High Hydrogen Fuels Research Articles

Zn constructs micro/nano porous structure to boost efficient oxygen evolution reaction for bulk NiFe alloy

Oxygen evolution reaction (OER) electrocatalysts play an important role in producing high purity hydrogen fuels in the water splitting reaction. However, developing bulk catalytic electrode with low-cost and efficient activity for OER is still a challenge. In this paper, the porous bulk NiFe alloys with nanosheet structure were fabricated by a facile microwave sintering powder metallurgy method coupled with Zn as space holder. The obtained porous bulk Ni0.75Fe0.25 alloy exhibits the high catalytic activity for OER with a low overpotential of 235 mV at 100 mA cm−2, a small Tafel slope of 26.1 mV dec−1 and superior stability in 1.0 M KOH. In addition, the residual Zn in the porous NiFe alloy can be dissolved to further improve the specific surface area, and a metal (oxy)hydroxide amorphous layer is formed through electrochemical self-reconstruction during the OER process. This Zn-doped porous bulk NiFe catalyst with high OER catalytic performance and outstanding stability can become a promising candidate for commercial water splitting.

Experimental Investigation Into the Role of Mean Flame Stabilization on the Combustion Dynamics of High-Hydrogen Fuels in a Turbulent Combustor

Abstract A bluff-body turbulent combustor is mapped for its thermo-acoustic stability across variation in airflow rate, nondimensionalized as the Reynolds number (Re) and fuel composition. The combustor stability is evaluated for three fuels, namely, pure hydrogen (PH), synthesis natural gas (SNG), and syngas (SG). The combustion dynamics display markedly different behavior across the fuels, in the extent of the unstable region, as well as the observed dominant Eigenvalues. At low Re, SNG displays stable combustion, while SG exhibits high amplitude oscillations at the fundamental duct acoustic mode. As the Re is increased, SNG displays very high amplitude oscillations at the duct acoustic mode, while SG exhibit relatively low amplitude oscillations at the third harmonic. In the case of PH, high amplitude oscillations observed at higher Re at the first harmonic. These peculiarities are investigated in light of the role of mean flame stabilization. The combustion dynamics of the fuels is influenced by the global equivalence ratio, as well as the jet momentum ratio. These effects significantly demarcate the dynamics of SNG and SG combustion. This is seen manifested in the mean flame structure of flame at high amplitude oscillations, whereby result in SNG flame to be present in the wake, while the SG flame resides in the shear layer. The driving by the flame because of their mean stabilization is quantified by a spatial Rayleigh index. It confirms the presence of large driving regions for SNG compared to that of SG, results in the observed differences in amplitude of the oscillations.

Proton-Conducting Graphene Membrane Electrode Assembly for High Performance Hydrogen Fuel Cells

Graphene oxide (GO) contains randomly distributed nonconductive sp3-C domains with planar acidity, making it simultaneously an electrical insulator and a proton conductor. GO’s ability for in-plane...

Investigation into the cause of high multi-mode combustion instability of H2/CO/CH4 syngas in a partially premixed gas turbine model combustor

In this paper, the fuel composition effects of H2/CO/CH4 syngas (0–100% for each component gas) on the self-excited high multi-mode (mainly the 3rd and 4th with their harmonics) combustion instability (CI) characteristics have been studied in a partially premixed swirl-stabilized gas turbine model combustor by investigating phase-resolved high-speed OH∗ planar laser induced fluorescence (OH-PLIF) and OH∗ chemiluminescence at a rate of 12.5kHz and analyzing the proper orthogonal decomposition (POD), spatio-temporal Rayleigh index (RI), and time-lag. Phase-synchronized OH-PLIF images suggested critical clues of CI driving mechanisms, including the periodic alternation of flame attachment/detachment and vortex coupling with everlasting flames at the outer recirculation zone due to high hydrogen fuels’ high reactivity. These PLIF results also demonstrated that the relatively short mixing length and highly fuel-dependent flame length are the root causes of a high instability-mode and sensible mode-shift. Thus, PLIF images were used to calculate the flame length by obtaining the intensity-weighted centroid for the more precise time-lag analysis. The spatio-temporal RI results indicated that the fuel composition affects the location and intensity of CI driving/damping, RI frequency, and instability mode and frequency. POD analysis from high-speed OH∗ images showed that the distinct coherent structures and large roll-up of flames are responsible for generating flame oscillations for each mode. High cross-correlation between the POD modes showed the convection of these coherent structures and axially-alternative swirl-like flame motions. At some particular compositions of H2/CH4/CO, high multi-mode CI was observed (e.g., the 3rd, 4th, and 6th modes appear simultaneously) and the original time-lag model could not be applicable, since the acoustic pressure wave is not simply sinusoidal but largely distorted. Thus, a new time-lag model using skewness time (τskew) was proposed to reflect the distortion from multi-mode CI and the accuracy of this model was verified using the experimental data.

Development and Testing of a Low NOx Hydrogen Combustion System for Heavy-Duty Gas Turbines

Interest in hydrogen as a primary fuel stream in heavy-duty gas turbine engines has increased as precombustion carbon capture and sequestration (CCS) has become a viable option for integrated gasification combined cycle (IGCC) power plants. The U.S. Department of Energy has funded the Advanced IGCC/Hydrogen Gas Turbine Program since 2005 with an aggressive plant-level NOx target of 2 ppm at 15% O2 for an advanced gas turbine cycle. Approaching this NOx level with highly reactive hydrogen fuel at the conditions required is a formidable challenge that requires novel combustion technology. This study begins by measuring entitlement NOx emissions from perfectly premixed combustion of the high-hydrogen fuels of interest. A new premixing fuel injector for high-hydrogen fuels was designed to balance reliable flashback-free operation, reasonable pressure drop, and low emissions. The concept relies on small-scale jet-in-crossflow mixing that is a departure from traditional swirl-based premixing concepts. Single nozzle rig experiments were conducted at pressures of 10 atm and 17 atm, with air preheat temperatures of about 650 K. With nitrogen-diluted hydrogen fuel, characteristic of carbon-free syngas, stable operation without flashback was conducted up to flame temperatures of approximately 1850 K. In addition to the effects of pressure, the impacts of nitrogen dilution levels and amounts of minor constituents in the fuel—carbon monoxide, carbon dioxide, and methane—on flame holding in the premixer are presented. The new fuel injector concept has been incorporated into a full-scale, multinozzle combustor can with an energy conversion rate of more than 10 MW at F-class conditions. The full-can testing was conducted at full gas turbine conditions and various fuel compositions of hydrogen, natural gas, and nitrogen. This combustion system has accumulated over 100 h of fired testing at full load with hydrogen comprising over 90% of the reactants by volume. NOx emissions (ppm) have been measured in the single digits with hydrogen-nitrogen fuel at target gas turbine pressure and temperatures. Results of the testing show that small-scale fuel-air mixing can deliver a reliable, low-NOx solution to hydrogen combustion in advanced gas turbines.

Nanofiber Cathodes for Low and High Humidity Hydrogen Fuel Cell Operation

A new fuel cell electrode fabrication scheme based on nanofiber electrospinning has been devised and nanofiber cathode membrane-electrode-assemblies (MEAs) were evaluated in a hydrogen/air fuel cell at 80ºC for low and high feed gas humidification conditions. MEAs were constructed from an electrospun mat with a fiber composition of 72wt% Pt/C, 15wt% poly(acrylic acid), and 13wt% Nafion. The Pt loading of the mat was 0.1 mg/cm². Mats were hot-pressed onto Nafion 212 membranes with a decal anode (at 0.4 mg/cm²). Under fully humidified conditions, the nanofiber cathode MEA generated very high power densities (e.g., 485mW/cm² at 0.6V vs. 345mW/cm² for a 0.1 mgPt/cm² decal cathode MEA). At lower feed gas humidities, the difference in power output for the nanofiber and decal MEAs was more pronounced, e.g., at 40%RH, the power density with the nanofiber cathode was more than double that for the decal MEA (132mW/cm² vs. 58mW/cm² at 0.6V).

Low Equivalent Weight Sulfonated Poly(Etheretherketone) Membranes for High Temperature Hydrogen Fuel Cell Applications

not Available.

Effects of coaxial air on nitrogen-diluted hydrogen jet diffusion flame length and NO x emission

Turbulent nitrogen-diluted hydrogen jet diffusion flames with high velocity coaxial air flows are investigated for their NO x emission levels. This study is motivated by the DOE Turbine program’s goal of achieving 2 ppm NO x from gas turbine combustors running on diluted high-hydrogen fuels. In this study, effects of coaxial air velocity and momentum are varied while maintaining low overall equivalence ratios to eliminate the effects of combustion product recirculation on flame lengths, flame temperatures, and resulting NO x emission levels. The nature of flame length and NO x emission scaling relationships are found to vary, depending on whether the combined fuel and coaxial air jet is fuel-rich or fuel-lean. In the absence of differential diffusion effects, flame lengths agree well with predicted trends, and NO x emissions levels decrease with increasing coaxial air velocity, as expected. Normalizing the NO x emission index with a flame residence time reveals that a global flame strain based on the difference between the fuel and coaxial air velocities is not a viable scaling parameter, as has traditionally been used. A new scaling relationship that accounts for enhanced mixing via flame length reduction is found to provide an excellent collapse of the data with the correct Damköhler number scaling.

Stability Characteristics of Turbulent Hydrogen Dilute Diffusion Flames

Diffusion flame combustion of high-hydrogen fuels in land-based gas turbine combustors may include dilution of the fuel with inert gases and high velocity fuel injection to reduce NOx emissions. Stability regimes of such combustors are investigated in this study by examining turbulent dilute diffusion flames of hydrogen/nitrogen mixtures, issuing into a quiescent environment from a thin-lipped tube. This study has revealed two distinctly different types of lifted flames: lifted, laminar-base flames, for which liftoff heights vary from 1 to 3 jet diameters above the jet exit and are controlled by differential diffusion, and lifted, turbulent-base flames that stabilize much further downstream and are dominated by turbulent processes. In addition, stability limits governing the detachment or reattachment of the flame to the lip of the burner are examined, as well as the limits governing transitions between the two types of lifted flames and transition from these lifted flames to blowout.

757 コモンレール式高応答高圧水素噴射弁の動特性シミュレーション(流体パワーによる駆動と制御II)

757 コモンレール式高応答高圧水素噴射弁の動特性シミュレーション(流体パワーによる駆動と制御II)