Increasing Hydrogen Addition Research Articles

Experimental and numerical study of H[formula omitted] enrichment on swirl/bluff-body stabilized lean premixed n-butane/air flame

This study focused on the stabilization of lean premixed flames of n-butane/H2/air with swirl/bluff-body. The research explored four different hydrogen fractions (0, 20%, 40%, and 80%) at a constant equivalence ratio and Reynolds number. The turbulent reacting flow was resolved using a combination of Delayed Detached Eddy Simulation (DDES) and Flamelet Generated Manifold (FGM) model. The velocity fields and reaction zones were obtained through Particle Image Velocimetry (PIV) and OH* chemiluminescence measurements respectively. H2 addition to n-butane significantly enhanced flame characteristics. The chemiluminescence imaging showed that the flame base became stronger with increasing hydrogen addition, reducing the risk of flame lift-off. Hydrogen addition not only increased the overall reaction rate but also changed the combustion intensity at the nozzle exit from weak to strong, which is crucial for flame stabilization. Interestingly, no flashback was observed even at 80% H2 addition to n-butane at the same level of power rating. The flow strain rate analysis of the PIV measurements showed that the inclusion of hydrogen skewed the strain rate probability density functions towards the positive side, indicating an increase in the burning rate. The results demonstrate a progressive increase in preferential diffusion of H2 from reactants to products as the H2 enrichment in the fuel rises and resulted in a more intense flame. Also, the present simulation results were validated with the PIV data, and they showed good agreement. Specifically, an 80% H2 blend exhibited a 16% peak enhancement in flame surface density compared to pure n-butane while concurrently reducing CO2 emissions by 23.2%. The incorporation of H2 also led to the increased vortex strength and strain rate within the flame.

Investigations on conical lean turbulent premixed hydrogenated natural gas flames

Hydrogen's ability to enhance carbon neutrality in combustion processes puts forward the use of hydrogenated fuels, both in the form of fuel and an energy carrier as a potential decarbonization solution. However, because of the nature of hydrogen, blending it with hydrocarbons causes crucial structural changes in the flame structure, including higher flame propagation velocities and higher flame temperatures, decreased instantaneous flame thickness, and increased risks of flame flashback and an increasing potential of NOx emissions due to higher flame temperatures. These attributes encourage a thorough examination of hydrogenated blends of hydrocarbon fuels. Using lean premixed fuels is another technique to achieve efficient and cleaner combustion. However, due to the problem of flame instability in lean premixed combustion, forecasting the design points in terms of flame attributes is critical for better combustor designs.In this study, conical (Bunsen type) lean premixed turbulent flames of hydrogenated natural gas-air mixtures are experimentally studied. Through chemiluminescence measurements of the OH* and CH* radicals and laser-induced Mie scattering, lean natural gas-air premixed flames are examined with subsequently increasing hydrogen addition rates up to 20% by volume and keeping the premixture velocity constant. The obtained data is utilized for exploring the dynamics of the turbulent flame front. The main turbulent premixed flame parameters we identified relate to the instantaneous and average topology of the flame such as the turbulent flame brush thickness and flame height. We also inferred global combustion parameters like the turbulent flame propagation speed from the experimental findings.

Direct numerical simulation of NH3/air combustion with H2 addition under HCCI relevant conditions

In the present work, two-dimensional direct numerical simulations (DNS) of NH3/air turbulent combustion with H2 addition under homogeneous-charge compression ignition (HCCI) relevant conditions were performed to explore the ignition and combustion characteristics. Three hydrogen addition levels in the fuel were considered with molar fractions of 0.0 (pure ammonia), 0.1 and 0.8. The corresponding one-dimensional laminar flames were also simulated to provide reference solutions. The general combustion characteristics were first presented. It was found that turbulence and thermal stratification facilitate the ignition process. The ignition occurs earlier with increasing hydrogen addition levels and temperature fluctuations. After ignition, high heat release rate (HRR) occurs simultaneously over the entire domain with low temperature fluctuations while significant HRR occurs in narrow sheets with high temperature fluctuations. HRR is significantly enhanced in positive curvature regions of the cases with high hydrogen addition levels due to the preferential diffusion of H and other radicals. The combustion mode was examined based on the analysis of the displacement speed and species transport equation budget. The mean displacement speed is decreased with increasing temperature fluctuations and the budget analysis suggests that high temperature gradient facilitates deflagration. The reaction fronts are thinner with increasing H2 addition levels, and the combustion mode of deflagration is promoted. The effects of turbulence intensity on the flame structure and combustion mode were evaluated. The ignition occurs earlier and the area of the reaction front increases with increasing turbulence intensity. The magnitude of the temperature gradient also increases with increasing turbulence intensity, which facilitates the occurrence of deflagration. The turbulent flame structures were compared with the corresponding 0D ignition and 1D thermally stratified flame results, and it was found that the mean turbulent flame structure can be well approximated by 1D thermally stratified flames.

Inhibitory effects of water mist containing alkali metal salts on hydrogen–natural gas diffusion flames

Fire extinguishing technologies of fine water mist containing additives have good application prospects. Additives that are efficient, nontoxic, nonpolluting, widely used, economical and reliable provide a reference for the application and promotion of fine water mist fire extinguishing systems containing alkali metal salts. In this paper, six potential alkali metal salt additives were selected: potassium carbonate (K2CO3), sodium carbonate (Na2CO3), potassium oxalate (K2C2O4·H2O), potassium acetate (CH3COOK), potassium chloride (KCl), and potassium bicarbonate (KHCO3); these additives were delivered into the fires as mists of their solutions at certain concentrations, the extinguishing time was recorded, and the minimum fire extinguishing concentration (MEC) of fine water mist containing alkali metal salt was tested by using a cup burner experimental apparatus. In addition, different types of alkali metal salts were compared to determine the anions and cations with better fire suppression performance levels. The suppression efficiencies of different ratios of additive packages for hydrogen-doped natural gas diffusion flames were studied to determine a specific ratio of additive packages. Based on the results of the experiment, in contrast to the pure water mist, the suppression efficiency of alkali metal salt greatly improved. The cation extinguishing ability was K+>Na+, and CO32- and CH3COO− were better than other anions in alkali metal salts. An efficient compound additive was identified as 1.5% K2CO3 + 0.5% CH3COOK. With increasing hydrogen addition, the MEC of fine water mist with additives increased.

Experimental study on effects of compression ratio, ignition timing, and hydrogen addition on ignition delay and combustion rate of heavy-duty truck engine fueled with liquefied methane

ABSTRACT Natural gas (NG) is a potential alternative fuel for carbon neutral and has been received increasing attentions on its combustion behaviors in engine. However, there is little systematic quantitative investigation on the combustion characteristic of purified NG (methane) engine. In this study, the sweeping tests for compression ratio (CR), ignition timing, and hydrogen addition were conducted on a heavy-duty truck liquid methane engine, and the influence factors of ignition delay and combustion rate at each stage were quantitatively investigated. Some new findings and interesting conclusions were obtained. Overall, CR especially the higher CR has small effect on the ignition delay of methane engine (less than 2 deg). Under all the conditions discussed, the ignition delay almost linearly increases with the advance of ignition timing, resulting in the slight advance of start of combustion (SOC). Compared with ignition timing, hydrogen addition has larger effect on SOC since it reduces ignition delay largely (up to 7.3 deg at 1400rpm). By increasing hydrogen addition, the CA10–50 shortens slightly while CA50–90 elongates largely, resulting in a rising trend in CA10–90 finally. All these have extended the research on methane engine and are useful to improve its combustion performance.

Explosion characteristics of n-decane/hydrogen/air mixtures

Hydrogen can be used in conjunction with aviation kerosene in aircraft engines. To this end, this study uses n-decane/hydrogen mixtures to investigate the explosion characteristics of aviation kerosene/hydrogen in a constant volume combustion chamber with different hydrogen addition ratios (0, 0.2, 0.4), wide effective equivalence ratios (0.7–1.7), an initial temperature of 470 K, and initial pressures of 1 and 2 bar. The results show that the explosion pressure and explosion time decrease linearly with increasing hydrogen addition ratio. The effect of initial pressure is also discussed. A comparison of the adiabatic explosion pressures indicates that the hydrogen addition effect varies at different initial pressures and effective equivalence ratios owing to heat loss. In addition, the maximum pressure rise rate and deflagration index increase with increasing hydrogen concentration, which is more obvious for rich mixtures and high hydrogen concentrations.

Experimental and Numerical Study on the Effect of Hydrogen Addition on Laminar Burning Velocity of Ethanol–Air Mixtures

To understand the effect of hydrogen addition on the laminar burning velocity (LBV) of ethanol–air mixtures, experiments were conducted in a constant volume combustion chamber with the high-speed schlieren photography technique. The experiments were carried out under the equivalence ratios (ERs) of 0.7–1.4, an initial temperature of 400 K, an initial pressure of 0.1 MPa, and hydrogen fractions of 30% and 90% by volume, respectively. The effects of ER, initial temperature, initial pressure, and hydrogen fractions on the LBV were investigated. Moreover, adiabatic flame temperature (AFT), heat release rate (HRR), flow rate sensitivity analysis, and ROP (rate of production) analysis were also performed. Results showed that LBV increased with increasing hydrogen addition and temperature but decreased with increasing pressure. The hydrogen addition significantly increased the HRR of ethanol–hydrogen–air flames. The sensitivity analysis showed that R5 (O2 + H = O + OH) significantly influenced the LBV.

Investigation on combustion characteristics and emissions of biogas/hydrogen blends in gas turbine combustors

In the present work, numerical investigations are performed to study the combustion characteristics of biogas fuel blended with hydrogen at various compositions for a non-premixed swirling flame in a can-type gas turbine combustor. The amount of hydrogen enrichment varies from 0 to 50% by volume. A numerical approach using the non-premixed flamelet model, turbulent standard (k–ε) model, and P-1 radiation model was adopted for simulating the can-type combustor power at a fixed operating power of 60 kW. The steady laminar flamelet model was used to analyze the effect of hydrogen enrichment, global equivalence ratio with different swirl numbers on a stable flame operation, temperature distribution and contours, velocity streamline contours, NO emissions, and species concentrations. The results indicate that hydrogen enrichment and the variation of the equivalence ratio and the swirl numbers significantly impacted the flame macrostructure. Hydrogen enrichment in the fuel intensifi combustion, leading to higher flame temperature and wider flammability than bure biogas. Maximum NO emissions in the outlet chamber have been dropped by 43 and 78 (ppm @15 % by volume of O2) for the biogas and biogas-50% H2, respectively, due to the reduced flame temperature leading to reduction in thermal NOx formation with reduction equivalence ratio from 0.5 to 0.2. The flame temperature and NO emissions at ϕ=0.2 with a high rate of hydrogen (50% H2) are close to the results of pure biogas (0% H2) at the same equivalence ratio. The results show that CO and CO2 emissions decrease with increasing hydrogen addition and decreasing the equivalence ratio; due to a decrease in the amount of carbon, the cooling effect, and an increase in the OH concentration.

The influence of hydrogen addition on the combustion characteristics of a common-rail CI engine fueled with waste cooking oil biodiesel/diesel blends

In this study, the effect of hydrogen assisted intake air on combustion characteristics of a diesel fuel-waste cooking oil biodiesel (WCOB) blend fueled CI engine has been extensively studied. While the diesel and B25 (75% diesel fuel+25% WCOB) fuels used as the main fuel were sprayed directly into the cylinder, the hydrogen, the secondary fuel was mixed with the intake air at 10, 20, 30 and 40 lpm flow rates and taken into the cylinder. The maximum in-cylinder pressure (CP) values decreased with B25 fuel compared to diesel fuel. But B25‑hydrogen dual-fuel mode operation exhibited higher maxium CP and RoPR value according to diesel fuel. It was seen that hydrogen has a more significant effect on premixed pilot fuel combustion phase compared to the diffusion combustion phase. It was observed that the combustion duration (CD) of neat B25 fuel lower than that of diesel fuel, generally. In case of B25‑hydrogen dual-fuel mode operation, CD increased depending on increasing hydrogen addition rate. It was seen that hydrogen enrichment has no adverse effect on ringing intensity (RI).

Effects of hydrogen as a solid solution element on the deformation behavior of a near-alpha titanium alloy

The effects of hydrogen on the room-temperature mechanical properties and the deformation behavior of near-alpha alloy Ti–6Al–3Nb–2Zr–1Mo were systematically investigated. It was found that hydrogen addition increased the strength and plasticity of titanium alloy, while the impact toughness firstly increased for the sample with 65 wppm hydrogen and then decreased at higher hydrogen content. The strength was increased due to the pinning effect and the solid-solution strengthening effect of hydrogen, while the plasticity was improved by the increase of dislocation mobility and the breakage of beta laths. The increase of impact toughness at 65wppm hydrogen resulted from the enhancement of dislocation motion and multiplication, but further increasing hydrogen addition would reduce impact toughness by decreasing the cohesion strength at interfaces and grain boundaries and the breakage of beta laths. In addition, deformation behaviors of titanium alloys with different hydrogen content were discussed. Hydrogen inhibited twinning and enhanced dislocation slip to some extent. Cross-slip was hindered and planar slip was favored due to the decrease of stacking fault energy after hydrogenation. Further, basal slip and pyramidal slip were activated while prismatic slip was suppressed by hydrogen addition.

Experimental Investigation of LPG/H2/Air Premixed Flame Stability Zone

Flame stability, environmental changes and fossil fuel shortage represent major challenges to any successful combustion device utilization. In this study, the stability zone of laminar premixed ILPG/ -air flames was investigated experimentally. Non-swirling burners with different diameters (10, 12.5, and 17 mm) were employed to characterize the flashback and blow-off limits. Different hydrogen blends (0%-50%) at equivalence ratios (ER) (0.6-1.4) were used. The results show that maximum flashback limits occurred at ER slightly richer than stoichiometric, with the mixture flow rate at a flashback of (3.75, 7.25 and 14) LPM for the 50% hydrogen blending ratio and a burner diameter of (10, 12.5 and 17 mm), respectively. When hydrogen blending was 50% at stoichiometric condition, the critical velocity gradient at flashback increased from (469.9-650.8 1/s) with 10 mm diameter, and the critical velocity gradient at blow-off increased from (1538-2936 1/s). It was observed that the flashback limits decreased with increasing burner diameter. Its limit increased with increasing hydrogen addition to the ILPG. The blow-off limit increased with increasing fuel concentration. This paper further presents the stability zone for ILPG/air combustion for a non-swirling burner with a 10-mm diameter and different hydrogen blends. It was found that the stability zone was narrow on the lean combustion side and enhanced with increasing diameter and hydrogen addition.

Effect of hydrogen enrichment on swirl/bluff-body lean premixed flame stabilization

This paper reports the mechanism of hydrogen enrichment in stabilizing swirl/bluff-body CH4/air lean premixed flame. Large Eddy Simulation (LES) coupled with Thickened Flame (TF) model was performed to resolve the turbulent reacting flow. A detailed chemistry was used to describe the oxidization of CH4/H2/air mixtures. Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence of OH (OH-PLIF) simultaneous measurements were conducted to obtain the velocity fields and flame structures respectively. The numerical methods were validated by experimental data and showing good agreements. Both the experimental and numerical results show that, the flame brush attachment tends to leave the inner shear layer with increasing hydrogen addition, which will reduce the risk of flame lift-off. The chemical analyses prove that the attachment of CH4/air flame is inherently weak. On the one hand, the CH4/air flame is stabilized by the hot products inside the recirculation. On the other hand, the burnt gas suppresses the oxidation of H2 and CO through H2 + OH = H + H2O and CO + OH = CO2 + H, respectively. Although the proportion of CH4 decomposition through CH4 + OH = CH3 + H2O will be reduced by hydrogen addition, the path of CH4 + H = CH3 + H2 will be enhanced significantly. Hydrogen addition will not only increase the overall reaction rate, but also change the combustion intensity at the nozzle exit from relatively weak to strong, which is also important for flame stabilization. The robust flame attachment obtained by hydrogen addition can attributed to the enhanced reactions of H2 + OH = H + H2O and CH4 + H = CH3 + H2.

Study on the propagation characteristics of hydrogen/methane/air premixed flames in variable cross-section ducts

The flame propagation characteristics of hydrogen/methane/air mixtures with different hydrogen addition ratios (φ=0, 10 %, 20 %, 30 %, 40 % and 50 %) in different variable cross-section ducts were studied. A high-speed camera and pressure sensors were used to collect flame images and determine the overpressure dynamics. The results show that the smooth flame front will be twisted and folded, when the flame propagates to the abrupt position of the cross-section area of the duct. The larger the abrupt change rate of the duct cross-section is, the more obvious the disturbance to the flame and the more severe the turbulence. With increasing hydrogen addition ratio, the flame propagation speed and overpressure in the four kinds of variable cross-section ducts studied increase. The time for the flame front to reach the downstream end is gradually shortened, and the flame propagation time when the flame propagates from the smaller cross-section tube to the larger cross-section tube is more severely shortened with increasing hydrogen addition ratio than that when the flame propagates from the larger cross-section tube to the smaller cross-section tube. The increase of the overpressure caused by the addition of hydrogen is more significant when the flame propagates from the smaller cross-section tube to the larger cross-section tube. When the flame propagates from the smaller cross-section tube to the larger cross-section tube or from the larger cross-section tube to the smaller cross-section tube, the larger the abrupt change rate of the duct cross-section is, the larger the maximum overpressure.

An experimental comparative study of the stabilization mechanism of biogas-hydrogen diffusion flame

This work describes an experimental study of the effect of hydrogen addition on the stabilization characteristics of laminar biogas diffusion flame. The focus is to identify and compare various factors influencing the blowoff process. Three compositions of biogas, BG40, BG50 and BG60 were considered and the amount of hydrogen added was varied from 5% to 25% of the biogas by volume.With increasing hydrogen addition, the critical flow velocity beyond which the flame blows off increases faster than the laminar burning velocity (LBV) does, indicating that flame stabilization is not solely dependent on laminar burning velocity. An exponential relationship is observed between LBV and flame propagation speed. Therefore, both flame propagation speed and LBV, together with other factors, contribute to flame stabilization. The reason for no stable lift for either biogas or H2-biogas flame is analyze by Schmidt number calculation, and the results agree with the literature. Also found is that hydrogen added to biogas accelerates the fuel mass diffusion, which may play an important role for stabilization of the nozzle-attached flame.The CO2-C3H8 and BG60 flames were compared to exclude the possible dominant role played by insufficient heat release and/or excessive heat loss due to CO2 present in biogas. Tested on varied-size burners show that flame stabilization depends on burner pore size, where larger diameter allows better flame stability. The universal equation for predicting blowout/blowoff velocity in the literature was found to be invalid for H2-enriched biogas flame and a new scaling law was put forwards.

Combustion and Heat Release Characteristics of Biogas under Hydrogen- and Oxygen-Enriched Condition

Combustion and heat release characteristics of biogas non-premixed flames under various hydrogen-enriched and oxygen-enriched conditions were investigated through chemical kinetics simulation using detailed chemical mechanisms. The heat release rates, chemical reaction rates, and molar fraction of all species of biogas at various methane contents (35.3–58.7%, mass fraction), hydrogen addition ratios (10–50%), and oxygen enrichment levels (21–35%) were calculated considering the GRI 3.0 mechanism and P1 radiation model. Results showed that the net reaction rate of biogas increases with increasing hydrogen addition ratio and oxygen levels, leading to a higher net heat release rate of biogas flame. Meanwhile, flame length was shortened with the increase in hydrogen addition ratio and oxygen levels. The formation of free radicals, such as H, O, and OH, are enhanced with increase in hydrogen addition ratio and oxygen levels. Higher reaction rates of exothermic elementary reactions, especially those with OH free radical are increased, are beneficial to the improvement in combustion and heat release characteristics of biogas in practical applications.

Research on combustion and emission characteristics of a lean burn gasoline engine with hydrogen direct-injection

An experimental investigation on effects of hydrogen fractions (0%∼11.09%) on lean burn combustion and emission characteristics of SI gasoline engine was carried out on a modified premixed gasoline engine equipped with a hydrogen direct-injection system, under the condition of the excessive air coefficient from 1.0 to 1.5. With the increasing hydrogen addition fraction, the combustion speed increases, mean effective pressure and thermal efficiency are improved. Moreover, flame development and propagation duration are shortened, the peak cylinder pressure increases and its corresponding crank angle advances, the maximum rate of heat release, both the maximum mean gas temperature and the maximum rate of pressure rise increase, while HC and CO emissions decrease and NOx emissions increase. Hydrogen direct injection does not reduce volumetric efficiency, thus engine power performance improves. The addition of hydrogen makes stable combustion at 1.5 excessive air coefficient possible, and the effective thermal efficiency increases, along with a significant reduction in CO and NOx.

Numerical study on combustion and emission in a DISI methanol engine with hydrogen addition

Combustion, carbon monoxide (CO), Nitrous oxide (NO), formaldehyde (HCHO) and unburned methanol (CH3OH) emissions characteristics in a direct injection spark ignition (DISI) methanol engine with hydrogen addition ratio from 5% to 15% have been investigated numerically based on the detailed methanol oxidation reaction mechanism combined with the nitrogen oxides (NOX) reaction mechanism using the PREMIX code of CHEMKIN program with AVL FIRE software. Maximum cylinder pressure, maximum heat release rate and highest cylinder temperature increase and their corresponding crank angles advance with hydrogen addition from 0 to 15%. CO emission decreases and NO emission increases with increasing hydrogen addition ratio, whereas, formaldehyde and the unburned methanol significantly reduce with increasing hydrogen addition. Thus, hydrogen addition can provide a new way to address formaldehyde and unburned methanol unregulated emissions in a DISI methanol engine.

Effect of hydrogen on mold filling behavior of TiAl alloy

Since TiAl alloy requires superior mold filling capability, this study used hydrogen to improve its mold filling capability by introducing the hydrogen into the molten alloy. The mold filling was evaluated by pouring the molten alloys containing various levels of hydrogen into a thin perforated sheet graphite mold. The volume percentage filling the mold was increased with increasing hydrogen addition. And the increasing tendency became very slight after the hydrogen reached 15 kPa. In addition, the pore formation of the alloy was also examined by X-ray radiographs.

Effects of hydrogen addition on combustion characteristics of n-decane/air mixtures

To explore the possibility of simultaneously extending the lean extinction limit and reducing the emission levels with hydrogen addition, a computational study is performed to investigate the effects of hydrogen addition on the fundamental combustion characteristics of n-decane/air mixtures. It is found that a small amount of hydrogen addition can significantly promote the reactivity of n-decane/air mixtures, leading to shortened ignition delays at high temperatures, increased laminar flame speeds, and reduced extinction residence times. The results on emissions show that the addition of hydrogen leads to a reduction in CO emission index under fuel rich conditions, while NO emission index increases with increasing hydrogen addition for all the conditions examined. The extent of the hydrogen addition effects on different combustion responses at varying pressures has also been investigated. In addition, sensitivity analysis has been conducted to identify the key reactions that are responsible for the enhanced reactivity associated with hydrogen addition. The present results further demonstrate that with the aid of hydrogen addition, leaner and hence cleaner combustion can be achieved without compromising static flame stability.

Low-Energy Collisions of Pyrazine and d6-Benzene Molecular Ions with Self-Assembled Monolayer Surfaces: The Odd−Even Chain Length Effect

The low-energy reactive collisions of two independent probe ions, pyrazine and d6-benzene, illustrate an odd−even hydrocarbon chain length effect for a wide range of hydrocarbon self-assembled monolayer (SAM) surfaces. SAM surfaces prepared from alkanethiols ranging from CH3(CH2)10SH to CH3(CH2)17SH chemisorbed to polycrystalline gold are shown to exhibit an odd−even effect where the orientation of the terminal methyl group determines the reaction behavior of the thin film. X-ray photoelectron spectroscopy shows the surfaces to be homogeneously covered and provides evidence for the presence of a thiolate (Au−SR) on the SAM surface. When 30 eV incident ions were used, the extent of hydrogen addition to the incident probe ion was larger for odd carbon chain length SAM surfaces when compared to the even chain length films. For an odd chain length SAM surface, the terminal methyl group exposes a C−H bond perpendicular to the surface, increasing hydrogen addition reactivity for the probe ions. The low-energy p...