Fuel Flow Velocity Research Articles

Enhancing fuel transport and cell performance by an anodic wedge-shaped channel in a paper-based microfluidic fuel cell

Paper-based self-pumping microfluidic fuel cells (PMFCs) typically exploit the wicking effects in porous papers to enable passive reactant delivery and co-laminar flow, eliminating micro pumps and physical membranes. PMFCs have been regarded as promising micro-power sources for next-generation paper-based electrochemical microfluidic assays for biomedical applications. However, the PMFC performance is fundamentally limited by the low capillary flow velocity and ineffective diffusive fuel transport. In this study, a novel PMFC with an anodic wedge-shaped channel is developed. The anodic wedge-shaped channel enables reactant convection at improved fuel flow velocity. Visualization experiments suggest that the fuel flow velocity can be improved by about 23 times in this anodic wedge-shaped channel configuration as compared to that in conventional single-layer paper-based flow channel. In addition, favorable features like localized enhancement of fuel transport and reduced fuel crossover are also observed in this novel configuration. Due to enhanced convective-diffusive fuel transport, the cell performance can be improved 245.8 % as compared to the single-layer case. The peak power density reaches 59.9 mW cm−2 and the limiting current density achieves 305.9 mA cm−2, outperforming most of the previous PMFCs. This anodic wedge-shaped channel configuration can also be potentially used in paper-based assays to enhance reactant delivery.

Numerical study on the cavitation flow characteristics of high-pressure fuel in injector orifices based on compressible non-isothermal model

The flow inside the orifices in diesel injector largely determines the injection characteristics, which further affects the performance of the diesel engine. In this paper, numerical simulation is conducted to characterize the fuel flow with characteristics of two-phase cavitation, high speed, high pressure, high turbulence intensity, and high viscosity in two crucial orifice locations. The OZ orifice is selected as a benchmark to select the appropriate turbulence model and cavitation model. The simulation results from different turbulence and cavitation models are analyzed, and the combination of the realizable k–ɛ turbulence model and the Zwart–Gerber–Belamri cavitation model proves to be superior. Then, based on the validated models, the compressibility and non-isothermal characteristics of the fuel and two geometric parameters of the nozzles in an injector are emphatically discussed to depict the cavitation flow. The results suggest that the compressibility and non-isothermal characteristics of fuel affect the mass flow rate, fuel flow velocity, and cavitation extent within the orifices with a maximum deviation of the mass flow rate of 7.1%. However, their influence on the orifice flow coefficient is relatively minor with a maximum deviation of 0.8%. The mass flow rate and flow coefficient are both positively correlated with the rounded edge radius and taper coefficient. A greater rounded edge radius and taper coefficient can lead to a better fuel flow capacity in the nozzle orifice.

Entropy Generation and Exergy Assessment of Methane–Nitrous Oxide Diffusion Flames in a Triple-Port Burner

A triple-port burner was used in this study, and a numerical simulation was employed to investigate the entropy generation rate of CH4–N2O diffusion flames at the R ratio = 1 . Here, R ratio refers to the ratio of the oxidizer flow velocity to the fuel flow velocity. In order to scrutinize the decomposition effect of N2O on entropy generation, an oxygen-enriched gas with the same nitrogen to oxygen ratio as N2O (N-to- O = 2 ) was used in CH4–N2–O2 diffusion flames. Besides, because the N2O could decompose into the oxygen-enriched gas, the oxygen-enriched effect was also studied by the CH4–air diffusion flames that were conducted in this research. The entropy generation rate comprises of three items in this study, including heat conduction, mass diffusion, and chemical reaction. As a result, the different reaction pathways would take part in the major reaction pathway in CH4–N2O diffusion flames, causing more entropy generation rate being produced through the more intense reactions in CH4–N2O diffusion flames. The irreversibility in CH4–air diffusion flames are dominated through heat conduction and chemical reaction, which is an identical result in CH4–N2–O2 diffusion flames. However, in CH4–N2O diffusion flames, chemical reactions dominated the irreversibility because of the more intense reaction caused by the thermal effect of N2O decomposition. As a result, the decomposition effect of N2O influences the availability of CH4–N2O diffusion flames.

The Burning Characteristics of Transformer Oil Spill Fire on Horizontal and Inclined Substrate Under Continuous Leakage Condition

Abstract Spill fire is a typical fire type that endangers industrial safety. This work systematically investigates the burning characteristics of transformer oil spill fire under different fuel leakage rates and substrate tilt angles, and the fuel flow hydrodynamic parameters. According to the flame spread behavior and substrate temperature distribution, the spill fire spread process is divided into four stages and the substrate is divided into three zones. The relative difference between max burning length and stable burning length is positively correlated with the substrate tilt angle. The increase of fuel flow velocity contributes to the flame spread velocity, but the increase of fuel flow velocity and the decrease of fuel layer thickness weaken the accelerating effect of surface flow on flame spread, which leads to a decreasing trend of flame spread velocity increase. The spill fire mass burning rate is 0.161–0.358 times of pool fire, and the increase of heat loss due to fuel flow and the radiant heat loss through the fuel layer dissipated through the substrate are the main reasons for the lower mass burning rate than pool fire. The research results provide basic data and references for further research on the formation mechanism of heavy oil spill fire and the prevention and control of small-scale spill fire.

Thermal effect and oxygen-enriched effect of N2O decomposition on soot formation in ethylene diffusion flames

This study experimentally investigated the effect of nitrous oxide (N2O) decomposition on soot formation in N2O/ethylene diffusion flames. The effect of N2O decomposition on the soot formation mechanism was examined in three oxidation cases (Cases Case I–III). In Case I, N2O was used as the oxidant; in Case II, an oxygen-enriched N2/O2 mixture (67 % N2 + 33 % O2) was used as the oxidant; and in Case III, standard air (79 % N2 + 21 % O2) was used as the oxidant. A triple-port burner was used to generate diffusion flames with various R (ratio of the oxidizer flow velocity to the fuel flow velocity) values (R = 0–6). The soot concentration was measured through laser-induced incandescence, and the soot temperature was determined using two-color pyrometry. The measured soot temperatures increased significantly due to the thermal effect in the upstream position of the N2O/C2H4 flames. The oxygen-enrichment effect on soot formation increased gradually from 10 % to 60 % as R increased from 0.5 to 6. The integration of the soot concentration along the flame length revealed that the soot formation rate and soot oxidation rate might rebalance under the N2O decomposition effect.

Numerical Study on the Effect of Wall Thickness on the Combustion Characteristics of Non-premixed Hydrogen Micro-jet Flame

The effect of wall thickness on the combustion characteristics of nonpremixed hydrogen micro-jet flames was studied by two-dimensional numerical computation with a detailed reaction kinetics for the development of hydrogen micro-burner. The hydrogen jet diffusion flames achieved by micro-tubes with the same inner diameter and length but different wall thicknesses were investigated. The heat exchange between solid tube and gases were included in the numerical computation. The distributions of flame temperature, OH radicals, details of thermal interaction, and combustion efficiency were analyzed for comparison. It was found that the temperature distribution, flame shape, and heat recirculation are changed with the fuel flow velocity, and they are affected by wall thickness. The mechanism of wall thickness on the combustion characteristics of hydrogen jet diffusion flame was clarified. Finally, an interesting numerical experiment was conducted to give a further explanation of the effect of heat recirculation and to provide guidance of the thermal management of the micro-burner.

Study of the influence laws of the flow and cavitation characteristics in an injector control valve

AbstractFuel cavitation can cause damage to the structure of an injector control valve, which can further affect the service life of the injector. Therefore, it is of great importance to carry out research on the mechanism of cavitation in injector control valves. In this study, the dynamic evolution of the cavitation and fuel flow characteristics during the opening of a ball valve in a high‐pressure common rail injector control valve were studied. First, a transient CFD simulation of the cavitation during the opening of the control valve was performed using dynamic mesh technology to analyze the evolution and formation mechanism of the cavitation. The cavitation was influenced by the fuel flow velocity, which was affected by the sealing cone angle and the ball valve movement. Additionally, the fuel reflux could effectively inhibit the development of cavitation. By comparing with the pressure, velocity, and mass flow rate of the fuel under conditions without cavitation, it was found that the cavitation had a remarkable effect on reducing the hydraulic shock to the ball valve and sealing cone as well as stabilizing the fluctuation of the fuel velocity in the control chamber. In addition, the cavitation noticeably decreased the fuel mass flow rate (by up to 32% at 0.015 ms) and increased the average pressure in the chamber (by up to 29.1% at 0.01 ms), ultimately leading to a slower response of the control valve. The analysis of different inlet pressures of the control valve indicated that the increase in the inlet pressure caused the cavitation to extend upward along the sealing cone, and that the cavitation ring area and the cavitation strength increased.

Thermoacoustic instability and flame transfer function in a lean direct injection model gas turbine combustor

This paper discusses the combustion dynamic characteristics of hydrogen/methane flames and the flame response to fuel flow fluctuation in a model lean-direct injection gas turbine combustor. The results show that a higher frequency longitudinal thermoacoustic instability is triggered as hydrogen/methane ratios increase. The mode shift is accompanied by shortening flame length and hence decreasing convection time delay between fuel injection and flame location. The flame transfer function (FTF) subject to fuel flow rate modulation is determined over a range of frequencies for hydrogen/methane volume ratios of 25:75, 50:50, and 75:25 at a fixed equivalence ratio of 0.55. The input and output of the FTF are the velocity fluctuation of fuel-mixture at the inlet of the burner and the heat release fluctuation of flame in the combustion zone, respectively. Because of the difficulty of measuring fuel flow velocity at the inlet of the combustor while the flame exists, the fuel transfer function (FLTF) is measured and used along with the intermediate flame transfer function (ITF) to determine the FTF. The transfer functions are measured at frequencies up to 600 Hz and the FTF above 600 Hz is determined from the flame response at higher harmonic frequencies. Results of the FLTF measurement show that an acoustic resonance is formed within the fuel injector and the resonance frequency changes with the hydrogen/methane ratio as well as the length of the fuel feedline. The gain of FTF at a given frequency decreases as the hydrogen content increases and the absolute value of the slope of the phase plot, which is related to the convection time delay between fuel injector tip and flame location, decreases as the hydrogen enrichment ratio increases. Using the measured FTF as input to an open-source simulator, the occurrence of instability is predicted and compared with experimental results. The modeling results agree very well with the experimental data in predicting the occurrence of unstable combustion, the frequency at which unstable combustion occurs, and the acoustic mode inside the combustor.

Investigation on the process of injection of commercial grade and blended fuel in a diesel engine

Purpose. A computational valuation of the parameters of the process of commercial grade and blended fuel flow in the injector nozzle of a locomotive diesel engine, and its impact on spraying conditions in the combustion chamber. Methodology. The scientific investigation is based on using the technique of a comparative numerical experiment. Modern numerical methods in computational fluid dynamics are used for simulating fuel flow and spraying processes in the injector nozzle and combustion chamber. Findings. It was found that when working with commercial grade fuel with maximum pressure in the area of the injector well of 85MPa, the fuel flow velocity in the fuel injection nozzle hole reaches 434 m/s, whereas when working with fuel blended with alcohol the velocity decreases to 429 m/s (at a 25% alcohol concentration). Due to the lower pressure of saturated vapours of the blended fuel, as compared to that of commercial grade fuel, the fuel-air mixing conditions degrade at the operating duty being investigated. Originality. The investigation helped to study the impact of blended fuel composition on changes in the processes of its flow in the injector nozzle, and on the injection into the combustion chamber and the fuel-air mixing conditions. The study results helped to develop recommendations on ensuring effective ICE operation with blended fuel. Practical value. A change in the conditions of blended fuel spraying and fuel-air mixing should be taken into account when choosing effective fuel injection advance angles and fueling principles in order to ensure high ICE economic and ecological performance.

Optical Diagnostics in a High-Pressure Combustor with Gaseous Oxygen and Kerosene

This paper presents analysis of results from optical diagnostics in a high-pressure combustor burning gaseous oxygen (GOX) and liquid kerosene RP-2 fuel through a jet-swirl coflow injector. The objectives of the experiment were to measure flame stabilization and position under high-pressure conditions. Data were obtained at pressures from 2 to 16.5 MPa and mixture ratios from 2.9 to 20. High-speed cameras captured side-on chemiluminescence and infrared images of the flame. Results show that the flame-spreading angle from the injector ranges from approximately 3 to 6 deg, varying with pressure and propellant mass flow rate. A novel borescope was used to image the flame from upstream of the GOX post, enabling visualization of the flame near its stabilization location. The flame stabilization characteristics change significantly with the fuel flow velocity (which is proportional to pressure). At low pressures and fuel flow velocities, the flame appears to be distributed azimuthally in a nearly axisymmetric manner. At higher velocities, helical spirals of luminosity develop near the GOX post. In addition, the side-on views reveal concentrated streaks of, presumably, fuel entering the combustion chamber. These results suggest that computations must resolve the individual fuel injection orifices, to capture the flame stabilization.

Portable Generator Based on Direct-Flame Metal-Supported Solid Oxide Fuel Cells (MS-SOFCs)

Metal-Supported solid oxide fuel cells (MS-SOFCs) tolerate rapid thermal cycling [1,2]. This makes them ideally suited for applications requiring rapid start-up time, or tolerance to thermal fluctuations arising from load-following or intermittent fuel flow. In direct flame mode, SOFCs are heated by a flame impinging on the anode side of the cell, and the flame also partially oxidizes the fuel to electrochemically- active species (such as hydrogen and carbon monoxide) [3–6]. In this work, we have developed a prototype consumer product by retrofitting MS-SOFCs to a commercial propane-fueled camping stove (Figure 1). The power produced by the fuel cells is conditioned by a simple microelectronic circuit to provide LED lighting and USB mobile phone charging. Previous efforts [7] to systematically characterize the behavior of MS-SOFCs in direct-flame mode in carefully controlled lab environment will be summarized, including the impact of: air-to-fuel ratio in the flame, fuel flow velocity, burner-to-MS-SOFC distance, catalyst composition, and application of thermal insulation to the cell. The insight from these experiments was used in the present work to guide the design of a free-standing prototype, including cell size and stacking arrangement, and interaction with the stove flame and microelectronics. The prototype performance is shown in Figure 2. The MS-SOFC stack can be heated up from room temperature to delivery of useful power in less than 10 seconds. Operation points in LED mode and USB-charger mode fall on the overall operating curve of the MS-SOFC stack, and successful charging of smartphones is demonstrated. [1] M.C. Tucker, Progress in metal-supported solid oxide fuel cells: A review, J. Power Sources. 195 (2010) 4570–4582. doi:10.1016/j.jpowsour.2010.02.035. [2] J. Mougin, A. Brevet, J.-C. Grenier, R. Laucournet, P.-O. Larsson, D. Montinaro, L.M. Rodriguez-Martinez, M.A. Alvarez, M. Stange, L. Bonneau, E. Concettoni, L. Stroppa, Metal Supported Solid Oxide Fuel Cells: From Materials Development to Single Cell Performance and Durability Tests, ECS Trans. 57 (2013) 481–490. doi:10.1149/05701.0481ecst. [3] M. Horiuchi, S. Suganuma, M. Watanabe, Electrochemical Power Generation Directly from Combustion Flame of Gases, Liquids, and Solids, J. Electrochem. Soc. 151 (2004) A1402. doi:10.1149/1.1778168. [4] M.M. Hossain, J. Myung, R. Lan, M. Cassidy, I. Burns, S. Tao, J.T.S. Irvine, Study on Direct Flame Solid Oxide Fuel Cell Using Flat Burner and Ethylene Flame, ECS Trans. 68 (2015) 1989–1999. doi:10.1149/06801.1989ecst. [5] M. Vogler, M. Horiuchi, W.G. Bessler, Modeling, simulation and optimization of a no-chamber solid oxide fuel cell operated with a flat-flame burner, J. Power Sources. 195 (2010) 7067–7077. doi:10.1016/j.jpowsour.2010.04.030. [6] K. Wang, R.J. Milcarek, P. Zeng, J. Ahn, Flame-assisted fuel cells running methane, Int. J. Hydrogen Energy. 40 (2014) 4659–4665. doi:10.1016/j.ijhydene.2015.01.128. [7] M.C. Tucker, A.S. Ying, Metal-Supported Solid Oxide Fuel Cells Operated in Direct-Flame Configuration, J. Power Sources. (2017). Figure 1

The influence of eccentric needle movement on internal flow and injection characteristics of a multi-hole diesel nozzle

The internal flow characteristics and injection characteristics of each nozzle hole in a multi-hole diesel nozzle are significantly affected by transient needle movement which studies have shown to be unconventional (eccentric). This eccentric needle movement (unconventional movement of needle within nozzle) is considered as one of the main causes responsible for injection start delay and also variations in fuel injection quantities and spray patterns from symmetric multi-hole nozzles. Needle eccentricity movement creating conditions (causes) and the effect of the eccentric behavior on flow in a symmetric multi-hole diesel nozzle, were computationally studied by examining the in-nozzle geometrical flow area of each nozzle hole during the transient movement of the needle. Based on experimentally determined needle displacement, moving mesh technique was employed in modeling the eccentric needle movement in the computational domain during the simulation. After which the effects of eccentricity within nozzle on in-nozzle hole flow characteristics (cavitation distribution, fuel flow velocity distribution) and injection characteristics (fuel injection rate) were investigated. With a direct effect on flow distribution within nozzle holes, eccentric needle movement has a direct effect on injection and can therefore be considered as one of the main causes of non-homogeneity during fuel injection process. At low needle lift, cavitation distribution, fuel flow velocity and fuel injection rate of each nozzle hole vary considerably and are highly dependent on the needle position. The progressive variations in fuel injection rate non-uniformity from the nozzle are caused to some extent, by the rate of change in in-nozzle geometrical flow area for each nozzle during injection process. The nozzle hole close to the needle displacement shows high level of sensitivity with regards to eccentric needle movement. This nozzle hole therefore exhibits the most variations of injection characteristics under all the cases of eccentricities. Also, with varying degree of needle eccentricity, rate of non-uniform coefficient of cycle fuel injection quantity within the nozzle varies disproportionately.

Direct-Flame Metal-Supported Solid Oxide Fuel Cells

Metal-Supported solid oxide fuel cells (mSOFCs) tolerate rapid thermal cycling [1,2]. This makes them ideally suited for applications requiring rapid start-up time, or tolerance to thermal fluctuations arising from load-following or intermittent fuel flow. In direct flame mode, SOFCs are heated by a flame impinging on the anode side of the cell, and the flame also partially oxidizes the fuel to electrochemically- active species (such as hydrogen and carbon monoxide) [3–6]. In this work we study the behavior of mSOFCs in direct-flame mode, which has not been reported previously to the best of our knowledge. The results are of fundamental interest, and also inform the feasibility of utilizing mSOFCs to produce power in situations where fuel is burned in an open flame (such as cooking, well-head or land-fill gas flaring, water heating, etc.). Figure 1 shows an mSOFC partially heated by an impinging butane flame. The cell tolerated very high thermal gradient, estimated to be ~250°C/cm. This particular cell has survived about 100 cycles between room temperature and ~800°C, with extremely rapid startup in less than 10 seconds when the cell is exposed to flame. Figure 2 shows the polarization performance of an mSOFC operating with direct propane flame. The low open circuit voltage is consistent with previous direct-flame results using anode-supported SOFCs [[3–6]], and is due to the low concentration of active species in the flame, as most of the fuel is completely oxidized in the flame before reaching the mSOFC anode. The power output is much lower than that achieved previously for mSOFCs with pure hydrogen fuel [7], but is marginally higher than identical mSOFCs operated with gasified charcoal [8]. This paper will present a systematic study of the impact of various operational parameters on direct-flame mSOFC temperature, performance, and durability. Key parameters of interest are: air-to-fuel ratio in the flame, fuel flow velocity, burner-to-mSOFC distance, catalyst composition, and application of thermal insulation to the cell. [1] M.C. Tucker, Progress in metal-supported solid oxide fuel cells: A review, J. Power Sources. 195 (2010) 4570–4582. doi:10.1016/j.jpowsour.2010.02.035. [2] J. Mougin, A. Brevet, J.-C. Grenier, R. Laucournet, P.-O. Larsson, D. Montinaro, L.M. Rodriguez-Martinez, M.A. Alvarez, M. Stange, L. Bonneau, E. Concettoni, L. Stroppa, Metal Supported Solid Oxide Fuel Cells: From Materials Development to Single Cell Performance and Durability Tests, ECS Trans. 57 (2013) 481–490. doi:10.1149/05701.0481ecst. [3] M. Horiuchi, S. Suganuma, M. Watanabe, Electrochemical Power Generation Directly from Combustion Flame of Gases, Liquids, and Solids, J. Electrochem. Soc. 151 (2004) A1402. doi:10.1149/1.1778168. [4] M.M. Hossain, J. Myung, R. Lan, M. Cassidy, I. Burns, S. Tao, J.T.S. Irvine, Study on Direct Flame Solid Oxide Fuel Cell Using Flat Burner and Ethylene Flame, ECS Trans. 68 (2015) 1989–1999. doi:10.1149/06801.1989ecst. [5] M. Vogler, M. Horiuchi, W.G. Bessler, Modeling, simulation and optimization of a no-chamber solid oxide fuel cell operated with a flat-flame burner, J. Power Sources. 195 (2010) 7067–7077. doi:10.1016/j.jpowsour.2010.04.030. [6] K. Wang, R.J. Milcarek, P. Zeng, J. Ahn, Flame-assisted fuel cells running methane, Int. J. Hydrogen Energy. 40 (2014) 4659–4665. doi:10.1016/j.ijhydene.2015.01.128. [7] A. Kromp, J. Nielsen, P. Blennow, T. Klemensø, A. Weber, Break-down of losses in high performing metal-supported solid oxide fuel cells, Fuel Cells. 13 (2013) 598–604. doi:10.1002/fuce.201200165. [8] M.C. Tucker, C. Taylor, M. LaBarbera, C.P. Jacobson, Operation of Metal-Supported SOFC with Charcoal Fuel, ECS Trans. 57 (2013) 2929–2937. Figure 1

FUNCTION K - AS A LINK BETWEEN FUEL FLOW VELOCITY AND FUEL PRESSURE, DEPENDING ON THE TYPE OF FUEL

Regarding the application of vegetable oil based fuels in diesel engines, it is necessary to fully examine and understand the processes which take place in fuel delivery systems, namely, the processes of injection, mixture formation and combustion as well as emission characteristics. The paper provides an analysis of fuel flow in high pressure tubes of the fuel injection system, with the aim of determining function K as a link between fuel flow velocity and fuel pressure, and observing the influence of certain physical characteristics of the fuel upon the given function. The analysis presents the speed of sound and density, as fuel characteristics which affect the K function. The paper determines the speed of sound, density and bulk modulus for four fuels (pure rapeseed oil RO, biodiesel B100, a mixture of biodiesel and diesel B50, and diesel D), and forms appropriate K functions for each fuel in the pressure range from the atmospheric one to 1600 bar.

Delayed Neutrons Effect on Power Reactor with Variation of Fluid Fuel Velocity at MSR Fuji-12

As the nuclear reactor operate with liquid fuel, controlling velocity of the fuel flow on the Molten salt reactor very influence on the neutron kinetics in that reactor system. The effect of the pace fuel changes to the populations number of neutrons and power density on vertical direction (1 dimension) from the first until fifth year reactor operating had been analyzed on this research. This research had been conducted on MSR Fuji-12 with a two meters core high, and LiF-BeF2-ThF4-233UF4 as fuel composition respectively 71.78%-16%-11.86%-0.36%. Data of reactivity, neutron flux, and the macroscopic fission cross section obtained from ouput of SRAC (neutronic calculation code has been developed by JAEA, with JENDL-4.0 as data library on the SRAC calculation) was being used for the calculation process of this research. The calculation process of this research had been performed numerically by SOR (successive over relaxation) and finite difference methode, as well as using C programing language. From the calculation, regarding to the value of power density resulting from delayed neutrons, concluded that 20 m/s is the optimum fuel flow velocity in all the years reactor had operated. Where the increases number of power are inversely proportional with the fuel flow speed.

Transient mass transport and cell performance of a PEM fuel cell

This study aims to establish an unsteady, three-dimensional mathematical model of proton exchange membrane fuel cells (PEMFCs) with four serpentine flow field designs. The effects of the serpentine flow field designs on the transient characteristics of the PEMFCs are evaluated in terms of transient response of local current density and mass concentration under sudden change in loading. When the operating voltage is 0.7V, the weak electrochemical reactions result in a local current density distribution that is only minimally affected by the serpentine flow field designs. However, when operating voltage instantaneously drops from 0.7V to 0.5V, electrochemical reactions increase. To ensure a sufficient fuel cell oxygen supply, the oxygen mass fractions are high and uniform in the cathode gas diffusion and cathode catalyst layers, which cause overshoot phenomena in the local current density distribution. Because the inlet fuel flow rate is identical in all PEMFCs, the inlet fuel flow velocity decreases as the cathode inlet number increases. When the operating voltage abruptly drops, the low inlet fuel velocity prevents the PEMFC from maintaining a steady state. Therefore, the transient response time needed to reach a steady state in the quadruple serpentine flow field design is longest when overshoot or undershoot phenomena occur. Additionally, cells with large inlet fuel flow rates perform best and reach a steady state condition fastest when cell voltage changes occur suddenly.

Combustion characteristics of non-premixed methane micro-jet flame in coflow air and thermal interaction between flame and micro tube

The combustion characteristics of non-premixed methane micro-jet flame in coflow air were investigated experimentally and numerically. A detailed reaction mechanism was employed in the two-dimension numerical computation. The thermal interaction between the flame and solid tube was considered by using fluid-solid coupled thermal boundaries in the numerical computation. Four typical flames, lifted flame, attached flame, hemisphere flame and umbrella flame, were observed in different fuel flow velocity ranges in experiments. The flame heights, blow off and extinction limits in coflow airs at different velocities were measured. The OH and CH distributions of non-premixed micro-jet flames were obtained by experiments, and the computational results agree well with those from the experiments. The computational temperature distributions show that there are thermal interactions between flames and solid tube. The heat exchanges through surfaces of the solid tube were analyzed in detail. The fresh fuel gas in the solid tube is preheated by the thermal recirculation. Consequently, the combustion intensity of the micro-jet flame is enhanced. The thermal interaction is essentially affected by the flame shape, and it is significant for the hemisphere flame.

Numerical analyses of transient flow characteristics within each nozzle hole of an asymmetric diesel injector

In order to simultaneously study the differences in transient flow characteristics within each nozzle hole of an asymmetric multi-hole diesel injector used in off-road machinery, a three-dimensional gas–liquid two-phase flow model of cavitation was developed, which takes the influence of injection conditions and bubble number density into consideration. The computational model was validated by comparing it with the experiment conducted by Winklhofer. The result shows high level of consistency and sensitivity. Following the successful verification of the model, the differences in transient flow characteristics within each nozzle hole based on a P-type asymmetric multi-hole nozzle with sac were analyzed using the model. Results obtained from simulation shows that the cavitation phenomenon, velocity profile and mass flow rate in each nozzle hole of an asymmetric injector differ greatly. The hole with the higher nozzle hole angle (wider angle between nozzle hole axis and needle axis) was more inclined to cavitate, therefore the cavitation effect intensity is directly related to the size of the nozzle hole angle. During the lifting stages of the needle valve, the cavitation effect for each nozzle hole and the fuel flow velocity are gradually enhanced while on the contrary, the fuel flow velocity decreases and cavitation effect slightly increases at the closing stages of the needle valve lift. Also, the cavitation morphology at the same needle valve lift in any nozzle hole differs during opening and closing stages of fuel injection. In addition, the fuel flow velocity profile from the needle valve opening at the sac and into the hole of each nozzle shows that, in the order of increasing nozzle hole angle βi, the velocity effect gradually reduces as a result of dramatic change in flow direction.

Study on the combustion characteristics of non-premixed hydrogen micro-jet flame and the thermal interaction with solid micro tube

The combustion characteristics of non-premixed hydrogen micro-jet flames in co-flow air were investigated in a wide fuel flow velocity range experimentally and numerically to extend the knowledge on non-premixed micro flame. The direct flame images were captured by a digital reflex camera with long exposure time, and the OH radical distributions in the flames were measured by the laser induced fluorescence technique. The experimental observation shows that the flame height and shape change with the deceasing fuel flow velocity. A detailed chemical reaction mechanism was employed in the numerical computations with considering the heat transfer between gas and solid micro-tube. The computed distributions of OH concentrations agree qualitatively with those obtained by the experiments. The flame structure and thermal interaction between the flame and solid tube were inspected in detail. It was found that the thermal interactions at high, intermediate and low fuel flow velocities are different. The details of the thermal interactions between flames and solid tube are depended on the shape of the micro flame, which essentially affects the temperature distribution.

Air-fuel Mixing and Fuel Flow Velocity Modeling of Multi Holes Injector Nozzle on CNG Marine Engine

This research deals with the computational modeling assessment of a new multi holes injector nozzle for a sequential port injection CNG engine. The objective of this paper was to investigate the characteristics of a new multi holes injector nozzle on CNG engine. The methodology of this research is using computational modeling of the fuel flow of the new injector nozzle was made using Cosmos FloWok. The investigation is focused in the characteristics of the fuel-air mixing and flow velocity on CNG engine effect using the new multi holes injector nozzle. The result of the computational modeling of the fuel flow of the new injector nozzle increased the spray distribution, fuel-air mixing and fuel flow velocity.