Fuel Utilization Efficiency Research Articles

A flame fuel cell stack powered by a porous media combustor

A flame fuel cell stack is successfully assembled and operated in this paper. A micro-tubular solid oxide fuel cell (mT-SOFC) stack was directly operated in and powered by a fuel-rich methane flame in a porous media combustor. The combustor consists of a combustion region and a hot zone. The combustion region and the hot zone are connected by an expansion region, which is designed to match the combustion kinetics and the electrochemical kinetics, thereby increasing the fuel utilization efficiency of the stack. With a 36-Al2O3-tube stack located in the hot zone, the temperature field and composition distribution were found to be suitable for the operation of high-temperature SOFCs with traditional materials. Four mT-SOFCs are arranged in a parallel configuration and placed in the center of the 36-tube stack, with the power reached 3.6 W at 0.6 V when the fuel-rich methane flame was operated at an equivalence ratio of 1.6. The maximum electrical efficiency was 6% with a fuel utilization efficiency of 23%. The present configuration demonstrated a promising technology for a self-sustained combined heat and power (CHP) system.

Impact Factors Analysis of the Hot Side Temperature \tof Thermoelectric Module

The thermoelectric generator (TEG) plays a crucial role in converting the waste energy of exhaust into electricity, which ensures energy saving and increased fuel utilization efficiency. In the urban driving cycle, frequent vehicle operation, like deceleration or acceleration, results in continuous variation of the exhaust temperature. In order to make the operating performance stable, and to weaken the adverse effects of the frequent variation of the exhaust temperature on the lifetime and work efficiency of the electronic components of TEG systems, the output voltage of the thermoelectric (TE) module should stay more stable. This article provides an improved method for the temperature stability of the TE material hot side based on sandwiching material. From the view of the TEG system’s average output power and the hot side temperature stability of the TE material, the analyzing factors, including the fluctuation frequency of the exhaust temperature and the physical properties and thickness of the sandwiching material are evaluated, respectively, in the sine and new European driving cycle (NEDC) fluctuation condition of the exhaust temperature. The results show few effects of sandwiching material thickness with excellent thermal conductivity on the average output power. During the 150–170 s of the NEDC test condition, the minimum hot side temperatures with a BeO ceramic thickness of 2 mm and 6 mm are, respectively, 537.19 K and 685.70 K, which shows the obvious effect on the hot side temperature stability of the BeO ceramic thickness in the process of acceleration and deceleration of vehicle driving.

Modeling of passive vapor feed alkaline membrane direct methanol fuel cell

A two-dimensional model for passive vapor feed alkaline anion membrane direct methanol fuel cell (AAEM-DMFC) is developed to investigate the effects of open ratio, carbon dioxide (CO2) exit length, micro-porous layer (MPL) and porous layer’s hydrophobicity. The results show that decreasing the open ratio and enlarging the CO2 exit can relieve the methanol crossover. The fuel utilization efficiency can be significantly improved with the help of methanol recovery. The back-flow water direction shifts toward anode at low current density. The anode MPL (AMPL) can effectively mitigate the methanol intake from the tank and methanol crossover, however, the cathode MPL (CMPL) enhances the methanol intake and crossover at low current density. Moreover, the minimum methanol crossover can be achieved under an appropriate AMPL contact angle at high current density. Increasing the ACL hydrophobicity and vapor transport layer (VTL) hydrophilicity contributes to reducing methanol crossover. Overall, good water management and low methanol crossover can be achieved by optimizing porous layer structure, open ratio and carbon dioxide (CO2) exit length. The simulation results presented in this study can provide further guidance on the optimization of passive vapor feed AAEM-DMFC.

A novel method for analysis and prediction of methanol mass transfer in direct methanol fuel cell

Two-phase gas/liquid flows coupled with electrochemical reactions in the anode of direct methanol fuel cell (DMFC) are quite complicated transport phenomena. The methanol transport is a key factor influencing the performance as well as fuel utilization efficiency. In this paper, a dimensionless correlation of methanol mass transfer in DMFC anode is proposed. Firstly, a method for detecting methanol concentration in catalyst layer was developed, which is the key parameter to obtain the mass transfer coefficient. Then, the influences of the various factors on the mass transfer coefficient, including physical properties of fluid, structures of the electrode, cell configuration and cell operation conditions, were investigated. And a correlation between four dimensionless groups, i.e., Sh, Re, Sc and Π (ratio of consumption and feeding rate of methanol), was deduced using the dimensional analysis. Finally, MEA optimization and fuel utilization efficiency evaluation based on the above analysis is performed. A maximum power density of 178 mW cm−2 at 80 °C and atomistic air is achieved, 40% higher than that of commercial one made by Johnson Matthery.

Palladium-nitrogen coordinated cobalt alloy towards hydrogen oxidation and oxygen reduction reactions with high catalytic activity in renewable energy generations of proton exchange membrane fuel cell

Oxygen reduction reaction (ORR) is one of the most important processes in energy conversion and conservation in proton exchange membrane fuel cell (PEMFC). In PEMFC, developing non-platinum based catalyst by understanding the catalytic activity for both oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) is essential for energy storage/conversion. Herein, we report preparation of such a bi-functional and durable catalyst consists of palladium and nitrogen coordinated cobalt and its catalytic activity is discussed methodically. Palladium cobalt bimetallic alloy nanoparticles dispersed over graphitic carbon nitride (Pd-Co/gCN) serves as an efficient anode and cathode catalyst in proton exchange membrane fuel cell for energy conversion. Incorporation of cobalt with palladium in nitrogen rich support material optimally modifies the bond strength of palladium-hydrogen (Pd-H) complex and promotes HOR, results in significant improvement of overpotential at the anode whereas, the nitrogen coordinated cobalt predominantly enhances the ORR activity at the cathode in acidic medium. Effects of mass transfer on the kinetics of ORR were investigated with rotating disc electrode (RDE). The hydrodynamic voltammograms were investigated to determine the kinetic parameters using the Koutecky–Levich equation. Our study presents an experimental realization of unveiling a good power density with high fuel utilization efficiency in a single cell for electrochemical energy conversion with complete elimination of platinum.

High performance of protonic solid oxide fuel cell with BaCo0.7Fe0.22Sc0.08O3−δ electrode

Solid oxide fuel cells (SOFCs) have attracted tremendous attention for their combination of environmental power generation and fuel flexibility. Proton conducting SOFCs (P-SOFCs) demonstrate advantages over oxygen-ion conducting SOFCs, such as less activation energies on ionic transport and higher fuel utilization efficiency. Central to the devices is a suitable cathode with high catalytic activity. Herein, a cubic perovskite BaCo0.7Fe0.22Sc0.08O3−δ (BCFSc) has been applied as the cathode in proton-conducting solid state fuel cell (SOFC) with BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte. Peak power densities of 760, 591, 452 and 318 mW cm−2 are obtained at 650, 600, 550 and 500 °C with humidified hydrogen as the fuel and air as the oxidant. A low polarization resistance of 0.05 Ω cm2 under open circuit at 650 °C is observed.

Effect of cobalt precursors on Co3O4 anodic catalyst for a membrane-free direct borohydride fuel cell

The fuel discharging efficiency of direct borohydride fuel cell (DBFC) depends on both the anodic catalyst activity and borohydride hydrolysis. In this paper, Co3O4 anodic catalysts prepared from different cobalt sources used in DBFC have been investigated. It showed that the catalytic performance of Co3O4 was associated with its microstructure that relied on the precursor. The maximum power densities obtained was 40, 62 and 28 mW cm−2 of DBFC with Co3O4 catalyzed anode from CoCl2 (marked DBFC-A), Co(NO3)2 (marked DBFC-B) and Co(CH3COO)2 (marked DBFC-C), respectively. The Co3O4-A has the highest number of electron transfer (n = 7.06) which is close to the theoretical value (n = 8), and DBFC-A showed good voltage stability with specific capacity of 720 mAh.g−1. A rapid voltage attenuation occurred in DBFC-B with the specific capacity of 330 mAh.g−1 because Co3O4 from Co(NO3)2 has the higher catalytic activity for both borohydride oxidation reaction (BOR) and hydrolysis which lead to the lower fuel utilization efficiency.

A cost-effective approach to reducing carbon deposition and resulting deactivation of oxygen carriers for improvement of energy efficiency and CO2 capture during methane chemical-looping combustion

The objective of this research is to investigate the effect of steam on reducing carbon deposition during CH4 chemical looping combustion (CLC) on a fixed bed reactor. Steam proved to be significantly effective not only for the fuel utilization efficiency of CLC but also for the stability of the oxygen carrier (OC). The evaluation tests were performed with CuO/γ-Al2O3 OCs prepared with three different methods. The results showed that OC prepared using co-precipitation method performed the best with the highest reactivity for CH4 combustion at low temperature (700°C) compared to that prepared using mechanical mixture and impregnation methods. It was also found that the carbon deposition was the main reason for the low combustion efficiency and the deactivation of OCs in redox cycles. For OCs at 800°C, after 10 cycles without steam, 25–44% CO2 selectivity reductions were observed, accompanied by Barrett-Joyner-Halenda (BJH) pore volume decreases of 31–47%. With the steam introduction, the CO2 selectivity consistently achieved ∼100% in 10-cycle CLC, and the pore volumes of OCs decreased by only 11–22%, which was mostly attributed to the carbon-steam gasification reaction. The OCs for CH4 CLC with and without steam were characterized by using different methods, including surface area and pore analysis, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), H2 temperature programming reduction (TPR), and scanning electron microscope (SEM). The results demonstrated that steam could easily gasify the carbon deposition, greatly intensify the redox degree of OCs at 800°C, and strengthen the redistribution of Cu on the surface of Al2O3, contributing to the fine and uniform distribution of CuO. Therefore, steam can be successfully used for considerable enhancement of the overall performance of CH4 CLC.

Assessment of sensible heat storage and fuel utilization efficiency enhancement in rubber sheet drying

A sensible heat storage unit was tested in the conventional method of rubber drying. The heat storage unit gradually releases the heat to the rubber sheet smoke room. This retains temperature in the range (40–60°C) for prolonging storage in the smoke room. Therefore, the frequent supply of wood to the furnace is trimmed down. Effects of the heat storage brick stack height on heat storage characteristics and applications for rubber sheet drying were investigated. The experiments were conducted at three heat storage heights, 50, 100, and 150cm. For all cases, the temperature of the brick stack was found to increase sharply during the initial period and remained constant for a period of time before slowly declining. This is a result of the heat storage system that maintains the high temperature by slightly releasing the generated heat. Thermal efficiencies of heat storage system varied between 33 and 28% for the heights of 50 to 150cm. The drying time of the rubber sheets using 100cm heat storage was 78h, while the thermal efficiency of the drying system was 6.71%. The frequency of wood addition was reduced from about five to six times per day to one time or less per day.

CLIMATE FACTORS INFLUENCE OVER HEAT ENGINEERING CHARACTERISTICS, ENERGY EFFICIENCY AND EVALUATION OF ENVIRONMENTAL CONSEQUENCES OF GAS FUEL COMBUSTION

The problem of interconnection the principal characteristics of Earth climate, combustion process and fuel utilization efficiency has been considered. Atmospheric (free) air serving as an oxidizer in combustion processes is differed by inner availability the water vapor. Absolute content of water vapor is defined by an air temperature and its relative humidity. Humidity impact of atmospheric air on fuel principal heat engineering (power) characteristics has been investigated, namely regarding the theoretical combustion temperature, as well as of low and high combustion value. Reduction of each of mentioned characteristics by growth of air water vapor content has been proved. The thermodynamic analysis of dependence the efficiency of fuel utilization on combustion air parameters has been carried out by varying its temperature and humidity. It has been stated for the first time that an air preheating till 373 K ensuring monotonous enhancement of efficiency and fuel consumption reduction in case of dry combustion air causes the efficiency lowering in case of wet combustion air (oxidizer). Negative influence of combustion air humidification is increased by rise the air temperature and humidity – up to air saturation (dew point reach). Ten main climate zones are highly differed between themselves by temperature and moisture characteristics, thus changing an impact upon combustion process for fossil and alternative fuels. Evaluation of interconnection the climate features and combustion processes has been carried out basing upon energy efficiency and environmental consequences including analysis of greenhouse impact and input of greenhouse gases (CO2) into global warming the climate.

Experimental study on the energy flow of a gasoline-powered vehicle under the NEDC of cold starting

In order to evaluate and improve the fuel utilization efficiency of gasoline-powered vehicle, the vehicle energy flow test was conducted on chassis dynamometer under the NEDC of cold starting. Based on the tested data, the vehicle energy balance was built under the whole NEDC. Research results show that the distributions of various kinds of energy flow were largely influenced by vehicle operating conditions. Apart from idling conditions, the brake thermal efficiency of internal combustion engine (ICE) is mainly between 10% and 35%. At the initial stage of NEDC, the brake thermal efficiency is very low due to the cold starting. Under urban driving cycle (UDC), the percentage of pumping loss is usually below 10%, and under extra urban driving cycle (EUDC), it further decreases and even approaches to zero. The exhaust gas energy flow is mainly influenced by the mass flow rate of exhaust gas, while its percentage in total fuel energy depends largely on exhaust gas temperature. In general, the coolant energy flow is less sensitive to the ICE operating conditions, but its percentage fluctuates wildly under the transient conditions of NEDC. In most cases, the percentage of ICE coolant energy flow is between 13% and 35% with dramatic fluctuations, and the sudden deceleration of vehicle causes the generation of sharp peaks of the percentages of pumping loss and coolant energy flow.

A study on the Chinese nuclear energy options and the role of ADS reactor in the Chinese nuclear expansion

China has the advantage of learning from the mistakes made by nations that have developed their nuclear power energy system in the last century. Such mistakes encompass the lack of sustainable development of the nuclear energy and poor planning in the back-end of the nuclear fuel cycle. The present paper studies the evolution of a double strata cycle with fast reactor gradually replacing the LWR. It starts from 2035 and covers the historical development of nuclear energy in China to the year 2100. The paper studies the ADS impact on the NFC and estimates the number and the deploying schedule of the ADS reactors to limit the accumulation of minor actinides. The other aspects considered here are natural uranium resources, fuel utilization efficiency, proliferation and diversion risks, spent fuel production and overall materials flow. Additionally, perturbation calculations were performed to evaluate the impact of the uncertainty on key parameters. The results are discussed in view of the Chinese nuclear fuel cycle plan and their policy implications are thoroughly evaluated.

Exergy analysis of methane cracking thermally coupled with chemical looping combustion for hydrogen production

This paper proposes a novel hydrogen production process by Methane Cracking thermally coupled with Chemical Looping Combustion (MC–CLC) which provides an advantage of inherent capture of CO2. The energy utilisation performance of the MC–CLC process is compared with that of conventional Methane Cracking with combusting CH4 (MC-CH4) and Methane Cracking with combusting H2 (MC-H2) using exergy analysis, with focus on exergy flows, destruction and efficiency. The three MC processes are simulated using Aspen Plus software with detailed heat integration. In these processes, the majority of the exergy destruction occurs in the combustors or CLC mostly due to the high irreversibility of combustion. The CO2 capture unit has the lowest exergy efficiency in the MC-CH4 process, leading to a lower overall exergy efficiency of the process. The combustor in the MC-H2 process has a much higher energy efficiency than that in the MC-CH4 process or the CLC in the MC–CLC process. Although the use of H2 as fuel decreases the H2 production rate, the MC-H2 process provides the advantage of an absence of CO2 generation, and stores more chemical exergy in the solid carbon which can be utilised appropriately. The MC–CLC process obtains the highest exergy efficiency among the three models and this is primarily due to the absence of a CO2 capture penalty and the CLC’s higher fuel utilization efficiency than the conventional combustion process.

Математическая модель определения начального участка гетерогенного факела и ее адаптация

This paper describes a new mathematical model of aerodynamics and heat transfer at the initial section of heterogeneous flame continuum, which largely determine the fuel utilization efficiency of the boiler unit. It pro-vides an analytical description of volatile organic emissions depending on the temperature. This temperature relates to heating coal-dust particles; at that, the ignition of air and volatile-matter mixture is considered both at the known temperature and at the known lower threshold of mixture explosion. These two approaches lead to the same results at determination of an initial flame section. Model reliability is ensured by the known experimental data obtained at determination of concentration limits of air and volatile-matter mixture ignition, period to mixture ignition and other data.

Effective Pathway to Improve Indoor Thermal Comfort in Rural Houses: Analysis of Heat Efficiency of Elevated Kangs

AbstractRural households are mainly heated using kangs in northern China. In this study, elevated kangs (EK) were constructed in six rural houses in Zhuanglang County. Indoor and outdoor temperatures were monitored hourly in houses using the traditional type of kang (TK) and the elevated kang. A polynomial regression model was designed to analyze the time series data on fuel consumption and temperature change. The thermal effectiveness of the two types of kang was modeled according to the daily life scenario of rural households. The results show that the EK can improve fuel efficiency and the indoor thermal comfort of rural residents in winter. At a given fuel consumption, the EK Tha (hourly average temperature difference during the heating period) was 5.1°C higher than the TK Tha in Gaoyahan village and 6.6°C higher than the TK Tha in Xiawan village. At a given indoor temperature, EK fuel consumption was less than that of TK. Use of the EK improved fuel utilization efficiency, which indicated that the me...

Estimating the energy density of direct borohydride–hydrogen peroxide fuel cell systems for air-independent propulsion applications

The energy density of DBPFCs (direct borohydride–hydrogen peroxide fuel cells) is estimated for air-independent propulsion applications. The performance of DBPFCs containing heat-treated electrocatalysts supported on multiwalled carbon nanotubes is evaluated. The open circuit voltage and the maximum power density are 1.44 V and 243 mW/cm2, respectively, whereas the voltage efficiency is 17.9% at the maximum power density. Based on experimental results, the energy density is estimated to be 63.2 Wh/kg (87.1 Wh/L), which is much lower than those of other power sources. The degree of influence of various parameters on the energy density is ranked in the following order: fuel utilization efficiency > voltage efficiency > H2O2 (hydrogen peroxide) concentration > NaBH4 (sodium borohydride) concentration > maximum power density. Performance targets comprising of fuel utilization efficiency of 90%, voltage efficiency of 40%, H2O2 concentration of 50 wt%, NaBH4 concentration of 20 wt%, and maximum power density of 650 mW/cm2, have been determined. Under these conditions, the energy density and fuel volume are expected to be 378.5 Wh/kg (541.4 Wh/L) and 1.57 L, respectively, which would allow them to be used widely as power sources for air-independent propulsion.

Design and Fabrication of a 600W Anode Supported Flat Tubular SOFC Stack

Keywords: SOFC stack, flat tube, metallic support, Ag-Cu air braze, Introduction Recently, great interests are focused on Solid Oxide Fuel Cells for future energy economy. In order to reduce the cost and increase the lifetime of SOFCs, lowering the working temperature is necessary. To meet the demands, new stack structures and materials are developed. Among them, flat tubular stacks are shown to be promising for their performance and fabrication techniques, and also metallic materials are applied as interconnect and support for their characteristics [1]. In this work, we design and fabricate a 600W anode supported flat tubular SOFC stack. The stack is composed of 36 flat tubular cassettes made by FeCrAl alloy. Cells composed of NiO-YSZ (anode)/ YSZ (electrolyte)/LSM-YSZ (cathode) are sealed on cassettes by Ag-Cu air braze. Experimental The schematic diagram of stack structure is shown in Fig 1. A short stack is composed of several metallic cassettes made by FeCrAl (a commercial product: 1Cr21Al4). Five frames are located on the surface of the cassette, on which cells are sealed on the anode side by Ag-Cu air brazing. Ag-Cu brazes also serve as the electrical connect to the anode. FeCrAl interconnects with Ag mesh serve as the electrical connect to the cathode. Ag wires connect th e Ag-Cu braze with interconnects. Fuel inlet pipe is located at one end of the cassette and outlet is on the other end. Pipes are sealed by Ag rings with ceramic tubes. Fuel flows along the pipes and the ceramic tubes. Cells of 5x5cm2 are produced as described in previous results [2]. Anode substrates of NiO-YSZ are produced by conventional tape casting and sintering methods. YSZ electrolytes of 15 um are produced by spray and cathodes of 4x4cm2 LSM/YSZ are produced by screen printing. Results and Discussion Stack of 36 cassettes are produced and tested. Humidified H2(2-3% H2O) is applied as the fuel and air as the oxidant. A mean open circuit voltage of 1.03V per cassette is obtained under working temperature 750 centigrade. The stack has been tested for 1000 hours. Ag-Cu braze and FeCrAl show good stability and reliability. Fig.2 shows the performance of the 36-cassette stack under different fuel flow. When 15slm H2 is supplied to the stack, a maximum output of 614W and an average power density of 213mw/cm2are obtained. The fuel utilization efficiency is 51%. Conclusions An anode supported flat tubular stack is designed and produced. Stack of 36 cassettes are produced and tested with humidified H2 as fuel. An average power density of 213mw/cm2is obtained, higher than those reported results of the stacks [1].

Breed-and-burn strategy in a fast reactor with optimized starter fuel

The in situ breed-and-burn (B&B) strategy in fast reactor is capable of offering very high fuel utilization efficiency. CANDLE (Constant Axial shape of Neutron flux, nuclide densities and power shape During Life of Energy) or TWR (Traveling Wave Reactor) is a possible scheme to implement the B&B strategy. The approach in realizing the equilibrium state of CANDLE is based on neutron source supply from ignition zone with enriched uranium or plutonium. And burnable poison is usually employed to compensate the extremely high excess reactivity during the startup. In the present work, the optimization of the starter fuel with only plutonium and depleted uranium is performed to reduce the initial positive excess reactivity swing and to flatten the power distribution. The optimization is done with refer to a nominal steady state CANDLE core. In this regard the swing of the reactivity is limited during the startup. And the initial power shape is flattened significantly compared with that without optimization. It is proved that constructing the ignition zone with refer to the equilibrium state of a CANDLE is effective and feasible to improve the operation performance during the startup.

Design and Fabrication of a 600W Anode Supported Flat Tubular SOFC Stack

A 600W anode supported flat tubular SOFC stack is designed and fabricated. FeCrAl alloy is applied as metallic cassette. Ag-Cu serve as seal to the anode and metallic cassette and electrical connect to anode. After tested for 1000 hours, the jointing of FeCrAl, Ag-Cu braze and anode shows good stability. With cells of Ni-YSZ/YSZ/LSM-YSZ, a maximum output of 614W and an average power density of 213mw/cm2 are obtained in this stack configuration. The fuel utilization efficiency is high as 51%.

Sustainability of the Chinese nuclear expansion: Natural uranium resources availability, Pu cycle, fuel utilization efficiency and spent fuel management

The civil nuclear energy deployment in China is important for future “Nuclear Renaissance” of China and worldwide. Compared to the other nations that developed their nuclear power energy system in last century, China can take advantage of the research and mistakes made by those states in relation to the back-end of the nuclear fuel cycle (NFC). The spent fuel accumulated by decades of operations of civil nuclear power is today a big burden for the industry. China must carefully plan the NFC for a sustainable development of the nuclear energy with special consideration to close the fuel cycle. The present paper addresses the NFC options and implications of a LWR scenario development and of a fast reactor park developed after 2035 and 2050, and covers the historical development of nuclear energy in China (i.e. from the first criticality of the first reactor) to the year 2100. The paper studies the partition and transmutation strategy with the use of accelerator driven system (ADS) to burn the minor actinides (MA) to understand the ADS impact on the NFC and to estimate the number and the necessary deploying schedule of the ADS reactors to limit the minor actinides stock build up. The other aspects taken into consideration for the comparison of the different scenarios are the natural uranium resourced used, the efficiency of fuel utilization, the proliferation and diversion risks associated to each scenario and the overall spent fuel production and flow. The code INFCIS developed by the International Atomic Energy Agency (IAEA) is used in the present study.