Hydrogen Mass Flow Rate Research Articles

Numerical investigations on an improved counterflow double-channel micro combustor fueled with hydrogen for enhancing thermal performance

In this work, an improved counterflow double-channel micro combustor is designed. Computational Fluid Dynamics software Fluent is used to conduct numerical investigations on the thermal performance comparison between the old and improved counterflow double-channel micro combustors. It is found that the improved counterflow double-channel micro combustor has much higher and more uniform wall temperature compared that of the old one under various hydrogen mass flow rates, hydrogen/air equivalence ratios and solid materials. To make a quantitative comparison, the main results are presented as follows: (a) The improved combustor achieves the largest thermal enhancement at the hydrogen mass flow rate of 5.25 × 10−7 kg/s when the hydrogen mass flow rate is ranged from 5.25 × 10−7 kg/s to 9.8245 × 10−7 kg/s. Namely, the mean temperature of upper and right wall is improved by about 9.66 K and 13.53 K, respectively, and the mean nonuniformity of upper and right wall temperature is reduced by about 23.24% and 26.79%, respectively. (b) The improved combustor achieves the largest thermal enhancement at the hydrogen/air equivalence ratio of 0.6, when the hydrogen/air equivalence ratio is ranged from 0.9 to 0.5. Namely, the mean temperature of upper and right wall is improved by about 27.55 K and 29.55 K, respectively, and the mean nonuniformity of upper and right wall temperature is reduced by about 23.24% and 19.51%, respectively. (c) The improved combustor achieves the largest thermal enhancement at the solid material of silicon carbide when the solid material is changed from quartz to silicon carbide. Namely, the mean temperature of upper and right wall is improved by about 16.77 K and 18.38 K, respectively, and the mean nonuniformity of upper and right wall temperature is reduced by about 26.47% and 28.41%, respectively. Finally, some guidelines are proposed for applications of the improved counterflow double-channel micro combustor in the micro-thermophotovoltaic system.

Thermofluidic compression effects to achieve combustion in a low-compression scramjet engine

The compression provided by a scramjet inlet is an important parameter in its design. It must be low enough to limit thermal and structural loads and stagnation pressure losses, but high enough to provide the conditions favourable for combustion. Inlets are typically designed to achieve sufficient compression without accounting for the fluidic, and subsequently thermal, compression provided by the fuel injection, which can enable robust combustion in a low-compression engine. This is investigated using Reynolds-averaged Navier–Stokes numerical simulations of a simplified scramjet engine designed to have insufficient compression to auto-ignite fuel in the absence of thermofluidic compression. The engine was designed with a wide rectangular combustor and a single centrally located injector, in order to reduce three-dimensional effects of the walls on the fuel plume. By varying the injected mass flow rate of hydrogen fuel (equivalence ratios of 0.22, 0.17, and 0.13), it is demonstrated that higher equivalence ratios lead to earlier ignition and more rapid combustion, even though mean conditions in the combustor change by no more than 5% for pressure and 3% for temperature with higher equivalence ratio. By supplementing the lower equivalence ratio with helium to achieve a higher mass flow rate, it is confirmed that these benefits are primarily due to the local compression provided by the extra injected mass. Investigation of the conditions around the fuel plume indicated two connected mechanisms. The higher mass flow rate for higher equivalence ratios generated a stronger injector bow shock that compresses the free-stream gas, increasing OH radical production and promoting ignition. This was observed both in the higher equivalence ratio case and in the case with helium. This earlier ignition led to increased temperature and pressure downstream and, consequently, stronger combustion. The heat release from combustion provided thermal compression in the combustor, further increasing combustion efficiency.

Investigation effect of hydrogen addition on the performance and exhaust emissions of Pongamia pinnata biodiesel fueled compression ignition engine

ABSTRACTIn the recent decades, the energy demand for transport and industrial sector has increased considerably. Fossil fuels which were the major fuel source for decades are no more sustainable. Biodiesel is an efficient alternative compared to depleting fossil fuels. The prospect of biodiesel as the best alternative fuel is a reliable source compared to depleting fossil fuels. Hydrogen is also considered as an attractive alternative fuel producing low emission with improved engine performance. This paper investigates the performance and emission characteristics of a single cylinder compression ignition engine using hydrogen as an inducted fuel and biodiesel, aka Pongamia pinnata as injected fuel. The experiments are conducted for different quantities of hydrogen induction through the intake manifold in order to improve the performance of the engine. The performance parameters such as brake thermal efficiency, brake specific fuel consumption, exhaust temperature and emission quantities like HC, NOX, CO, CO2 of biodiesel fueled CI engine with variable mass flow rate of hydrogen are investigated. The performances of biodiesel combined with hydrogen at varying mass flow rates are also compared. The 10 LPM hydrogen induction with biodiesel provided 0.33% increase of brake thermal efficiency compared with diesel and increase of 3.24% to biodiesel at 80% loading conditions. The emission of HC decreased by 13 ppm, CO decreased by 0.02% by volume and CO2 decreased by 3.8% by volume for biodiesel with induction of hydrogen at 10 LPM to that of neat biodiesel for 80% load conditions.

Numerical investigations on thermal performance of double-layer four-channel micro combustors for micro-thermophotovoltaic system

In order to extend the output power of the micro-thermophotovoltaic system, it is necessary to assemble multiple single-channel micro combustors into a multiple-channel micro combustor. As a result, how to assemble multiple single-channel micro combustors into a multiple-channel micro combustor comes to be an interesting issue. In this work, the counterflow combustion concept is used in a double-layer four-channel micro combustor, and three representative double-layer four-channel micro combustors are designed. Extensive numerical investigations are conducted to compare the thermal performance of the three different double-layer four-channel micro combustors under various hydrogen mass flow rates, hydrogen/air equivalence ratios and solid materials. Moreover, the purely counterflow double-layer four-channel micro combustor is compared with the counterflow single-layer double-channel micro combustor in our previous work under various H2 mass flow rates, hydrogen/air equivalence ratios and solid materials. It is found that the purely counterflow double-layer four-channel micro combustor can keep more uniform wall temperature. And the purely counterflow double-layer four-channel micro combustor has better thermal performance compared with that of the counterflow single-layer double-channel micro combustor. Moreover, some critical values are given for keeping the merit of the purely counterflow double-layer four-channel micro combustor.

CFD modelling of hydrogen starvation conditions in a planar Solid Oxide Fuel Cell

Abstract The aim of this study was to highlight the interest of using CFD technique as a diagnostic tool of a malfunctioning Solid Oxide Fuel Cells. Hydrogen starvation of a SOFC due to nitrogen dilution is one of the cell dysfunctions and can lead to its degradation. Identification of the starvation point allows to improve cell performance and establish the best conditions for degradation tests. To illustrate a potential of the CFD tool, several simulations of a single planar SOFC and its behaviour under hydrogen starvation were performed and analysed. The results showed that at lower cell voltage values of 0.3 and 0.5 V significant gradients in the electric current were noticed due to a local reduction in hydrogen concentration. The CFD analysis allowed defining desirable mass flow rate of hydrogen to SOFCs to avoid fuel starvation. The model constitutes a helpful tool for optimizing cell design and operational conditions.

Comprehensive analysis of hydrogen compression and pipeline transportation from thermodynamics and safety aspects

Hydrogen delivery is a critical contributor to costs, emissions, and energy consumption associated with hydrogen pathways involving central plant production. Pipeline transmission appears to be the most economical means of transporting large quantities of hydrogen over great distances. The aim of this study is to analyze H2 compression and pipeline transportation processes with safety issues related to water electrolysis and H2 production for different values of the hydrogen mass flow rate: 0.2, 0.5, 1.0, 2.0, and 2.8 kg/s. Pipelines are operated at an initial pressure of 10 MPa at 300 K. Depending on the hydrogen mass flow rate, various types of compressors have been proposed, including reciprocating, conventional multistage centrifugal compressors, and an eight-stage integrally geared centrifugal compressor based on the concept of advanced centrifugal stages. Another problem analyzed in this study is H2 pipeline transport from the compressor outlet site to salt caverns under heat-transfer conditions. In order to avoid the choking condition, recompression of H2 is necessary at appropriately selected transportation distances. Simulations are conducted to determine the maximum safe distance of the pipeline to subsequent booster stations depending on the mass flow rate, pipeline diameter, ambient temperature, thermal insulation thickness, and ground-level heat transfer conditions. This analysis makes it possible to select pipeline diameters of 0.065 m, 0.1 m, 0.15 m, and 025 m, depending on the pre-determined hydrogen mass flow rate, at the transportation distance of 50 km. If the H2 pipeline gets damaged and an uncontrollable release of hydrogen occurs, hydrogen pipeline transport poses a potential hazard to humans and the surroundings. In the case of a hydrogen jet fire, zones with a fatal effect on humans are presented.

PROTON EXCHANGE MEMBRANE FUEL CELL/SUPERCAPASITOR HYBRID POWER MANAGEMENT SYSTEM FOR A GOLF CART

This paper presented the transformation of a golf cart system powered lead acid battery into an environmental friendly hybrid vehicle. The design developed by using an advantage contributes by the uprising alternative power source candidate which is Proton Exchange Membrane Fuel Cell (PEMFC) and the maintenance free energy storage device, a supercapacitor (SC). The fuel cell (FC) stack was an in house manufactured with 450 W (36 V, 12.5 A) power, while the SC was from Maxwell Technologies (48 V, 165 F). This two power sources were controlled by the mechanical relay, meanwhile the reactant (hydrogen) are control by mass flow controller (MFC) both signaled by a National Instrument (NI) devices. The power management controller are programmed in the LabVIEW environment and then downloaded to the NI devices. The experimental result of the power trend was compared before and after the transformation with the same route to validate the effectiveness of the proposed power management strategy. The power management successfully controls the power sharing between power sources and satisfies the load transient. While the reactant control managed to vary the hydrogen mass flow rate feed according to the load demand in vehicular applications.

Scramjet Combustion Efficiency Measurement via Tomographic Absorption Spectroscopy and Particle Image Velocimetry

The combustion efficiency of a scramjet is a metric that evaluates the overall performance of the engine. Until recently, combustion efficiency was measured using indirect approaches such as a one-dimensional control volume calculation or a calorimeter and wall pressure tap measurements. A novel nonintrusive direct approach for the measurement of combustion efficiency is presented that combines the optical diagnostic techniques tunable diode laser absorption tomography and stereoscopic particle image velocimetry. Experimental results are presented for measurements of the University of Virginia’s Supersonic Combustion Facility in both the scram and ram-modes of operation. The tunable-diode-laser-absorption-tomography/stereoscopic-particle-image-velocimetry method directly measures the converted hydrogen (via water vapor) mass flow rate exiting the dual-mode scramjet and compares this to the facility-measured injected hydrogen fuel mass flow rate. A complementary computational fluid dynamics study was performed and results are available for the scram-mode operating condition. The results reported show excellent agreement between the tunable-diode-laser-absorption-tomography/stereoscopic-particle-image-velocimetry-measured combustion efficiency and the computational-fluid-dynamics-predicted combustion efficiency for the scram-mode of operation, which are both near 99%. The tunable-diode-laser-absorption-tomography/stereoscopic-particle-image-velocimetry-measured combustion efficiency for the ram-mode of operation is shown to be lower than that of the scram-mode operation: at 79%.

Heat Transfer Enhancement in vertical Mounted Tube Subjected to Uniform Heat Flux by using Electrolysis Bubble

In the present work, experimental and numerical investigations had been carried out to investigate the effect of sub-millimeter bubbles injection on heat transfer coefficient of upward flowing water in vertical mounted tube subjected to uniform heat flux. The experimental apparatus consists of a test rig designed and built to conduct the experiments. A circular tube, test section was designed and constructed from the copper and heated by an electrical heater on its outer surface. The dimensions of copper pipe was (length= 0.7m, diameter= 0.05 m, thickness= 1.5 mm). Water temperature at inlet was kept constant at (32°C). Thermocouples distributed longitudinally at different radial distances between cylinder surface and its center at seven sections, in addition to the fluid inlet and outlet were used to measure temperatures. Bubbles generation was performed in test section by using a proper ionization current that will be passed across the anode and cathode electrodes to produce hydrogen bubbles and oxygen bubbles at different intensities. The experiments were conducted using heat fluxes (13641 and 22736) W/m, water mass flow of (2, 3 and 4) lit/min, mass flow rate of hydrogen and oxygen bubbles were (0.02 , 0.025) lit/min respectively and Reynolds number (1214, 1783 and 2300) for water. The results showed that an enhancement of 25.5% was obtained in the averaged Nusselt number with using ionization bubbles compared with the case without bubbles.

Investigation of ignited hydrogen leaks from tube fittings

A combined experimental and numerical investigation of ignited hydrogen leaks from a compression fitting attached to a steel tube was conducted for a range of hydrogen mass flow rates controlled between 0.033 slpm and 1.0 slpm. Horizontal and vertical fitting orientations were considered in this study. The experiments involved temperature measurements of the fitting surface as well as thermal imaging of the corresponding flow field. The numerical simulations, which were performed using a commercial computational fluid dynamics (CFD) software, provided steady-state temperature distribution in the flow domain as well as in the fitting and the steel tube. It was observed that as the fitting and the tube were heated by the mass-flow controlled flame, the hydrogen leak path contracted, which resulted in a steady ignited leak and a maximum temperature of the fitting below 320 °C across the considered cases.

Combustion Heat-Release Effects on Supersonic Compressible Turbulent Boundary Layers

Influences of heat release by the hydrogen combustion in supersonic turbulent boundary layers are numerically studied using Reynolds-averaged Navier–Stokes equations. The adopted Reynolds-averaged Navier–Stokes methodology is first validated by comparing the numerical results with the existing experimental data. Studies on the effects of the flame perpendicular position inside the boundary layer reveal that, while the flame is restricted around the edge of the boundary layer, the heat release may slightly reduce rather than increase the wall heat flux because of the suppression effect on the turbulent energy transport due to heat release. However, as the flame moves toward the wall, the skin-friction reduction effect would not be obviously strengthened, but the wall heat flux could be dramatically enhanced by the increase of near-wall chemical reactions. At a given hydrogen mass flow rate, the injection scheme with a higher injection height and a lower injection velocity could be helpful to achieve a larger skin-friction reduction while maintaining a lower wall heat flux. Finally, analysis of the heat-release effects on the velocity law of the wall shows that van Driest’s velocity law largely deviates from the computational results, whereas White’s velocity law remains close to the numerical results within a region of approximately .

Evaluation of the performance of a hydrogen enriched combustion system for ceramic sector

In this experimental study, the energy and exergy analyses were performed to determine optimum hydrogen mass flow rate for hydrogen enrichment application in a ceramic kiln. The effects of multiple-point and single-point injection of hydrogen at different mass flow rates on energy and exergy efficiencies were evaluated. The hydrogen-enriched natural gas combustion experiments were carried out for a ceramic kiln including 102 burners. Optimum hydrogen flow rates were determined as 1.08 kg/h and 1.16 kg/h for multiple-point and single-point applications, respectively. For 40 × 40 cm ceramic tile production at the optimum hydrogen mass flow rate and with minimum natural gas consumption, energy efficiencies were found as 63.13% and 62.63% and exergy efficiencies were reached as 43.12% and 42.74% for multiple-point and single-point applications, respectively. A significant difference between multiple-point and single-point applications has not been found for both energy and exergy efficiencies. The hydrogen enrichment system has a short payback time after the first three months of operation in the present study. It is concluded that application of hydrogen enrichment in ceramic kilns have a great potential for energy saving and energy efficiency.

Thermal design analysis of a 1 L cryogenic liquid hydrogen tank for an unmanned aerial vehicle

Thermal design analysis of a 1-L cryogenic liquid hydrogen storage tank without vacuum insulation for a small unmanned aerial vehicle was carried out in the present study. To prevent excess boil-off of cryogenic liquid hydrogen, the storage tank consisted of a 1-L inner vessel, an outer vessel, insulation layers and a vapor-cooled shield. For a cryogenic storage tank considered in this study, the appropriate heat inleak was allowed to supply the boil-off gas hydrogen to a proton electrolyte membrane fuel cell as fuel. In an effort to accommodate the hydrogen mass flow rate required by the fuel cell and to minimize the storage tank volume, a thermal analysis for various insulation materials was implemented here and their insulation performances were compared. The present thermal analysis showed that the Aerogel thermal insulations provided outstanding performance at the non-vacuum atmospheric pressure condition. With the Aerogel insulation, the tank volume for storing 1-L liquid hydrogen at 20 K could be designed within a storage tank volume of 7.2 L. In addition, it was noted that the exhaust temperature of boil-off hydrogen gas was mainly affected by the location of a vapor-cooled shield as well as thermal conductivity of insulation materials.

Calculation Model and Application Research of Molar Formation Enthalpy for Real Gas

Compared to condensed phase, effect of pressure on molar formation enthalpy for gas phase can not be ignored. To study calculation method of molar formation enthalpy for real gas, calculation formula of isothermal enthalpy difference is deduced under temperature and pressure coupled interaction by SHBWR equation of state, and whose applicability inspection is finished by experimental data of molar formation enthalpy for superheated steam. Results show that, calculation accuracy of model increases along with the increase of temperature, but decreases along with the increase of pressure. When working temperature is more than 800 K, the established model can calculate molar formation enthalpy for real gas accurately. Steady state properties of a thermal power system is analyzed based on the established model according to Hesss Law, result show that, heat flux of the system increases under pressure action, and mass flow rate of hydrogen the system needs decreases at the same time.

Hydrogen electronic injection system for a diesel power generator

This work presents an electronic control system developed for hydrogen injection in a diesel power generator. The full system is basically constituted by a gas fuel injection rail with injection valves, a speed sensor and an electronic control unit. The electronic injection system was installed and tested in a diesel power generator of 44 kW rated power. The tests were carried out with hydrogen injected in the intake manifold and diesel oil directly injected in the combustion chamber. The results show the injection valve opening periods necessary to obtain hydrogen mass flow rates equivalent to 5%, 10%, 15% and 20% of the diesel oil mass replaced. The measured hydrogen mass flow rate injected is presented as a function of load power demand and hydrogen concentration in the fuel.

Pyrolysis kinetics and combustion of thin wood by an advanced cone calorimetry test method

Pyrolysis kinetics analysis of extractives, holocellulose, and lignin in the solid redwood over the entire heating regime was possible by specialized cone calorimeter test and new mathematical analysis tools. Added hardware components include: modified sample holder for the thin specimen with tiny thermocouples, the methane ring burner with stainless-steel mesh above cone heater, and the water vapor sensor in heated gas sampling lines. Specialized numerical deconvolutions were applied to the oxygen and water vapor analyzer signals to synchronize with the rapid-responding CO/CO2 analyzer signals. From this data, the mass flow rates of carbon, hydrogen, and oxygen within the wood volatiles as function of time were obtained, which allowed deducing the mass flow rate of significant molecules of wood volatiles that have their origins in the wood constituents of extractives, holocellulose, and lignin. Accurate analytical solution of pyrolysis kinetics of appropriate competitive reactions that continuously conserved carbon, hydrogen, and oxygen mass flow rates was obtained for piecewise exponentially-shaped, spatially uniform temperature within the specimen as implemented conveniently in MS Excel spreadsheet.

Experimental and three-dimensional numerical investigations on H2/air continuous rotating detonation wave

Results of both experimental and three-dimensional numerical studies on H2/air continuous rotating detonation are presented. Tangentially injected H2/O2 hotshot jet was used to ignite the engine successfully. Under the condition of air and hydrogen mass flow rates of 265 and 7.7 g/s and the ambient pressure of 11 kPa, H2/air continuous rotating detonation has been realized for about 300 ms. Time–frequency characteristics of the measured results were analyzed by different methods, and the results agreed well with each other. The detonation wave propagated stably during the test, with the propagation frequency variation of 5.35–5.85 kHz. The mean propagation velocity was 1674.3 m/s, which was about 85.0% of the theoretical value. Corresponding three-dimensional numerical simulation was carried out. Flow field structure of the rotating detonation wave was analyzed, and the curvature effect was also considered. Propagation processes of both the experiment and simulation results were compared. The variation of detonation wave propagation frequency of the simulation case was 6.262–6.27 kHz, with the mean propagation velocity of 1870.1 m/s, which was larger than the experiment result. Distribution of the mean combustor pressure along the axis direction was analyzed. Within the heat release zone, the mean pressure decreased greatly, and it changed gently beyond this zone. The changing tendency of both the experimental and numerical results agreed with each other, but there were differences between the pressure values.

Exergy analysis of a high pressure multistage hydrogen gas storage system

This study presents a parametric study on the performance aspects, through exergy analysis, of the multistage hydrogen gas storage subsystem in a hydropower-based-hydrogen gas fueling station producing 3 kg of hydrogen per hour and storing it. In order to perform an exergy analysis, the following parameters are taken into consideration: (i) mass flow rate of hydrogen (3 kg/h), (ii) inlet pressure of hydrogen (ranging from 1 to 200 bar), (iii) hydrogen storage pressure (ranging from 200 to 900 bar), (iv) dead state temperature (at 25 °C), (v) efficiency of electrical motor (90%), (vi) mechanical efficiency (95%), and (vii) polytropic efficiency (90%). It is obtained that increasing inlet pressure of hydrogen gas decreases the energy consumption for compression and storage process while increasing exergy efficiency. Moreover, it is noticed that increasing storage pressure increases the exergy content of hydrogen gas.

Experimental study of detonation in a cryogenic two-phase H 2–O 2 flow

Direct initiation and propagation of detonation through a cryogenic two-phase flow constituted by liquid oxygen droplets in gaseous hydrogen at 100 K are experimentally investigated. The influence of droplet size distribution is characterized in a cryogenic gaseous helium and liquid oxygen two-phase flow. Droplet sizing and detonation experiments are conducted by varying different parameters: distance from the injector, helium and hydrogen mass flow rates, global equivalence ratio and addition of gaseous nitrogen. Droplet size distributions reveal quick vaporization of the smallest droplets of the cryogenic jet. Results in terms of wave velocity, pressure, and detonation cells show that a detonation wave can be directly initiated, with a propagation wave velocity of 20% higher than the Chapman–Jouguet value. Cell size measurements show that the mixture sensitivity is not affected by the presence of droplets. Addition of gaseous nitrogen reduces only slightly the peak pressure, but the detonation velocity is reduced by about 30%.

Thermal performance of a micro-combustor for micro-gas turbine system

Premixed combustion of hydrogen gas and air was performed in a stainless steel based micro-annular combustor for a micro-gas turbine system. Micro-scale combustion has proved to be stable in the micro-combustor with a gap of 2 mm. The operating range of the micro-combustor was measured, and the maximum excess air ratio is up to 4.5. The distribution of the outer wall temperature and the temperature of exhaust gas of the micro-conbustor with excess air ratio were obtained, and the wall temperature of the micro-combustor reaches its maximum value at the excess air ratio of 0.9 instead of 1 (stoichiometric ratio). The heat loss of the micro-combustor to the environment was calculated and even exceeds 70% of the total thermal power computed from the consumed hydrogen mass flow rate. Moreover, radiant hunt transfer covers a large fraction of the total heat loss. Measures used to reduce the heat loss were proposed to improve the thermal performance of the micro-combustor. The optimal operating status of the micro-combustor and micro-gas turbine is analyzed and proposed by analyzing the relationship of the temperature of the exhaust gas of the micro-combustor with thermal power and excess air ratio. The investigation of the thermal performance of the micro-combustor is helpful to design an improved microcombustor. (C) 2006 Elsevier Ltd. All rights reserved.