Hydrogen Volume Fraction Research Articles

Numerical Investigation of a Free-Piston Hydrogen-Gasoline Engine Linear Generator

The free-piston engine linear generator (FPELG) is being investigated by many researchers because of its high thermal efficiency and its variable compression ratio. However, all researchers focused on the FPELG characteristics with mono-fuel. Therefore, in this paper, the performance of the FPELG that has adopted gasoline with hydrogen as fuel is investigated. The method of coupling the zero-dimensional dynamics model with the multi-dimensional CFD (Computational Fluid Dynamics) combustion model was applied during the simulation process. According to the results, the piston TDC (Top Dead Center), the piston peak piston velocity, and the system operation frequency show a negative correlation with the increase of hydrogen fractions. However, the peak in-cylinder pressure was increased with the hydrogen volume fraction increase, due to the fast flame speed and short combustion duration characteristics of hydrogen. Meanwhile, the indicated efficiency of the free-piston engine was increased from 32.3% to 35.3% with the hydrogen volume fraction change from 0% to 4.5%, when the free-piston engine operates at stoichiometric conditions with fixed ignition timing. In addition, with the ignition timing advance increase, the piston TDC was decreased. The peak piston velocity and the peak in-cylinder pressure were in negative correlation with the ignition timing advance. While the engine indicated that the efficiency was increased with the equivalent degree of ignition timing from 20° to 16°. Therefore, the ignition timing of the FPELG under the spark-ignition combustion mode is supposed to be an effective and practical control variable.

Effects of obstacle position and hydrogen volume fraction on premixed syngas-air flame acceleration

There have been many studies concerning on the influence of obstacles on gas explosion, but the understanding of some phenomena is still not clear, such as explosion overpressure or the change of flame velocity with the position of obstacles. This work aims to figure out the coupling effects of obstacle position (L1, L2, L3 from near to far) and hydrogen volume fraction (φ) on syngas-air flame acceleration and overpressure variation in a closed duct. Detailed flame structure evolution in the acceleration process was visualized by a high-speed camera, and overpressure was recorded by pressure transducers. Results show that the effect of obstacles moving backward is not always monotonous on the flame acceleration, which affects the maximum flame speed and maximum overpressure. Such as when φ = 0.5, the flame acceleration that is reflected as the flame propagation speed normalized by the laminar flame speed, ranks as L2 > L3 > L1. Because the obstacles strengthened turbulence on the tulip- or distorted tulip-shaped flame in L2. While when φ = 0.1, the flame acceleration ranks as L1 > L2 > L3 since the effect of turbulence is reduced. It is found that maximum overpressure is related to both flame acceleration and local overpressure. Local overpressure is the transient overpressure before the flame front touches obstacles. Obstacles moving backward is beneficial for local overpressure accumulation. Hence, the maximum overpressure increases with obstacle position moving backward when φ ≥ 0.1. This study clarifies the role of obstacle position and hydrogen volume fraction on flame acceleration, which may help to guide the application of syngas in a complex environment.

Numerical study of the effect of hydrogen leakage position and direction on hydrogen distribution in a closed enclosure

In this paper, the transient hydrogen gas leakage in a closed cylinder chamber is being numerically simulated. The results of the simulation were compared against an experimental and two other numerical simulations results. To identify the behavior of hydrogen gas and the risks of its leakage and diffusion of hydrogen gas, the model parameters are studied. Parameters investigated are the height of leakage hole location and leakage direction in the chamber. In each case, the hydrogen volume fraction graphs and created hazard region height at various time and also hazard region completely disappearing time, are investigated and high-risk states are marked.

Experimental study on explosion characteristics of premixed syngas/air mixture with different ignition positions and opening ratios

This paper explains the basic knowledge to understand the relationship between overpressure wave behavior and the structure of flame propagation, especially the effects of the ignition position and opening ratio on the combustion dynamics. The explanations are based essentially on the experimental investigations of premixed syngas/air explosions carried out at a constant equivalence ratio of 1 and the hydrogen volume fraction of 0.3 in a rectangular half-open combustion chamber. The initial temperature T0 and pressure p0 were 298 K and 0.1 MPa, respectively. The four ignition positions were set at 0, 150, 450 and 750 mm off the left of the combustion chamber. Four different opening ratios of the duct were employed, including 0.25, 0.5, 0.75, and 1. The obtained results show that ignited at IP0, the increased opening ratio would cause the distorted tulip flame to disappear, accompanied by the propagation direction change of flame front. At the same ignition position, when the opening ratio increased, the oscillation amplitude of overpressure, and the velocities of the right-hand and left-hand flame all rose, but the overpressure growth rate and maximum overpressure decreased. As the ignition position approached the opening end, the overpressure and the flame front oscillations became more intense. It is indicated that different ignition positions and opening ratios exerted obvious effect on the flame front propagation and the overpressure.

Effect of Additives on Ni‐Based Catalysts for Hydrogen‐Enriched Production from Steam Reforming of Biomass

The catalytic steam reforming of biomass for hydrogen production is investigated in a fixed‐bed reactor. A suitable additive and precursor is found in various additives (cobalt, strontium, and lanthanum) and nickel salt precursors (nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate). Synthesized samples are characterized by X‐ray diffraction (XRD), NH3 temperature‐programmed desorption (TPD), H2 temperature‐programmed reduction (TPR), and transmission electron microscopy (TEM). Results show that Co and La doping of the Ni/Al2O3 catalyst improves the dispersion of surface‐active particles and reduces the particle size, increasing H2 production. The hydrogen volume fraction of La‐modified catalysts with 10% Ni is 38.96%, which is higher than 30.39% for the unmodified Ni/Al2O3 catalyst. The lowest hydrogen yield of Ni–Sr/Al2O3 catalyst is 19.22%. This low catalytic activity is due to the reaction of Ni–Sr/Al2O3 with SiO2 found in biomass ash, which generates silicate without catalytic effect. The silicate melts and adheres to the catalyst surface at a high temperature, inhibiting the catalysis of nickel active sites. The maximum hydrogen yield obtained with nickel acetate as catalyst precursor is 51.41%, which is due to nickel acetate decomposing and forming more NiO in the amorphous state and improving the performance of catalyst.

Experimental study on the combustion-induced rapid phase transition of syngas/air mixtures under different conditions

In this work, the explosion pressure oscillation characteristics of premixed syngas/air mixtures were studied experimentally in the duct with different hydrogen concentrations and opening ratios. The results indicate that the overpressure changes as the hydrogen fraction and opening ratio varies, and the venting can mitigate the phenomenon of CRPT by increasing the opening ratio of the duct. With the increase of hydrogen volume fraction, from 10% to 50%, the rise rate of explosion overpressure increases rapidly, the maximum overpressure increases and the shortening time of reaching the maximum pressure decreases gradually. With the opening ratio increasing, the resistance, the turbulence and the pressure peak decrease gradually. Moreover, if the ratio is greater than 0.5, it has a small effect on the pressure peak; when the ratio is less than 0.5, it has a significant effect on the pressure peak. Through analyzing the dominant periods and average amplitudes of the oscillations, it can be found that the syngas combustion has an obvious combustion-induced rapid phase transition phenomenon in the opening duct. The decrement of the opening ratio and the increment of the hydrogen concentration contribute the average amplitude to increasing.

Gas dynamic-thermal-concentration fields and evaporation process of quartz particles in Ar–H2 inductively coupled plasma

The gas dynamic-thermal-concentration fields and evaporation process of quartz particles in the TICP torch of argon–hydrogen plasma have been studied. The effects of different methods of supplying hydrogen on the hydrogen concentration and gas temperature distributions, as well as on the vortex flow patterns have been discussed. The particle injection conditions in the pure argon and argon–hydrogen plasma have been determined. The dependences of the axial gas temperature and velocity distributions on the hydrogen volume fraction, flow rate of central gas and particle feed rate have been established. The effect of hydrogen volume fraction and different methods of supplying hydrogen on the evaporation degree of quartz particle in the TICP torch has been determined. The influences of the particle injection conditions (flow rate of central gas, probe tip position and injection patterns) on the evaporation degree in the TICP torch have also been evaluated. The specific heat cost for quartz particle evaporation has been calculated to evaluate the utilization efficiency of thermal energy.

Effect of hydrogen addition on the operating characteristics of a free piston linear engine

A free piston linear engine (FPLE) with glow plug ignition was designed and manufactured. This paper investigated effects of hydrogen addition on the FPLE performance and emission characteristics. Experimental results showed that the FPLE can be started manually and then steady FPLE operating state is achieved. Compared with the crankshaft model engine, the FPLE has a greater speed around the top dead centre. The peak acceleration of the FPLE (4100 m/s2) is more than three times greater than that of the crankshaft model engine. Results also showed that the FPLE performance including the indicated power, indicated thermal efficiency and indicated mean effective pressure improves remarkably with hydrogen addition. The optimal FPLE performance is achieved when the hydrogen volume fraction is 4%. However, the engine performance cannot be further improved when the hydrogen volume fraction continues to increase due to the occurrence of over-advanced combustion phasing. Moreover, the FPLE operating range is significantly broaden and the operating stability is improved with hydrogen addition since the fast burning speed and wide flammability of hydrogen. Besides, the heat release rate, in-cylinder peak pressure and pressure rise rate are also obviously enhanced. The high-speed flame images showed the flame color becomes lighter and the yellow area is smaller compared with that of pure methane condition, indicating that the hydrogen addition to the fuel contributes to burn completely and reduce the soot formation.

Numerical study of hydrogen/methane buoyant fires using FireFoam

Hydrogen/methane buoyant fires with various hydrogen volume fractions ranging from 0% to 20% were numerically studied in this paper. The modified eddy dissipation concept combustion model for multi-fuels in the large eddy simulation (LES) framework was employed for combustion, and especially the infinitely fast rate based on “global” concept was improved. Combined with the weighted sum of gray gas model for emission/absorption coefficient, the finite volume discrete ordinates model was used to compute the radiative heat transfer. The predicted centerline temperature, velocity, and flame height are in good consistence with the measured data. Furthermore, the detailed analysis was conducted on the dependency of the parameters such as centerline temperature and velocity, flame height, and soot volume fraction on hydrogen volume concentration.

Mechanical Properties of X70 Welded Joint in High-Pressure Natural Gas/Hydrogen Mixtures

The effect of hydrogen on the mechanical properties of X70 welded joint was investigated in simulated natural gas/hydrogen mixtures at 10 MPa. The hydrogen volume fraction was set as 0, 5.0 and 10.0 vol.%. The slow strain rate tensile test showed that the reduction in the area of the welded zone (WZ) metal was reduced more than that of the base metal. The variation in fatigue crack growth rate (FCGR) from high to low followed the order: heat-affected zone (HAZ) metal, base metal and WZ metal. In addition, the difference became more obvious with increasing hydrogen volume fraction. For the HAZ metal, the FCGR in 10.0 vol.% hydrogen mixtures was approximately 22 times of that in nitrogen. Furthermore, based on FCGR and fracture mechanics, the predicted fatigue life of the X70 pipeline with an initial flaw depth of 0.5 mm dropped sharply from 34,302 cycles to 3457 cycles even though 5.0 vol.% hydrogen was added in the simulated natural gas.

An experimental study on premixed syngas/air flame propagating across an obstacle in closed duct

This paper studies the effect of obstacle on the propagation of the premixed flame. Experiments are conducted in a closed rectangular duct that house a pair of fence-type obstacles with various blockage ratios (BR = 0, 0.3, and 0.5) mounted both on top and bottom walls of the duct employing the stoichiometric syngas/air mixtures with various hydrogen volume fractions (0% ≤ x(H2) ≤ 50%). High-speed camera and piezoelectric pressure gauges are respectively employed to track the propagation of the premixed flame complex and overpressure dynamics. The presence of obstacles changes the flame front shape and breaks the flame surface. The flame will still invert and the tulip flame forms after propagation through the obstacle opening. There is a new pattern of tulip flame development because of the vortex motion caused by the obstacles. After inversion, obstacles and hydrogen volume fractions are coupled to affect the propagation dynamics. The flame maintains in tulip shape as x(H2) = 0%, but the flame oscillates and undergoes a more drastic shape change as x(H2) ≥ 10%. The characteristic time decreases, but the maximum flame tip speed increases, as hydrogen volume fraction increases significantly as 0% ≤ x(H2) < 10% and gradually as x(H2) ≥ 10%. The presence of the obstacles has no effect on the flame touching the duct walls, but accelerates the flame inversion and propagation to the discharge vent. The maximum flame tip speed increases with blockage ratios. Finally, the corresponding of flame tip speed and overpressure profile is specially observed and discussed.

Production of hydrogen-rich gas from waste rigid polyurethane foam via catalytic steam gasification.

Catalytic steam gasification of waste rigid polyurethane foam, in the fixed-bed reactor, was performed to produce hydrogen-rich gas. The influence of nine kinds of additives on the yield of products (gaseous, solid and liquid product) and the volume fraction of hydrogen was investigated. Among the additives, calcium carbonate, as the catalyst, could effectively enhance the gas yield and the volume fraction of hydrogen. A three-factor three-level completely randomised factorial (3 × 3 × 3) design, with calcium carbonate as the catalyst, was applied to investigate the influence of experimental conditions (temperature, steam flowrate and catalyst dosage) on the volume fraction of gaseous product components. The data were processed with SPSS statistical software. The result showed that the main effects of one variable, the interactive effects between two factors and the interactive effects among three factors all have statistical high significance. The best catalysed process is realised when calcium carbonate is the catalyst, gasification temperature is 1100°C, steam flowrate is 0.7 kg h-1, catalyst dosage is 10 wt% of waste rigid polyurethane foam. Under this condition, the volume fraction of hydrogen reaches up to 79.85%.

Research on hydrogen risk and hydrogen control system in marine nuclear reactor

A hypothesized severe accident induced by LOCA with safety injection failure is investigated. The hydrogen generation rate and steam release rate are calculated by using the severe accident analysis program. Then, the three-dimensional computational fluid dynamics code GASFLOW is employed to simulate the two-dimensional flow field and the transport and distribution of hydrogen in the cabin. Based on the hydrogen behavior, a hydrogen control system, six NIS type PARs and three igniters, is proposed. The feasibility of the hydrogen control system is verified by comparing the volume fraction of hydrogen, flame acceleration factor and deflagration to detonation transition factor of each compartment when the hydrogen control system is started or not. The operation of hydrogen control system will lead to high temperature and high pressure, so measures should be taken to remove the heat in the marine nuclear reactor cabin.

Experimental study on hydrogen behavior and possible risk with different injection conditions in local compartment

Comparing with the large containment, the gas can not flow freely within the local compartment due to the small volume of the compartment in case of serious accident, which affects the hydrogen flow distribution, and it will determines the location where high concentration occurs in compartment. In this paper, hydrogen distribution and possible hydrogen risk in the vessel under the different conditions are investigated. The results show that when the initial gas momentum is increased, the ability of gas enters into the upper region of the vessel will be strengthened, and the hydrogen volume fraction in the upper region of the vessel is higher. Comparing with horizontal source direction, when source direction is vertically towards upper space, hydrogen is more likely to accumulate in the upper region of the vessel. With the increasing of steam mass flow, the dilution effect of steam on the hydrogen volume fraction will be strengthened, while the pressure in the vessel is also increased. When steam flow is decreased, the hydrogen explosion risk is higher in the vessel. The experiment data can provide technical support for the validation of the CFD software and the mitigation of hydrogen risk in the containment compartment.

On the propagation dynamics of lean H2/CO/air premixed flame

Syngas is a promising alternative fuel. The combustion of lean H2/CO meets the demand of high efficiency with low emission. In this paper, the propagation dynamics of lean H2/CO/air premixed flame in a closed duct were experimentally investigated at an atmospheric condition. Propagation of the premixed flame is recorded by using high-speed cinematograph, and results show that the tulip flame is attained in all cases while the occurrence of tulip distortion is determined by both equivalence ratios and hydrogen volume fractions. The flame tip location and speed are attained through using image processing technique. Results show that the analytical theory, which is firstly proposed to model the flame acceleration in tulip flame propagation phase, can be used to predict the early phase flame tip motion in some limited cases. In fuel-lean combustion, with the effect of the diffusive-thermal instability, the analytical theory underestimates the flame tip motion, but overestimates the time instant of the flame initial touching the lateral walls. The overpressure build-up is specially scrutinized in conjunction with the scaled flame tip speed. The disorderly scaled flame tip speed of distorted tulip flame indicates that the distorted tulip flame is a phenomenon which relates to pressure waves. The pressure wave is of importance for tulip distortion, but it cannot change the overpressure build-up directly. Finally, both the flame-wall interaction and the combustion instability have a crucial effect on flame propagation dynamics, and these factors should be accounted for the build of flame propagation models.

Optimization and study of performance parameters in an engine fueled with hydrogen

Engine performance parameters, including fuel conversion efficiency (FCE), power, torque and specific fuel consumption (SFC), can be affected by variables such as ignition timing (IGT), injection timing (IT) and hydrogen volume fraction (H2%). In this paper an engine fueled with different H2/CNG blend rations from 0 to 50% volume under ignition and injection timing at different speeds were investigated. For model validation, the engine operating conditions were simulated using the AVL fire software and compared with experimental results. The statistical comparison showed that there was no significant difference between them. Also, a support vector machine (SVM) was used to study the engine's behavior according to the variables studied. The SVM model predicted the FCE, power, torque, SFC and CO with error of less than 4%. The Genetic Algorithm (GA) was used to find optimal IGT, IT and H2% values to achieve optimum engine performance. Therefore, the results showed that the optimum engine operating conditions depend on the engine speed. Also, the results showed that independent variables (IT, IGT and H2%) maximize the engine performance and minimize SFC and CO emission. So that the optimum use of hydrogen in this research at different engine speeds was between 20% and 30%.

Effect on hydrogen risk of total amount of inert gas during post-inerting in AP1000 NPP

To study the hydrogen risk at severe accident of LB-LOCA of cold leg in 1# SG compartment with gravity injection failure and hydrogen igniters without power in AP1000 NPP, we investigate the effect of total amount of inert gas on reducing hydrogen risk during AP1000 post-inerting. The total amount of inert gas is 42 tons, 56 tons and 70 tons respectively. We analyze the average volume fraction of hydrogen, flame acceleration factor and deflagration to detonation transition factor in 1# SG compartment and in the upper space of containment, and the pressure in containment. The results show that, post-inerting can reduce hydrogen risk in containment at severe accident, the more the total amount of inert gas is injected, the lower the possibility of FA and DDT is. Moreover, we must ensure that containment filtration and discharge system is functioning normally at accident conditions to prevent containment from overpressure.

Dynamic hazard evaluation of explosion severity for premixed hydrogen–air mixtures in a spherical pressure vessel

To evaluate dynamic explosion severity levels of premixed hydrogen–air mixtures, pressure sensors were used to test explosion pressure in a spherical pressure vessel (inner diameter: 0.34 m). ANSYS Fluent 19.0 three-dimensional software was used to simulate the explosion process. The results revealed that when the hydrogen volume fraction was 30 vol%, the explosion pressure and pressure rise rate reached maximum values at 1.0 atm. As the initial pressure increased, the explosion pressure, and pressure rise rate increased gradually. At initial pressures of 1.0, 1.2, 1.5, and 2.0 atm, the peak pressure levels were 0.85, 0.87, 0.92, and 0.99 MPa and the pressure rise rates were approximately 198, 241, 302, and 558 MPa/s, respectively. The initial pressure exerted greater effects on the pressure rise rate than did the explosion pressure. The simulation results were consistent with the experimental findings. Moreover, the simulation yielded multi-dimensional transient explosion parameters—such as turbulent kinetic energy distribution—that are difficult to obtain in experiments. The findings pertaining to the physical experiments, numerous simulations, and influence of initial pressure on the explosion reaction mechanism of premixed hydrogen–air mixtures were discussed.

Effects of hydrogen addition on the combustion characteristics of diesel fuel jets under ultra-high injection pressures

Many applications use hydrogen addition and high-pressure fuel injection technology to improve combustion performance. In this study, spray atomization and combustion characteristics of a diesel fuel jet, under the injection pressure of 350 MPa, injecting into a constant volume combustion vessel filled with air-hydrogen mixture at the diesel engine relevant condition are investigated by simulation method. A simplified mechanism of the n-heptane (C7H16) oxidation chemistry mechanism consisting of 26 reactions and 25 species integrated with the Kéromnès-2013 hydrogen combustion mechanism and EDC combustion model are utilized to predict the diesel fuel spray auto-ignition and combustion. The ambient gas is the mixture of air and hydrogen range in volume fraction from 0% to 10%. The ambient temperature and pressure is set to 1000 K and 3.5 MPa, respectively. The results indicate that as the hydrogen volume fraction is 2%, the minimum overall droplet SMD (Sauter Mean Diameter) is approximately 0.95 μm, which is obviously smaller than that of the case with the conventional high injection pressure. In cases that H2 v/v% larger than 4%, the maximum gaseous temperature increased significantly up to 2700 K. There are two peaks in the temperature growth rate curves as the hydrogen fraction of 8% and 10%. The high temperature at the outer edge of the spray is clearly seen due to its high value when the hydrogen fraction is larger than 4%. The hot reaction layer is the main location of CO formation. The H, OH radicals are formed at the edge of the spray where the temperature is high. The hydrogen species obviously promotes the oxidation and combustion of diesel fuel.

Numerical investigation on the effects of load conditions and hydrogen-air ratio on the combustion processes of a HSDI engine

Owing to high specific energy and low emissions production, hydrogen is a desirable alternative fuel. The combustion and emission performance can be improved by hydrogen addition injected in-cylinder, intake manifold and aspirated with air. However, engine loads and hydrogen-air ration have a significant effect on the performance, combustion and emission of the diesel-hydrogen (high speed direct injection) HSDI engine. In this paper, the CFD method is used to calculate the combustion process of a diesel-hydrogen dual HSDI engine working at constant speed of 4000 rpm, at different hydrogen added from intake port (hydrogen volume fraction of 0%–10%) and five engine loads (equivalent to 20%, 40%, 60%, 80% and 100% of its maximum output power), respectively. The modelling results showed that the in-cylinder pressure and temperature under low engine load were more affected by hydrogen addition. With increasing hydrogen volume fraction, the indicated expansion work and in-cylinder peak pressure increased, and combustion duration decreased due to faster fuel-air mixing and spray flame speed.