1,720,968 research outputs found
Computational and Experimental Analysis of Direct CNG Injection and Mixture Formation in a SI Research Engine
No full text
Multidimensional Modeling of Natural Gas Jet and Mixture Formation in Direct Injection Spark Ignition Engines—Development and Validation of a Virtual Injector Model
No full textDuring the last few years, the integration of CFD tools in the internal combustion (IC) engine design process has continually increased, allowing time and cost savings as the need for experimental prototypes has diminished. Numerical analyses of IC engine flows are rather complex from both the conceptual and operational sides. In fact, these flows involve a variety of unsteady phenomena and the right balance between numerical solution accuracy and computational cost should always be reached. The present paper is focused on computational modeling of natural gas (NG) direct injection (DI) processes from a poppet-valve injector into a bowl-shaped combustion chamber. At high injection pressures, the gas efflux from the injector and the mixture formation processes include turbulent and compressible flow features, such as rarefaction waves and shock formation, which are difficult to accurately capture with numerical simulations, particularly when the combustion chamber geometry is complex and the piston and intake/exhaust valve grids are moving. In this paper, a three-dimensional moving grid model of the combustion engine chamber, originally developed by the authors to include simulation of the actual needle lift, has been enhanced by increasing the accuracy in the proximity of the sonic section of the critical valve-seat nozzle, in order to precisely capture the expansion dynamics the methane undergoes inside the injector and immediately downstream from it. The enhanced numerical model was then validated by comparing the numerical results to Schlieren experimental images for gas injection into a constant-volume bomb. Numerical studies were carried out in order to characterize the fuel-jet properties and the evolution of mixture formation for a centrally mounted injector configuration in the case of a pancake-shaped test chamber and the real engine chamber. Finally, the fluid properties calculated by the model in the throat section of the critical nozzle were taken as reference data for developing a new effective virtual injector model, which allows the designer to remove the whole computational domain upstream from the sonic section of the nozzle, keeping the flow properties virtually unchanged there. The virtual injector model outcomes were shown to be in very good agreement with the results of the enhanced complete injector model, substantiating the reliability of the proposed novel approach.</jats:p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Numerical Assessment on the Influence of Engine Calibration Parameters on Innovative Piston Bowls Designed for Light-Duty Diesel Engines
Full text linkThe optimization of the piston bowl design has been shown to have a great potential for air–fuel mixing improvement, leading to significant fuel consumption and pollutant emissions reductions for diesel engines. With this aim, a conventional re-entrant bowl for a 1.6 L light-duty diesel engine was compared with two innovative piston designs: a stepped-lip bowl and a radial-bumps bowl. The potential benefits of these innovative bowls were assessed through 3D-CFD simulations, featuring a calibrated spray model and detailed chemistry. To analyse the impact of these innovative designs, two different engine operating conditions were scrutinized, corresponding to the rated power and a partial load, respectively. Under the rated power engine operating condition, a start of injection sensitivity was then carried out to assess the optimal spray–wall interaction. Results highlighted that, thanks to optimal injection phasing, faster mixing-controlled combustion could be reached with both the innovative designs. Moreover, the requirements in terms of swirl were also investigated, and a higher swirl ratio was found to be necessary to improve the mixing process, especially for the radial-bumps design. Finally, at part-load operating conditions, different exhaust gas recirculation (EGR) rates were analysed for two injection pressure levels. The stepped-lip and radial-bumps bowls highlighted reduced indicated specific fuel consumption (ISFC) and soot emissions values over different rail pressure levels, guaranteeing NOx control thanks to the higher EGR tolerance compared with the re-entrant bowl. The results suggested the great potential of the investigated innovative bowls for improving efficiency and reducing emissions, thus paving the way for further possible optimization through the combination of these designs
CFD-supported calibration optimization of a retrofit hydrogen–diesel dual-fuel engine
No full textDual-fuel (DF) hydrogen–diesel engines could offer a retrofit-compatible pathway for medium-/heavy-duty transport decarbonization. In this study, a 6-cylinder
compression ignition engine retrofitted for hydrogen port fuel injection is investigated through a CFD-supported framework. A validated 3D-CFD model, based
on an extensive experimental dataset, was applied to investigate injection strategies and calibration parameters in both retrofit and native DF engine modes. The
model accurately captures combustion behavior, emissions trends, and the factors limiting hydrogen energy share (HES). Results show that an optimized native DF
calibration enables up to 90% CO2 reduction relative to diesel operation while maintaining combustion stability. Particulate matter emissions are nearly eliminated
at high HES, whereas low HES combined with non-optimized diesel injection results in PM levels comparable to diesel-only operation. The analysis highlights the
decisive role of a coordinated optimization of HES and diesel calibration strategy in governing ignition dynamics, combustion efficiency, and soot formation
Numerical Investigation on mixture formation and combustion process of innovative piston bowl geometries in a swirl-supported light-duty diesel engine
Full text linkIn recent years, several innovative diesel combustion systems were developed and optimized in order to enhance the air and injected fuel mixing for engine e-ciency improvements and to mitigate the formation of fuel-rich regions for soot emissions reduction. With these aims, a three-dimensional computational fl uid dynamics (3D-CFD) numerical study was carried out in order to evaluate the impact of three di erent piston bowl geometries on a passenger car four-cylinder diesel engine, 1.6 liters. Once the numerical model was validated considering the baseline re-entrant bowl, two inno vative bowl geometries were defi ned: one based on the stepped-lip bowl; the other including a number of radial bumps equal to the nozzle holes number. Firstly, the rated power engine operating condition was investigated under nonreacting conditions to evaluate the piston bowl e ects on the in-cylinder mixing. Results highlight for both the innovative piston bowls better air utilization with respect to the re-entrant bowl: The stepped-lip bowl creates a dual toroidal vortex leading to a higher air/fuel mixing, while the radial-bumps bowl signifi cantly a ects the jet-To-jet interaction and promotes the recirculation of the fuel jet downstream to the bump, where the available oxygen enhances the mixing rate. After that, the combustion analysis was carried out for both rated power and partial-load engine operating conditions. Results confi rmed that thanks to the better air-fuel mixing, the combustion process can be improved thanks to the innovative bowl designs, both increasing the engine e-ciency at full-load condition and minimizing the engine-out soot emissions at partial-load operating point
- …
