جستجوی مقالات مرتبط با کلیدواژه « هیدروژن » در نشریات گروه « مکانیک »

In the present study, the combustion of hydrogen-air premixed mixture in a circular cross-section swiss-roll micro combustion chamber, designed as a heat source for micro thermophotovoltaic systems, has been investigated. The governing equations were solved using a three-dimensional steady state CFD method, considering detailed chemical kinetics and conjugate heat transfer. The parameters examined in this study include the average inlet velocity, equivalence ratio, and wall thermal conductivity. The thermal performance of the combustion chamber was evaluated by calculating the temperature of the inlet and outlet paths, wall temperature uniformity index, and efficiency. Results indicated that increasing the average inlet velocity leads to a deviation from the optimal heat exchange between the inlet and outlet paths and affects the wall temperature distribution. Although the average temperature of the outer wall increases with inlet velocity, the temperature distribution becomes more non-uniform. This increase in the non-uniformity reduces efficiency with higher inlet velocities. The study on the effect of the equivalence ratio showed that increasing it optimizes heat exchange between the inlet and outlet paths and enhances system efficiency. The impact of increasing the wall thermal conductivity up to 12W/m.K was analyzed, showing a positive influence on all parameters related to the thermal performance of the combustion chamber and efficiency. The maximum total efficiency was calculated to be 10.18%, demonstrating that swiss-roll micro combustion chambers can compete with other micro combustor geometries for use in micro thermophotovoltaic systems.

Hydrogen plays a key role in reducing reliance on fossil fuels in various energy production systems. While its use offers a promising alternative to carbon-based fuels, it presents significant challenges. The transition from carbon-rich hydrocarbons to hydrogen-based energy systems requires a thorough understanding of its dynamic effects. This study investigates the impact of hydrogen addition on the dynamic behavior of a partially premixed methane-air counterflow flame through experimental analysis and one-dimensional numerical simulations. The study examines the steady-state flame structure and response without acoustic excitation, assessing the influence of added hydrogen on the flame's heat release rate and thermal region thickness. Employing an acoustically excitable counterflow flame burner setup, the effects of increasing hydrogen content on methane-air flames are explored, and their dynamic response is analyzed using the CH* radical chemiluminescence method. The findings reveal that while hydrogen addition reduces the intensity of CH* radical emission in the absence of acoustic excitation, exposure to acoustic waves amplifies oscillations in the heat release rate and CH* radical emission intensity. This underscores the enhanced flame response function with hydrogen addition.

Considering the challenges related to the level of pollution and the limitation of fossil fuel resources, the design, construction and operation of all-electric ships with on clean energy resources is being developed. On the other hand, due to the prominent features of hydrogen and the possibility of achieving a zero-pollution hydrogen production, , in recent years, hydrogen has received much attention as the main fuel of the future. The growth of the hydrogen usage in the electric transportation industry has also been significant, and in the ships’ industry, the use of hydrogen fuel and the development of fuel cell technology have been significantly developed. In this paper, a conceptual design process of an all-electric fuel cell ship is proposed.To create a comprehensive and systematic approach in the proposed design process, by investigating the phases of internationally recognized projects in the field of design, construction and operation of fuel cell ships, a conceptual design flowchart has been presented. By using this flowchart and having the ship’s input parameters such as power capacity, energy required for each trip, load change rates, ship’s dimensions, fuel tank capacity, available space, and available technologies including fuel cell modules and hydrogen supplyment and storage methods, it is possible to design the basic power system of all-electric hybrid ship based on fuel cell.

The field has long acknowledged the detrimental effects of entropy waves, including heightened NOx emissions, combustion chamber instability, and noise production. Entropy oscillations, when accelerated, serve as a source of indirect noise, exacerbating the combustion chamber's instability. A computational study delved into the entropy noise within a lean-premixed H2/ ethylene burner to better comprehend these phenomena. Utilizing flamelet and large Eddy Simulation, the study shed light on the behavior of entropy waves and their impact on combustion dynamics. It particularly examined how various thermal and fluid conditions affect entropy noise in both thermally convective and adiabatic combustion chambers, focusing on temperature. In-depth analysis was conducted on elements like the strength of inlet turbulence, stoichiometric ratio, and the preheating level of the unburned mixture. The findings revealed intriguing connections between these factors and the acoustic system response. Notably, an increase in equivalence ratio, and temperature led to a heightened auditory response, suggesting that such conditions foster the generation and spread of entropy noise. Conversely, the study found that high turbulence intensity at the amplifier negatively impacted the transmission of entropy oscillations, thereby reducing the auditory response. This suggests that intense turbulence can interfere with entropy wave propagation, lessening their potential to produce significant acoustic effects.

In this study, the co-gasification of mazut as the primary fuel and black liquor as a supplementary fuel with the aim of hydrogen-rich syngas is investigated. Oxygen and steam have been chosen as gasification agents. The present research was done using the equilibrium method and Aspen Plus software. The presented model has been validated through an experimental gasification article consisting of combined fuel. Then, by analyzing the performance parameters of gasification, the optimum range of gasification temperature, the ratio of fuel compounds, and the ratio of gasification agent to fuel were determined. Finally, the effect of adding steam as a secondary gasifying agent on the performance parameters and composition of syngas was assessed. The results show that the best ratio of fuel composition ranges from 0.1 and 0.2 and the optimum gasification temperature is 1200-1400 centigrade. Moreover, choosing an appropriate range of oxygen to fuel and steam to fuel causes hydrogen-rich syngas; So that, hydrogen includes more than 50% of syngas.

In this research, a novel trigeneration system driven by biomass-solar energies has been investigated from energy exergy, economic and environmental viewpoints. The solar energy is used to produce hydrogen (by a PEM electrolyzer powered by thermal photovoltaic panels). To meet the intermittent nature of solar energy, it is used for hydrogen production. The hydrogen is used as fuel in the combustion chamber. The proposed gas turbine cycle consists of two high and low-pressure turbines and two compressors with an intercooler. A combined organic Rankine-vapor compression refrigeration cycle that uses the recovered heat from the gas turbine is used to produce refrigeration and air cooling in the interstage compressor. The obtained results provide that the combination of solar-based hydrogen production and biomass-based gas turbine leads to an increase in power production capacity. The proposed combined system provides an energy and exergy efficiency of 21% and 17% and the emission of 0.00884 kg/s of CO2. The highest capital cost rate among the components is attributed to the PEM electrolyzer, amounting to 15.44 $/hr, and the total cost of the products has reached 0.5627 $/MJ. Using an intercooler, the energy and exergy efficiencies of the system have increased by 6% and 4%, respectively.

Hydrogen is usually used as a means of storing the energy produced from renewable energy resources. The electrolyzer, meanwhile, is a system by which hydrogen can be produced sustainably. In the present paper, a Concentrated Photovoltaic Thermal/Organic Rankine Cycle (CPVT/ORC) system coupled with a PEM electrolyzer system is simulated and evaluated. Concentrated solar radiation is used as the input energy of the coupled system. Part of this radiation is converted directly into electrical energy using the Photovoltaic (PV) panel, and the rest enters the organic Rankine cycle system as heat. The heat in the cycle is converted into mechanical power by the turbine and finally into electrical energy by the generator. The total electrical power generated by the organic Rankin panel and cycle enters the electrolyzer for producing hydrogen. A combination of MATLAB and REFPROP software was used to simulate the system performance.  The most striking result is that that the net generating power of the system is equal to 3820 watts, which is equivalent to producing 0.02072 grams per second of hydrogen and 0.0829 grams per second of oxygen.

A novel scramjet multi-stage open cooling cycle for electricity and hydrogen co-production is proposed in which the fuel of scramjet is used as coolant of cooling cycle. Thermodynamic and exergetic examination of the advanced system have been conducted to appraise the system’s performance, electricity and hydrogen productions and multi-expansion effects. For the fuel mass flow rate of 0.4 kg/s, the cooling capacity of the new proposed cycle is computed 9.16 MW, the net electricity output is calculated about 3.38 MW and the hydrogen production is attained 42.16 kg/h. On the other hand, the exergetic results have proved the fact that PEM electrolyzer has the highest exergy destruction ratio by 44% among different components of the cycle. Moreover, the results of exergy analysis exhibited that employing the multi-expansion process concept outstandingly decline the overall exergy destruction of the system. In this case, the energy and exergy efficiencies of the overall set-up are acquired by 13.01% and 22.12%, correspondingly

Scenario writing is a way to draw the future workspace. Different scenarios suggest different strategies that will have different applications. In the process of scenario writing, real options are found to decide what goals should be chosen and what the means to achieve those goals could be. This article has extracted the descriptors and modes that have been adapted to Iran's conditions after the discussion and exchange of opinions in the expert meetings. Next, the Cross-Impact Balance (CIB) was formed to evaluate the parameters relative to each other, and the simulation of descriptors and states was performed in the ScenarioWizard software. The results introduced 9 scenarios to achieve different goals in the state space. They followed 7 scenarios of technology development in the energy sector and two scenarios of technology development in the strategic sector of industry and mining. In the results, it was found that 8 descriptors were compatible in only one state and the remaining 5 descriptors found meaning in more than one compatible state. The development of distributed generation up to 15 thousand megawatts to expand the systems of combined heat and power, as well as use in areas far from the grid, and determining the penetration rate of renewable sources of 10 thousand megawatts in the country's electric energy network were among the important numerical states selected in the descriptors. Expanding international relations, attracting foreign capital, using domestic government credit resources such as the budget and credits of the National Development Fund of Iran, the development of targeted industrial knowledge-based companies according to the needs of the country and simultaneous attention to planning, infrastructural and operational parameters were considered important in the discussion of the resilience of the power grid from the selected non-numerical states At the end of the results, battery, hydrogen and pumped-hydro storage were selected as the preferred technologies.

The hybrid microwave-combustion synthesis method is a facile and rapid pathway for fabrication of nanocatalysts. In this study, the effect of combustion atmosphere on physicochemical and catalytical properties of CuO/ZnO/Al2O3 nanocatalysts as the catalysts of the steam methanol reforming process was investigated. For this aim, three types of nanocatalysts under different oxygen concentration atmosphere were prepared. The characteristic properties of synthesized nanocatalysts were studied by XRD, FESEM, EDX, BET, and FTIR analyses. It was understood that the crystallinity of copper species is lower than the other samples which led to higher dispersion of copper sites as the main core for steam methanol reforming reaction. Moreover, higher surface area and better surface morphology of CZA-O60N40 resulted in higher methanol conversion. Nevertheless, its higher dispersion of Zn(100) crystallite facet led to more CO production as the undesired product.

The All Porous Solid Oxide Fuel Cell (AP-SOFC) is a concept that links the dual and single chamber Solid Oxide Fuel Cell (SOFC), combining advantages of both. The AP-SOFC does not need any sealant and crack generation in its electrolyte component does not terminate cell operation. In this study, the performance of a hydrogen-fuelled co flow planar AP-SOFC is investigated numerically for the first time. Governing equations include species, mass, momentum, charge and energy solved fully-couple with electrochemical equations. Due to lack of study on hydrogen-fuelled AP-SOFC, first the performance of a conventional hydrogen-fuelled SOFC is modeled and the results are compared with experimental results for the validation purpose, then changes in the model are made to apply the electrolyte porosity. Results show a 29% decline in maximum power density produced by the AP-SOFC compared to its conventional scheme with the same inputs. The main reason for this reduction in the cell performance is mostly the flow leakage of oxygen from the near air channel inlet to the fuel channel side. This leakage leads to displace the maximum cell temperature point.

The aim of this study is to evaluate the effect of hydrogen addition on a heavy-duty diesel engine performance and emission under RCCI combustion fueled with natural gas and diesel fuel. For this purpose, a single-cylinder heavy-duty diesel engine is used to operate at a low-load range from 5.6 to 7.7 bar gross IMEP, constant engine speed, and a fixed amount of diesel fuel. Furthermore, in order to reduce hydrocarbon fuels consumption, hydrogen is gradually added to natural gas while the total fuel energy content is kept to be constant. The results show that by adding hydrogen to natural gas in the RCCI engine at 5.6, 6.3, and 7.7 bar gross IMEP, the hydrogen energy share would be enhanced up to 35.7%, 23.70%, and 9.93%, respectively. And also, the overall hydrocarbon fuels consumption per cycle can be reduced up to 45.23%, 29.26%, and 12.07%, respectively. Although CO and UHC emissions decrease drastically, NOx increases significantly with the addition of hydrogen compared to RCCI combustion fueled with natural gas and diesel fuel.

In this study, we analyzed the energy, exergy of a multiple energy production system based on geothermal energy. The system under study consists of geothermal subsystems, Rankin organic cycle and PEM electrolyzer and thermoelectric application. The organic fluid used in the Rankin organic cycle contains refrigerant R123. The products of this system produce multiple energy, including electricity and hydrogen. Thermodynamic software for solving engineering equations (EES) was used to model the studied system and also to obtain the results of system analysis. The results were calculated and evaluated using the ambient temperature of Bandar Abbas for the hottest day. According to the studies of the parameters affecting the system outputs, we can name the turbine efficiency, inlet temperature to the evaporator, thermoelectric suitability criterion, pump efficiency and mass flow inlet to the evaporator. The results also showed that the current work geothermal system in a year compared to the ambient temperature of Bandar Abbas can produce 352816.2 kWh of power per year and as a result this system can meet the electricity needs of about 12 Iranian families during the year.

Due to the capability of using exhausted gases of power plants directly in reforming process and producing high quality syngas, the tri-reforming process is a considerable kind of reforming process. In the present study, a power generation system based on solid oxide fuel cell with specific capacity and equipped to the external reforming is proposed and investigated form the viewpoint of thermodynamics. In order to conduct the external reforming process, exhausted gases from the system including the steam, carbon dioxide and oxygen are recycled and utilized as the reforming agents in the reactor. In order to model the proposed system thermodynamically, the principals of mass and energy balance are applied in Engineering Equation Software (EES). Effects of such important parameters as the current density and solid oxide fuel cell operating temperature on the system performance indicators including the various voltages, fuel mass flow rate, power generation and the energy as well as the exergy efficiencies of the system are investigated. The parametric study results shows that for the lower values of the current density and higher values of the SOFC operating temperature as well as the fuel utilization factor, the system energy and exergy efficiencies enhances.

The aim of this study is to evaluate a heavy duty diesel engine operation under reactivity controlled compression ignition combustion fueled with diesel oil and natural gas enriched with hydrogen and nitrogen addition. In this study, a single cylinder heavy– duty diesel engine is set to operate at 9.4bar gross IMEP (Mid- Load). The amount of injected diesel oil per cycle into the engine combustion chamber assumes to be fixed and hydrogen and nitrogen (75:25 volumetric proportion of hydrogen: nitrogen) along with exhaust gas recirculation are gradually added to natural gas while the total fuel energy content is kept fixed. The results show that by adding hydrogen and nitrogen to natural gas, without the exposure to the excessive combustion noise, the hydrogen energy share can be enhanced up to 40.24% and the gross indicated efficiency more than 50% is achievable. Moreover, without significant engine power losses, the engine emission levels such as NOx, carbon monoxide, unburned hydrocarbon, and formaldehyde are reduced significantly.

In this paper, the effect of adding hydrogen to the performance of D87 gas engine has been discussed. The base system is an engine with power of 1000 kW and rotational speed of 1500 rpm which by changing the fuel system and compression ratio from 15 to 11.5 it is modified to a gas engine. Among many additives, hydrogen with its unique criteria seems to be the most promising additive which can significantly reduce fuel consumption and harmful emissions in internal combustion engines. It seems, the hydrogen is the best additive among various cases, which can greatly reduce fuel consumption and harmful emissions in internal combustion engines. Here the effect of adding different mass ratios of hydrogen fuel to natural gas fuel flint to see a change in behavior of flint fuel is examined. In this paper, the hydrogen mass ratios of 0, 0.002, up 0.014 are considered which is equivalent to adding 50% of chamber imported energy and according to these points the optimal point has been determined based on performance and pollution viewpoints. By considering these viewpoints, the optimal point of 0.006 for mass ratio of hydrogen which is equivalent to adding approximately 18% energy to the combustion chamber is achieved. Then the appropriate ignition timing for 0.006 of mass ratio with advance and retard of the ignition timing is estimated. The results show that 3 degree for advance of ignition timing is suitable for this mass ratio.

Implementing emission regulations in the transport sector is enforcing manufacturers to improve performance of Heavy Duty (HD) vehicles as they are accountable for 25% of CO2 emissions within EU. The currently reported research was involved with evaluating partial replacement of hydrogen with diesel fuel experimentally and intake air enrichment with oxygen in a heavy-duty diesel single cylinder engine. Fumigation of hydrogen was done into the intake system at two particular engine loads (6 and 12 bar IMEPn). Indicated efficiency was increased up to 4.6% at 6 bar IMEPn and 2.4% at 12 bar IMEPn, while reducing CO2 emissions by 58% and 32% at 6 and 12 bar IMEPn respectively. Applying diesel pre-injection was required in order to mitigate the high pressure rise rates known as combustion noise. Furthermore, intake air enrichment with oxygen resulted in faster combustion process. This could curb soot and minimised CO emissions to the detriment of NOx increase.

Concerning the adverse environmental impacts of fossil fuel consumption, many investigations have been performed on choosing more environmentally friendly fuel alternatives and sustainable resources. In this regard, hydrogen is considered to be one of the promising alternative fuels as its combustion features are the most similar to fossil fuels and it also falls into the category of renewable and clean fuels. This article studies the simulation of hydrogen-diesel combustion in heavy duty engine at full load and speed of 1600 rpm. All engine features including speed, spray angle, spray duration and input power are held fixed in the simulation. Variable parameter is the ratio of mass or hydrogen energy to diesel. Depending on input power of diesel, hydrogen is changed from 0% (pure diesel) to 70% (i.e. 70% is supplied from the input power of hydrogen and the remaining 30% from diesel fuel). The results of simulation show that hydrogen substitution with diesel at the best state leads to reduction of pollutants such as nitric oxides, carbon dioxide, unburned hydrocarbon, soot and carbon monoxide to 8%, 14%, 54%, 14% and 70%, respectively. This substitution however causes the reduction of indicated efficiency to 2.8%. Hydrogen substitution with diesel can also postpone the combustion, and resulting to increase PRR and HRR; however, this pressure enhancement does not lead to knocking.

The wind is one of developing sources of renewable energy in recent years. Wind power often is unusable at peak times. Therefore¡ a storage system or backup power is always necessary. In this study¡ a hybrid system was applied for a wind turbine to provide the reliable power. The hybrid system consisted of four main components: a wind turbine¡ electrolyzer¡ hydrogen storage and fuel cell. The extra electricity produced in fewer demand hours by wind turbine was conducted to a hydrogen and oxygen generator system. Hydrogen were stored in a tank. Then¡ hydrogen was introduced to a fuel cell unit in order to produce electricity at peak times (when the electricity produced by wind power was less than demand). The hydrogen production rate by alkaline electrolysis as well as the electricity production by PEM fuel cell was investigated. The maximum hydrogen produced by the system per hour average was 304 ml and the power produced by the fuel cell was 1008 mW. After the construction of the prototype¡ a case study for this system was done in Kouhin area.