Renewable Energy Global Innovations features: Theoretical Analysis for The Centrifugal Effect On Premixed Flame Speed in A Closed Tube

Significance Statement

The effect of centrifugal acceleration on the mixed flame speed has over time been observed to be significantly important in both theoretical research and engineering application. Recently, empirical investigations on the novel inter-turbine burner engine and the Ramgen engine have shown that they possess significant benefits on performance, since they apply the concept of combustion in high centrifugal fields. Previous studies on centrifugal forces have revealed that high centrifugal acceleration possess significant strengthening effect on combustion. On the contrary, little exists on the adaptation, derivation and harnessing of this power in written academia.

Researchers led by professor Yong Huang at the Collaborative Innovation Center of Advanced Aero-Engine, National Key Laboratory of Science and Technology, School of Energy and Power Engineering, Beihang University described the effect of centrifugal acceleration, specifically high centrifugal acceleration of more than 200 times the gravitational acceleration, on the premixed flame speed in a rotating closed tube. Their main objective was to derive a theoretical predicted correlation which would describe the laminar premixed flame speed in a centrifugal field with the aid of directly solving simplified governing equations on 1-D steady adiabatic flame by theoretical analysis. Their research work is now published in International Journal of Hydrogen Energy.

The research team begun by employing the 1-D steady adiabatic flame model which was fixed. The team then obtained the premixed flame speed in a rotating closed tube after considering the amplification effect of the closed tube on the laminar premixed flame speed. The researchers then, using the predicted correlation, obtained the physical mechanisms of the premixed flame speed in a rotating closed tube.

The authors observed that the flame speed accelerated by the centrifugal force was nearly proportional to the square root of the centrifugal acceleration in the rotating closed tube. The team also noted that the theoretical prediction was also able to revealed that the flame speed in a rotating closed tube was determined by the initial temperature, the critical ignition temperature, the adiabatic flame temperature and the thicknesses of reaction zone. Eventually, the premixed flame speed in a rotating closed tube was seen to increase nearly linearly with the increasing of the initial temperature or square root of the thicknesses of reaction zone, or with decreasing of the critical ignition temperature or the adiabatic flame temperature.

Herein, a theoretical analysis to study the effect of centrifugal acceleration, especially high centrifugal acceleration, that is, more than 200 times the gravitational acceleration of earth, on the premixed flame speed has been successfully presented. More importantly, a theoretical predicted correlation has been proposed to describe the premixed flame speed in a rotating closed tube. The results of the theoretical prediction have been seen to agree well with the empirical data obtained by Lewis & Smith. The result of the study verifies that the flame speed accelerated by the centrifugal force is nearly proportional to the square root of the centrifugal acceleration.

About The Author

Dr. Yong Huang is the chief professor in the Department of thermal power engineering, School of Energy and Power Engineering, Beihang University, Beijing, China. He was granted Bachelor Degree from Tsinghua University in 1985. Then, he obtained Master Degree and Doctoral Degree in Beihang University. He did postdoctoral research in Hong Kong University of Science and Technology.

He is one of the top experts in the field of gas turbine combustion in China. In the past years, he has won the second prize of science & technology improvement by Ministry of Aviation Industry of PRC(1993), the third prize of science & technology improvement by Ministry of Aviation Industry of PRC(1993), the second prize of science & technology improvement by Ministry of National Defence(2004).

His main research interests include the mechanism and prediction of ignition and lean blowout in gas turbine combustors, mechanism of atomization and design of atomizers, performance prediction of low pollution combustors, flow field analysis in combustors, and multipoint lean direct injection combustors, etc.

He proposed the concept of Flame Volume(FV) model to improve the prediction of lean blowout limit derived by Lefebvre. This is an important breakthrough for gas turbine combustors in recent years. And he proposed the concept of flame mixing time (FMT) to estimate the NOx formation and obtain good agreement with the experimental data done by NASA that was ever wrongly predicted by other methods. Besides, he firstly proposed the concept of loss of rotational kinetic energy in pressure swirl atomizers due to liquid viscosity to predict the spray cone angle of pressure swirl atomizers. His course, combustion and combustor, is one of excellent courses in Beihang University. He has published more than 150 academic papers.

Contact: yhuang@buaa.edu.cn

About The Author

Dr. Lei Sun is a PhD candidate in the Department of thermal power engineering, School of Energy and Power Engineering, Beihang University, Beijing, China. He was granted Bachelor Degree from Beihang University in 2012. He was a visiting researcher in Hokkaido University, Japan in 2016.

He is experienced in mathematical modeling and theoretical analyses for physical phenomena. He has won the first prize of National Mathematics Competition for College Students(2011), the second prize of National Physics Competition for College Students(2010), the third prize in the Zhou Pei-Yuan Mechanics Competition for College Students(2011), etc. His research topics include the mechanism and prediction of lean blowout in gas turbine combustors, multipoint lean direct injection combustors, and mechanism of atomization, etc. He has published 8 academic papers.

Contact: sunlei1988@buaa.edu.cn

About The Author

Ms. Yingyi Ji is an engineer of gas turbine engine in Aero Engine Corporation of China. She was granted Bachelor Degree from Beihang University in 2013. She received her master degree in Aeronautical Engineering from Beihang University in 2016, researching on the centrifugal effect on premixed flame speed and the optimization design on diffuser of lean direct injection combustor.

Her recent research includes heat transfer of perforated plate, Oxygen-deficient Combustion in low speed gas flow.

Contact: jiyingyi0319@sina.com

Reference

Lei Sun, Yong Huang, Yingyi Ji. Theoretical analysis for the centrifugal effect on premixed flame speed in a closed tube. International Journal of Hydrogen Energy, volume 42(2017) pages 18658 – 18667.

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Renewable Energy Global Innovations features: Polymeric Ionic Liquid Gel Electrolyte for Room Temperature Lithium Battery Applications

Significance Statement

Professor Bilal El-Zahab and doctoral students, Meer Safa, Amir Chamaani, and Neha Chawla from Florida International University (FIU) developed a free-standing gel polymer electrolyte (GPE) and evaluated its thermal and electrochemical properties in order to ascertain the overall performance of their synthesis in lithium battery applications. The new findings appeared in peer-reviewed journal, Electrochimica Acta.

The gel polymer electrolyte comprised of a pyrrolidinium-based polymeric ionic liquid (PIL), an imidazolium based ionic liquid [EMIM][TFSI], and the lithium salt [LiTFSI]. They compared two electrolytes: the gel polymer electrolyte and ionic liquid electrolyte to investigate stability and compatibility with lithium metal electrode using various electrochemical characterization techniques, including electrochemical impedance spectroscopy with further determination of their rate performance in a cell with LiFePO₄ cathode at room temperature.

Thermogravimetric analyses showed the prepared gel polymer electrolyte had a high thermal stability. The pair of polymeric ionic liquid and ionic liquid inside the gel polymeric electrolyte which contains ionic liquid and lithium salt content (LiTFSI) of about 80wt.% led to an improved ionic conductivity of approximately 3.35 mS×cm^-1 when measured at 25°C using electrochemical impedance spectroscopy.

The most notable improvement using the FIU team’s new gel polymer electrolyte was its improved cathodic limit and widened electrochemical stability window. The improved cathodic limit to below the plating potential of lithium made this gel polymer electrolyte a preferred choice in Li/LiFePO₄ cells. Moreover, the gel polymer electrolyte also showed higher lithium-ion transference number compared to the ionic liquid electrolyte indicating higher chemical affinity. This affinity was demonstrated using in Li/Li symmetrical cell that immensely outperformed the ionic liquid electrolyte.

The cyclic charge-discharge rate when observed at 40 cycles and 22°C showed that the gel polymer electrolyte batteries had a higher discharge capacity at higher C-rates compared to ionic liquid cells. The authors attribute this improved performance to the improved electrochemical and interfacial stability, and the increased Lithium transference number. The gel polymer electrolyte developed by the authors is an exciting development that can serve effectively as an electrolytic conductor with other lithium-ion electrodes.

About The Author

Mr. Meer Safa is a PhD candidate in Materials Science and Engineering at Florida International University working under the supervision of Dr. El-Zahab. He received his M.S. Materials Science and Engineering from Kungliga Tekniska Högskolan (KTH) in Sweden and his B.S. degree in Materials and Metallurgical Engineering from Bangladesh University of Engineering and Technology (BUET) in Bangladesh. His research concentrates on the synthesis of ionic liquids for the development of polymer electrolyte for lithium batteries and their electrochemical investigations. 

About The Author

Mr. Amir Chamaani is a Ph.D. candidate in Materials Science and Engineering at Florida International University. He received his M.S. in Nanomaterials Engineering from the Materials and Energy Research Center (MERC) in Tehran, Iran in 2011. He served as Research at MERC working on thin film anodes for Li-ion micro-batteries. He is currently a Dissertation Year fellow working under the supervision of Dr. El-Zahab on the development of polymer electrolytes, electrochemical, and materials characterizations of Lithium battery applications, especially Li-O₂ batteries. 

About The Author

Ms. Neha Chawla is a Ph.D. candidate in Materials Science and Engineering at Florida International University. She has received her M.S. in Materials Science and Engineering from Florida International University and her B.Eng. in Production Engineering from Mumbai University in India. She is currently working towards her Ph.D. under the supervision of Dr. El-Zahab developing cathodes for improved performance of lithium-oxygen batteries. 

About The Author

Dr. Bilal El-Zahab is an Assistant Professor of Mechanical and Materials Engineering at Florida International University (2012-present). He received in Ph.D. in Chemical Engineering from the University of Akron in Ohio and was a Postdoctoral Research Associate in Analytical Chemistry at Louisiana State University (2008-2010) and a Postdoctoral Associate in Chemical Engineering at Massachusetts Institute of Technology (2010-2012). His research interests include the development of advanced materials for energy storage and bioanaylical applications.  

Journal Reference

Meer Safa, Amir Chamaani, Neha Chawla, Bilal El-Zahab. Polymeric Ionic Liquid Gel Electrolyte for Room Temperature Lithium Battery Applications, Electrochimica Acta 213 (2016) 587-593.

Mechanical and Materials Engineering Department, Florida International University, Miami, Florida 33174, USA

 

 

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