1,721,116 research outputs found
Improving the combustion process of a homogeneous charge compression ignition engine running with triple fuel blend using response surface methodology
No full textIn the present study, performance of an HCCI engine powered with ethanol/toluene/n-heptane tri-fuel blend was optimized by using response surface method. The studied independent parameters were engine speed, lambda ratio, and fuel blends. The impact of these parameters on engine torque, COVimep, CA10, CA50, indicated thermal efciency, IMEP along with emissions of NOX, CO, and HC comprehensively investigated. According to the results, the optimal HCCI engine operation condition was proposed as engine speed of 1343 rpm, lambda value of 2.29, and ethanol ratio of 22%. At this condition, the engine outputs, i.e., IMEP, COVimep, indicated thermal efciency, CA10, and CA50, engine torque were estimated to be 4.21 bar, 4.28%, 0.37, 1.41 °CA, 4.62 °CA, and 8.2 Nm, respectively. The engine-out emissions, including HC, NOX, and CO emission, were predicted to be 243 ppm, 1.05 ppm, and 0.03%, respectively. The result indicates that using ethanol/toluene/nheptane fuel mixture improved the HCCI combustion and NOX emission. The near-zero NOX emissions were recorded at all fuel mixture. However, enhancing ethanol ratio in the fuel blends showed an increase in CO and HC emissions. Overall, this study showed that response surface technique could be used as a promising method to model the HCCI engines
Investigation of the Effects of Intake Manifold Pressure on Performance and Combustion Characteristics in an HCCI Engine
No full textHomogeneous charge compression ignition (HCCI) engines have significant advantages over spark ignition (SI) and compression ignition (CI) engines due to their high thermal efficiency and low NOx emissions. However, it is difficult to control the start of combustion. In this study, the effects of the intake manifold pressure on HCCI combustion were investigated experimentally at 373 K intake temperature in a four cylinders HCCI engine, which was transformed from the SI engine. It was observed that there was an advance in the start of combustion as the manifold pressure increased. It was also observed that the change in octane number had significant effects on the start of combustion. The highest thermal efficiency was recorded as 46.38% at 120 kPa manifold pressure using RON40 fuel. The increase in the volumetric efficiency that depends on the increase in manifold pressure provided an increase in maximum cylinder pressure and heat release. Figure A. In-cylinder pressure and heat release rate variations Purpose: This study aims to investigate the effects of the intake manifold pressure on HCCI combustion. Theory and Methods: A single cylinder, four stroke, port injection SI-HCCI engine was used in the experiments. Reference fuels which were RON0, RON20 and RON40 used in this study. Experimental study was performed at 1000 rpm engine speed, constant lambda 3 and constant 373 K inlet air temperature at different inlet air pressure of 100 kPa, 110 kPa, 120 kPa and 140 kPa in order to observe the controlling of HCCI combustion. Results: Since the increase in intake manifold pressure increases volumetic efficiency, maximum heat release and in-cylinder pressure also increase. Increasing the octane number delayed the combustion. Increasing the manifold pressure increased the rate of chemical reaction in the cylinder. Therefore, combustion starts at earlier crank angles. The highest indicated thermal efficiency was obtained as 46.38% with RON40 fuel at 120 kPa manifold pressure. At 140 kPa manifold pressure, most of the combustion occurs before TDC. This situation negatively affected the combustion efficiency. Under these conditions, increasing the octane number of the fuel made the combustion more controlled and slower. Conclusion: The manifold pressure directly affects the CA10. CA10 is advanced at the manifold pressure of 140 kPa and CA10 is delayed at 100 kPa and 110 kPa manifold pressure. In this study, it can be stated that the ideal manifold pressure is 120 kPa
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
Dynamic model of a four-cylinder four-stroke diesel engine and investigation of its vibrations
No full textTaşıtlarda sürüş güvenliği ve konforu olumsuz yönde etkileyen unsurlardan birisi titreşimlerdir. Taşıt titreşimlerinin temel kaynakları yol pürüzlülüğü ve motor titreşimleridir. İçten yanmalı motorda meydana gelen titreşimler, motorun çalışma prensibinin gereği olarak tamamen yok edilememektedir. Ancak hareketli parçaların kütlelerinde yapılacak optimizasyonlarla bu titreşimler azaltılabilir. Ayrıca uygun motor takozlarının kullanılmasıyla meydana gelen titreşimlerin karoseriye iletimi de minimize edilebilmektedir. Bu çalışmada dört silindirli dört zamanlı bir dizel motorunun dinamik modeli geliştirilmiş ve motor titreşimleri incelenmiştir. Geliştirilen model motor bloğunun üç eksendeki öteleme hareketlerini, bu eksenler etrafındaki dönme hareketlerini ve krank milinde meydana gelen hız dalgalanmalarını ihtiva eden yedi serbestlik derecesine sahip bir modeldir. Modelde silindir gaz basınç kuvvetleri, hareketli parçaların atalet kuvvetleri, hidrodinamik ve kuru sürtünme kuvvetleri, harici yük momenti ve marş momenti dikkate alınmıştır. Motor bloğunun sabit bir zemine önden iki ve arkadan bir takoz ile bağlandığı kabul edilmiştir. Analizin daha gerçekçi olması için tek silindirli bir dizel motorundan deneysel olarak elde edilen silindir içi basınç verileri kullanılmıştır. Modelin sayısal çözümü için Taylor seri metodu kullanılmış ve FORTRAN dilinde bir program hazırlanmıştır. Geliştirilen simülasyon programı kullanılarak farklı motor yüklerinin, silindir basıncında meydana gelen çevrimsel farklılıkların, biyellerin atalet kuvvetlerinin, birleştirilmiş krank ve volan atalet momentlerinin, pistonların atalet kuvvetlerinin, karşı ağırlıkların atalet kuvvetlerinin etkileri incelenmiştir. Uygun takoz parametrelerinin belirlenebilmesi için öncelikle her eksendeki optimum eşdeğer takoz parametreleri belirlenmiş daha sonra tork dönme ekseni dikkate alınarak üç takoz için ayrıklaştırma işlemi gerçekleştirilmiştir. Sonuç olarak, geliştirilen modelin içten yanmalı motorların titreşim kaynaklarının belirlenmesinde, bu titreşimleri azaltma çalışmalarında ve uygun takoz parametrelerinin belirlenmesinde kullanılabileceği belirlenmiştir.Vibrations are one of the factors that affect vehicle driving safety and comfort negatively. Principal sources of vehicle vibrations are ground roughness and engine vibrations. The vibrations occurring in the internal combustion engines are not completely eliminated because of the working principle of the engine. Despite that, vibrations can be reduced by optimizing the mass of the moving parts. In addition this, the transmission of the engine vibrations to the chassis frame can be minimized by using appropriate engine mountings. In this study, a dynamic model of a four-cylinder four-stroke diesel engine was developed and engine vibrations were investigated. The model developed has seven degrees of freedom involving three translational and three rotational movements of the engine block and the crankshaft speed fluctuations. In the model, the cylinder gas pressure forces, inertia forces of the moving parts, hydrodynamic and dry friction forces, external load torque and starter torque were taken into consideration. It was assumed that the engine block was fixed to a rigid ground with two fronts and one rear mount. To improve the reliability of the analysis, the cylinder pressure was taken from a single cylinder four stroke diesel engine experimentally. For the solution of dynamic model a method based on Taylor series was used and a simulation program was developed in FORTRAN. By using the prepared simulation program the influences of; different engine loads, the cyclic variation of the in-cylinder pressure, the connecting rods inertia forces, the combined flywheel and crankshaft inertia moment, inertia forces of pistons, inertia forces counterweights; were examined. In order to determine appropriate mount parameters, primarily optimal equivalent mount parameters were determined on each axes, then decoupling of equivalent parameters into three engine mounts was carried out by considering torque roll axis decoupling. As the result, it is proved that, the model developed can be used for determination of vibrations generated by the engine, reducing these vibrations and determining appropriate engine mounting parameters
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
DEĞİŞİK ARAÇ MODELLERİNİN RÜZGAR DİRENÇ KATSAYILARININ BİR RÜZGAR TÜNELİNDE BELİRLENMESİ
No full textKarayolu taşıtlarının aerodinamik karakteristiklerinin belirlenmesinde rüzgar
tünellerinden faydalanılmaktadır. Rüzgar tüneli testleri tam ölçekli modeller
kullanıldığında oldukça yüksek maliyetli ve zaman alıcı olmaktadır. Küçük
modellerin kullanılmasında ise Reynolds sayısı eşliği problemleri ile
karşılaşılmaktadır. Daha düşük ölçekli ve daha düşük hızlarda aerodinamik
direncin belirlenmesi için Reynolds sayısı bağımsızlığından yararlanılabilir.
Bu çalışmada Reynolds sayısı bağımsızlığından faydalanılarak düşük hızlı bir
rüzgar tünelinde üç değişik otomobil modeli ile bir otobüs modelinin
aerodinamik direnç katsayıları belirlenmeye çalışılmıştır. Test işlemlerinde
maksimum hızı 28 m/s ve deney kesit odası 292x292 mm olan bir rüzgar tüneli
kullanılmıştır. Otobüs modeli ayrıca ANSYS ile analiz edilmiş ve analiz
sonuçları deney sonuçları ile karşılaştırılmıştır.
1/24 ölçeğindeki BMW X5 E53, Alfa Romeo 156 ve Wolksvagen New Beetle
modelleri ile yapılan deneyler sonucunda aerodinamik direnç katsayıları
sırasıyla % 14, % 12,5 ve % 7,8 hata oranları ile bulunmuştur. Otobüs
modelinin aerodinamik direnç katsayısı ise deney sonuçlarına göre 0,65 ANSYS
verilerine göre ise 0,66 olarak belirlenmiştir. BMW X5 E53 modeli ve otobüs
modeli için Reynolds sayısı bağımsızlığı sağlanabilmişken diğer modeller için
Reynolds sayısı bağımsızlığı elde edilememiştir.
Sonuç olarak Reynolds sayısı bağımsızlığının küçük ölçekli ve düşük hızlı test
işlemlerinde tüm modeller için uygulanamayacağı ancak akış ayrılmasının
kendiliğinden gerçekleştiği küt ve köşeli modeller için uygun bir yöntem olduğu
belirlenmiştir.Wind tunnels are used to determine aerodynamic characteristics of road
vehicles. Wind tunnel tests are costly and time consuming when full scaled
models are used. However, when small models are used, Reynolds number
equality problems occur. Reynolds number independence can be used to
determine lower scaled aerodynamic resistance at lower speed.
In this study, using Reynolds number independence, aerodynamic resistance
coefficient of three different automobile models and a bus model are tested to
determine in a low speed wind tunnel. A wind tunnel that has 28m/s maximum
speed level and 292x292 mm test section is used in the tests. Bus model was also
analyzed with ANSYS and analysis results have copared with experimental
results.
As a result of tests in which 1/24 scaled BMW X5 E53, Alfa Romeo 156 and
Volkswagen New Beetle models are used, drag coefficient are found with this
error rate % 14, % 12,5 and % 7,8 respectively. Drag coefficient of bus model
has been found 0,65 according to experimental results and 0,66 according to
ANSYS datas. Although Reynolds number independence is acquired for BMW
X5 E3 model and bus model, it can not be acquired for the other models.
Consequently, it is determined that, Reynolds number independence can not be
applied for all models in small scaled and low speed tests, however, it is an
appropriate method for thick and cornered models that flow seperation occur
automatically
- …
