Hydrogen Volume Fraction Research Articles

Studies on the Performance of Engines Powered with Hydrogen-Enriched Biogas

Sustainability of energy supply has become a prime concern for energy producers and consumers alike. There is heightened awareness in the global community about the decreasing supply of conventional fossil fuels along with increasing fuel and energy demand and the consequent rise in unit energy cost. In addition to the sustainability aspect, the environmental impact of emissions from fossil fuel combustion is the focus of global targets for emissions reduction. In this context, the research and application of sustainable and non-polluting fuels become significant. Internal combustion (IC) engines are part of a significant energy-consuming sector, and the application of sustainable and non-polluting fuels within IC engines would be impactful. Biogas and hydrogen are viewed as sustainable and non-polluting alternatives to conventional fossil fuels. However, either of these used individually offer certain disadvantages. Experimental results and analysis of the performance and emissions characteristics of an IC engine fueled with biogas blended with 5, 10, and 15% hydrogen volume fractions are studied. An increase in hydrogen content increases the engine’s performance and power and reduces carbon monoxide (CO) and total hydrocarbons (THCs). However, nitrogen oxides (NOx) are found to increase due to higher combustion temperatures attributed to hydrogen. A 17.5% increase in brake power is observed for 15% hydrogen-enriched biogas, compared to plain biogas, at an equivalence ratio of 0.6. Similarly, a 17% increase in BTE, a 50% decrease in CO, a 68% decrease in UHC, but a 71% increase in NOx are observed for 15% hydrogen-enriched biogas.

Effects of longitudinal excitation on liquid hydrogen sloshing in spacecraft storage tanks under microgravity conditions

Based on the real physical model and operating environment of the spacecraft tank, the numerical model of the tank is established and the sloshing behavior of liquid hydrogen in the tank under different longitudinal excitations is studied in this work. The Realizable k- ε model is used to predict the fluid turbulence, and the mixture model is used to analyze the phase transitions and flows. The harmonic external excitation is loaded by the user-defined function (UDF). Based on the CFD sloshing model verified through comparison with experimental results, the influences of different longitudinal external excitation frequencies and amplitudes on the liquid hydrogen volume fraction in the tank are firstly analyzed. On this basis, including pressure and other physical quantities of the monitoring points and whole internal fluid domain during the sloshing simulation process are studied quantitatively. In addition, the relationship between the carrier amplitude of the sloshing curves and the external excitation amplitude is discussed. The simulation results show that in microgravity environment, compared with large amplitude excitation, high-frequency longitudinal harmonic excitation has a significant effect on the variation of physical parameters in the tank, which may become a negative factor for the safety of liquid hydrogen storage and supply systems. Meanwhile, the traditional baffle design has a limited influence on the liquid hydrogen motion under the high-frequency longitudinal excitation which may occur during the spacecraft changing load process. The results provide valuable information for the understanding of sloshing behavior and safety evaluation of the tank under longitudinal excitation.

Numerical investigation of combustion characteristics for hydrogen mixed fuel in a can-type model of the gas turbine combustor

Numerical simulations are performed to analyze the combustion characteristics of propane fuel mixed with different amounts of hydrogen in a can-type combustor. The volume fraction of the hydrogen fuel varies from 0% to 100% in the fuel mixture. The results indicate that the hydrogen enrichment of the fuel significantly affects the flow structure, mixture fraction, and combustion characteristics. An increase in the volume fraction of hydrogen significantly affects the mean mixture fraction distribution, promotes combustion, and increases the flame temperature and the width of the flammable range within the combustor. Therefore, the degree of temperature uniformity at the outlet of the combustor increases with hydrogen enrichment, corresponding to an increase of 49.64% in the uniformity factor. The hydrogen enriched fuel can also reduce the emissions of CO and CO2, owing to the reduced amount of carbonaceous fuel.

Numerical investigation on combustion regulation for a stoichiometric heavy-duty natural gas engine with hydrogen addition considering knock limitation

Aiming to further improve the thermal efficiency and reduce NOx emissions in the stoichiometric hydrogen-enriched natural gas (NG) engine, a detailed 3-D simulation model of stoichiometric operation heavy-duty NG engine is built based on the actual boundary conditions from high load bench test. The superimposed methods for knock regulation, combustion and emission control, including Miller valve timing, hydrogen volume fraction and EGR rate were proposed and investigated comprehensively. It reveals that the typically bimodal characteristic of heat release rate (HRR) curve is caused by knock, which seriously restricts the performance improvement of stoichiometric NG engine under high load condition. To predict and control the occurrence of the second peak of HHR accurately, a new parameter BI is defined. Moreover, the Miller timing with 20°CA of the intake valve late closing shows better combustion performance within the knock limit, accompanied by a slight increase in NOx emissions. Additionally, the 5% hydrogen blend, coupled with the Miller cycle, can further enhance the indicated thermal efficiency (ITE) of the NG engine due to the stronger effects on acceleration of laminar flame propagation velocity than the promotion of end-gas auto-ignition. Besides, the great potential of EGR rate for balancing NOx and ITE is also confirmed in the heavy-duty hydrogen-enriched NG engine adopting Miller cycle. Compared to the original indexes, combing with the regulation strategies of intake valve late closing (20°CA), hydrogen addition (5%) and EGR (17%) are proved to increase the indicated thermal efficiency by 1.89% and reduce NOx emissions by 11.47% within the knock limit.

Kinetics of non-premixed hydrogen–oxygen catalytic recombination reaction at ambient temperature

This study proposes the use of the hydrogen–oxygen catalytic recombination reaction to safely eliminate the leaked hydrogen in a confined environment. Experiments on the hydrogen–oxygen reaction catalyzed by using Pt/C as a catalyst are conducted at ambient temperature in a small cylindrical vessel. The macroscopic kinetic process of the hydrogen–oxygen recombination reaction is investigated, and the effects of the reaction parameters, such as the initial hydrogen volume fraction and catalyst layer position, on the reaction temperature and hydrogen conversion are examined. The reaction temperature and temperature rise rate are shown to reach the maximum values when the initial hydrogen fraction is 70 vol%. When the initial hydrogen fraction is ≤ 67 vol%, the hydrogen conversion reaches 100%. After the initial hydrogen fraction is > 67 vol%, the hydrogen conversion decreases significantly, and the hydrogen conversion is only 53% for the initial hydrogen fraction is up to 80 vol%. Moreover, the position of the catalyst layer has a significant effect on the reaction rate and heat distribution inside the vessel. When the catalyst layer is near the bottom of the reaction vessel, the reaction rate is accelerated and the released heat accumulates at the bottom of the vessel. The influence law of the aforementioned factors can provide a technical reference for applications of the hydrogen–oxygen catalytic reaction.

Numerical Study of Combustion and Emission Characteristics for Hydrogen Mixed Fuel in the Methane-Fueled Gas Turbine Combustor

The aeroderivative gas turbine is widely used as it demonstrates many advantages. Adding hydrogen to natural gas fuels can improve the performance of combustion. Following this, the effects of hydrogen enrichment on combustion characteristics were analyzed in an aeroderivative gas turbine combustor using CFD simulations. The numerical model was validated with experimental results. The conditions of the constant mass flow rate and the constant energy input were studied. The results indicate that adding hydrogen reduced the fuel residues significantly (fuel mass at the combustion chamber outlet was reduced up to 60.9%). In addition, the discharge of C2H2 and other pollutants was reduced. Increasing the volume fraction of hydrogen in the fuel also reduced CO emissions at the constant energy input while increasing CO emissions at the constant fuel mass flow rate. An excess in the volume fraction of added hydrogen changed the combustion mode in the combustion chamber, resulting in fuel-rich combustion (at constant mass flow rate) and diffusion combustion (at constant input power). Hydrogen addition increased the pattern factor and NOx emissions at the outlet of the combustion chamber.

Analysis of propagation characteristics of hydrogen flame in shock tube in integrated energy system

In order to study the explosion law of hydrogen and air premixed gas in the pipe-line, the author proposes an analysis of the propagation characteristics of hydrogen in the shock tube in the integrated energy system. Use a square transparent pipe with a size of 150 mm?150 mm?1000 mm, the shape of the explosion flame, the propagation velocity and the pressure change with the hydrogen volume fraction from 10-40% were observed through experiments. Flame spread and pressure were recorded and measured by high speed cameras and pressure sensors, respectively. Experimental results show that the explosion flame characteristics and pressure changes are greatly affected by the hydrogen volume fraction. With the increase of hydrogen volume fraction, the maximum velocity and maximum value of flame in pipe increase significantly. The maximum flame propagation speed is increased from 18.3-304.2 m/s, and the propagation time is shortened from 123.5-10.5 ms. The pressure peak increased from 2.95-34.06 kPa. The analysis of the propagating characteristics of the hydrogen flame in the shock tube in the integrated energy system can well reflect the intensity of the hydrogen explosion. Do not use abbreviations and acronyms in the abstract.

The free radical mechanism of the effects of different metal materials on hydrogen explosion

When the volume fraction of hydrogen is below 20% and above 25%, aluminium and nickel wires inhibit and promote the hydrogen explosion.

Flame propagation of premixed gas explosion with different equivalent ratio under corrugated fire-retardant core

Based on the self-built experimental set-up, the propagation law of explosion flame of hydrogen/methane premixed gas with different hydrogen volume fractions in different equivalent ratios was investigated under the action of a corrugated fire-retardant core. The experimental study shows that the flame isolation and suppression effect of the corrugated fire-retardant core at different equivalence ratios is either promoted or suppressed, the hydrogen/methane premixed gas ex?plosion flame is quenched without hydrogen mixing when ? = 0.8 and 1.0, and also quenched when ? = 1.2 in different hydrogen volume fractions. The corrugated flame-retardant core significantly affected the extinguishing of the explosion flame of the premixed gas when ? = 1.2, the flame propagation speed and overpressure showed a similar trend under different volume fractions of hydrogen. When the flame is quenched, the flame is depressed inward to form a reverse spherical cell flame, reverse diffusion combustion phenomenon occurs, and it lasts a long time, eventually, the combustion reaction extinguished. The flame penetrated the corrugated fire-retardant core during the rest of conditions. When ? = 1.0, the flame reaction of the hydrogen/methane premixed gas explosion under the action of the corrugated fire-retardant core is the most violent, and its propagation speed and overpressure jump rapidly until it reaches a peak.

Estimating the charge burning velocity within a hydrogen-enriched gasoline engine

This paper proposed a feasible method for estimating the turbulent burning velocity of gasoline/hydrogen blends in a spark-ignited (SI) engine based on the cumulative heat release fraction, engine speed and engine geometry. The experiment was conducted on a naturally-aspirated port-injection gasoline engine equipped with a hydrogen injection system. The engine was run at 1400 rpm with different loads and hydrogen volume fractions in the intake gas. The test results showed that the addition of hydrogen benefited increasing the burning velocity and advancing the relevant crank angle for the peak burning velocity, due to the high burning and diffusion velocities of hydrogen. At 1400 rpm, a manifolds absolute pressure of 61.5 kPa and stoichiometric conditions, the peak burning velocity was raised from 11.6 to 12.3 and 14.6 m/s, and the relevant crank angle for the peak burning velocity was advanced from 21.0 to 14.0 and 8.6 oCA when the hydrogen volume fraction in the intake increased from 0% to 3% and 6%, respectively. Moreover, the effect of hydrogen addition on enhancing the burning velocity of a gasoline engine was more pronounced at low loads than that at high loads.

Hydrogen-rich gas as a fuel for the gas turbines: A pathway to lower CO2 emission

Hydrogen-rich fuel for the gas turbines can be considered as a transient way from hydrocarbon fuel to zero-carbon hydrogen fuel. In this paper, thermodynamic analysis of a combined cycle power plant (CCPP) fired with a hydrogen-rich fuel obtained via various ways is performed to understand the effect of a transient to this fuel on the CO2 emission as well as the efficiency of a power plant. Hydrogen-rich fuel with different content of hydrogen is analyzed. Two types of hydrogen-rich fuel are considered: fuel obtained via methane dilution with hydrogen (hydrogen from internal fuel supply infrastructure) — first case; fuel obtained via steam methane reforming (on-board hydrogen production technology) — second case. The first case showed that hydrogen addition to methane non-linearly leads to a decrease in CO2: hydrogen-rich fuel with 20% of H2 volume fraction gives a reduction in CO2 emission of 7.2%; 50% of H2 gives 23.5% reduction; 75% of H2 gives 51.1% reduction. The second case is considering hydrogen-rich fuel obtained via steam methane reforming using a renewable energy source. Hydrogen volume fraction up to 75% in hydrogen-rich fuel can be obtained after the reforming process. When 100% of methane is reformed, the reduction in CO2 emission up to 27% can be achieved. The minimum achievable level in CO2 emission is 75.17 gCO2/kW for an on-board hydrogen production technology via steam methane reforming which is corresponding to a hydrogen-rich fuel obtained via H2 dilution up to 53%.

Effects of Machining Parameters on Electrochemical Multi-Field Coupling

Electrochemical machining involves three couplings between electric field, flow field and thermal field. The precipitation of hydrogen on the surface of the cathode will affect the entire electrochemical machining process and the final machining quality of the workpiece. Finite element software is used to analyze the effects of different voltages, electrolyte inlet pressure and interelectrode gap on current density, hydrogen volume fraction, conductivity and temperature distribution in this article. The research results show that the increase of processing voltage will increase the current density, hydrogen volume fraction and temperature, and decrease the conductivity of the solution. As the pressure of the electrolyte increases, the current density and conductivity increase, but the hydrogen volume fraction and temperature decrease. The current density, hydrogen volume fraction and temperature decrease, and the conductivity increases when the gap between electrodes increases. At the inlet, the current density and conductivity are relatively large, and gradually decrease along the electrolyte flow direction, while the hydrogen volume fraction and temperature are the smallest at the inlet, and gradually accumulate along the electrolyte flow direction, and reach the maximum at the outlet. Through multi-physics coupling simulation, the current density, temperature, conductivity and bubble distribution in electrochemical machining can be predicted, which can provide a theoretical basis for actual electrochemical machining process parameter selection.

Study on flame propagation of H2/LPG premixed gas in a tube

This work aims to is to study the flame propagation characteristics of the hydrogen/liquefied petroleum gas (LPG) premixed gas in a closed tube. With the aid of a self-developed square glass explosion tube and a high-speed camera, the characteristic parameters (i.e., flame structure, flame tip speed, maximum explosion overpressure, maximum rate of explosion pressure rise, deflagration index) were obtained and analyzed the explosion characteristics of the premixed gas. The results show that the time for the flame to reach the end of the pipe decreased, and the maximum explosion overpressure increases as the hydrogen addition ratio increases. However, the explosion overpressure and flame propagation velocity increased slowly when the hydrogen addition ratio was less than 40%, While the explosion overpressure and flame propagation velocity increased drastically in the range of hydrogen addition ratio 40–80%. Therefore, the key turning point for LPG hydrogenation is when the hydrogen volume fraction is 40%. The peak explosion flame propagation velocity and the peak explosion pressure showed the change law of increasing first and then decreasing with the equivalent ratio increasing. The Pmax and Vmax are 6.4 bar and 71.2 m/s respectively. The explosive flame structure of the premixed gas formed a "multiple tulip" structure after the typical tulip flame structure due to the influence of hydrodynamic. In addition, the propagation law of H2-LPG-Air premixed flame in the pipeline was influenced by the interaction of pressure wave and flame front velocity, and Pmax trajectory and Vmax curve showed similar oscillation law. Hence, the study provides crucial data for the prevention and control of H2-LPG-Air gas mixture combustion and explosion accidents.

Experimental and numerical study of the effect of initial temperature on the combustion characteristics of premixed syngas/air flame

The effects of different initial temperatures (T = 300–500 K) and different hydrogen volume fractions (5%–20%) on the combustion characteristics of premixed syngas/air flames in rectangular tubes were investigated experimentally. A high-speed camera and pressure sensor were used to obtain flame propagation images and overpressure dynamics. The CHEMKIN-PRO model and GRI Mech 3.0 mechanism were used for simulation. The results show that the flame propagation speed increases with the initial temperature before the flame touches the wall, while the opposite is true after the flame touches the wall. The increase in initial temperature leads to the increase in overpressure rise rate in the early flame propagation process, but the peak overpressure is reduced. The laminar burning velocity (LBV) and adiabatic flame temperature (AFT) increase with increasing initial temperature. The increase in initial temperature makes the peaks of H, O, and OH radicals increase.

Deflagration-to-Detonation Transition in Stochiometric Propane–Hydrogen–Air Mixtures

Hydrocarbon–hydrogen blends are often considered as perspective environmentally friendly fuels for power plants, piston engines, heating appliances, home stoves, etc. However, the addition of hydrogen to a hydrocarbon fuel poses a potential risk of accidental explosion due to the high reactivity of hydrogen. In this manuscript, the detonability of stoichiometric C3H8–H2–air mixtures is studied experimentally in terms of the run-up time and distance of deflagration to detonation transition (DDT). The hydrogen volume fraction in the mixtures varied from 0 to 1. Three different configurations of detonation tubes were used to ensure the DDT in the mixtures of the various compositions. The measured dependences of the DDT run-up time and distance on the hydrogen volume fraction were found to be nonlinear and, in some cases, nonmonotonic with local maxima. Blended fuel detonability is shown to increase sharply only at a relatively large hydrogen volume fraction (above 70%), i.e., the addition of hydrogen to propane in amounts less than 70% vol. does not affect the detonability of the blended fuel significantly. The observed nonlinear/nonmonotonic dependences are shown to be the manifestation of the physicochemical properties of hydrogen-containing mixtures. An increase in the hydrogen volume fraction is accompanied by effects leading to both an increase and a decrease in mixture sensitivity to the DDT. Thus, on the one hand, the increase in the hydrogen volume fraction increases the mixture sensitivity to DDT due to an increase in the laminar flame velocity and a decrease in the self-ignition delay at isotherms above 1000 K and pressures relevant to DDT. On the other hand, the mixture sensitivity to DDT decreases due to the increase in the speed of sound in the hydrogen-containing mixture, thus leading to a decrease in the Mach number of the lead shock wave propagating ahead of the flame, and to a corresponding increase in the self-ignition delay. Moreover, for C3H8–H2–air mixtures at isotherms below 1000 K and pressures relevant to DDT, the self-ignition delay increases with hydrogen volume fraction.

Solar hydrogen for high capacity, dispatchable, long-distance energy transmission – A case study for injection in the Greenstream natural gas pipeline

This paper presents the results of techno-economic modelling for hydrogen production from a photovoltaic battery electrolyser system (PBES) for injection into a natural gas transmission line. Mellitah in Libya, connected to Gela in Italy by the Greenstream subsea gas transmission line, is selected as the location for a case study. The PBES includes photovoltaic (PV) arrays, battery, electrolyser, hydrogen compressor, and large-scale hydrogen storage to maintain constant hydrogen volume fraction in the pipeline. Two PBES configurations with different large-scale storage methods are evaluated: PBESC with compressed hydrogen stored in buried pipes, and PBESL with liquefied hydrogen stored in spherical tanks. Simulated hourly PV electricity generation is used to calculate the specific hourly capacity factor of a hypothetical PV array in Mellitah. This capacity factor is then used with different PV sizes for sizing the PBES. The levelised cost of delivered hydrogen (LCOHD) is used as the key techno-economic parameter to optimise the size of the PBES by equipment sizing. The costs of all equipment, except the PV array and batteries, are made to be a function of electrolyser size. The equipment sizes are deemed optimal if PBES meets hydrogen demand at the minimum LCOHD. The techno-economic performance of the PBES is evaluated for four scenarios of fixed and constant hydrogen volume fraction targets in the pipeline: 5%, 10%, 15%, and 20%. The PBES can produce up to 106 kilotonnes of hydrogen per year to meet the 20% target at an LCOHD of 3.69 €/kg for compressed hydrogen storage (PBESC) and 2.81 €/kg for liquid hydrogen storage (PBESL). Storing liquid hydrogen at large-scale is significantly cheaper than gaseous hydrogen, even with the inclusion of a significantly larger PV array that is required to supply additional electrcitiy for liquefaction.

Combustion characterization of hybrid methane-hydrogen gas in domestic swirl stoves

Combustion of hybrid natural gas (methane) and hydrogen mixture in domestic swirl stoves has been characterized using hot-state experiments and numerical analysis. The detailed combustion mechanism of methane and hydrogen (GRI-Mech 3.0) has been simplified to obtain reduced number of chemical reactions involved (82 % reduction). The novel simplified combustion mechanism developed has been used to obtain combustion characteristics of hybrid methane-hydrogen mixture. The difference between the calculations from the detailed and the simplified mechanisms has been found to be <1 %. A numerical model, based on the simplified combustion model, is developed, rigorously tested and validated against hot-state tests. The results depict that the maximum difference in combustion zone’s average temperature is <13 %. The investigations have then been extended to hybrid methane-hydrogen mixtures with varying volume fraction of hydrogen. The results show that for a mixture containing 15 % hydrogen, the release of CO due to combustion reduces by 25 %, while the combustion zone’s average temperature reduces by 6.7 %. The numerical results and hot-state tests both confirm that the temperature remains stable when hybrid methane-hydrogen mixture is used in domestic swirl gas stoves, demonstrating its effectiveness in cooking processes.

Multiphysics Numerical Simulation of the Transient Process in Electrochemical Machining

To fully understand the electrochemical machining profile, a multi-physics coupling simulation model including flow-electric-temperature-structure field were established to analyze the corrosion process of the anode material and the change trend of temperature,hydrogen volume fraction, electrolyte conductivity and current density in the processing gap.The analysis results show that the temperature and hydrogen content gradually increase along the process direction.The current density and material removal showed a parabolic trend of the upper opening and the lower opening, respectively.The simulation of the different physical field changes in the electrochemical machining blade profile can not only better understand the complex physical phenomena in the machining, but also provide a theoretical basis for the selection of actual electrochemical machining parameters.

Thermodynamic Analysis of Binary and Trinary Power Cycles Fueled with Methane–Hydrogen Blends

The development of hydrogen energetics is a possible way to reduce emissions of harmful substances into the atmosphere in the production of electricity. Its implementation requires the introduction of energy facilities capable of operating on environmentally safe fuel. At the same time, from a technological point of view, it is easier to implement a gradual shift to the use of hydrogen in power plants by burning methane–hydrogen blends. This paper presents the results of thermodynamic studies of the influence of the chemical composition of the methane–hydrogen blend on the performance of binary and trinary power units. It is shown that an increase in the hydrogen volume fraction in the fuel blend from 0 to 80% leads to a decrease in the Wobbe index by 16% and an increase in the power plant auxiliaries by almost 3.5 times. The use of a trinary CCGT unit with a single-circuit WHB and working fluid water condensation makes it possible to increase the net efficiency by 0.74% compared to a binary CCGT with a double-circuit WHB and a condensate gas heater.

Experimental investigation on the temperature characteristics and hydrogen elimination effect of non-premixed hydrogen-oxygen recombination reaction at ambient temperature

Hydrogen-oxygen recombination is a safe and effective method of eliminating hydrogen before the explosion occurs. Most existing studies have focused on material modification, but the dynamic response of this reaction is rarely reported. In this paper, a series of experiments catalyzed by the Platinum-Carbon catalyst was carried out in a cylindrical container of 250 cm3 to study the effects of hydrogen volume fraction, catalyst position, and catalyst usage status on the temperature characteristics and hydrogen conversion. The results show that the reaction temperature on the catalyst surface not only increases and then decreases with the increase of hydrogen volume fraction but also decreases as the distance between the catalyst and the bottom increases, except for the 40 vol% volume fraction of hydrogen, and the maximum value occurs at the hydrogen volume fraction of 70 vol%. Moreover, there is an uncertainty in the temperature relationship between the catalyst surface and below as the volume fraction of hydrogen increases. The temperature peak structure on the catalyst surface is only influenced by the catalyst position and hydrogen volume fraction, and two temperature peaks can be observed in most cases. However, the hydrogen conversion is not affected by the catalyst position and its usage status.