1,721,089 research outputs found
Multidimensional modelling of spray impingement in modern diesel engines
No full textThis paper discusses a partially stratified technology for
engines running lean on natural gas. A single cylinder
research engine has been modified to enable direct
injection of a small quantity of natural gas through the
spark plug to the region of the electrodes, independent
of the overall lean homogeneous charge. Thus, a
Partially Stratified Charge (PSC) is formed within the
chamber allowing significant extension of the lean limit
of combustion. Although PSC has been shown to reduce
NOX emissions and improve combustion efficiency, high
hydrocarbon emissions have been observed and this
was thought to be due to poor mixing of the injected fuel
air charge.
The mixed experimental-numerical activity described
herein, carried out by the Universities of British
Columbia of Vancouver and Roma Tor Vergata, is aimed
at improving the micro-direct injection PSC process. The
numerical study has enabled a detailed analysis of the
fluid dynamics and combustion processes in the region
of the electrodes, early in the combustion cycle. The
model has been verified using experimental data from
the single cylinder research engine. The results suggest
that improving mixing of the PSC (by changing the way it
is injected into the combustion chamber) can
significantly reduce NOX. A multi-hole injection concept
has been designed and numerically tested, indicating a
potential improvement in both performance and
emissions
Experimental performance analysis of an annular diffuser with and without struts
No full textIn this paper, the performance analysis of an annular diffuser is presented. In a typical industrial gas turbine diffuser, a certain number of structural members, called struts, serve both as load bearings support and as passages for cooling air and lubricant oil.
Measurements were made in a 35% scaled down model of a PGT10 gas turbine exhaust diffuser with and without struts in order to determine the total and static pressure development and the effect of struts on both the local phenomena and the overall performance. More realistic flow conditions are made available by a ring of 24 axial guide vanes at inlet, which represent the last turbine rotor. The model has been tested on a wind tunnel facility developed at the University of Perugia with inlet speed around 80 m/s, allowing satisfactory accuracy for flow measurements and similarity with the PGT10 diffuser in terms of Reynolds number. Static pressure taps located at various streamwise positions on the hub and the casing allowed the estimation of pressure recovery development. A Pitot tube and a hot split-film anemometer were used to determine static and total pressure inside the diffuser at different axial positions. The comparison between the two cases, with and without the struts, was made also by the use of global parameters, which correlate static and total pressure.
In a previous paper, a detailed three-dimensional analysis of the flow path inside the diffuser was presented and the detrimental effect of the struts, in terms of flow separation and unsteadiness, was discussed. The stationary flow measurements and the investigation of the diffuser without the struts are presented in this paper. The whole research project represent a complete diffuser investigation available to develop an optimal design and to advance the computational and design tools for gas turbine exhaust diffusers
Energy Production and Performance of a Large Photovoltaic Roof
No full textThe market for photovoltaic is rapidly expanding and there are some large utility PV power plants, thousands of residential systems, and tens of thousands of remote power systems in use. Even if photovoltaic is a technology that has already demonstrated its effectiveness and holds great promise in electrical generation, the costs are still too high to guarantee a commercial competitivity. This paper presents the performance results of a 15 kWp photovoltaic power plant installed on the roof of a high school in central Italy. The system consists of 220 modules for a total of 22 arrays, which are connected to inverters to allow conventional appliances to be powered by photovoltaic electricity. The PV plant is remotely controlled and data on sun radiation, ambient temperature, modules temperature and power production are continuously acquired by a PC. The measured power plant performances during the year are presented in this paper
Flow development and turbulence length scales within an annular gas turbine exhaust diffuser
No full textThis paper presents the experimental investigation of a scaled down model of a PGT10 gas turbine diffuser by Nuovo Pignone S.p.A. The model was designed to operate in geometric and Reynolds number similarity with the GT diffuser, and 24 guide vanes are mounted at inlet to reproduce typical inlet conditions of an industrial gas turbine diffuser. The PGT10 diffuser has also six high-solidity struts, which support one of the shaft bearings and have lubricating oil supply inside. Two step-motors are used for the circumferential and radial displacement of the probes. Airflow through the test model is provided by an open circuit wind tunnel, which is powered by a 21 kW centrifugal fan. Two hot split-film probes in constant temperature mode were used to measure velocity fluctuations in main-flow, cross-flow and radial-flow directions, thus allowing a 3D characterization of the model’s flow field. Results are presented in terms of mean and fluctuating velocity components at different axial positions. The discussion is focused on the distortion of the flow produced by the struts and on the separation around the hub and the shell. A first set of measurement defines the flow field from the inlet to the exhaust at four axial sections. In three additional axial positions, behind the struts, a more detailed analysis has been made with measuring grid with a double number of nodes. The investigation of the flow field inside the diffuser is also presented by means of the turbulent scale of dissipating eddies, calculated with the Kolmogorov theory. The Kolmogorov length scale seems to be a powerful means to study fluid dynamic phenomena
Performance estimation and experimental measurements of a photovoltaic roof
No full textThe market for photovoltaic systems is rapidly expanding. Currently, there are a few large utility photovoltaic power plants, thousands of residential systems, and tens of thousands of remote power systems in use. Even if photovoltaics is a technology that has already demonstrated its effectiveness and holds great promise in electrical generation, the costs are still too high to guarantee a commercial competitivity. The study presented in this paper is part of a European XVII Thermie project entitled "Pilot project for photovoltaic, energetic and biohousing retrieval in a school", the aim of which was to install a photovoltaic plant and solar air collectors coupled with a sun breaker structure at a scientific high school in Umbertide, in central Italy. A 15 kWp photovoltaic power plant was mounted on the roofs of two blocks of the school building in spring 2001. The system consists of 220 modules for a total of 22 arrays, which are connected to inverters to allow conventional appliances to be powered by photovoltaic electricity. The photovoltaic plant is remotely controlled and data on sun radiation, ambient temperature, modules temperature and power production are continuously acquired by a PC. The measured power plant performances during the year are presented in this paper. Furthermore, the climate in the area has been simulated through the available experimental data and the system behavior under these conditions is predicted. The experimental data have been used to validate a predicting numerical model for photovoltaic plants performance
Design of a solar collector for year-round climatization
No full textSolar heating systems in buildings have increasingly been studied in the past two decades. In several applications the primary energy demand is now for both heating and cooling, and modern solar collectors should be designed to provide climatization during the whole year. Solar systems are seldom applied in Europe, and large buildings, such as office buildings and schools, continue to be built with mechanical ventilation systems. The study presented in this paper is part of a European XVII Thermie project entitled "Pilot project for photovoltaic, energetic and biohousing retrieval in a school", whose aim was to install a photovoltaic plant and solar air collectors coupled with a sun breaker structure at a scientific high school in Umbertide, in central Italy. This paper describes the research and development activities concerning a solar air collector suited for winter heating and summer ventilation, which was installed at the high school. The collector physical and numerical modelling of heat transfer and fluid flow in winter operation is presented. The system performance has been estimated as a function of different parameters in order to provide a tool for the design process. Furthermore, the climate in the area has been simulated through the available experimental data, and the system behavior under these conditions is presented. The collectors were installed at the scientific high school in Umbertide in spring 2001. Summer ventilation cooling is under testing and an experimental test period is foreseen next winter to validate the design of the collectors and their performance
Enhanced splash models for high pressure diesel spray
No full textMixture preparation is a crucial aspect for the correct operation of modern direct injection (DI) Diesel engines as it greatly influences and alters the combustion process and, therefore, the exhaust emissions. The complete comprehension of the spray impingement phenomenon is a quite complete task and a mixed numerical-experimental approach has to be considered. On the modeling side, several studies can be found in the scientific literature but only in the last years complete multidimensional modeling has been developed and applied to engine simulations. Among the models available in literature, in this paper the models by Bai and Gosman (Bai, C., and Gosman, A. D., 1995, SAE Technical Paper No. 950283) and by Lee et al. (Lee, S., and Ryou, H., 2000, Proceedings of the Eighth International Conference on Liquid Atomization and Spray Systems, Pasadena, CA, pp. 586-593; Lee, S., Ko, G. H., Ryas, H., and Hong, K. B., 2001, KSME Int. J., 15(7), pp. 951-961) have been selected and implemented in the KIVA-3V code. On the experimental side, the behavior of a Diesel impinging spray emerging from a common rail injection system (injection pressures of 80 and 120 MPa) has been analyzed. The impinging spray has been lightened by a pulsed laser sheet generated from the second harmonic of a Nd-yttrium-aluminum-garnet laser. The images have been acquired by a charge coupled device camera at different times from the start of injection. Digital image processing software has enabled to extract the characteristic parameters of the impinging spray with respect to different operating conditions. The comparison of numerical and experimental data shows that both models should be modified in order to allow a proper simulation of the splash phenomena in modern Diesel engines. Then the numerical data in terms of radial growth, height and shape of the splash cloud, as predicted by modified versions of the models are compared to the experimental ones. Differences among the models are highlighted and discussed. Copyright © 2007 by ASME
Modello 3D di celle a combustibile ad ossidi solidi alimentate da miscele di idrogeno e CO – Parte prima
No full textLo studio in oggetto, come analizzato nella
Parte prima, ha riguardato la modellizzazione
numerica tridimensionale di celle a
combustibile ad ossidi solidi (SOFC) di geometria
planare. Il modello matematico applicato
per la simulazione della SOFC è stato
analizzato nella prima parte del presente
articolo e in questa seconda parte verranno
dunque presentati la validazione del
modello e i risultati ottenuti considerando la
cella a combustibile alimentata da una miscela
di idrogeno e monossido di carbonio,
focalizzando l’attenzione sulla validazione
del modello sviluppato per l’ossidazione diretta
del monossido di carbonio all’interfac -
cia anodo/elettrolita.\ud
La validazione dei risultati ottenuti è stata effettuata
con dati sperimentali per diverse
condizioni operative per garantire la solidità
del modello stesso. Dai risultati ottenuti
si evidenzia l’importanza di considerare
l’ossidazione diretta del monossido di carbonio
e i suoi effetti sulle prestazioni della
cella a combustibile. L’approccio tridimensionale
ha consentito inoltre di valutare effetti
significativi all’interno della SOFC come
la non uniformità della distribuzione del
gas all’interno del canale anodico correlata
con effetti diffusivi di tipo in-plane
Optimization of CHCP (combined heat and power cooling) systems Operation Strategy Using Dynamic Programming
No full textIn this paper we introduce an enhanced methodology to determine the optimal control strategy for a complex trigeneration plant. The plant is designed to meet the thermal and electrical loads of a user and is connected to the electrical grid. We consider a single working-day and the plant set-points are determined on an hourly basis minimizing total energy cost, plant maintenance costs, and costs associated to switching on and off the power plant components. To realistically simulate the behavior of large power plants, a constraint on the minimum duration of on and off intervals is considered for each plant section.
The problem in study is discretized in time and plant states, represented as weighted graph, and the strategy that minimizes the total cost is determined using backward dynamic programming, whose computational effort is compatible with real practical applications.
Validity and usefulness of the proposed methodology are demonstrated optimizing the set-point of a combined heat, power and cooling system, under different seasonal load conditions and energy prices. We demonstrate that an optimized strategy would reduce the total daily cost from 8% to about 100%, depending on seasonal load, with respect to rule based control strategies, such as heat-tracking and electrical tracking
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