Reforming system for co-generation of hydrogen and mechanical work

The paper describes a new design for a reforming system for converting hydrocarbon fuels into pure hydrogen. The system is based on an autothermal reforming (ATR) reactor operating at elevated pressures followed by membrane-based hydrogen separation. The high-pressure membrane discharge stream is combusted and expanded through a turbine generating additional power. Process simulation modeling illustrates the effect of pressure and other operating parameters on system performance and demonstrates a system reforming efficiency approaching 80%. When coupled with a PEM fuel cell and an electrical generator, fuel to electricity efficiency is above 40%. Other anticipated benefits of the system include compact size, simplicity in control and fast start up.     

Experimental investigation of performance and emissions of the SICAI-hybrid engine systems

The use of hybrid electrical engines can provide more efficiency by reducing fuel consumption and emissions. In the research, the experimental studies on the created hybrid electric engine were presented. The hybrid engine combines an electric motor with the internal combustion engine (ICE) which is operated under spark assisted controlled auto-ignition (SICAI) combustion mode with the alternative fuels consisting of different ratios of methane–hydrogen blends. In order to establish the hybrid engine, firstly, efficiency graphs of the electrical motor were obtained experimentally. The battery charge status was also checked. The operating range of the SICAI engine in the hybrid system was identified considering performance and efficiency parameters. Based on these parameters, a hybrid algorithm was established to control the operating of the created hybrid engine system. Thus, the experimental studies were carried out for 100% methane, 90% methane-10% hydrogen, 80% methane-20% hydrogen and, 70% methane-30% hydrogen blends (by volume) at wide opening throttle (WOT) and, 50% WOT positions. Consequently, the results were discussed in terms of efficiency and emissions.     

Influences of hydrogen and various gas fuel addition to different liquid fuels on the performance characteristics of a spark ignition engine

This study reports the impacts of dual fuel mixtures on the theoretical performance characteristics of a spark ignition engine (SIE). The effects of addition of liquefied hydrogen, methane, butane, propane (additive fuels) into gasoline, iso-octane, benzene, toluene, hexane, ethanol and methanol fuels (primary fuels) on the variation of power, indicated mean effective pressure (IMEP), thermal efficiency, exergy efficiency, were examined by using a combustion model. The fuel additives were ranged from 10 to 50% by mass. The results exhibited that the ratios of hydrogen, methane, butane, propane noticeably affect the performance of the engine. The maximum increase ratio of power is 82.59% with 50% of toluene ratio and its maximum decrease ratio is 10.84% with 50% of methanol ratio in hydrogen mixtures. The maximum increase ratio of thermal efficiency and exergy efficiency are observed as 26.75% and 32.23% with the combustion of benzene-hydrogen mixtures. The maximum decrease ratio of thermal efficiency is 29.71% with the combustion of 50% of methanol ratio and it is 21.95% for the exergy efficieny with the combustion of 50% of ethanol ratio in hydrogen mixtures. The power, IMEP, thermal efficiency and exergy efficiency of primary fuels demonstrate different variation characteristics with respect to type and ratio of additive fuels.     

A computational study on the combustion of hydrogen/methane blended fuels for a micro gas turbines

To understand the combustion performance of using hydrogen/methane blended fuels for a micro gas turbine that was originally designed as a natural gas fueled engine, the combustion characteristics of a can combustor has been modeled and the effects of hydrogen addition were investigated. The simulations were performed with three-dimensional compressible k-ε turbulent flow model and presumed probability density function for chemical reaction. The combustion and emission characteristics with a variable volumetric fraction of hydrogen from 0% to 90% were studied. As hydrogen is substituted for methane at a fixed fuel injection velocity, the flame temperatures become higher, but lower fuel flow rate and heat input at higher hydrogen substitution percentages cause a power shortage. To apply the blended fuels at a constant fuel flow rate, the flame temperatures are increased with increasing hydrogen percentages. This will benefit the performance of gas turbine, but the cooling and the NO_x emissions are the primary concerns. While fixing a certain heat input to the engine with blended fuels, wider but shorter flames at higher hydrogen percentages are found, but the substantial increase of CO emission indicates a decrease in combustion efficiency. Further modifications including fuel injection and cooling strategies are needed for the micro gas turbine engine with hydrogen/methane blended fuel as an alternative.     

Predicting efficiency of solar powered hydrogen generation using photovoltaic-electrolysis devices

Hydrogen fuel for fuel cell vehicles can be produced by using solar electric energy from photovoltaic (PV) modules for the electrolysis of water without emitting carbon dioxide or requiring fossil fuels. In the past, this renewable means of hydrogen production has suffered from low efficiency (2–6%), which increased the area of the PV array required and therefore, the cost of generating hydrogen. A comprehensive mathematical model was developed that can predict the efficiency of a PV-electrolyzer combination based on operating parameters including voltage, current, temperature, and gas output pressure. This model has been used to design optimized PV-electrolyzer systems with maximum solar energy to hydrogen efficiency. In this research, the electrical efficiency of the PV-electrolysis system was increased by matching the maximum power output and voltage of the photovoltaics to the operating voltage of a proton exchange membrane (PEM) electrolyzer, and optimizing the effects of electrolyzer operating current, and temperature. The operating temperature of the PV modules was also an important factor studied in this research to increase efficiency. The optimized PV-electrolysis system increased the hydrogen generation efficiency to 12.4% for a solar powered PV-PEM electrolyzer that could supply enough hydrogen to operate a fuel cell vehicle.     

基于价值损耗的燃料电池混合动力能量管理策略评价

为了评价燃料电池混合动力系统能量管理策略的经济性,对基于状态机和模糊逻辑2种能量管理策略的燃料电池混合动力叉车的价值损耗进行分析。首先,通过分析燃料电池和锂电池的工作特性,分别构建依赖实际工况的燃料电池单体电压衰减率模型和锂电池容量衰减率模型;同时定义计及燃料电池氢耗量的燃料电池混合动力系统的综合价值损耗指标。其次,通过测试叉车极限工况,计算燃料电池功率和锂电池容量,并根据母线电压确定锂电池SOC范围。最后,设计基于状态机和模糊逻辑的2种燃料电池混合动力叉车能量管理策略,并通过仿真分析在叉车一次循环工况下2种能量管理的价值损耗。研究结果表明:相较于模糊逻辑策略,采用状态机策略造成燃料电池寿命损耗提高7.81%,氢耗量提高1.89倍,锂电池寿命损耗减小21.33%。     

S.I. engine fuelled with gasoline,methane and methane/hydrogen blends: Heat release and loss analysis

Experiments were carried out to investigate the performance of different fuels used in a internal combustion engine: gasoline, methane and fuel blends containing methane with 5%, 10% and 15% hydrogen by volume, respectively. A two-litre naturally aspirated bi-fuel engine with port fuel injection was used. The engine was operated stoichiometrically. For each fuel the spark advance for best efficiency was determined. Experiments were conducted at 2000 rpm and 2 bar brake mean effective pressure. A heat release analysis and a loss analysis were performed for all fuels. The main findings are that increasing the hydrogen fraction of the methane hydrogen fuel blend decreases the overall burn duration. This decrease is predominantly achieved by a shortened duration of the fist stage of combustion (ignition to 5% mass fraction burned). The faster combustion comes along with an increase in fuel conversion efficiency. The different losses for gasoline and pure methane operation interact such that equal fuel conversion efficiencies result. However, care has to be taken when comparing fuel conversion efficiencies among the different fuels as the relative error in fuel conversion efficiency for the gaseous fuels is 0.2% at most, whereas it is about 1% for gasoline.     

Exergetic performance coefficient analysis of a simple fuel cell system

In this paper, a fuel cell power generation system fed by hydrogen is analyzed by different performance criteria over the entire range of potential operating conditions. First law efficiency and net power output are considered for conventional energetic indices of performance, and exergy destruction rate is taken into consideration as an exergetic performance criteria. A new exergetic criterion called the exergetic performance coefficient (EPC) is introduced and is applied to the system model based on zero-dimensional approach. The system model consists of the following components: fuel cell stack, afterburner, fuel and air compressors, and heat exchangers. The effects of the operating conditions on the system performance are studied parametrically. The obtained results based on the exergetic performance coefficient criterion are compared with first law efficiency, power output and exergy destruction rate. Results show that design insights of fuel cell systems can be considerably improved when conventional energetic analyses are supplemented with EPC criterion.     

Exergy analysis of an integrated fuel processor and fuel cell (FP–FC) system

Fuel cells have great application potential as stationary power plants, as power sources in transportation, and as portable power generators for electronic devices. Most fuel cells currently being developed for use in vehicles and as portable power generators require hydrogen as a fuel. Chemical storage of hydrogen in liquid fuels is considered to be one of the most advantageous options for supplying hydrogen to the cell. In this case a fuel processor is needed to convert the liquid fuel into a hydrogen-rich stream. This paper presents a second-law analysis of an integrated fuel processor and fuel cell system. The following primary fuels are considered: methanol, ethanol, octane, ammonia, and methane. The maximum amount of electrical work and corresponding heat effects produced from these fuels are evaluated. An exergy analysis is performed for a methanol processor integrated with a proton exchange membrane fuel cell, for use as a portable power generator. The integrated FP–FC system, which can produce 100 W of electricity, is simulated with a computer model using the flow-sheeting program Aspen Plus. The influence of various operating conditions on the system efficiency is investigated, such as the methanol concentration in the feed, the temperature in the reformer and in the fuel cell, as well as the fuel cell efficiency. Finally, it is shown that the calculated overall exergetic efficiency of the FP–FC system is higher than that of typical combustion engines and rechargeable batteries.     

Optimization and efficiency analysis of methanol SOFC-PEMFC hybrid system

In order to improve the power generation efficiency of fuel cell systems employing liquid fuels, a hybrid system consisting of solid oxide fuel cell (SOFC) and proton exchange membrane fuel cell (PEMFC) is proposed. Utilize the high temperature heat generated by SOFC to reform as much methanol as possible to improve the overall energy efficiency of the system. When SOFC has a stable output of 100 kW, the amount of hydrogen after reforming is changed by changing the methanol flow rate. Three hybrid systems are proposed to compare and select the best system process suitable for different situations. The results show that the combined combustion system has the highest power generation, which can reach 350 kW and the total electrical efficiency is 57%. When the power of the tail gas preheating system is 160 kW, the electrical efficiency can reach 75%. The PEM water preheating system has the most balanced performance, with the electric power of 300 kW and the efficiency of 66%.     

Performance analysis of hybrid solid oxide fuel cell and gas turbine cycle (part I): Effects of fuel composition on output power

In this paper, the model of hybrid solid oxide fuel cell (SOFC) and gas turbine (GT) cycle is applied to investigate the effects of the inlet fuel type and composition on the performance of the hybrid SOFC–GT cycle. The sensitivity analyses of the impacts of the concentration of the different components, namely, methane, hydrogen, carbon dioxide, carbon monoxide, and nitrogen, in the inlet fuel on the performance of the hybrid SOFC–GT cycle are performed. The simulation results are presented with respect to a reference case, when the system is fueled by pure methane. Then, the performance of the hybrid SOFC–GT system when methane is partially replaced by each component within a corresponding range of concentration with an increment of 5% at each step is investigated. The results point out that the output powers of the SOFC, GT, and cycle as a whole decrease sharply when methane is replaced with other species in majority of the cases.     

Fuel cells for carbon capture and power generation: Simulation studies

The decarbonization of hydrocarbons is explored in this work as a method to produce hydrogen and mitigate carbon dioxide (CO₂) emissions. An integrated process for power generation and carbon capture based on a hydrocarbon fueled-decarbonization unit was proposed and simulated. Ethane and propane were used as fuels and subjected to the thermal decomposition (decarbonization) process. The system is also composed of a carbon fuel cell (CFC) and hydrogen fuel cell (HFC) for the production of power and a pure CO₂ stream that is ready for sequestration. The HFC is a high-temperature proton exchange membrane fuel cell operating at 200 °C. Simulations were performed using ASPEN HYSYS V.10 for the entire process including the CFC and HFC being operated at various operating temperatures (200–800 °C). The power output from the CFC and the HFC as well as the overall process efficiency were calculated. The model incorporates an energy recovery system by adopting a counter-current shell and tube heat exchangers and a turbine. The water produced from the fuel cell system can be utilized in the plant to recover the heat from the furnace. The results showed a 100% carbon capture with a nominal plant capacity of 108 MWe produced when propane fuel was fed to the decarbonizer. The CFC theoretical efficiency is 100% and the practical efficiency was taken as 70% when all internal polarizations were considered. The results showed that, in the case of propane, the CFC power output was 89 MWe when the CFC operated at 650 °C, and the HFC power output was around 45 MWe at 200 °C with an overall actual plant efficiency of 35% and 100% carbon capture. Sensitivity analysis recommends a hydrocarbon fuel cost of 0.011 $/kW as the most feasible option. The results reported here on the decarbonization of hydrocarbon fuels are promising toward the direct production of hydrogen with full carbon dioxide sequestration at a potentially lower cost especially in rural areas. The overall actual efficiencies are very competitive to those of conventional power plants operated without carbon capture.     

An experimental study of syn-gas production via microwave plasma reforming of methane,iso-octane and gasoline

A newly developed microwave plasma system for fuel reforming was tested for three different hydrocarbon fuels. The microwave plasma system was powered by a low cost commercial magnetron and power supply. The microwave power was delivered to the nozzle from the magnetron via a coaxial cable, which offers tremendous flexibility for system design and applications. A non-premixed configuration was achieved by delivering a separate stream of fuel to the plasma plume, which is composed of diluted oxygen only. The feasibility of syn-gas production capability of the microwave plasma system was demonstrated and the reforming characteristics of methane, iso-octane and gasoline were compared. The effects of input power, injected fuel amount, total flow rate and O/C ratio were evaluated. The production rates of both hydrogen and carbon monoxide were proportional to the input power and the inverse of the total flow rate. As a result, the maximum efficiency of 3.12% was obtained with iso-octane for power consumption of 28.8 W, O/C ratio of 1, and 0.1 g/min of fuel supply. Liquid fuels produced more syn-gas and showed better efficiency than methane for the same input powers and O/C ratios.     

Fuel flexibility study of an integrated 25 kW SOFC reformer system

The operation of solid oxide fuel cells on various fuels, such as natural gas, biogas and gases derived from biomass or coal gasification and distillate fuel reforming has been an active area of SOFC research in recent years. In this study, we develop a theoretical understanding and thermodynamic simulation capability for investigation of an integrated SOFC reformer system operating on various fuels. The theoretical understanding and simulation results suggest that significant thermal management challenges may result from the use of different types of fuels in the same integrated fuel cell reformer system. Syngas derived from coal is simulated according to specifications from high-temperature entrained bed coal gasifiers. Diesel syngas is approximated from data obtained in a previous NFCRC study of JP-8 and diesel operation of the integrated 25 kW SOFC reformer system. The syngas streams consist of mixtures of hydrogen, carbon monoxide, carbon dioxide, methane and nitrogen. Although the SOFC can tolerate a wide variety in fuel composition, the current analyses suggest that performance of integrated SOFC reformer systems may require significant operating condition changes and/or system design changes in order to operate well on this variety of fuels.     

Thermodynamic study of integrated proton exchange membrane fuel cell with vapour adsorption refrigeration system

With the rising usage of fossil fuels, there is an urgent need to develop new technologies specifically based on renewable energy sources to power the vehicles running on fuel. A fuel cell is an electrochemical cell that is used to convert the chemical energy of a fuel directly to electric power. Fuels cells possess advantages such as smaller size, high efficiency, silent operation, etc. However, there can be significant variations in the size and power output of the fuel cells depending upon the application. The focus of this paper is to estimate the performance of an integrated system comprising of Polymer Exchange Membrane Fuel cell (PEMFC) and vapour adsorption refrigeration system to produce electric output and cooling effect simultaneously. The adsorption system in this study is based on activated carbon and methanol combination. The effect of operating parameters such as the operating temperature, current density and evaporator temperature on the energy and exergy efficiency of the system is presented. The study shows a remarkable improvement in the performance of the integrated system compared to PEMFC alone. The results show that the system energy and exergy efficiency decrease as the current density value increases. Maximum system energy and exergy efficiency of 63.01% and 29.88% are achieved. In addition, a maximum energy efficiency of 65.39% was reported at an evaporator temperature of 5 °C and a current density of 0.8 A/cm².     

Performance assesment of hydrogen and ammonia combustion with various fuels for power generators

This paper proposes the use of hydrogen and ammonia as possible fuels for power generators and to do so the combustion is modelled by using different types of fuels which are; hydrogen, gasoline, diesel, ethanol, methanol, propane, butane and natural gas to see the effects of these fuel sources on combustion. The main aim of using a clean fuel is to decrease the greenhouse emissions, and by looking at the results, the reduction in CO₂ emissions shows that blending hydrogen and ammonia will result in a reduction for the deleterious emissions occurring after combustion. The reason behind using a dual fueled system is to make use of the secondary fuel source as a combustion promoter to help increase the low flame temperatures of ammonia that causes it not to ignite when used solely. In the modelling of combustion the maximum power output is set to 3.65 kW as this is the maximum power output for the power generator used in the experimental studies. In the studies the increase of clean fuel percentage in the fuel blend cause a reduction in the performance measures as expected with the lower energy density and lower heating values that ammonia offers but the reduction in CO₂ and NO_x emissions makes it a fuel source worth using with a combustion promoter.     

Part-load,startup, and shutdown strategies of a solid oxide fuel cell-gas turbine hybrid system

Current work on the performance of a solid oxide fuel cell (SOFC) and gas turbine hybrid system is presented. Each component model developed and applied is mathematically defined. The electrochemical performance of single SOFC with different fuels is tested. Experimental results are used to validate the SOFC mathematical model. Based on the simulation model, a safe operation regime of the hybrid system is accurately plotted first. Three different part-load strategies are introduced and used to analyze the part-load performance of the hybrid system using the safe regime. Another major objective of this paper is to introduce a suitable startup and shutdown strategy for the hybrid system. The sequences for the startup and shutdown are proposed in detail, and the system responses are acquired with the simulation model. Hydrogen is used instead of methane during the startup and shutdown process. Thus, the supply of externally generated steam is not needed for the reforming reaction. The gas turbine is driven by complementary fuel and supplies compressed air to heat up or cool down the SOFC stack operating temperature. The dynamic simulation results show that smooth cooling and heating of the cell stack can be accomplished without external electrical power.     

An experimental investigation of reverse vortex flow plasma reforming of methane

This paper focuses on the reforming of methane into hydrogen rich gas by means of gliding arc plasma stabilized in a reverse vortex flow. Parametric tests utilizing a 42 mm diameter reactor investigated the effects of electrode gap distance, reaction chamber exit diameter, steam input, methane input (fuel to oxygen ratio), and power input. Over the range of conditions tested, reactor performance was most sensitive to methane input. Decreasing the diameter of the reaction chamber exit impeded the performance of the reformer. A set of factorial tests determined the optimal operating conditions of the system to be at flow rates of 2 slpm nitrogen, 0.56 slpm oxygen, 1.25 slpm methane, an electrode gap distance of 34.5 mm, an outlet diameter of 12.65 mm, and a power input of 260 W. At these conditions the system yielded 83.3% hydrogen selectivity, 79.8% methane conversion and efficiency of 43.5%. Physical operating boundaries of the system defined by soot production and arc extinction were identified.     

Natural gas internal combustion engine hybrid passenger vehicle

The implementation of hybrid electric vehicles powered with alternative fuels is critical in reducing national dependence on imported crude oil, addressing the detrimental environmental impact of increasing petroleum usage worldwide, and sustaining the national economy. The question is not whether changes should be made, but instead centers on identifying pathways that will lead to the greatest environmental and economic benefits. To avoid misuse of limited infrastructure investment, the objective of this research is to consider a broad range of relevant factors to determine desirable power plant–fuel combinations for hybrid electric vehicles. In the long term, fuel cells may dominate this application, but at least in the short term, proton exchange membrane fuel cells (PEMFCs) will not likely offer immediate substantial benefit over internal combustion (IC) engines. Environmentally friendly operation of the PEMFC results partly due to low‐temperature operation but primarily due to the requirement of a clean fuel, hydrogen. In addition, the differential benefits from power plant choice can be overshadowed by the advantages obtained from hybrid electric vehicle technology and alternative fuels. Consequently, the fuel flexibility of IC engines provides an advantage over the relatively fuel inflexible PEMFC. The methane/hythane IC engine hybrid option, as developed and presented here, is a promising pathway that avoids the barriers encountered with conventional non‐hybrid natural gas vehicles, namely range, power and fueling infrastructure difficulties. Dynamometer testing of the natural gas hybrid prototype on the certification FTP‐72 duty cycle revealed very low emissions and mileage greater than 33 miles per gallon gasoline equivalent. This hybrid option utilizes a domestic, cost‐effective fuel with renewable sources. With multi‐fuel capability (methane, hythane and gasoline) it is also designed for use within the emerging hydrogen market. This hybrid option offers reliability and cost‐effective technology with immediate wide spread market availability. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental results of hydrogen enrichment of ethanol in an ultra-lean internal combustion engine

An investigation was made to determine the effects of hydrogen enrichment of ethanol at ultra-lean operating regimes utilizing an experimental method. A 0.745 L 2-cylinder SI engine was modified to operate on both hydrogen and ethanol fuels. The study looked at part throttle, fixed RPM operation of 0%, 15%, and 30% hydrogen fuel mixtures operating in ultra-lean operating regimes. Data was collected to calculate NO and HC emissions, power, exhaust gas temperature, thermal efficiency, volumetric efficiency, brake-specific fuel consumption, and Wiebe burn fraction curves.