Energy efficiency of membrane-based fuel processors – PEM fuel cell systems

This work presents a simulative energy efficiency analysis performed on fuel processor – PEMFC systems, considering methane as fuel and steam reforming or autothermal reforming as processes to produce hydrogen. Computation of energy efficiency takes into account the power required by the auxiliary units, coupling of the fuel processor with the fuel cell as well as heat recovery and integration.     

Active fuel design—A way to manage the right fuel for HCCI engines

Homogenous charge compression ignition (HCCI) engines feature high thermal efficiency and ultralow emissions compared to gasoline engines. However, unlike SI engines, HCCI combustion does not have a direct way to trigger the in-cylinder combustion. Therefore, gasoline HCCI combustion is facing challenges in the control of ignition and, combustion, and operational range extension. In this paper, an active fuel design concept was proposed to explore a potential pathway to optimize the HCCI engine combustion and broaden its operational range. The active fuel design concept was realized by real time control of dual-fuel (gasoline and n-heptane) port injection, with exhaust gas recirculation (EGR) rate and intake temperature adjusted. It was found that the cylinderto- cylinder variation in HCCI combustion could be effectively reduced by the optimization in fuel injection proportion, and that the rapid transition process from SI to HCCI could be realized. The active fuel design technology could significantly increase the adaptability of HCCI combustion to increased EGR rate and reduced intake temperature. Active fuel design was shown to broaden the operational HCCI load to 9.3 bar indicated mean effective pressure (IMEP). HCCI operation was used by up to 70% of the SI mode load while reducing fuel consumption and nitrogen oxides emissions. Therefore, the active fuel design technology could manage the right fuel for clean engine combustion, and provide a potential pathway for engine fuel diversification and future engine concept.     

Atomization performance and TG analysis of Fischer–Tropsch fuel compared with RP-3 aviation fuel

As many potential alternative jet fuels would be used in the in-service engine, such as the most promising Fischer–Tropsch (F–T) jet fuel, it's necessary to test their performance in compared with petroleum derived jet fuel. In this study, atomization performance of F–T fuel and traditional RP-3 jet fuel were assessed based on three parameters including Sauter mean diameter, Spray cone angle, and Distribution index N. Thermogravimetric (TG) analysis is also conducted for kinetics analysis. TG experiments of F–T fuel and RP-3 were carried out in order to establish the relationship between atomization and TG characteristics. Burnout index B_f and uniform parameter α derived based on TG experiments were defined in this study. The qualitative relationship between B_f, α and atomization parameters were given for rapid evaluation of alternative jet fuel's atomization characteristics.     

Direct reforming of Methane–Ammonia mixed fuel on Ni–YSZ anode of solid oxide fuel cells

To control the temperature distribution in the Ni–YSZ (yttria-stabilized zirconia) anode of solid oxide fuel cells (SOFCs) by efficiently utilizing the heat generated by electrochemical reactions, the supply of methane–ammonia mixed fuel is proposed. The reaction characteristics of reforming/decomposition of the mixed fuel on a Ni–YSZ catalyst are experimentally investigated. A mixture gas of methane, steam, ammonia, and balance argon is supplied to a packed bed catalyst placed in a quartz tube in an electric furnace. The crushed Ni–YSZ anode of SOFCs is used as the catalyst. The exhaust gas composition is analyzed by gas chromatography and the streamwise temperature distribution of the catalyst bed is measured by an infrared camera. It is found that ammonia decomposition preferentially proceeds and steam methane reforming becomes active after sufficient ammonia has been consumed. A low-temperature region is formed by steam methane reforming owing to its strongly endothermic nature. Its position moves downstream while its magnitude decreases as the ammonia concentration in the fuel increases. This shows that the local temperature distribution can be controlled by tuning the ratio of methane to ammonia in the mixed fuel. It is also found that, at a certain mixture ratio, the mixed fuel realizes a hydrogen production rate higher than that for only methane or ammonia.     

When will fossil fuel reserves be diminished?

Crude oil, coal and gas are the main resources for world energy supply. The size of fossil fuel reserves and the dilemma that “when non-renewable energy will be diminished” is a fundamental and doubtful question that needs to be answered. This paper presents a new formula for calculating when fossil fuel reserves are likely to be depleted and develops an econometrics model to demonstrate the relationship between fossil fuel reserves and some main variables. The new formula is modified from the Klass model and thus assumes a continuous compound rate and computes fossil fuel reserve depletion times for oil, coal and gas of approximately 35, 107 and 37 years, respectively. This means that coal reserves are available up to 2112, and will be the only fossil fuel remaining after 2042. In the Econometrics model, the main exogenous variables affecting oil, coal and gas reserve trends are their consumption and respective prices between 1980 and 2006. The models for oil and gas reserves unexpectedly show a positive and significant relationship with consumption, while presenting a negative and significant relationship with price. The econometrics model for coal reserves, however, expectedly illustrates a negative and significant relationship with consumption and a positive and significant relationship with price. Consequently, huge reserves of coal and low-level coal prices in comparison to oil and gas make coal one of the main energy substitutions for oil and gas in the future, under the assumption of coal as a clean energy source.     

Catalytic exhaust gas fuel reforming for diesel engines—effects of water addition on hydrogen production and fuel conversion efficiency

Previous work in our laboratory has shown that the exhaust gas assisted fuel reforming process has the potential to provide a solution to the diesel engine exhaust emission problems. When simulated reformer product gas rich in hydrogen is fed to the engine, a reduction of both NO_x and smoke emissions can be achieved. In this paper, the optimisation of the reforming process by water addition in the reactor is presented. Using a prototype catalyst at 290°C reactor inlet temperature, up to 15% more hydrogen in the reformer product was obtained compared to operation without water. The process has been found to be mainly a combination of the fuel oxidation, steam reforming and water gas shift reactions. The reforming process efficiency has been shown to improve considerably with water addition up to a certain level after which the adverse effects of the exothermic water gas shift reaction become significant.     

Who are the early adopters of fuel cell vehicles?

All new technologies, including automotive technologies, are first purchased by early adopters. These consumers are currently posed with the choice of purchasing a fuel cell vehicle (FCV) or a variety of other alternatively fueled vehicles, including battery electric vehicles (BEVs). For FCVs to be commercially successful they need to carve out their own niche in the automotive market, something which may prove challenging in the face of strong BEV market growth. The results in this paper come from a questionnaire survey of 470 FCV owners and 1550 BEV owners. The paper explores the socio-economic profile, travel patterns, and attitudes of FCV buyers and compares them to the buyers of BEVs. The result suggests that the adopters of BEVs and FCV are similar in gender, level of education, household income, and have similar travel patterns. They have differences in age, ownership of previous alternative fuel vehicles, attitudes towards sustainability, and more FCV owners live in rented homes and apartment buildings. The results of the study suggest that FCVs may appeal to consumers who live in homes where they cannot recharge a BEV or install their own charger. FCVs still have several challenges to overcome, including the lack of hydrogen refueling stations and a lack of FCV models to choose from.     

Food versus fuel: What do prices tell us?

Sorting out the impacts of biofuels on global agricultural commodity prices is impossible without turning to data and distinguishing between the short-run versus the long-run impacts. Using time-series prices on fuels and agricultural commodities, the aim is to investigate the long-run cointegration of these prices simultaneously with their multivariate short-run interactions. Results indicate no direct long-run price relations between fuel and agricultural commodity prices, and limited if any direct short-run relationships. In terms of short-run price movements, sugar prices are influencing all the other agricultural commodity prices except rice. With sugar the number one world input for ethanol, results indicate increased ethanol production is potentially influencing short-run agricultural commodity prices. Overall, results support the effect of agricultural commodity prices as market signals which restore commodity markets to their equilibria after a demand or supply event (shock).     

Coking-free direct-methanol-flame fuel cell with traditional nickel–cermet anode

This paper presents a systematic study of a direct-flame solid oxide fuel cell (DF-SOFC) operating on methanol and ethanol flames by SEM, EIS, I-V polarization and mass spectrometer (MS) characterizations and numerical simulation. The experimental study demonstrated that, by adopting a conventional Ni + Sm_0.2Ce_0.8O_1.9 (SDC) anode, irreversible carbon deposition and a drop of cell performance was observed when running the cell on an ethanol flame, while no carbon was deposited by operating on a methanol flame. Fuel cell stability tests indicated significant degradation in performance after 3 h of operation on an ethanol flame, while no degradation was observed after 30 h of operation on a methanol flame. A simple qualitative explanation of the difference observed in the electrochemical performance for the fuel cell operating on a methanol flame and an ethanol flame is presented based on numerical simulation.     

Shock waves in multiphase flow of fuel–coolant interaction

The interaction of fuel and coolant (FCI) is a complex multiphase process due to the fact that the fragmentation and heat transfer process are not easy to cast in simple mathematical formulas. This paper, a theoretical model has been developed by considering multiphase flow shock wave propagating of fuel–coolant interaction. Analysis of a steady-state vapour explosion in one dimension has been carried out by applying the conservation laws of mass, momentum, energy and the appropriate equation of state for an interaction of molten dioxide uranium and water. Using the model, we predicted the pressure magnitudes behind shock wave of vapour explosion varied with the initial volume fraction of vapour, melt mass concentrations, liquid entrained fraction and when they were considered as dangerous.     

Thermodynamic analysis of ethanol processors – PEM fuel cell systems

This work presents a simulative energy efficiency analysis performed on fuel processor – PEM fuel cell systems, considering ethanol as fuel and steam reforming or autothermal reforming as processes to produce hydrogen.     

In-situ exsolved NiFe alloy nanoparticles on Pr0.8Sr1.2(NiFe)O4-δ for direct hydrocarbon fuel solid oxide fuel cells

NiFe alloy (NFA) nanoparticles decorated Ruddlesden-Popper (RP) type layered perovskite structure Pr_0.8Sr_1.2(NiFe)O_4-δ (RP-PSNF) have been fabricated by in-situ reduction of cubic perovskite Pr_0.32Sr_0.48Ni_0.2Fe_0.8O_3-δ (P–PSNF) in H₂ at 800 °C. When used as the solid oxide fuel cell (SOFC) anode material, the RP-PSNF-NFA based ceramic anode demonstrates a comparable catalytic activity to Ni-based anode. The SOFC single cell with RP-PSNF-NFA-Gd_0.2Ce_0.8O_2−δ (GDC) anode exhibits a maximum power density of 983 and 770 mW cm⁻² in humidified H₂ and C₃H₈ at 800 °C, respectively. More importantly, the single cell shows a high durability at the current density of 250 mA cm⁻² in humidified C₃H₈ at 800 °C, demonstrating an excellent coking resistance. Overall, this work suggests that RP-PSNF-NFA is a promising anode for direct hydrocarbon fuel SOFCs.     

Study of molten carbonate fuel cell—microturbine hybrid power cycles

The interaction realized by fuel cell—microturbine hybrids derive primarily from using the rejected thermal energy and combustion of residual fuel from a fuel cell in driving the gas turbine. This leveraging of thermal energy makes the high temperature molten carbonate fuel cells (MCFCs) ideal candidates for hybrid systems. Use of a recuperator contributes to thermal efficiency by transferring heat from the gas turbine exhaust to the fuel and air used in the system.Traditional control design approaches, consider a fixed operating point in the hope that the resulting controller is robust enough to stabilize the system for different operating conditions. On the other hand, adaptive control incorporates the time-varying dynamical properties of the model (a new value of gas composition) and considers the disturbances acting at the plant (load power variation).     

Ag and Ag–Mn nanowire catalysts for alkaline fuel cells

Low loadings of Ag and Ag–Mn nanowire catalysts were applied to the surface of a CNT-base electrode. The catalyzed electrodes had a 60 mV larger onset potential and promoted the ORR via the direct 4 electron pathway. The Ag/CNT, Ag–Mn/CNT, and CNT samples produced a Tafel slope of about 70 mV/decade which confirmed the ORR activation was limited by the migration of oxygen molecules to active surface sites. The catalytic performance of the Ag and Ag–Mn nanowires was also comparable to that of a bulk catalyst but at a much lower loading. Electrochemical test results showed that the Ag and Ag–Mn catalysts exhibited similar performance. The Ag–Mn nanowire catalysts were synthesized using a unique electroless deposition procedure to co-deposit Ag and Mn. ICP confirmed that 2 to 9 at% Mn was present in the nanowires. XPS and XRD analysis showed that the Ag–Mn nanowires were composed of Mn in solid solution with Ag and a thin surface layer containing MnO and MnO₂. The Ag–Mn nanowires were expected to be the most active. The equivalent performance between Ag and Ag–Mn samples was attributed to the presence of inactive MnO and low concentrations of MnO₂ in the nanowires. Although MnO₂ is known to be active towards the ORR, the dominant Mn species in the nanowires was MnO.     

Bio-diesel as an alternative fuel for diesel engines—A review

The present review aims to study the prospects and opportunities of introducing vegetable oils and their derivatives as fuel in diesel engines. In our country the ratio of diesel to gasoline fuel is 7:1, depicting a highly skewed situation. Thus, it is necessary to replace fossil diesel fuel by alternative fuels. Vegetable oils present a very promising scenario of functioning as alternative fuels to fossil diesel fuel. The properties of these oils can be compared favorably with the characteristics required for internal combustion engine fuels. Fuel-related properties are reviewed and compared with those of conventional diesel fuel. Peak pressure development, heat release rate analysis, and vibration analysis of the engine are discussed in relation with the use of bio-diesel and conventional diesel fuel. Optimization of alkali-catalyzed transesterification of Pungamia pinnata oil for the production of bio-diesel is discussed. Use of bio-diesel in a conventional diesel engine results in substantial reduction in unburned hydrocarbon (UBHC), carbon monoxide (CO), particulate matters (PM) emission and oxide of nitrogen. The suitability of injection timing for diesel engine operation with vegetable oils and its blends, environmental considerations are discussed. Teardown analysis of bio-diesel B20-operated vehicle are also discussed.     

Direct methanol–air fuel cells with membranes plus circulating electrolyte

A new approach for direct methanol–air fuel cells (DMFC), with the advantage of reduced methanol crossover is discussed in this paper. Methanol traces in the circulated electrolyte are recovered and CO₂ bubbles in the cells are removed due to the forced methanol–electrolyte stream through the cell.Degradation of the catalyst is reduced since fuel cell electrodes degrade on activated stand without load to a higher extent than under load because high voltage on open circuit promotes carbon oxidation, catalyst changes, etc. Therefore, life expectancy increases with circulating electrolyte by removing the electrolyte from the cells between operating periods.     

How fuzzy logic can improve PEM fuel cell MPPT performances?

This paper addresses the development of new variable step size fuzzy based MPPT controller. In this study, the fuzzy logic approach is firstly used to auto-scale the variable step size of the Incremental Conductance (IC) MPPT controller. Secondly, the proposed variable step size fuzzy based MPPT controller is used to track the output power of the PEM fuel cell system composed of 7 kW fuel cell supplying a 50Ω resistive load via a DC-DC boost converter controlled using the proposed MPPT. The proposed variable step size fuzzy-based MPPT controller is compared to the conventional fixed step size IC, the variable step size IC and the fuzzy scaled variable step size IC MPPTs using the implemented Matlab/Simulink PEM Fuel Cell power system model. Comparative simulation results between the four studied MPPTs show better performances for the proposed fuzzy based variable step size MPPT in term of: response time reduction between 3.6% and 82.35%; overshoot reduction between 34.55% and 100%; and ripple reduction between 70.93% and 100%, improving as consequence the fuel cell lifetime affected by high current ripple.     

Biomass-integrated gasification fuel cell systems – Part 2: Economic analysis

For the seven technically feasible Biomass-Integrated Gasification Fuel Cell (B-IGFC) systems investigated in this two-part system analysis, the interactions between the used biomass gasification processes, gas processing technologies and SOFC concepts are investigated primarily employing ASPEN PLUS™ flowsheeting models. Based on the results of the system simulations, the power production costs are estimated for the various B-IGFC systems. The impact of the most important assumptions made for the presented thermo-economic system analysis is assessed through a sensitivity analysis.     

Direct internal reforming molten carbonate fuel cell with core–shell catalyst

A sort of core–shell catalyst as a novel anti-alkali-poisoning concept was prepared, tested and applied in the direct internal reforming molten carbonate fuel cell (DIR-MCFC). Results showed that the core–shell catalyst possessed good alkali-poisoning resistance capacity, which was explained well by the micropore model of the catalyst. And the cell performance could keep above 0.75V during 100 h test. When the steam carbon ratio was 2 (S/C = 2) and the current density was 150 mA cm⁻², the cell potential varied from 0.826 to 0.751 V and the voltage fluctuant phenomenon was explained specifically. Furthermore, the short stack (three cells) was also assembled, and the maximum output power density of the short stack was 338.4 mW cm⁻². The above results indicated that the core–shell catalyst could be applied into the DIR-MCFC successfully.