Power generation properties of Direct Flame Fuel Cell (DFFC)

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Journal of Physics: Conference Series OPEN ACCESS Power generation properties of Direct Flame Fuel Cell (DFFC) To cite this article: S Endo and Y Nakamura 214 J. Phys.: Conf. Ser. 557 12119 View the article online for updates and enhancements.

1 Journal of Physics: Conference Series OPEN ACCESS Power generation properties of Direct Flame Fuel Cell (DFFC) To cite this article: S Endo and Y Nakamura 214 J. Phys.: Conf. Ser View the article online for updates and enhancements. Recent citations - Personal power using metal-supported solid oxide fuel cells operated in a camping stove flame Michael C. Tucker - Rich-burn, flame-assisted fuel cell, quickmix, lean-burn (RFQL) combustor and power generation Ryan J. Milcarek and Jeongmin Ahn - Micro-tubular flame-assisted fuel cells Ryan J. MILCAREK et al This content was downloaded from IP address on 17/1/218 at 3:27

2 PowerMEMS 214 Journal of Physics: Conference Series 557 (214) doi:1.188/ /557/1/12119 Power generation properties of Direct Flame Fuel Cell (DFFC) S Endo 1 and Y Nakamura 2 1 Division of Mechanical and Space Engineering, Hokkaido University, N13 W8, Kita-ku, Sapporo, Hokkaido, , Japan 2 Department of Mechanical Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tenpaku, Toyohashi, Aichi, , Japan 1 endo-sho@mech-hm.eng.hokudai.ac.jp 2 yuji@me.tut.ac.jp Abstract. This paper investigated the effect of cell temperature and product species concentration induced by small-jet flame on the power generation performance of Direct Flame Fuel Cell (DFFC). The cell is placed above the small flame and heated product gas is impinged toward it and this system is the simplest and smallest unit of the power generation device to be developed. Equivalence ratio ( ) and the distance between the cell and the burner surface (d) are considered as main experimental parameters. It turns out that open circuit voltage (OCV) increases linearly with the increase of temperature in wide range of equivalence ratios. However, it increases drastically at which the equivalence ratio became small ( ) showing inner flame clearly. This result suggests that OCV depends on not only cell temperature but also the species concentration exposed to the cell. It is suggested that Nernst equation might work satisfactory to predict OCV of DFFC. 1. Introduction Direct Flame Fuel Cell (DFFC), which is known as the one of solid oxide fuel cells (SOFCs; promising future power source [1]), can generate electricity by adopting flame directly to it. One of the potential features of DFFC is to be a good candidate of the miniaturized thermo-electro system in comparison with those of SOFCs. For SOFC-based power generation system, gas supplying system becomes rather massive [2], moreover, a heater is required to preheat the cell to work well. DFFC does not need such facility (i.e. the gas chamber and heater) because the fuel (gas) and heat are supplied by the flame. However, since the generated power might strongly be related to the thermal and species status exposed to the cell, there must be most suitable combination of cell and the flame for DFFCbased power generation system. Because the main target is to develop the miniaturizing power generation system based on DFFC, the applied flame must be also small and stable. Here, we propose to use the miniaturized jet flame (small-scale jet flame) [3] and see how the combination between DFFC and micro-jet flame work as the unique small power generation device. In this work, we investigated the effect of cell temperature and product gas species concentration at the vicinity of the cell on the power generation performance of DFFC, especially the open circuit voltage (OCV), by using of fuel-rich premixed micro-jet flame. Content from this work may be used under the terms of the Creative Commons Attribution 3. licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1

PowerMEMS 214 Journal of Physics: Conference Series 557 (214) 12119 doi:1.188/1742-6596/557/1/12119 2. Experimental Figure 1 shows the schematic drawing of experimental setup.

3 PowerMEMS 214 Journal of Physics: Conference Series 557 (214) doi:1.188/ /557/1/ Experimental Figure 1 shows the schematic drawing of experimental setup. Methane and oxygen were used as a fuel and oxidizer, respectively. Although each gas flow rate changed, total flow rate was fixed at 1. m/s. The flow rates were controlled by the needle valve and the accuracy is well validated with soap-film flowmeter. 1. mm inner diameter burner was used to form the small-scale jet flame. Flame was partially premixed flame whose equivalence ratio was too rich to propagate itself to prevent any flashback. DFFC cell used in this work was developed/supplied by Kikusui Chamical Indstries Co., Ltd. and placed horizontally above the flames. The positions of burner and cell were adjusted with optical stage. The distance between the cell and the micro-burner (d) was varied from 5. mm to 3. mm to modify their heat and species interaction. Equivalence ratio ( ) was varied from 1.9 to 5. because DFFC cannot produce electricity under [4]. K-type thermocouple was used to measure the cell temperature and discharge voltage (OCV) was measured by digital sensor (GRAPHTEC GL-22). The current value was obtained from the measured voltage and resistance. The change of flame shape was observed with DV camera. A gas chromatography was used to identify the product gas exposed onto the cell surface. Figure 1. Schematic drawing of experimental setup. 3. Result and discussion Figure 2 shows an example of the change of flame shape by the change of equivalence ratio and distance d. From this figure, it is obvious that the flame becomes smaller with the decrease of equivalence ratio and the flame shape is largely distorted by the distance d (especially, d=3mm). Under, except for d=3. mm, the inner flame was formed. Figure 3 shows the relationship between the cell temperature and OCV in various experimental conditions. It is understood that the OCV tends to linearly increase with the increase of cell temperature, however, it is also found that there was a singular points which OCV drastically increases in spite of the small change in temperature. Since the singular points in Fig.3 corresponds to the ones obtained at, it can be considered that gas species concentration changed with the change of flame shape in comparison with. From this result, it is expected that the power generation performance of DFFC depends on not only cell temperature but also gas species concentration within the flame. It is important to investigate how this singular point is given in detail in order to understand the controllability of power generation performance of DFFC. Next, let us look into deeply for the relation between the change of flame shape and OCV. 2

PowerMEMS 214 Journal of Physics: Conference Series 557 (214) 12119 doi:1.188/1742-6596/557/1/12119 Figure 2.

mm 35 37 39 41 43 45 Temperature [ ] Figure 3. Relationship of cell temperature and open circuit voltage in various equivalence ratios.

4 PowerMEMS 214 Journal of Physics: Conference Series 557 (214) doi:1.188/ /557/1/12119 Figure 2. Change of flame shape by the change of equivalence ratio and distance between burner and DFFC cell. Open circuit voltage [mv] d=3. mm d=4. mm d=5. mm Temperature [ ] Figure 3. Relationship of cell temperature and open circuit voltage in various equivalence ratios. Figure 4 shows the change of flame shape by the change of distance from d=3.5 mm to 3. mm under =2.. From this figure, it is found that the inner flame disappeared at d=3.2 mm and such disappearance seems abrupt (not continuous) event. Figure 5 shows the relationship of OCV and cell temperature at each position. It is obvious that the closer the cell gets to the inner flame, the larger the OCV becomes and the voltage sharply decreased after the inner flame disappeared. More importantly, OCV increases even though the cell temperature hardly changed. These results indicate that the OCV performance changes by the change of distance d and this should correspond to the change of gas species concentration exposed onto the cell surface. Figure 6 shows the gas analysis by GC at each position under =2.. It is understood that oxygen remains relatively when the inner flame disappeared and hydrogen, on the other hand, carbon monoxide were hardly formed. This change would affect the obtained OCV as found in previously. 3

PowerMEMS 214 Journal of Physics: Conference Series 557 (214) 12119 doi:1.188/1742-6596/557/1/12119 Figure 4. Change of flame shape by the change of distance between burner and DFFC cell under =2.

Relationship of open circuit voltage and cell temperature at various distances between burner and cell. 5 45 4 35 3 25 2 15 1 5 Temperature [ ] Volume ratio [%] 6 5 4 3 2 1 d=3. mm d=3.2 mm d=3.

5 PowerMEMS 214 Journal of Physics: Conference Series 557 (214) doi:1.188/ /557/1/12119 Figure 4. Change of flame shape by the change of distance between burner and DFFC cell under =2.. Open circuit voltage [mv] Opem circuit voltage Temperature Distance between burner and cell [mm] Figure 5. Relationship of open circuit voltage and cell temperature at various distances between burner and cell Temperature [ ] Volume ratio [%] d=3. mm d=3.2 mm d=3.5 mm d=4. mm d=5. mm H2 O2 CO Figure 6. Analysis result of gas species concentration within the flame at each position under =2.. The difference of OCV performance under same condition can be considered to correspond to the local gas concentration at the vicinity of the cell and there is a theoretical equation called Nernst equation to evaluate the OCV [5]. Nernst equation is written as where is the Nernst potential (OCV), is the absolute value of stoichiometric coefficient for oxygen, is the number of transferred electrons, F is the Faraday constant ( s A/mol), R 4

6 PowerMEMS 214 Journal of Physics: Conference Series 557 (214) doi:1.188/ /557/1/12119 is the universal constant (8.314 J /(mol K)), T is the cell temperature (K), and are the partial pressures of oxygen at the cathode and anode (Pa), respectively. According to Nernst equation, the OCV becomes large when the oxygen pressure of anode side is extremely small even the temperature is constant. Figure 7 shows the predicted OCV using Nernst equation with measured oxygen concentration detected by GC for, while ambient value is used for. Although there is a quantitative difference between the measured and predicted OCVs, an abrupt decrease of OCV is clearly captured as shown in dashed arrow in the figure. Open circuit voltage [mv] Distance between burner and cell [mm] Figure 7. Comparison of the measured open circuit voltage and the calculation result of Nernst equation 4. Conclusion In this work, we investigated the power generation performance of DFFC with micro-jet flame. The open circuit voltage (OCV) increases linearly with the increase of cell temperature when the inner flame does not appear clearly. On the other hand, when the inner flame is formed, the OCV increases drastically. These results imply that the OCV depends on not only the cell temperature but also the gas species concentration generated by the flame. Nernst equation might work to predict such drastic behaviour. Acknowledgments The authors are grateful for support provided by Kikusui Chamical Indstries Co., Ltd. References [1] You H, Gao H, Chen G, Abudula A and Ding X 211 Journal of Power Sources [2] Wang K, Ran R, Hao Y, Shao Z, Jin W and Xu N 28 Journal of Power Sources [3] Lee K H and Kwon O C 27 Chemical Engineering Science [4] Kronemayer H, Barzan D, Horiuchi M, Suganuma S, Tokutake Y, Schulz C and Bessler W G 27 Journal of Power Sources [5] Hanna J, Lee W Y, Shi Y and Ghoniem A F 214 Progress in Energy and Combustion Science [6] You H Abuliti A, Ding X and Zhou Y 27 Journal of Power Sources

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Journal of Physics: Conference Series PAPER OPEN ACCESS AC-DC Transfer Difference Measurements using a Frequency Output Thermal Converter To cite this article: G M Geronymo et al 2018 J. Phys.: Conf. Ser.