1,721,023 research outputs found
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
Atık Kızartma Yağı Biyodizeliyle Çalışan Direkt Enjeksiyonlu Bir Dizel Motorun Yanma Performans ve Emisyon Özellikleri
No full textAppropriate 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
Investigation of the effects of using fusel oil as fuel blend in a spark ignition engine on engine performance and emissions
No full textArtan enerji ihtiyacı ve çevre kirliliği nedeniyle, buji ile ateşlemeli motorlarda etanol, metanol, doğal gaz, hidrojen ve LPG gibi alternatif yakıtlar kullanılmaktadır. Oktan sayısının yüksek olması ve biyokütle kaynaklardan üretilmesi nedeniyle alkoller alternatif yakıtlar arasında önemli bir yere sahiptir. Bu çalışmada etil alkol üretiminde yan ürün olarak elde edilen ve Türkiye'de değerlendirilmeyen fuzel yağı ile kurşunsuz benzin karışımlarının (F5, F10, F20, F30 ve F50) buji ile ateşlemeli bir motorda motor performansına ve egzoz emisyonlarına etkisi deneysel olarak incelenmiştir.
Deneyler dört zamanlı, tek silindirli, enjeksiyonlu ve buji ile ateşlemeli Hydra marka motorda gerçekleştirilmiştir. Kurşunsuz benzin-fuzel yağı karışımlarının etkilerini ve farklı motor çalışma parametrelerindeki değişimleri değerlendirebilmek için değişik gaz kelebek açıklıkları, motor hızları ve ateşleme avanslarında deneyler yapılmıştır. Değişik motor hızlarında ve maksimum motor momentini veren ateşleme zamanında yapılan deneylerde, fuzel yağı ilavesi ile motor momentinde artış olmuş ve en yüksek artış F10 yakıtı ile elde edilmiştir. Aynı deney şartlarında tüm yakıtlarda termik verim değerleri birbirine yakın elde edilmiştir. Bütün motor hızlarında ve farklı ateşleme avanslarında gerçekleştirilen deneylerde özgül yakıt tüketimi, karışımdaki fuzel yağı miktarına bağlı olarak artış göstermiştir. En yüksek artış F50 yakıtında elde edilmiştir. Maksimum motor momentini veren ateşleme zamanında, farklı yük ve motor hızlarında gerçekleştirilen deneylerde termik verim, karışımdaki fuzel yağı miktarına bağlı olarak artış göstermiş ve en yüksek artış F50 yakıtıyla elde edilmiştir. Farklı motor devri ve ateşleme avanslarında HC ve CO emisyonları kurşunsuz benzine göre diğer tüm yakıtlarda artış göstermiştir. NOx emisyonları motor devrine ve karşımlardaki fuzel yağı miktarına bağlı olarak azalma göstermiştir. Maksimum motor momentini veren motor devrinde ve farklı ateşleme avanslarında gerçekleştirilen deneylerde kurşunsuz benzine göre tüm yakıtlarda NOx emisyonları azalmıştır.Due to the increasing energy demand and environmental pollution, alternative fuels such as ethanol, methanol, natural gas, hydrogen and LPG used in spark ignition engines. Alcohols have an important place in alternative fuels because of their's high octane numbers and production from biomass sources. In this study, in a spark ignition engine unleaded gasoline and fusel oil, that is obtained by product of production of ethyl alcohol and don't evaluated in Turkey, blends' (F5, F10, F20, F30 ve F50) effects on engine performance and exhaust emissions has investigated experimentally.
Experimental works have performed on four stroke, single cylinder, fuel injection and spark ignition Hydra engine. To evaluate effects of unleaded gasoline-fusel oil blends and changes in different engine operating parameters, experiments have conducted different throttle openings, engine speeds and ignition advances. The engine torque has increased by the addition of fusel oil in different engine speeds and maximum engine torque advance experiments and the highest torque increase has obtaines with the F10 fuel. At the same experimental conditions the thermal efficiency values have obtained close to each other. At the all engine speeds and different ignition advance experiments specific fuel consumption has increaseddepending on amaoun of oil in the mixture. The highest increase has obtained in F50 fuel. At the maximum engine torque advance, different loads and engine speeds experiments thermal efficiency has increased depending on the amount of oil in the mixture and maximum increase has obtained with F50 fuel. HC and CO emissions has increased all blends according to unleaded gasoline at different engine speeds and ignition advances. NOx emissions has increased depending on engine speed and amount of fusel oil in the blends. At the maximum engine torque and different ignition advance experiments NOx emissions had reduced according to unleaded gasoline
İzo-propanol Yakıtı Kullanımının HCCI Yanma Karakteristikleri, Motor Performansı ve Egzoz Emisyonları Üzerine Etkileri
No full textAn Investıgatıon Of The Effects Of Compressıon Ratıo On Combustıon And Performance In A Homogeneous Compressıon Ignıtıon Engıne
No full textHomojen dolgulu sıkıştırma ile ateşlemeli (HCCI) motorların yaygın kullanımı için yüksek yüklerdeki vuruntu ve düşük yüklerdeki ateşelenememe problemlerinin giderilmeleri gerekmektedir. Vuruntu ve ateşlenememe bölgeleri arasında sınırlı bir çalışma aralığına sahip HCCI motorların çalışma aralığının genişletilmesi gerekmektedir. Bu çalışmada tek silindirli, sıkıştırma oranı değiştirilebilir, buji ile ateşlemeli bir motorun ateşleme sistemi devre dışı bırakılarak HCCI yanması sağlanmıştır. HCCI çalışma aralığını genişletebilmek için emme havası giriş sıcaklığı, hava/yakıt oranı, motor hızı, sıkıştırma oranı değiştirilmiş ve bu şartlar altında RON20, RON40, RON60 ve RON80 yakıtları deney yakıtı olarak kullanılmıştır. Emme havası giriş sıcaklığı olarak 40 oC, 60 oC, 80 oC ve 100 oC belirlenmiş ve deney motorunun sıkıştırma oranı 9, 10, 11 ve 12 olarak değiştirilmiştir. Bu şartlar altında motor hızı 800 min-1 ile 1600 min-1 aralığında değiştirilmiş ve farklı HFK değerlerinde deneyler gerçekleştirilmiştir. Silindir içi basınç, ısı yayılım oranı, indike termik verim, indike ortalama efektif basınç, çevrimsel farklılıklar, efektif moment, efektif özgül yakıt tüketimi, yanma süresi ve egzoz emisyonları tam yük şartlarında incelenmiştir. HCCI yanmasını sınırlayan vuruntu ve ateşlenememe bölgeleri belirlenmiştir. Emme havası giriş sıcaklığının artırılması HCCI motorun daha geniş bir aralıkta çalışmasını sağladığı tespit edilmiştir. Ayrıca emme havası giriş sıcaklığının artırılması yüksek oktanlı yakıtların da HCCI modda çalışmasını sağlamıştır. HCCI yanması giriş hava sıcaklığının artmasıyla avansa alınmış ve vuruntu oluşumu artmıştır. En geniş çalışma aralığı sıkıştırma oranının 10 olduğu şartlarda RON20 yakıtı ile sağlanırken, sıkıştırma oranının 11 olduğu durumda RON40 yakıtı ile elde edilmiştir. Düşük sıkıştırma oranı şartlarında RON20 ve RON40 yakıtı ile HCCI yanması sağlanırken, sıkıştırma oranının artırılması ile RON60 yakıtı ile ve dar bir aralıkta da olsa RON80 yakıtıyla HCCI yanması gerçekleşmiştir. Aşırı zengin ve aşırı fakir çalışma şartlarında çevrimsel farklılıkların oldukça fazla olduğu gözlenmiştir. Sıkıştırma oranının artırılması HC ve CO emisyonlarının azalmasına sebep olurken, NOx emisyonları ise kötüleşmiştir.For widespread use of homogeneous charged compression ignition (HCCI) engines, it is required to overcome the problems like knocking at high loads and misfire at low loads. It is necessary to extend the operating range of HCCI engines which are limited to knocking and misfire regions. In this study, HCCI combustion in a single cylinder engine having variable compression ratio was obtained by disabling the ignition system of the engine. In order to extend the HCCI operation range, the intake air temperature, air/fuel ratio, engine speed, compression ratio were changed and under these conditions RON20, RON40, RON60 and RON80 fuels were used as test fuels. The intake air temperature were kept constant at 40 oC, 60 oC, 80 oC and 100 oC and compression ratio of the test engine were swept as 9, 10, 11 and 12. Under these conditions, the engine speed was swept between 800 min-1 and 1600 min-1 and experiments were carried out at different lambda values. In-cylinder pressure, heat release rate, indicated thermal efficiency, indicated mean effective pressure, cyclic differences, brake moment, brake specific fuel consumption, combustion duration and exhaust emissions were investigated at full load conditions. Knocking and misfiring regions, which limit the HCCI combustion, were identified. It was found that increasing intake air temperature allows the HCCI engine to work in a wider range. In addition, increasing intake air temperature ensured that high octane fuels can be used in HCCI mode. HCCI combustion was advanced by increasing intake temperature and knocking tendency had increased. The largest operation range was obtained with RON20 fuel at a compression ratio of 10 and with RON40 fuel at a compression ratio of 11. At low compression ratios HCCI combustion was only achieved with RON20 and RON40 fuels while at higher compression ratios HCCI combustion was achieved with RON60 and even in a narrow range with RON80. It was observed that the cyclic variations were quite large at extremely rich and lean working conditions. Increasing compression ratios caused a decrease in HC and CO while the NOx emissions increased
An experimental research on the determination of the combustion characteristics of ABE fuel in a port injection HCCI engine
No full textRecent studies have shown that the use of n-butanol, a type of long-chain alcohol, in internal combustion engines yields highly promising results. However, the production efficiency of bio-butanol is low and quite costly. Therefore, researchers suggest using butanol in the ABE (acetone-butanol-ethanol) format without purification until a more cost-effective and efficient method of bio-butanol production is found. This study examined the effects of ABE and n-heptane mixtures on the operating range, combustion phase, and emissions in an HCCI mode. Tests were conducted at intake temperatures of 310 K and 350 K, at variable lambda values and engine speeds. ABE content and increased intake temperature allowed for the extension of homogeneous charge compression ignition (HCCI) mode operating range. The widest operating range was obtained with ABE20 at intake temperature of 350 K. Conventional HCCI combustion, which happens at small crank angles, was slowed down and controlled by ABE. Slow oxidation reactions cause the indicated thermal efficiency to increase. The highest indicated thermal efficiency was determined as 43.73 % by using ABE40. However, carbonmonoxide and hydrocarbons emissions, which are the biggest drawbacks of HCCI engines, increased with ABE mixture fuels. In conclusion, ABE demonstrated the potential to be promising biofuel for 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
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