Effects of hydrogen injection strategy on the hydrogen mixture distribution and combustion of a gasoline/hydrogen SI engine under lean burn condition

Hydrogen is a carbon free energy carrier with high diffusivity and reactivity, it has been proved to be a kind of suitable blending fuel of spark ignition (SI) engine to achieve better efficiency and emissions. Hydrogen injection strategy affects the engine performance obviously. To optimize the combustion and emissions, a comparative study on the effects of the hydrogen injection strategy on the hydrogen mixture distribution, combustion and emission was investigated at a SI engine with gasoline intake port injection and four hydrogen injection strategies, hydrogen direct injection (HDI) with stratified hydrogen mixture distribution (SHMD), hydrogen intake port injection with premixed hydrogen mixture distribution (PHMD), split hydrogen direct injection (SHDI) with partially premixed hydrogen mixture distribution (PPHMD) and no hydrogen addition. Results showed that different hydrogen injection strategy formed different kinds of hydrogen mixture distribution (HMD). The ignition and combustion rate played an important role on engine efficiency. Since the SHDI could use two hydrogen injection to organize the HMD, the ignition and combustion rate with the PPHMD was the fastest. With the PPHMD, the brake thermal efficiency of the engine was the highest and the emissions were slight more than that with the PHMD. PHMD achieve the optimum emission performance by its homogeneous hydrogen. The engine combustion and emission performance can be optimized by adjusting the hydrogen injection strategy.     

Effect of Ni nanoparticle distribution on hydrogen uptake in carbon nanotubes

Ni decoration on carbon nanotubes (CNTs) performed by electroless nickel (EN) deposition is investigated. The effect of Ni particle distribution on hydrogen uptake of CNTs is also studied. The chemical composition, crystal structure and microstructure of the CNTs with or without Ni loading are characterized using an inductively coupled plasma spectrometer (ICP), X-ray diffraction meter (XRD) and transmission electron microscope (TEM) coupled with an energy dispersive spectroscope (EDS). The hydrogen uptake in CNTs with or without Ni loading is measured using a high-pressure microbalance at room temperature under a hydrogen pressure of 6.89 MPa. The experimental results show that fine and well-dispersed metallic Ni nanoparticles can be obtained by EN. The density and particle distribution depend on deposition temperature and time. An enhanced hydrogen storage capacity of CNTs can be obtained by Ni decoration, which provided a spillover reaction. The hydrogen storage capacity of the as-received CNTs was 0.39 wt.%. As much as 1.27 wt.% of hydrogen can be stored when uniformly distributed nano-sized Ni particles are formed on the surface of the CNTs. However, the beneficial effect is lost when the active sites for either physical or chemical adsorption are blocked by excessive Ni loading.     

Understanding hydrogen adsorption performance of lithium-doped MIL-101(Cr) by molecular simulations: Effects of lithium distribution

Metal-organic frameworks (MOFs) have been recognized as one of the most compelling physical adsorption hydrogen storage materials owing to their ultrahigh surface area and excellent hydrogen adsorption performance. In order to further improve their hydrogen adsorption performance, lithium doping is an effective approach to increase the number of hydrogen adsorption sites as well as enhance the interaction strength towards hydrogen molecules according to grand canonical Monte Carlo(GCMC) simulations. However, in previous simulation studies, lithium ions were commonly assumed to be randomly distributed in MOF frameworks. In fact, the lithium-doped MOFs were prepared by immersing MOFs in a lithium salt solution and then drying them under high temperatures, in which the distribution of Li⁺ in MOF frameworks is elusive. In this work, the lithium-doped MIL-101 models (i.e., Immersion model) with varying lithium contents were constructed according to experimental operation and their hydrogen adsorption performance from GCMC simulations was also investigated in comparison with the equivalent models with randomly distributed lithium ions (i.e., Random model). It is found that in contrast to the uniform distribution of lithium ions in Random model, the accumulation of lithium ions was inspected in Immersion models especially at high loadings, leading to the reduced pore size. On the contrary, the hydrogen adsorption capacities of Immersion models are significantly improved owing to the enhanced interaction strength with hydrogen molecules resulting from the reduced pore size and the strengthened charged-induced dipole interaction.     

Assessing the viability of the ACT natural gas distribution network for reuse as a hydrogen distribution network

The Australian Capital Territory (ACT) has legislated and aims to be net zero emissions by 2045. Such ambitious targets have implications for the contribution of hydrogen and its storage in gas distribution networks Therefore, we need to understand now the impacts on the gas distribution network of the transition to 100% hydrogen. Assessment of the viability of decarbonising the ACT gas network will be partly based on the cost of reusing the gas network for the safe and reliable distribution of hydrogen. That task requires each element of the natural gas safety management system to be evaluated.This article describes the construction of a test facility in Canberra, Australia used to identify issues raised by 100% hydrogen use in the medium pressure distribution network, consisting of nylon and polyethylene (PE) as a means of identifying measures necessary to ensure ongoing validity of the network's regulatory safety case.Evoenergy (the ACT's gas distribution company) have constructed a Test Facility, incorporating an electrolyser, a gas supply pressure reduction and mixing skid a replica gas network and a domestic installation with gas appliances. Jointly with Australian National University (ANU) and Canberra Institute of Technology (CIT) the Company has commenced a program of “bench testing”, initially with 100% hydrogen to identify gaps in the safety case specifically focusing on the materials, work practices and safety systems in the ACT.The facility is designed to assess: ? Materials in use including aged network materials and components ? Construction and installation techniques both greenfield and live gas work ? Purging and filling techniques ? Leak detection both underground and above ground ? Emergency response and make safe techniques ? Issues associated with use of hydrogen in light commercial and domestic appliances.To educate and train: ? Technicians and gas fitters on infrastructure installation and management ? Emergency response services on responding to hydrogen related emergencies in a network environment; and ? manage public perceptions of hydrogen in a network environment.Australia has an enviable safety record for the safe and reliable transport, distribution and use of natural gas. The ACT natural gas network owned and operated by Evoenergy is one of the newest in Australia and has leveraged off the best materials and practices in Australia to build its network.The paper addresses major safety issues relating to the production/storage, distribution and consumer end use of hydrogen injected into existing gas distribution networks. The analysis is guided by the Safety Management System. The Hydrogen Testing Facility described in the paper provide tools for evaluation of hydrogen safety matters in the ACT and Australia-wide.Testing to date has confirmed that polyethylene and nylon pipe and their respective jointing techniques can contain 100% hydrogen at pressures used for the distribution of natural gas. Testing has also confirmed that current installation work practices on polyethylene and nylon pipe and joints are suitable for hydrogen service. This finding is subject to variation attributable to staff training and skill levels and further testing has been programmed as outlined in this paper.Testing of gas isolation by clamping and simulated repair on the hydrogen network has established that standard natural gas isolation techniques work with 100% hydrogen at natural gas pressures.     

Numerical study of high temperature proton exchange membrane fuel cell (HT-PEMFC) with a focus on rib design

The rib size is a critical engineering design parameter for high temperature proton exchange membrane fuel cell (HT-PEMFC) stack development, yet it hasn't been studied for HT-PEMFC. A three-dimensional, non-isothermal model was developed in this work to investigate the effect of channel to rib width ratios (CRWR) on the performance of HT-PEMFC. The reaction heat caused by entropy change was divided into cathodic half-reaction heat and anodic half-reaction heat. The results show that the ratio value significantly influence the gas diffusion, electron conduction and the distribution of current density in the porous electrodes. Increasing this ratio facilitates gas transport in the porous electrode but causes higher ohmic loss due to longer distance for electron conduction. As a result, an optimal ratio of about 1 is observed, which results in a peak power density of 0.428 W/cm². High current density is observed under the channel with a small ratio value while a high ratio value would cause high current density to appear under the rib, signifying the rib size effect on electrochemical behavior of HT-PEMFC. Apart from the electrical power output, the CRWR value also greatly influences the fluid flow and temperature distribution inside the cell, which would influence the long-term stability of HT-PEMFC. In the subsequent studies, efforts will be made to develop new stack configurations with more uniform gas distribution, short electron conduction path and low temperature gradient.     

Modeling and analysis of flow distribution in an A-type microchannel reactor

Flow distribution among microchannels is a fatal factor affecting the performance of laminated microchannel reactors for hydrogen production. Homogeneous flow strongly depends on the structural design of the microchannel reactor. The present work concentrates on improving the flow distribution in microchannel reactors for hydrogen production by optimization of the structural design. An innovative A-type microchannel reactor for hydrogen production with one inlet/two outlets was developed and analyzed. The equivalent electrical resistance network model was used to calculate the flow distribution in the microchannel reactor which was validated by computational fluid dynamics (CFD). The influences of structural parameters on flow distribution in the A-type were investigated quantitatively. The calculated results showed that longer microchannels with a higher aspect ratio and a small side length in the manifolds were beneficial for attaining uniform flow distribution in the A-type microchannel reactor. Furthermore, it was found that flow distributions among the microchannels in the A-type were much more uniform than those in the conventional Z-type microchannel reactor with one inlet/one outlet. Finally, an optimization strategy was proposed to optimize the manifold geometries to obtain a comparatively even flow distribution among microchannels.     

Hydrogen production by supercritical water gasification of biomass: Particle and residence time distribution in fluidized bed reactor

Particle distribution and residence time distribution (RTD) in supercritical water fluidized bed reactor (SCWFBR) greatly affect the hydrogen yield through determining the two phase mixing and reaction time. A Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the solid distribution and RTD of feeding materials. The effect of four types of feeding methods and feeding rates on solid distribution and RTD were evaluated based on the simulation results. Results showed that double symmetrical feeding pipe with an feeding mouth angle of 45° provides more uniform solid distribution and longer residence time compared with those of other three types. A nonlinear relationship between feeding rate and RTD was observed, and an optimum feeding rate was found to be related to the best solid-fluid mixing in the study.     

Assessment of using hydrogen in gas distribution grids

Substantial changes in the energy system are necessary to achieve greenhouse gas neutrality. Green hydrogen is a key to defossilisation. Politicians frequently mention the use of hydrogen in the building sector to supply decentrally produced heat as a potential field of application. An advantage repeatedly mentioned is that the existing gas distribution network infrastructure is an important asset that could still be used in the future. However, there is a lack of analyses of the conversion of gas distribution networks to hydrogen focussing on the economic implications on the costs of the distribution network infrastructure. The paper provides insights using a techno-economic model network analysis (MNA) tool called gas Distribution grId modelliNg tOol (DINO). The analysis is carried out for Germany and considers hydrogen use in all counties. The results are compared to a synthetic methane and electrification scenario. In the hydrogen scenario, the total need for distribution grids is decreasing until 2050 by at least 130,000 km. The network length of the synthetic methane scenario is slightly lower and that of the electrification scenario drops to zero. The annual operation costs are lower in all scenarios as gas demand and infrastructure are reduced. Nevertheless, the total annual cost in the hydrogen scenario is potentially two times higher than in the case of the synthetic methane scenario and more than four times higher than in the electrification scenario. Based on the present results, it is questionable whether an advantage of the continued use of the existing gas distribution grid infrastructure in case of synthetic gas or hydrogen scenarios exists.     

Influence of microstructure-driven hydrogen distribution on environmental hydrogen embrittlement of an Al–Cu–Mg alloy

The hydrogen trap sites and corresponding hydrogen binding energies in an Al–Cu–Mg alloy with the different microstructures were investigated to unravel the environmental hydrogen embrittlement (HE) behavior of the alloy. The results showed that hydrogen can reside at interstitial lattices, dislocations, S′-phase, and vacancies. In the aged specimen with the highest hydrogen content, it was firstly reported that hydrogen resided at S′-phase particles with relatively high binding energy, which is a determinant factor on HE resistance of the alloy. In the cold-rolled specimen, high content of hydrogen trapped at dislocations with a reversible nature leads to intergranular hydrogen-assisted cracking. In the solution-treated specimen, hydrogen migration to the surface due to low trap density results in low hydrogen content and prevents the GBs from reaching critical hydrogen concentration. The obtained results clearly reveal that trap site density, and the nature of trap sites can determine environmental HE susceptibility of the alloy.     

Effect of humidification on distribution and uniformity of reactants and water content in PEMFC

Restricted by experimental conditions, it is difficult to analyze reactants distribution and uniformity through experiment. A simulation model is established by experiment fuel cell. Hydrogen humidification has a great impact on hydrogen distribution and concentrates in inlet and serpentine sections. At anode side membrane water content increases significantly when hydrogen relative humidity is over 50%. Air humidification has little effect on air distribution and water content. The oxygen mass fraction only decreases with relative humidity increase. Hydrogen humidification has greater influence on the distribution of reactants and membrane water content than air humidification, but hydrogen humidification needs to control the relative humidity of hydrogen within a suitable range. According to the simulation results in this article, the relative humidity of hydrogen should be controlled at 25%–50%. This paper proposes mass fraction difference coefficient, as uniformity evaluation index. When hydrogen relative humidity is 50%, uniformity of reactants distribution is the best.     

Current density distribution in an HT-PEM fuel cell with a poly (2, 5-benzimidazole) membrane

High-temperature proton exchange membrane (HT-PEM) fuel cells were more useable than traditional low-temperature proton exchange membrane fuel cells. To investigate the current density distribution in a single HT-PEM fuel cell with a poly (2, 5-benzimidazole) membrane, a modified current distribution measuring device was developed. This device included not only a current distribution measuring gasket to collect local current but also a segmented gas diffusion layer (GDL) to hinder electron transfer in the GDL along the gas flow direction. The effects of this device installation configuration and operating conditions on the current density distribution were analyzed. One of the important findings was that proton transfer along an in-plane direction in the membrane and electron transfer along an in-plane direction in the GDL really occur in HT-PEM fuel cells. These results were very helpful for the optimization of the flow field and operating parameters of the HT-PEM fuel cells.     

Performance analysis of HT-PEFC stacks

The performance analysis of a five-cell HT-PEFC stack is presented. The stack was operated either with pure hydrogen or synthetic reformate on the anode side and air on the cathode side. The overall electric performance and the heat management were analyzed. The local performance was assessed by current density and temperature distribution measurements. For this purpose, a tailor-made measuring board was integrated into the stack assembly. It is shown how the choice of fuel gas composition, reactant stoichiometry, flow direction and cooling affect the current density and temperature distribution.     

Creation of heterojunction in CdS supported on N,S-rGO for efficient charge separation for photo-reduction of water to hydrogen

An efficient CdS supported on nitrogen and sulfur-doped reduced graphene oxide (N,S-rGO) has been prepared by a high-temperature gas-solid reaction for the first time. This catalyst was about ten times more efficient compared to pristine CdS in the dissociation of water to hydrogen. The high-temperature gas-solid reaction promotes chemical interaction between CdS and reduced graphene oxide (rGO) forming a heterojunction at the interface for transfer of photogenerated electrons from CdS to rGO. Doping of rGO with N and S enhances electron mobility and charge carrier density on the surface of the catalyst. The synergy between the efficient electron transfer, the enhanced electron mobility and the high charge carrier density results in a high activity of the prepared catalyst for photo-reduction of water to hydrogen. A detailed microstructural analysis for understanding the interaction amongst preparation technique, microstructure and activity, is also presented.     

Determination of the pore size distribution of micro porous layer in PEMFC using pore forming agents under various drying conditions

In this paper, the effect of the pore size distribution of a micro-porous layer (MPL) on the performance of polymer electrolyte membrane fuel cells (PEMFC) was investigated using self-made gas diffusion layers (GDLs) with different MPLs for which the pore size distribution was modified using pore forming agents under different drying conditions. When MPL dried at high temperature, more macro pores, approximately 1,000–20,000 nm in diameter, and less micro pores, below 100 nm, were observed relative to when MPL was dried at low temperature. Self-made GDLs were characterized by a field-emission scanning electron microscope (FE-SEM), mercury porosimetry and self-made gas permeability measurement equipment. The performance of the single cells was measured under two different humidification conditions. The results demonstrate that the optimum pore size distribution of MPL depended on the cell operating humidification condition. The MPL dried at high temperature performed better than the MPL dried at low temperature under a low humidification condition; however, MPL dried at low temperature performed better under a high humidification condition.     

Direct measurement of lateral current density distribution in a PEM fuel cell with a serpentine flow field

In a proton exchange membrane (PEM) fuel cell, local current density can vary drastically in the lateral direction across the land and channel areas. It is essential to know the lateral current density variations in order to optimize flow field design and fuel cell performance. Thus the objective of this work is to directly measure the lateral current density variations in a PEM fuel cell with a serpentine flow field. Five 1 mm-width partially-catalyzed membrane electrode assemblies (MEA), each corresponding to a different location from the center of the gas channel to the center of the land area are used in the experiments. Current densities for fuel cells with each of the partially-catalyzed MEAs are measured and the results provide the lateral current density distribution. The measurement results show that in the high cell voltage region, local current density is the highest under the center of the land area and decreases toward the center of the channel area; while in the low cell voltage region local current density is the highest under the center of the channel area and decreases toward the center of the land area. Besides, the effects of cathode flow rates on the lateral current density distribution have also been studied. Furthermore, comparisons have also been made by using air and oxygen in the cathode and it is found that when oxygen is used the local current density under the land is significantly enhanced, especially in the low cell voltage region.     

Numerical study on effects of hydrogen direct injection on hydrogen mixture distribution,combustion and emissions of a gasoline/hydrogen SI engine under lean burn condition

A numerical study on effects of hydrogen direct injection on hydrogen mixture distribution, combustion and emissions was presented for a gasoline/hydrogen SI engine. Under lean burn conditions, five different direct hydrogen injection timings were applied at low speeds and low loads on SI engines with direct hydrogen injection (HDI) and gasoline port injection. The results were showed as following: firstly, with the increase of hydrogen direct injection timing, the hydrogen concentration near the sparking plug first increases and then decreases, reaching the highest when hydrogen direct injection timing is 120°CA BTDC: Secondly, hydrogen can speed up the combustion rate. The main factor affecting the combustion rate and efficiency is the hydrogen concentration near the sparking plug: Thirdly, in comparing with gasoline, the NO_X emissions with hydrogen addition increase by an average of 115%. For different hydrogen direct injection timings, the NO_X emissions of 120°CA BTDC is the highest, which is 29.9% higher than the 75°CA BTDC. The hydrogen addition make the NO_X emissions increase in two ways. On the one hand, the average temperature with hydrogen addition is higher. On the other hand, the temperature with hydrogen addition is not homogeneous, which makes the peak of temperature much higher. In a word, the main factor of NO_X emissions is the size of high temperature zone in the cylinder: Finally, because the combustion is more complete, in comparing with gasoline, hydrogen addition can reduce the CO and HC emissions by 32.2% and 80.4% respectively. Since a more homogeneous hydrogen mixture distribution can influence a lager zone in the cylinder and reduce the wall quenching distance, these emissions decrease with the increase of hydrogen direct injection timing. The CO and HC emissions of 135°CA BTDC decrease by 41.5% and 71.4%, respectively, compared to 75°CA BTDC.     

Preferred test conditions for measuring flow rate distribution between cells in a polymer electrolyte fuel cell stack

A new and practical testing technique was developed for measuring the flow rate distribution between cells in a stack that did not contain any internal sensors. The flow rate distribution is obtained by measuring the hydrogen limiting current of each cell in the stack while a mixed gas of hydrogen and dimethyl ether is supplied to the anode and hydrogen to the cathode. In order to measure large flow rate deviations between cells, it is necessary to decrease the flow rate of the anode hydrogen and to sufficiently humidify the cells. The faster the increasing rate of the current, the more the apparent hydrogen limiting current increases than the theoretical electrochemical equivalent current. However, the relative flow rate deviations between cells can be obtained by a practical accuracy using the ratio of the apparent hydrogen limiting current. Humidification of the cell is indispensable for the measurement and a method using dry anode gas and humidified cathode gas is recommended. The preferred test conditions for measuring the flow rate distribution between cells in a PEFC stack are proposed.     

Effects of density distribution of growing frost layer on radiation transfer

Our main interest concerned the effects of the density distribution on radiation transfer in scattering media. The frost layer in the early growth stage under the control of diffusion was chosen as the media. Numerical analysis of the radiation transfer was carried out by using a modified Monte Carlo method on the basis of geometrical optics. A diffusion‐limited aggregation theory was introduced to simulate the growth of a frost layer with a treelike structure. The relation between the density distribution and the transmittance of the simulated model was made clear by the numerical analysis. On the basis of these results, optical measurements in the visible wavelength region were utilized to evaluate the density distribution in the frost layer, which varied with cooling condition, on the transmittance values. © 2001 Scripta Technica, Heat Trans Asian Res, 30(5): 439–450, 2001     

Temperature distribution in a liquid-cooled HT-PEFC stack

A liquid (heat transfer oil) cooling system for high temperature polymer electrolyte fuel cell (HT-PEFC) stacks in the power range above 1 kW_el using encapsulated cooling cells was designed. Calculations showed that it is sufficient to cool every third cell to maintain an operating temperature of about 160 °C. An HT-PEFC stack module including 12 cells with an active area of 320 cm² each was assembled and tested experimentally regarding the temperature distribution from cell to cell. It was found that sufficient cooling with an oil inlet temperature of 160 °C is guaranteed up to a current density of 450 mA/cm² when operated with synthetic reformate (42% H₂, 57% N₂, 1% CO). At this current density, the maximum temperature difference from cell to cell does not exceed 8.3 K. Additionally, this cooling system provided enhanced protection against leaks.     

Topology optimization of the catalyst distribution of planar methane steam reformers

Wall-coated nickel-based methane steam reformers are extensively used in hydrogen production. In such devices, nickel-based catalyst is coated on the walls and heat is supplied for the reforming process. Due to the existence of endothermic and exothermic characteristics, big temperature differences appear in the reformers, which is likely to cause serious mechanical degradation of the catalyst. This study conducts a topology optimization of the catalyst distribution to reduce the maximum temperature differences of the reformers. Nine cases with different inlet gas compositions and heating fluxes are optimized. For comparison, methane conversion rates are constrained to have the same values as the corresponding reference cases. Results show that optimized catalysts discretely distribute on the wall with different lengths. The narrow catalysts distribute upstream, while the wide catalysts distribute downstream. The optimized results not only largely reduce the maximum temperature differences (24%–82%) and improve temperature uniformity (40%–85%), but also maintain high methane conversion rates. The proposed approach could help to design the catalyst distribution of reformers.