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Enhanced densification and thermoelectric properties of Ca3Co4O9 ceramics fabricated by solid-state combustion and hot-pressing
(2026-11-15)
Thatawong, Bhoowadol
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Sriondee, Manlika
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Chongsatan, Wistsarut
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Palaporn, Dulyawich
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Pinitsoontorn, Supree
The Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> powders were synthesized by the solid-state combustion method and then calcined at 775-875 °C for 6 h. The combination of combustion-derived fine powders and hot pressing was adopted to improve the densification and thermoelectric (TE) performance of Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> ceramics. Dense Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> ceramics were subsequently fabricated by hot-pressing to investigate the influence of hot-pressing temperature (800-950 °C, 2 h) on phase formation, microstructure, electrical, and TE properties. The Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> powder was obtained after calcination at 800 °C for 6 h and exhibited an average particle size of 0.55 μm. XRD analysis confirmed that Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> was the predominant phase in all hot-pressed samples. XPS analysis further confirmed the presence of oxygen vacancy (V<inf>O</inf>++)-related defects and mixed-valence cobalt species. FESEM observations revealed a dense microstructure composed of plate-like grains with an average grain size ranging from 0.61 to 0.96 μm. The bulk density ranged from 4.31 to 4.46 g/cm3, indicating dense ceramics. The electrical resistivity (ρ) decreased with increasing measured temperature for all samples. Among all samples, the ceramic hot-pressed at 900 °C exhibited the lowest ρ at 600 °C. The Seebeck coefficient (S) significantly increased from 150 μV/K to 223 μV/K, while the thermal conductivity (κ) decreased with increasing temperature. Due to the favorable combination of low ρ and high S, the sample hot-pressed at 900 °C achieved the highest power factor (PF) and a maximum dimensionless figure of merit (ZT) of 0.17 at 600 °C.
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EFFECT OF FIRING TEMPERATURES ON THE PHASE STRUCTURE AND ELECTRICAL PROPERTIES OF BNT-BT-0.1NT CERAMICS SYNTHESIZED VIA THE SOLID-STATE COMBUSTION TECHNIQUE
(2025-01-01)
Thatawong, Bhoowadol
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Tagerd, Kanyanut
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Vittayakorn, Naratip
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Udeye, Thanya
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Bongkarn, Theerachai
Lead-free ceramic materials of 0.9(0.92Bi0.5Na0.5TiO3-0.08BaTiO3)-0.1NaTaO3 or BNT-BT-0.1NT were obtained using glycine as fuel by a solid-state combustion process. The significance of heat treatment conditions, including calcination at 600-800°C for 2 h and sintering at 1075-1175°C for 2 h, on the structure of the phase, microstructure, electrical and energy-storage properties of BNT-BT-0.1NT ceramics were performed. The perovskite phase was presented for all powder samples. BNT-BT-0.1NT powders calcined at the temperature of 750°C for 2 h showed a 100% pure perovskite phase. The particles morphology exhibited spherical shapes with a wide distribution. As the calcination temperature increased, the average particle size grew from 340 nm to 370 nm. Rietveld refinement confirmed that the BNT-BT-0.1NT ceramics possessed a uniform ABO3 structure with cohabiting of rhombohedral (R), tetragonal (T), and cubic (C) phases. With a rise in sintering temperature, the average grain size expanded from 0.85 μm to 2.66 μm, while the remnant polarization (P<inf>r</inf>) and coercive field (E<inf>c</inf>) decreased. The samples sintered at 1150oC for 2 h, the ceramic highlighted the highest dielectric constant (ε<inf>max</inf> ~ 1827), high density of 5.83 g/cm3. Under an applied electric field of 70 kV/cm, the maximum energy storage density reached 0.71 J/cm3.
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Influence of ethanol biodiesel blends on a diesel engine's efficiency and exhaust emission characteristics
(2022-01-01)
Kanokkhanarat, Phobkrit
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Karin, Preechar
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Depaiwa, Nattawoot
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Wongpattharaworakul, Veerayut
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Srisurangkul, Chadchai
The harm caused by polluted air occurs from dust, smoke, or soot. One of the main causes of pollutions is exhaust emission that comes from diesel engines of cars, trucks, buses, heavy machines, or generators for industrial because their thermal efficiency, torque, and performance are higher than the other engines. To reduce the emission from diesel engines, the fuel substitute for biodiesel which is made from based palm oil is one of the alternatives to use. So, the purpose of this paper is an experimental investigation of the engine performance, combustion characteristics, and smoke intensity of commercial biodiesel fuels (B10 and B20), pure biodiesel fuel (B100), and pure biodiesel blended with ethanol fuels (B100E5 and B100E10), which were performed at various loads (56, 84, 112, and 140Nm) and conducted at constant engine speeds (1000, 1500, and 2000 rpm). The experimental results show that pure biodiesel fuel (B100) and pure biodiesel blended with ethanol fuels (B100E5 and B100E10) have engine performance and combustion characteristics similar to commercial biodiesel fuels (B10 and B20). However, pure biodiesel fuels (B100) and pure biodiesel blended with ethanol fuels (B100E5 and B100E10) can reduce the emissions as the smoke intensity from commercial biodiesel (B10 and B20) is more than 50%.
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Experimental investigation of the impact ethanol-biodiesel-diesel blended fuels on combustion, emission, and performance of compression ignition diesel engine
(2022-01-01)
Wai, P.
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Karin, P.
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Phairote, W.
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Chollacoop, N.
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Kosaka, H.
This research was directed to reduce the global diesel engine emissions and dependency on finite fossil fuel reserves. The ethanol was blended by weight ratio with commercial “B20” fuel (20% palm oil's biodiesel and 80% diesel) as B20E5 (95% B20 with 5% ethanol), B20E10 (90% B20 with 10% ethanol) and B20E20 (80% B20 with 20% ethanol). The results of the engine's performance, combustion, emission, and agglomerate particles size using blended fuels were compared with the results of based commercial B20 fuel. All fuel samples were tested on a four-cylinder direct injection diesel engine at a constant load of 140Nm with engine speeds of 1000RPM, 1500RPM and 2000RPM. When the engine speed increased, the brake-specific fuel consumption decreased, and the brake thermal efficiency increased. The B20E20 shows the highest brake-specific fuel consumption because of the low energy content of the fuel blend and the highest thermal efficiency because of a better combustion process. The ethanol-blended fuels show higher peaks of in-cylinder pressure and heat release rate than the base B20 fuel, with B20E20 as the highest. Ethanol blended fuels have significant advantages in particulate matters reduction, especially in idle engine speed. The blended fuels decreased soot and CO<inf>2</inf> emissions and increased NO<inf>x</inf> emission. The agglomerate particles size distribution was analysed with 100 samples for each fuel by using Scanning Electron Microscopy (SEM) and Image J tools. The average agglomerate particle size of B20, B20E5, B20E10 and B20E20 are 0.253 µm, 0.245 µm, 0.225 µm and 0.187 µm, respectively. As conclusion, adding ethanol to diesel fuel provide strong advantages on soot reduction and higher engine efficiency due to the enrich of fuel oxygen.
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Heat transfer of a coil-tube heat exchanger in the freeboard zone of a rice husk fluidized-bed combustor
(2021-10-01)
Chokphoemphun, S.
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Eiamsa-ard, S.
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Promvonge, P.
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Thongdaeng, S.
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Hongkong, S.
This research presents an investigation on heat recovery from a fluidized-bed combustor by using coil-tube heat exchangers positioned inside the freeboard zone. Rice husk was used as a fuel at a constant mass flow rate of 8 kg/h. Heat recovery experiments were performed at four different air mass flow rates (6.0248, 6.8077, 7.8163, and 8.8646 kg/h) using coil-tube heat exchangers wrapped around with steel wires in three different configurations (2_Coil wires, 4_Coil wires and Full length). Air was supplied to the coil-tube heat exchanger with two different air flows corresponding to flue gas flow: co-flow and counter-flow. The results showed that the outlet temperature tended to decrease with an increase in air flow rate in the coil-tube heat exchanger. The outlet temperatures obtained from the system with co-flow were greater than the one with counter-flow by 7–17 °C (2–15%) depending on the coil-tube heat exchanger configuration. The heat transfer rates in heat recovery process were in the range of 279–425 J/s. In addition, it was found that the heat transfer rate and the outlet temperature of the air from the coil-tube heat exchanger increased with an increase in the number of coil wires wrapped around the outer surface of the coil-tube heat exchanger.
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The effects of operating conditions and the biomass component on combustion efficiency and emission performance of a swirling fluidized-bed combustor fired using
(2021-01-01)
Udomsup, Janya
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Choomjaihan, Prasan
This work presents a study for biomass possible to bring renewable energy in a swirling fluidized bed combustor (SFBC). The main objective of this experimental work was to study the biomass component and excess air of biomass. Palmyra palm shell, Leucaena (lam.), and water hyacinth are using as fuel in the tests. Quartz sand of 600-850 µm and static bed height of 20 cm was used as inert bed material. For all of the tests, the feed rate was fixed as 45 kg h-1 for variable excess air (of 40%, 60% and 80%). As the experimental results, the temperature profiles in SFBC were obviously seen deviate when tests with higher excess air. In the test run, the highest cellulose (palmyra palm shell) for 80% excess air had CO and NO emissions were found in quite stable level (less than 250 and 300 ppm, respectively). The combustion efficiency more than 99% could be achieved in this work.
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Rice husk combustion characteristics in a rectangular fluidized-bed combustor with triple pairs of chevron-shaped discrete ribbed walls
(2019-09-01)
Chokphoemphun, Suriya
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Eiamsa-Ard, Smith
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Promvonge, Pongjet
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Chuwattanakul, Varesa
An experimental combustion work using the rice husk as a fuel was performed in a rectangular fluidized bed combustor with triple pairs of chevron-shaped discrete ribbed walls. The effect of percent excess air (EA = 40%-70%) on temperature distribution and gas emissions in a rectangular fluidized-bed combustor on combustion behaviors (temperature distributions inside the bed, exhaust gas emissions and combustion efficiency) is reported. The free-board had a rectangular shape which modified by increasing the chamber size from 300 × 100 mm2 to 600 × 200 mm2 or two times of the bottom chamber and 2400 mm in height. Triple pairs of rib configurations, namely, 30° chevron-shaped discrete ribbed walls were introduced and placed in the bottom part of the combustion chamber to generate counter-rotating vortices in the chamber. The results show that the fluidized bed combustor with 30° chevron-shaped discrete ribbed walls at 40% percent excess air provides the higher temperature than other of 861 °C. Among the studied excess air percentages, the highest combustion efficiency of 99.2% is obtained at EA = 60%. In addition, combustion at EA = 60% shows the lowest emissions CO, CO<inf>2</inf>, O<inf>2</inf> and NO<inf>x</inf> of 236.8%Vol, 2.55 ppm, 13.53 %Vol, 110.2 ppm, respectively.
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Effect of self-entrainment and porous geometry on stability of premixed LPG porous burner
(2016-06-25)
Laphirattanakul, Ponepen
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Laphirattanakul, Arwut
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Charoensuk, Jarruwat
This paper presents findings on combustion stability of a self-entrained, rich-premixed LPG porous burner. Alumina (Al<inf>2</inf>O<inf>3</inf>) porous foams, with 15 ppi carved into bulked and hollowed cylindrical shapes were placed at a convertible burner tip, while the conventional porous-free burner was used as a base case for comparison. Visual flame propagation, temperature and the percentage of oxygen in a premixed zone were monitored at different firing rates. Initially, the tests were carried out based on basic geometry of bulky porous cylindrical foam under a free flame mode. At this part, the limitation of burner operation was realized in term of premixed equivalence ratio which was a result from self-entrainment. Later, an improvement was made on porous geometry and its effect on burner performance was considered with the previous version. It was found that propagation of flame within a porous matrix had significant contribution to temperature of the premixed zone as a result of radiation. Discussion was made relating to two competing factors controlling flame propagation within the porous burner i.e.; local flame speed and local convective effect. Combustion stability was found with domination of flame speed over convection when Φ < 4.1 in the premixed zone corresponding to illumination of the porous medium with the temperature of premixed zone being greater than 200°C. Beyond 980 kW/m2 (equivalent to 4 L/min of LPG) where convection effect dominated, heat recirculation within porous domain was broken down resulting in formation of soot burning outside porous medium corresponding to considerably drop of temperature. At this range, such short characteristic resident time, lower than 2 s, was observed with Φ > 4.1 in premixed zone. The hollowed cylinder, however, yielded stable flame throughout the operation range at the central port while propagation was maintained in a porous matrix which acted as a flame holder even at high firing rate. The temperature of premixed zone was also observed higher compared with bulked porous burner while the central port could eliminate flow blockage which otherwise gave significant adverse effect on primary air entrainment.
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Combustion behavior in a dual-staging vortex rice husk combustor with snail entry
(2008-11-01)
Eiamsa-ard, S.
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Kaewkohkiat, Y.
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Thianpong, C.
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Promvonge, P.
The combustion characteristics of rice husk fuel in a dual-staging vortex-combustor (DSVC) are experimentally investigated. In the present work, the vortex flow is created by using a snail entrance mounted at the bottom of the combustor. The temperature distributions at selected locations inside the combustor, the flue gas emissions (CO, CO<inf>2</inf>, O<inf>2</inf>, NO<inf>x</inf>), and the combustion/thermal efficiency are monitored. Measurements are made at a constant rice husk feed rate of 0.25 kg/min with various excess airs (37%, 56%, 74% and 92%) and different secondary air injection fractions (λ = 0.0, 0.15 and 0.2), respectively. The combustion chamber is 1800 mm high and 300 mm in diameter (D) with a centered exhausted pipe while the middle chamber of the combustor is set to 0.5D. The smaller section at the middle chamber is introduced to split the chamber to be dual-staging chamber where a large central toroidal recirculation zone induced by swirl flow through the small section is generated in the top chamber. The experimental results reveal that the highest temperature inside the combustor is about 1000 °C whereas both the thermal and the combustion efficiency are 41.6% and 99.8% for 74% excess air without the secondary air injection (λ = 0.0). In addition, the emissions are CO<inf>2</inf> = 8.1%, O<inf>2</inf> = 9.3%, CO = 352 ppm, NO<inf>x</inf> = 294 ppm and small amount of fly ash. Therefore, the DSVC shows an excellent performance, low emissions, high stabilization and ease of operation in firing the rice husk. © 2008 Elsevier Ltd. All rights reserved.

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