and 1000 K) and ambient density (14.8 and 30 kg/m3). The results from both numerical approaches have been compared to the experimental values of ignition delay (ID), flame lift-off length (LOL), and soot volume fraction distributions. TCI was found to have a weak influence on ignition delay for the conditions simulated, attributed to the low values of the scalar dissipation relative to the critical value above which auto-ignition does not occur. In contrast, the flame LOL was considerably affected, in particular at low oxygen concentrations. Quasi-steady soot formation was similar; however, pronounced differences in soot oxidation behaviour are reported. The differences were further emphasised for a case with short injection duration: in such conditions, TCI was found to play a major role concerning the soot oxidation behaviour because of the importance of soot-oxidiser structure in mixture fraction space. Neglecting TCI leads to a strong over-estimation of soot oxidation after the end of injection. The results suggest that for some engines, and for some phenomena, the neglect of turbulent fluctuations may lead to predictions of acceptable engineering accuracy, but that a proper turbulent combustion model is needed for more reliable results. © 2014 Taylor & Francis.

Temperature measurements of the bluff body surface of a Swirl Burner using phosphor thermometry

Flames are often stabilised on bluff-bodies, yet their surface temperatures are rarely measured. This paper presents temperature measurements for the bluff body surface of the Cambridge/Sandia Stratified Swirl Burner. The flame is stabilized by a bluff body, designed to provide a series of turbulent premixed and stratified methane/air flames with a variable degree of swirl and stratification. Recently, modellers have raised concerns about the role of surface temperature on the resulting gas temperatures and the overall heat loss of the burner. Laser-induced phosphorescence is used to measure surface temperatures, with Mg4GeO6F:Mn as the excitation phosphor, creating a spatially resolved temperature map. Results show that the temperature of the bluff body is in the range 550-900 K for different operating conditions. The temperature distribution is strongly correlated with the degree of swirl and local equivalence ratio, reflecting the temperature distribution obtained in the gas phase. The overall heat loss represents only a small fraction (<0.5%) of the total heat load, yet the local surface temperature may affect the local heat transfer and gas temperatures. © 2014 The Combustion Institute.

Tentative analysis of Swirl defects in silicon crystals

Swirl defects in dislocation-free Czochralski (CZ) silicon crystals have been investigated by preferential etching, transmission electron microscopy (TER I) and electron energy loss spectroscopy (EELS) mode of a scanning transmission electron microscope (STEM). Two kinds of Swirl defects have been found with a good correspondence between striated pattern consisting of hillocks and the buried micro-defects. The Swirl defects were identified as perfect dislocation loop cluster and tetrahedral precipitate, respectively. In addition, a kind of tiny micro-defects is found to be distributed preferentially in the vicinity of the Swirl pattern although there is no detectable correspondence between hillocks and the micro-defects. The energy-filtered images have been obtained by the plasma peaks at different parts of a coherent precipitate with the Si matrix. The experimental results show some indications of the existence of oxygen and carbon in the core of the precipitate and suggest that oxygen and carbon may play important roles in the formation of Swirl defect. (C) 2000 Elsevier Science B.V. All rights reserved.

Determination of sulfur-containing compounds in diesel oils by comprehensive two-dimensional gas chromatography with a sulfur chemiluminescence detector

This article reports an analytical method for separating, identifying and quantitating sulfur-containing compounds and their groups in diesel oils (170-400degreesC) using comprehensive two-dimensional gas chromatography coupled with a sulfur chemiluminescence detector. The identification of target compounds and their groups was based on standard substances, the group separation feature and the-effect of comprehensive two-dimensional gas chromatography. The quantitative analysis on major sulfur compounds and total sulfur was carried out based on the linear response of sulfur chemiluminescence detector and the internal standards method. The results of total sulfur determination in the samples were compared with those from ASTM D 4294 standard method, the R.S.D. percentage were <6.02%, correctness of this method can meet the industrial requirement. To the end, the method developed was used to investigate the sulfur-containing compounds in different diesel oils, the result shows that the distribution of sulfur-containing compounds in diesel oils from different process units are apparently different. The sulfur compounds in fluid catalytic cracking (FCC), residuum fluid catalytic cracking (RFCC) diesel oils mainly exist in the form of alkyl-substituted dibenzothiophenes that add up to about 40-50% of the total sulfur, while this number is only 6-8 and 20-28% in visbreaking (VB) and delayed-coking (DC) diesel oils, respectively. (C) 2003 Elsevier B.V. All rights reserved.

Considerações sobre biodiesel como biocombustível alternativo ao diesel.

Biodiesel é definido como o produto da reação de gordura animal ou vegetal com álcool (ou transesterificação). Tecnicamente podemos dizer que dos triglicerídeos presentes nessas matérias graxas (óleos vegetais ou animais), ésteres monoalquílicos (como os ésteres de etila e de metila) são produzidos pela reação com um álcool primário (etanol ou metanol) em meio preferencialmente alcalino. Esses ésteres também podem ser obtidos a partir de ácidos graxos livres, mas, nesse caso, a reação é de esterificação, e sua condução deve ser em meio preferencialmente ácido. As principais matérias-primas para a produção nacional do biodiesel são: soja, milho, girassol, amendoim, algodão, canola, mamona, babaçu, palma (dendê) e macaúba, entre outras oleaginosas existentes no país. O combustível também pode ser obtido a partir de óleos residuais e de gorduras animais. Além de ser uma tecnologia limpa, o emprego do biodiesel no óleo diesel de petróleo polui menos o meio ambiente, pode reduzir a dependência brasileira das importações de petróleo e trazer vantagens econômicas, pois sua produção e o cultivo das matérias-primas podem criar milhares de novos empregos, inclusive na agricultura familiar, principalmente nas regiões mais pobres do Brasil.

Dinamica populacional do bicho-mineiro (Perileucoptera coffeella) em cafeeiro no Distrito Federal.

Este trabalho foi conduzido em Planaltina-DF, para verificar a flutuacao populacional do bicho-mineiro (Perileucoptera coffeella) no cafe variedade "Mundo Novo". As avaliacoes foram realizadas quinzenalmente, coletando-se, ao acaso, folhas de cafe do terco inferior, medio e superior. esse material, apos coletado, foi encaminhado ao laboratorio, onde se faziam as avaliacoes de: numero de lesoes por folha, lagartas vivas, mortas e percentual de infestacao. Os resultados obtidos permitem concluir que a parte alta da planta e a mais preferida para a oviposicao do bicho-mineiro; e a maior infestacao, ocorre nos meses de junho a outubro, coincidindo com o periodo de menor precipitacao pluviometrica, epoca em que se deve concentrar o controle de praga.

Dinamica populacional do percevejo-de-renda (Vatiga iludens) na cultura da mandioca no Distrito Federal.

Este trabalho refere-se a dinamica populacional do percevejo-de-renda, Vatiga illudens (Drake, 1922) (Hemiptera: Tingidae) da mandioca (Manihot esculenta Crantz) no Distrito Federal no periodo de 1994 a 1997. Dentro da area util de parcela do experimento, foram efetuadas amostragens quinzenais durante o ciclo da cultura, utilizando-se da seguinte tecnica: de cada cinco plantas previamente marcadas, colhia-se uma folha e contava-se o numero de ninfas e adultos nela depositados. O nível de dano do percevejo-de- renda foi avaliado com base na ocorrencia dos sintomas do ataque dos insetos nas folhas das plantas em escala de notas crescentemente de 0 a 5. Os resultados mostram que as variedades mansas (Mantiqueira e Jacana) são as mais infestadas e as bravas (IAC-12829 e EAB-629) as menos infestadas pelo percevejo-de-renda. A maior ocorrencia da praga concentra-se no primeiro semestre do ano. Apesar da eficiencia do inseticida no controle do percevejo-de-renda, conforme demostrado no presente trabalho, recomenda-se o uso de variedades tolerantes com o controle mais adequado.

Efeito do sistema de preparo do solo e rotacao de culturas na dinamica de populacao de artropodes do solo.

2002