1,720,983 research outputs found
Laminar flame speed of fossil/air and biofuels/air combustion
No full textTraditional fossil fuels are considered to be largely responsible for the atmospheric environmental degradation. Biofuels can contribute to reducing the dependency on fossil fuels and to lowering greenhouse gas emissions due to aviation transport and can be considered as both renewable and sustainable energy sources. Indeed, biofuels are recognized as "net zero CO2 emission". In fact, carbon dioxide absorbed by plants during the growth of the biomass is roughly equivalent to the amount of carbon produced when the fuel is burned in a combustion engine - which is simply returning the CO2 to the atmosphere. This would allow the biofuel to be approximately carbon neutral over its life cycle. Thus the goal of this paper is to investigate the possibility to replace current aviation fuels with next generation biofuels. In particular, in the following, a comparative study of the bio-fuels flame speed, flame temperature ad emissions at different operative conditions with those of conventional fuels, has been performed. Results have actually shown that renewable fuels could play a critical role in pollutants abatement and for the next generation energy sources
Thermodynamic characteristics of a turboprop engine with heat exchangers for unmanned aerial vehicles
No full textUAVs are becoming of always greater importance, both in military and civil applications. One of the main reasons of their growth is the realization of very efficient and reliable guiding systems, that allow a thorough remote vehicle control. An important UAV aspect is the endurance capability. A flight length of 24 hours or more is often required for their missions. This makes the engine fuel consumption a fundamental aspect. For a power range comprised between 300 - 900 kW, the turboprop engine is commonly used. To reduce the engine fuel consumption, and consequently increase the UAV endurance characteristics, a turboprop with intercooling and regeneration has been studied. Regeneration is a techniques that allows to recover the exhaust gas heat at the power turbine outlet, to pre-heat air at the combustion chamber inlet. This allows to reduce the specific fuel consumption. The intercooled compression process allows to reduce the compressor absorbed power and consequently rise the output power. A thermodynamic numeric program that simulates the behavior of a turboprop with regeneration at different engine and operating conditions has been developed. The program allows to compute the thermodynamic working cycle and hence the main engine performances, as specific power, thermal efficiency and specific fuel consumption. An offdesign analysis is then performed to evaluate the engine behavior when operating at different conditions respect to the design point. © 2013 by Roberto Andriani
Off-design characteristics of low-fuel consumption gas turbine engine for long-range UAV
No full textUAVs are becoming of always greater importance, both for civil and military uses. Some UAV missions require a flight length of many hours, sometimes lasting more than two days. In these cases, the engine fuel consumption characteristics become of primary importance. In this sense, it is interesting to study the effects of some techniques, as intercooling and regeneration, on the engine power and fuel consumption, in particular in a turboprop engine, commonly used for this kind of missions. These effects have been studied by means of a thermodynamic numeric program that simulates the behavior of a turboprop engine with intercooling and regeneration, or with regeneration only. The program allows to do a parametric study, computing the main engine characteristics, as thermal efficiency, specific power and specific fuel consumption, for different operating conditions. After the parametric study, an off-design analysis has been performed, to see how the main engine parameters change
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
Performance of a Turboprop Engine with Heat Recovery in Off-Design Conditions
No full textThe research for fuel consumption and pollution reduction in new generation aero engines has indicated intercooling and regeneration as very effective methods for this purpose. Hence, different countries have joined their efforts in common research programs, to develop new gas turbine engines able to reduce considerably the fuel consumption and the ambient impact by means of these two techniques. To study their effects on the engine performance and characteristics, a thermodynamic numerical program that simulates the behavior of a turboprop engine with intercooling and regeneration in different operating conditions has been developed. After the parametric study, and the definition of the design conditions, the off-design analysis is carried on, comparing the main characteristics of the intercooled-regenerated turboprop with those of a conventional engine. Then, once a particular mission profile was fixed, the engine performance, in particular the equivalent power, the fuel consumption and the heat exchanger weight were discussed
Feasibility study of a supercritical cycle as a waste heat recovery system
No full textFollowing the increasing interest of aero-naval industry to design and build systems that might provide fuel and energy savings, this study wants to point out the possibility to produce an increase in the power output from the prime mover propulsion systems of aircrafts. The complexity of using steam heat recovery systems, as well as the lower expected cycle efficiencies, temperature limitations, toxicity, material compatibilities, and/or costs of organic fluids in Rankine cycle power systems, precludes their consideration as a solution to power improvement for this application in turboprop engines. The power improvement system must also comply with the space constraints inherent with onboard power plants, as well as the interest to be economical with respect to the cost of the power recovery system compared to the fuel that can be saved per flight exercise. A waste heat recovery application of the CO2 supercritical cycle will culminate in the sizing of the major components. Copyright © 2013 by ASME
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
- …
