1,721,006 research outputs found
Experimental Studies on Methanol Sprays for IC Engine Applications
No full textIn this work, studies have been conducted on sprays of methanol and its emulsions with diesel towards assessing the potential of methanol as an alternative fuel for IC engines. Methanol can be used in compression ignition engines as a methanol-in-diesel emulsion, and in spark ignition engines as a direct gasoline-substitute. Evaporating spray characteristics of methanol-in-diesel emulsions and pure methanol are studied in a high-pressure chamber with optical access. In the first part of the study, a comparison between two measurement methods (DBI and scattering) along with two post-processing methods (line-fit and threshold) to measure liquid length of a diesel spray is presented. The second part of the study involved assessing the stability of methanol-in-diesel emulsions with conventional surfactants such as sorbitan monooleate (Span-80®) and polyoxyethylene sorbitan monooleate (Tween-80®). The hydrophilic-lipophilic balance (HLB) values of the surfactant were varied from 7 to 15 to investigate the role of the surfactant on stability of the macroemulsion. It was observed that macroemulsions with up to 10 wt.% of methanol were stable. The macroemulsion with an HLB value of 10 gave the best stability results. In the third part of the study, the emulsion sprays were characterized in a constant volume chamber at injection pressures of 500 bar, 1000 bar, and 1500 bar in an inert atmosphere of nitrogen at 50-bar and 900-K. Interestingly, the liquid-length of the methanol-in-diesel emulsion spray with 10 wt.% of methanol using a mixture of Span-80® and Tween-80® as a surfactant is higher by around 25% as compared to that of the diesel spray, even though methanol is far more volatile than the components of diesel. This is attributed to the higher boiling point of the surfactant used, as confirmed by experiments with a low boiling point surfactant, i.e., 1-dodecanol, and recent observations from the literature. Next, microemulsions of diesel-methanol were produced by using various surfactants such as 1-dodecanol, pentanol, and butanol. Among these, 1-dodecanol was chosen as the most suitable surfactant for the microemulsion owing to its ability to create microemulsions with up to 25 wt.% of methanol, and its high cetane number. The evaporating spray liquid-length is observed to be insensitive to the methanol percentage in the emulsion when 1-dodecanol is used as the surfactant.
The fourth part of the study focused on evaluating whether the phenomenon of micro-explosion in emulsion fuel droplets occurs at engine-relevant conditions of pressure and temperature. In a first-of-its-kind observation, emulsion droplets in the size range of 50 to 150-µm in a high-pressure, high temperature (50 bar, 900 K) environment did not exhibit the phenomenon of micro-explosion even up to 11 milliseconds, which is close to the timescales of relevance in practical engines. This is possibly because these timescales are not sufficient for phenomena such as coalescence of the dispersed phase and internal bubble formation to occur, which are normally precursors to micro-explosions. In the fifth part of the study, pure methanol sprays were characterized at injection pressures of 200 bar, 300 bar, 400 bar, and 480 bar in an inert atmosphere of nitrogen at three engine-relevant conditions. Data generated on liquid and vapour penetration at these conditions highlight the effect of the surrounding gas temperature and density on the spray physics. In the last part, a validated computational spray model of methanol sprays is developed using a commercial CFD solver, namely, CONVERGE-CFD. Overall, the data generated in the present work is expected to aid engine designers in adapting both compression ignition and spark-ignition engines for methanol fuel
Reacting Flow Simulations with Detailed Chemistry: Applications in IC Engines & Gas Turbines
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A COMPARISON OF DIESEL AND JATROPHA METHYL ESTER (JME) SPRAY CHARACTERISTICS: EFFECT OF NOZZLE ENTRY RADIUS
No full textIn the present article, diesel and Jatropha methyl ester (JME) sprays are compared in a detailed manner in terms of their macroscopic and microscopic spray characteristics. The comparison is made at injection pressures of 500, 1000, and 1500 bar by injecting the fuels through a nozzle having a single hole of 200 mu m diameter and 70 mu m entry radius into a spray chamber (with optical access). From the measurements of macroscopic spray structure, it is observed that the spray tip penetration is faster and spray cone angle is narrower by approximately 10% for JME than those of diesel, indicating that the JME spray atomization is poor. Droplet sizes are measured for diesel and JME sprays at 4 ms after the start of injection using particle/droplet image analysis, which showed that the Sauter mean diameter (SMD) of JME sprays is higher by around 5% as compared to that of diesel. Subsequently, a nozzle with a hole diameter of approximately 200 mu m having an entry radius of 10 mu m is studied to understand the effect of nozzle entry radius on breakup of diesel and JME sprays. Computational fluid dynamic modeling of inner-nozzle flow showed that there is significant inner-nozzle cavitation for this nozzle. A comparison of spray structure at injection pressures of 500 and 1500 bar showed that the spray tip penetration is slower and spray cone angles are wider by approximately 5% to 12% for sprays from the cavitating nozzle than those from the noncavitating nozzle. Droplet size comparison showed that SMD of spray from the cavitating nozzle is lower by approximately 5% as compared to that from the noncavitating nozzle. Thus improvement in spray atomization due to inner-nozzle cavitation may be able to compensate for the inferior atomization of JME, although with an associated penalty in the coefficient of discharge
Numerical and Experimental Studies on a Syngas-Fired Ultra Low NOx Combustor
No full textSimulations and exhaust measurements of temperature and pollutants in a syngas-fired model trapped vortex combustor for stationary power generation applications are reported. Numerical simulations employing Reynolds-averaged Navier-Stokes (RANS) and large eddy simulations (LES) with presumed probability distribution function (PPDF) model were also carried out. Mixture fraction profiles in the trapped vortex combustor (TVC) cavity for nonreacting conditions show that LES simulations are able to capture the mean mixing field better than the RANS-based approach. This is attributed to the prediction of the jet decay rate and is reflected on the mean velocity magnitude fields, which reinforce this observation at different sections in the cavity. Both RANS and LES simulations show close agreement with the experimentally measured OH concentration; however, the RANS approach does not perform satisfactorily in capturing the trend of velocity magnitude. LES simulations satisfactorily capture the trend observed in exhaust measurements which is primarily attributed to the flame stabilization mechanism. In the exhaust measurements, mixing enhancement struts were employed, and their effect was evaluated. The exhaust temperature pattern factor was found to be poor for baseline cases, but improved with the introduction of struts. NO emissions were steadily below 3 ppm across various flow conditions, whereas CO emissions tended to increase with increasing momentum flux ratios (MFRs) and mainstream fuel addition. Combustion efficiencies similar to 96% were observed for all conditions. The performance characteristics were found to be favorable at higher MFRs with low pattern factors and high combustion efficiencies
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A method for measurement of planar liquid volume fraction in dense sprays
No full textA methodology for measurement of planar liquid volume fraction in dense sprays using a combination of Planar Laser-Induced Fluorescence (PLIF) and Particle/Droplet Imaging Analysis (PDIA) is presented in this work. The PLIF images are corrected for loss of signal intensity due to laser sheet scattering, absorption and auto-absorption. The key aspect of this work pertains to simultaneously solving the equations involving the corrected PLIF signal and liquid volume fraction. From this, a quantitative estimate of the planar liquid volume fraction is obtained. The corrected PLIF signal and the corrected planar Mie scattering can be also used together to obtain the Sauter Mean Diameter (SMD) distribution by using data from the PDIA technique at a particular location for calibration. This methodology is applied to non-evaporating sprays of diesel and a more viscous pure plant oil at an injection pressure of 1000 bar and a gas pressure of 30 bar in a high pressure chamber. These two fuels are selected since their viscosity values are very different with a consequently very different spray structure. The spatial distribution of liquid volume fraction and SMD is obtained for two fuels. The proposed method is validated by comparing liquid volume fraction obtained by the current method with data from PDIA technique. (C) 2012 Elsevier Inc. All rights reserved
Evaluation of nitric oxide kinetics in high-pressure flames (up to 5 atm)
No full textNitric oxide kinetics in laminar, counterflow diffusion flames at pressures from 1 to 5 atm are assessed by comparing predictions of NO concentration ([NO]) using comprehensive chemical kinetic mechanisms with highly quantitative laser-induced fluorescence (LIF) measurements. The most recent Gas Research Institute (GRI) mechanism, version 3.0, is used and is compared with the older version 2.11 mechanism. Results indicate that there is significant improvement in the predictive capability of the GRI 3.0 mechanism over the 2.11 mechanism with regard to predicting the magnitude of [NO] as well as the trend of [NO] variation with pressure. However, there is still substantial difference between [NO] predictions and measurements, especially at lower pressures, indicating a need for further refinement of NO kinetics
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