Hydrogen Enrichment Research Articles

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.

Assessment of spark-energy allocation and ignition environment on lean combustion in a twin-plug Wankel engine

Due to the elongated shape of the combustion chamber and strong one-way flow characteristic, changing the location of enhanced combustion is an effective means to ameliorate the indicated efficiency of the Wankel engine. For this purpose, strengthening combustion can happen by allocating spark-energy in the desired location along with a favorable ignition environment. In this study, three-dimensional CFD simulations were implemented and the numerical results were compared with existing measured data, in which ignition environment variations were achieved by hydrogen enrichment within the intake manifold of a spark-ignition Wankel engine. Based on CONVERGE code with the SAGE detailed chemistry solver, the twin-plug engine model was then used to assess the location of strengthened combustion employing a spark-energy allocation from the perspective of species evolution, combustion characteristics, and emissions formation. The results indicate that enhancing spark-energy at the leading side of the rotor chamber has an overall higher burned volume rate and faster species evolution due to the later connection of two burning sources prior to quenching. Increasing the hydrogen content in the ignition environment causes richer active radicals and higher turbulence, ultimately promoting flame propagation and combustion intensity. A larger T-plug spark-energy decreases the indicated mean effective pressure, heat release rate, and thermal efficiency because of the intensified wall heat flux and the lower mass burning rate at the leading side. There is no doubt that the introduction of hydrogen enrichment presents a positive effect on both thermal efficiency and specific fuel consumption at the price of a slighter increase of nitrogen oxide formation due to higher mass fraction of high-temperature regions. It is recommended that enhancing local mass burning rate in the leading part of the rotor chamber under the hydrogen-enriched ignition environment can provide a great potential in the quest towards high-efficiency Wankel rotary engine.

Hydrogen-Rich Gas Stream from Steam Gasification of Biomass: Eggshell as a CO2 Sorbent

The present study investigates the steam gasification of biomass with an in-process CO2 capture. The work is aimed at achieving hydrogen enrichment while reducing the carbon dioxide (CO2) concentra...

CFD analysis on particle diameter in hydrogen-enriched diesel engine for different piston bowl geometries

Hydrogen is considered as one of the best alternative fuels for internal combustion engines because of its unique combustion properties. Especially, after impingement of the spray against a combustion chamber of the piston, the spatial distribution of the droplet diameter is one of the most important factors for exhaust emissions, but it is complex to study sufficiently because of the difficulties encountered in measuring the droplet diameter. To achieve controlled combustion, an attempt is made to investigate the effect of change in bowl geometry and its special distribution in the combustion chamber of a diesel engine with and without the enrichment of Hydrogen. The objective of this study is to analyse the effect on particle diameter of the injected fuel to the combustion chamber with hydrogen enriched with 2 LPM flow rate with diesel fuel and compare the results using the CFD analysis for different combustion bowl geometries. Abbreviations: CA: crank angle; CI: compression ignition; CFD: computational fluid dynamics; CO: carbon monoxide; HCCI: homogeneous charge compression ignition; HC: hydrocarbons; ICEM: internal combustion engine meshing; µm: micrometres; LPM: litres per minute; NOx: oxides of nitrogen

Experimental investigation on biogas enrichment with hydrogen for improving the combustion in diesel engine operating under dual fuel mode

Biogas valorization as fuel for internal combustion engines is one of the alternative fuels, which could be an interesting way to cope the fossil fuel depletion and the current environmental degradation. In this circumstance, an experimental investigation is achieved on a single cylinder DI diesel engine running under dual fuel mode with a focus on the improvement of biogas/diesel fuel combustion by hydrogen enrichment. In the present investigation, the mixture of biogas, containing 70% CH4 and 30% CO2, is blended with the desired amount of H2 (up to 10, 15 and 20% by volume) by using MTI 200 analytical instrument gas chromatograph, which flow thereafter towards the engine intake manifold and mix with the intake air. Depending on engine load conditions, the volumetric composition of the inducted gaseous fraction is 20–50% biogas, 2–10% H2 and 45–78% air. Near the end of the compression stroke, a small amount of diesel pilot fuel is injected to initiate the combustion of the gas–air mixture. Firstly, the engine was tested on conventional diesel mode (baseline case) and then under dual fuel mode using the biogas. Consequently, hydrogen has partially enriched the biogas. Combustion characteristics, performance parameters and pollutant emissions were investigated in-depth and compared. The results have shown that biogas enriched with 20% H2 leads to 20% decrease of methane content in the overall exhaust emissions, associated with an improvement in engine performance. The emission levels of unburned hydrocarbon (UHC) and carbon monoxide (CO) are decreased up to 25% and 30% respectively. When the equivalence ratio is increased, a supplement decrease in UHC and CO emissions is achieved up to 28% and 30% respectively when loading the engine at 60%.

Evolution of surface oxides and impurities in high vacuum heat treated Nb: A TEM and TOF-SIMS in-situ study, mechanism and repercussions on SRF cavity applications

A detailed in-situ study of the transformations occurring in the top nano-layer of a chemically treated Nb sample undergoing thermal cycling was performed using transmission electron microscopy (TEM) and time of flight secondary ion mass spectrometry (TOF-SIMS) techniques, with an objective to understand the effects of high temperature degassing (HTD) treatment of superconducting radio frequency cavity. TEM imaging of the top layer at various temperature provided evidences of the evolution of top oxide layer, while the associated chemistry explored through TOF-SIMS spectra and depth profiles revealed an interesting transformation of the oxide layer in to a carbide-dominated layer between ~200–400 °C. The oxide layer transformation dominated at the vacuum-oxide interface until 250 °C, beyond which, oxygen diffusion and carbon enrichment at the metal-oxide interface and associated reactions transitioned the layer to a thin Nb(OC) mixed layer up to ~1–2 nm from top surface, followed by a uniform carbide layer of ~5 nm thickness. Furthermore, desorption of bulk H was found to be co-related to the oxide layer transition up to 350 °C, beyond which, near surface hydrogen enrichment became the dominating factor. Finally, the proposed mechanisms were applied to understand the surface contamination and nitrogen doping during standard HTD of Nb samples.

Effects of hydrogen enrichment on CH4/Air turbulent swirling premixed flames in a cuboid combustor

Effects of H2-enrichment on structures of CH4/air turbulent swirling premixed flames affected by high intensity turbulence in a gas turbine model combsutor are investigated by conducting direct numerical simulations. Two stoichiometric mixture conditions, of which volume ratio of CH4:H2 = 50:50 and 80:20, are simulated by considering a reduced chemistry (25 species and 111 reactions). Results showed qualitatively different flame shapes and reaction zone characteristics between the cases. For the higher H2-ratio case, the flame is stabilized both in the inner and outer shear layers. For the lower H2-ratio case, the flame is stabilized only in the inner shear layer and extinction occurs in the outer shear layer. Comparison of the reaction zone characteristics with unstrained and strained laminar flames in phase space showed that H2 mass fraction for the lower H2-ratio case and reaction rate profiles for both cases deviate from the corresponding laminar values. Analysis of fuel species conservation equation suggests that the turbulent transports are substantially influential to determine local and global flame structures. These findings would be useful for designing practical H2-enriched gas turbine combustor in the aspect of flame structures under high intensity turbulence.

Effect of electrochemical regeneration on the surface of a graphite adsorbent loaded with an organic contaminant

A regeneration efficiency of greater than 100% was obtained for electrochemical regeneration of a graphite interaction compound loaded with a phenol adsorbate. Time-of-flight secondary ion mass spectrometry was employed to study the effect of electrochemical regeneration on the graphite adsorbent. Using this technique, the elemental composition of the graphite surface was determined as a function of depth. The surface composition of the adsorbent was compared in three states: a fresh graphite before adsorption, after loading with a phenol adsorbate and after electrochemical regeneration. The fresh graphite exhibited a hydrogen and oxygen-rich surface layer approximately 150 nm thick. After loading with the adsorbate, the adsorbent had a thicker surface layer, approximately 370 nm, and significant enhancement in the hydrogen and oxygen abundance extending beyond 600 nm from the surface. After electrochemical regeneration, the graphite adsorbent showed an oxygen-rich layer, slightly thicker than the fresh case at approximately 220 nm, and a very much lower hydrogen enrichment at the surface. These results demonstrate that whilst the electrochemical regeneration effectively removes the phenol model pollutant, it also oxidises the exposed carbon surface. This oxidation may lead to new adsorption sites, but also has a significant impact on the estimation of adsorbent life.

Hydrogen enrichment on diesel engine with biogas in dual fuel mode

Fossil fuels fulfill a major part of the world's energy demand. Higher demand for energy, depletion of fossil fuels and environmental impacts are the key motivational factors to explore alternate energy sources. Biogas and Hydrogen seem to be the promising alternate gaseous fuels. In this paper, the performance and emission studies were performed on a stationary dual fuel engine using fuel combinations of diesel, biogas-diesel, hydrogen-diesel, and hydrogen-biogas-diesel. Experimental results reveal that the performance of dual fuel mode with hydrogen-biogas-diesel fuel improved, and emissions were reduced in comparison to the neat diesel operation. The Brake Thermal Efficiency (BThEff) was improved by 3.09%, Brake Specific Diesel Consumption (BSDC) was reduced by 71.05%, and Brake Specific Energy Consumption (BSEC) decreased by 12.13%. The emission parameters CO, HC, and NOx, were reduced by 88.09%, 5.68%, and 83.01% respectively. Injection timing, which was obtained at 21°CA BTDC, was optimized experimentally for the selected optimum hydrogen-biogas-diesel fuel.

Second-law thermodynamic analysis on premixed syngas flames

Exergy destructions in laminar premixed syngas flames, with varied fuel compositions and changed pressures, were numerically studied. Chemical reactions are found to be the dominant source for exergy destruction, followed by heat conduction and mass diffusion. As a result of the trade-off between the increased exergy destruction rates and narrowed flame thickness, the total exergy destruction increases by about 1% with hydrogen enrichment, but is nearly unchanged with pressure elevation. Specifically, with hydrogen enrichment, the exergy destruction from heat conduction decreases due to the narrowed flame thickness, whereas those from mass diffusion and chemical reactions increase because of higher diffusivity of H2, H and H2O and higher reactivity of H2 than CO, respectively. In contrast, with pressure elevation, the higher temperature gradient and mole fraction gradients result in increased exergy destruction from heat conduction, but the exergy destruction from chemical reactions decrease due to the narrowed flame thickness.

Second-law thermodynamic analysis on premixed syngas flames

Exergy destructions in laminar premixed syngas flames, with varied fuel compositions and changed pressures, were numerically studied. Chemical reactions are found to be the dominant source for exergy destruction, followed by heat conduction and mass diffusion. As a result of the trade-off between the increased exergy destruction rates and narrowed flame thickness, the total exergy destruction increases by about 1% with hydrogen enrichment, but is nearly unchanged with pressure elevation. Specifically, with hydrogen enrichment, the exergy destruction from heat conduction decreases due to the narrowed flame thickness, whereas those from mass diffusion and chemical reactions increase because of higher diffusivity of H2, H and H2O and higher reactivity of H2 than CO, respectively. In contrast, with pressure elevation, the higher temperature gradient and mole fraction gradients result in increased exergy destruction from heat conduction, but the exergy destruction from chemical reactions decrease due to the narrowed flame thickness.

Modelling and analyzing the impact of hydrogen enriched natural gas on domestic gas boilers in a decarbonization perspective

Decarbonization of energy economy is nowadays a topical theme, and several pathways are under discussion. Gaseous fuels have a fundamental role for this transition, and the production of low carbon-impact fuels is necessary to deal with this challenge. The generation of renewable hydrogen is a trusted solution since this energy vector can be promptly produced from electricity and injected into the existing natural gas infrastructure, granting storage capacity and easy transportation. This scenario will lead, in the near future, to hydrogen enrichment of natural gas, whose impact on the infrastructures is being actively studied. The effect on end-user devices such as domestic gas boilers, instead, is still little analyzed and tested, but is fundamental to be assessed. The aim of this research is to generate knowledge on the effect of hydrogen enrichment on the widely used premixed boilers: the investigations include pollutant emissions, efficiency, flashback and explosion hazard, control system and materials selection. A model for calculating several parameters related to combustion of hydrogen enriched natural gas is presented. Guidelines for the design of new components are provided, and an insight is given on the maximum hydrogen blending bearable by the current boilers.

Turbulent flame structure characteristics of hydrogen enriched natural gas with CO2 dilution

This paper investigated the hydrogen enriched methane/air flames diluted with CO2. The turbulent premixed flame was stabilized on a Bunsen type burner and the two dimensional instantaneous OH profile was measured by Planar Laser Induced Fluorescence (PLIF). The flame front structure characteristics were obtained by extracting the flame front from OH-PLIF images. And the turbulence-flame interaction was analyzed through the statistic parameters. The role of hydrogen addition as well as CO2 dilution on the features of turbulent flame were revealed by those parameters. In this work, hydrogen fractions of 0, 0.2 and CO2 dilution ratios of 0, 0.05 and 0.1 were studied. Results showed that hydrogen addition can enhance turbulent burning velocity ST/SL through decreasing the scale of the finer structure of the wrinkled flame front, caused by the smaller flame instability scale. In contrast, CO2 dilution decreased turbulent burning velocity ST/SL due to its inactive response to turbulence perturbation and larger flame wrinkles. For all flames, the probability density function (PDF) profile of the local curvature radius R shows a bias to positive value, resulted from the flame intrinsic instability. The PDF profile of R decreases with CO2 dilution, while the value of local curvature radius corresponding to the peak PDF is larger. This indicates that larger wrinkles structure was generated due to CO2 dilution, which leads to the decrease in ST/SL as a consequence. Hydrogen addition increases the flame volume and results in more intense combustion. CO2 dilution has a decrease effect on flame volume for both XH2 = 0 and XH2 = 0.2 while the decrease is obvious at XH2 = 0.2, ZCO2 = 0.1. In all, hydrogen enrichment improves the combustion while CO2 can moderate combustion. Therefore, adding hydrogen and CO2 in natural gas can be a potential method for adjusting the combustion intensity in combustion chamber during the combustor design.

Formula omitted] enrichment impact on the chemiluminescence of biogas/air premixed flames

A numerical and experimental study of chemiluminescent signals of OH*, CH*, C2* and CO2* is conducted for hydrogen enriched CH4/CO2/air premixed laminar flames. Biogas blends (CH4/CO2) with 0≤χCO2≤30% are enriched in the range 0≤χH2≤10% and burned under lean conditions (0.82≤φ≤1) in a Bunsen burner. Light is captured by a spectrometer and the intensity of chemiluminescent radicals is calculated by subtracting a background emission from the intensity at predefined wavelengths. Flame pictures are also taken and post-processed to calculate flame area. The simulations are conducted in Cantera using a freely propagating flame routine coupled with the GRI-Mech 3.0 mechanism, without the nitrogen kinetics. The impact of hydrogen enrichment in light emission through thermal-diffusion, concentration and chemistry/kinetics effects is studied numerically using False argon and False hydrogen. Intensity ratios, in particular OH*/CH* and CO2*/CH*, display linear trends with hydrogen concentration. OH*/CH*, OH*/C2*, CH*/C2* and CO2*/CH* are used to estimate the equivalence ratio (φ) in hydrogen enriched biogas flames. An exponential function is proposed to model the behavior of both numerical and experimental curves. OH*/CH* displays the best results with great agreement with simulations. OH*/C2*, CH*/C2* and CO2*/CH* are able to infer φ with proper calibration.

Assessment of combustion and exhaust emissions in a common-rail diesel engine fueled with methane and hydrogen/methane mixtures under different compression ratio

This study investigates the potential usage of the methane and hydrogen enriched methane in a turbocharged common-rail direct injection diesel engine. Methane and hydrogen/methane mixtures are sent through the air intake manifold of the engine. The engine is operated at four different loads and three different compression ratios. Results are compared amongst single diesel and dual-fuel operations at different compression ratios and load conditions. Compared to diesel, dual-fuel operations mostly generate higher and advanced peak in-cylinder gas pressure, more combustion noise, late pilot injection and start of combustion, advanced combustion center, substantial variations at ignition delay and combustion duration, a significant increase in cyclic variations at low and medium loads, and earlier heat release. Hydrogen enrichment decreases evidently specific fuel consumption. Concerning emissions, compared to diesel operation, dual-fuel operations produce higher total hydrocarbon (THC) and nitrogen oxides (NOx) but lower carbon dioxide (CO2). Hydrogen substitutions decrease THC and CO2 emissions of methane dual-fuel operations approximately between 9-29% and 1–32%, respectively. Smoke emission of dual-fuel operations is less than that of diesel at low and medium loads, whereas it sharply increases at high load. Knocking occurs at high compression ratio and load conditions with dual-fuel operations and dramatically increases with increasing hydrogen ratio. Decreasing the compression ratio notably reduces the combustion noise as well as some emissions, such as NOx, CO2 and smoke, for entire load ranges of dual-fuel and diesel operations.

Experimental Evaluation of Performance and Combustion Characteristics in a Hydrogen–Methane Port Fueled Diesel Engine at Different Compression Ratios

This paper investigates the performance and combustion characteristics of a common-rail diesel engine fueled with methane and hydrogen enrichment of methane under different loads (2.15, 4.3, 6.45, ...

Engine’s behavior on hydrogen addition of waste cooking oil fueled light duty diesel engine - A dual fuel approach

Foremost aim of this work is to study the influence of hydrogen induction on tail pipe exhaust emissions of a compression ignition engine fueled with waste cooking oil biodiesel (WCOB). Waste cooking oil biodiesel was mixed with mineral diesel fuel by a volume fraction of 50% (WCOB50). In addition to this pure hydrogen was inducted into the intake along with air at the volume flow rate of 2, 4 and 6 lpm. The test was conducted in a single cylinder agricultural based direct injection light duty diesel engine at various load conditions. At first, test results were correlated with neat diesel fuel and WCOB50 fuel at all loads. WCOB50 fuel indicates an insignificant reduction in BTE when compared to neat diesel fuel. Emission study revealed that WCOB50 usage moderately increases NOx emission and depreciates CO, HC and smoke opacity. However, hydrogen enrichment significantly decreased exhaust emissions such as smoke opacity, HC and CO except for NOx emission. Also, the BTE of the engine gradually improved with the increasing volume flow rate of hydrogen in the intake. At maximum power output in cylinder pressure and heat release rate were found to be higher for maximum hydrogen flow rate.

Numerical investigation of turbulent combustion with hybrid enrichment by hydrogen and oxygen

In this study, the NG + H2/air + O2 turbulent flame is numerically investigated using the Computational Fluid Dynamics CFD code. The modulation of combustion and radiation is performed respectively by the Eddy Dissipation Model and the Discrete Ordinate Model. The turbulence modeling is carried out by Shear Stress Transport (SST/k-ω) turbulence model. The H2 amount in the fuel mixture varies under constant volumetric fuel flow between 0 and 60% and the oxidant is composed by 80% air and 20% pure oxygen. The results obtained show the hydrogen addition to Natural Gas improves the mixing between the reactants, reduces their residence time and reduces the length and thickness of the flame. On the other hand, the hydrogen enrichment minimizes the CO2 and CO production and increases the NOx level.

Climate and environmental response to the break-up of Pangea during the Early Jurassic (Hettangian-Pliensbachian); the Dorset coast (UK) revisited

Abstract Between the end-Triassic mass extinction and the Toarcian Oceanic Anoxic Event, the Early Jurassic witnessed important changes in carbon burial, palaeogeography and paleoceanography, which were linked to the initial breakup of Pangaea. In order to better understand the climate and environmental impact of this phase of major tectonic rearrangement we revisited a key section along the Dorset coast (UK) and used a multi-proxy geochemical approach for its analysis. Carbon isotopes (δ13C) measured on organic matter were corrected for the influence of changes in the type of organic matter. The thus obtained δ13C-HI index and an additional δ13Ccarb record measured on bulk carbonate indicate a suite of carbon-isotope excursions (CIEs) including the negative main CIE (Triassic-Jurassic boundary to early Sinemurian) the negative Sinemurian-Pliensbachian boundary CIE and the positive margaritatus Zone (late Pliensbachian) CIE. Based on elevated hydrogen index values and enrichments in Mo, U, V, total organic carbon (TOC) and pyrite, the Hettangian-Sinemurian interval was interpreted to have been characterised by high productivity conditions and strong oxygen depletion of the basin. The chemical alteration index (CIA), clay mineralogy, and δ18O data provide independent evidence for increased continental runoff triggered by humid climate conditions on the adjacent continent during this time period. The strongest oxygen-depleted conditions were inferred for the lowermost Hettangian interval, coincident with the onset of the main negative CIE. A further less strongly oxygen-depleted interval was recorded through the negative CIE near the Sinemurian-Pliensbachian boundary (jamesoni and ibex Zones). This interval was characterised by drier conditions and possibly cooler water temperatures (e.g. CIA, δ18Ocarb and kaolinite/illite ratio). Based on low CIA values and kaolinite/illite ratios, the Pliensbachian climate is considered to have been generally drier, superimposed by more humid episodes restricted to the davoei and margaritatus Zones. The long-term trend to drier conditions is explained by: (1) diminished atmospheric CO2 contents due to a reduction in emissions of volcanogenic greenhouse gases, and/or; (2) changes in the palaeogeography and current patterns related to the break-up of Pangaea and more specifically to the opening of the Hispanic corridor.

In Situ Hydrogen Uptake and NO x Adsorption on Bifunctional Heterogeneous Pd/Mn/Ni for a Low Energy Path toward Selective Catalytic Reduction.

Facilitating catalyst accessibility of H2 and NOx at the catalyst surface remains a great challenge in catalytic selective catalytic reduction (SCR). The efficient conversion of NOx into N2 under mild conditions is an attractive pathway as SCR usually requires high operating temperature which consumes extra operating energy and restricts the possible locations of an SCR device. The H2 supply concentration of conventional H2-SCR is relatively sparse (0.5–2%), which leads to a relatively high operating temperature to activate H. We developed a H2-SCR process with the monolithic catalyst which combined with localized rarefied hydrogen enrichment enhanced by porous nickel and adsorption of NOx on Mn oxide with only 0.08, 0.25, and 0.42% palladium can achieve over 80% NO removal efficiency at 120, 100, and 90 °C. Maximizing the role of nickel foam-fixed hydrogen and Mn oxide in combination with NO can provide enriched NOx and H2 atmosphere for adjustable valence state Pd to yield positive catalytic behavior.