Fuels, Volume 6, Issue 2 (June 2025) – 10 articles

An efficient adaptive modeling criterion for the polymer electrolyte membrane fuel cell (PEMFC) is proposed in this paper, which can facilitate its precise simulation, design, analysis and control. In this work, a number of state-of-the-art algorithms have been adapted to optimize the complex electrochemical PEMFC model. Investigations are carried out not only from the conventional perspective of modeling accuracy but also from a new perspective represented by the impact of process computational time. Here, a novel technique of PEMFC modeling is proposed based on a meta-heuristic optimization algorithm called the wild horse optimizer (WHO). The proposed technique is concerned with the impact of the computational time on dynamic PEMFC modeling. A comprehensive statistical analysis was performed on the results of competing meta-heuristic optimizers that were adapted to a common PEMFC modeling problem. Among them, the proposed WHO approach’s results showed a promising performance in terms of its accuracy and minimum computational time over the other state-of-the-art approaches. For further evaluation of the WHO approach, it was used to optimize additional commercial PEMFC stack models. The results of the WHO approach highlighted its superior performance from the point of view of a high accuracy with a low computational burden, which supports its suitability for online applications. Full article

The objective of this research is to examine the dynamics of parent/child well interaction in unconventional plays, an issue that has gained prominence as high-quality inventory reduces and the number of infill wells escalates. To achieve this, the research will identify and analyze the factors influencing the interaction between parent/child wells and quantify the impacts of time, distance, and geological formation within the context of the DJ basin. The short-term estimate, considered as the next 12 months of cumulative oil production, is forecasted using decline curve analysis (DCA), and the long-term estimates come from the estimated ultimate recovery (EUR) of oil. The impact of the interaction on the parent well is determined as the difference between the recovery of the pre-frac hit and the post-frac hit. The child wells are compared to unaffected wells from the same unit. The average distance between parent and child wells is kept constant, and the time gap between the pre-existing and infill wells is statistically compared to observe the impact of time. The same procedure is followed for distance, orientation, and formation. The findings indicate that stimulation of child wells can lead to a depletion-induced stress shadow around the parent wells, potentially resulting in asymmetrical fracture growth. Consequently, the proximity of parent wells may contribute to a decrease in the performance of the child wells. On the contrary, parent wells with frac hits experienced varied outcomes, including improved production, reduced production, or no noticeable change at all. When the distance between parent and child well decreases, the negative impact on child wells increases. Increasing the time gap between pre-existing wells and infill wells shows an adverse impact on child wells. The impact on child wells was not observed when the parent well had been producing for less than 5 months. An interesting pattern emerged when analyzing the orientation of wells; child wells drilled at a perpendicular angle to their parent wells did not exhibit changes in performance. Within the geological context, the Niobrara Formation was found to have a more substantial negative impact on well interactions than the Codell Formation. In conclusion, time and distance play a crucial role in parent/child well interaction. Despite the existence of studies on parent/child well interactions within the literature, a comprehensive and detailed analysis specifically targeting the DJ Basin—particularly focusing on the intricacies of well interactions within the Niobrara and Codell Formations—has not yet been undertaken. Full article

Hydrogen–methane gas mixtures are increasingly recognized as a viable path toward achieving carbon neutrality, leveraging existing natural gas infrastructure while reducing greenhouse gas emissions. This study investigates a novel static mixing device designed for blending hydrogen and methane, employing both experimental tests and three-dimensional computational fluid dynamics (CFD) simulations. Hydrogen was introduced into a methane flow via direct injection, with experimental mixtures ranging from 5% to 18% hydrogen. The mixture quality was assessed using a specialized gas chromatograph, and the results were compared against simulated data to evaluate the mixer’s performance and the model’s accuracy. The system demonstrated effective blending, maintaining uniform hydrogen concentrations across the outlet with minimal variations. Experimental and simulated results showed strong agreement, with an average accuracy error below 2%, validating the reliability of the CFD model. Smaller nozzles (0.4 mm) achieved greater mixing uniformity, while larger nozzles (0.6 mm) facilitated higher hydrogen throughput, indicating trade-offs between mixing precision and flow capacity. The mixing device proved compatible with existing pipeline infrastructure, offering a scalable solution for hydrogen integration into natural gas networks. These findings underscore the mixer’s potential as a practical component in advancing the hydrogen economy and achieving sustainable energy transitions. Full article

Hydrogen internal combustion engines (ICEs) have gained significant attention as a promising solution for achieving zero-carbon emissions in the transportation sector. This study investigates the conversion of a 2 L Diesel ICE into a lean hydrogen-powered ICE, focusing on key challenges such as hydrogen mixing, pre-ignition, combustion flame development, and NOx emissions. The novelty of this research lies in the specific modifications made to optimize engine performance and reduce emissions while utilizing the existing Diesel engine infrastructure. The study identifies several important design changes for the successful conversion of a Diesel engine to hydrogen, including the following: Intake port design: transitioning from a swirl to a tumble design to enhance hydrogen mixing; Injection and spark plug configuration: using a lateral injection system combined with a central spark plug to improve combustion; Piston design: employing a lenticular piston shape with adaptable depth to enhance mixing; Mitigating Coanda effect: preventing hydrogen issues at the spark plug using deflectors or caps; and Head design: maintaining a flat head design for efficient mixing, while ensuring adequate cooling to avoid pre-ignition. These findings highlight the importance of specific modifications for converting Diesel engines to hydrogen, providing a solid foundation for further research in hydrogen-powered ICEs, which could contribute to carbon emission reduction and a more sustainable energy transition. Full article

The power to weight ratio of power plants is an important consideration, especially in the design of Unmanned Aircraft System (UAS). In this paper, a UAS with an MTOW of 35.3 kg, equipped with a fuel cell as a prime power supply to provide electrical power to the propulsion system, is considered. A pressure vessel design that can estimate and determine the total size and weight of the combined power plant of a fuel cell stack with hydrogen and air/oxygen vessels and the propulsion system of the UAS for high-altitude operation is proposed. Two scenarios are adopted to determine the size and weight of the pressure vessels required to supply oxygen to the fuel cell stack. Different types of stainless-steel materials are used in the design of the pressure vessel in order to find an appropriate material that provides low size and weight advantages. Also, the design of a hydrogen pressure vessel and mass estimation are also considered. The estimated sizes and weights of the hydrogen and oxygen vessels of the power plant and propulsion system in this research offer a maximum of four hours of flying time for the UAS mission; this is based on a Horizon (H-1000) Proton Exchange Membrane (PEM) stack. Full article

The purpose of this study is to reveal the characteristics of a Pd/Cu membrane and Ni/Cr catalyst adopted in a biogas dry reforming (BDR) membrane reactor by the numerical simulation procedure. The commercial software COMSOL Multiphysics ver. 6.2 was adopted in the numerical simulation. COMSOL is one type of commercial software that can solve multiphysics phenomena, i.e., chemical reaction, fluid dynamics, heat transfer, etc. The impact of the initial reaction temperature and the thickness of the Pd/Cu membrane on the performance of the BDR membrane reactor using an Ni/Cr catalyst is also investigated. The initial reaction temperatures adopted were 400 °C, 500 °C, and 600 °C, and the thicknesses of the Pd/Cu membrane were varied at 20 μm, 40 μm, and 60 μm. It was discovered that when the initial reaction temperature was raised, the molar concentration of H₂ increased while the molar concentrations of CH₄ and CO₂ decreased. Because the penetration resistance of the Pd/Cu membrane decreased with the decrease in the thickness of the Pd/Cu membrane, the molar concentrations of H₂ remaining in the Pd/Cu membrane and sweep chamber rose with the decrease in the thickness of the Pd/Cu membrane. Full article

Low-temperature Fischer–Tropsch (LTFT) synthesis converts syngas to diesel/wax at 200–250 °C. The LTFT reaction has recently received renewed interest, as it can be used for converting syngas from renewable sources (biomass and waste) to high-value fuels and chemicals. Conventional LTFT reactors, such as fixed-bed and slurry reactors, are not entirely suitable for bio-syngas conversion due to their smaller scale compared to fossil fuel-based syngas processes. This review explores advancements in intensifying LTFT reactors suitable for bio-syngas conversion, enabling smaller scale and dynamic operation. Various strategies for enhancing heat and mass transfer are discussed, including the use of microchannel reactors, structured reactors, and other designs where either one or both the heat and mass transfer are intensified. These technologies offer improved performance and economics for small LTFT units by allowing flexible operation, with increased syngas conversion and reduced risk of overheating. Additionally, this review presents our outlook and perspectives on strategies for future intensification. Full article

This study presents an integrated strategy to optimize biofuel production from Chlorella sorokiniana (CSO) and Chlorella vulgaris (CVU) by combining salt-induced stress and thermal pretreatment. The microalgae were cultivated in anaerobic digestate effluent (ADE) under stress and non-stress conditions to evaluate nutrient availability’s impact on biomass composition. Salt stress significantly enhanced lipid accumulation, with CVU exhibiting a 51.6% increase. Thermal pretreatment of biomass at 90 °C for 10 h achieved the highest methane yield (481 mL CH₄/g VS), with CVU outperforming CSO. Milder pretreatment conditions (40 °C for 4 h) were more energy-efficient for CSO, achieving a yield of 2.67%. Fatty acid profiles demonstrated species-specific biodiesel properties, with CSO rich in oleic acid (33.47%) offering enhanced oxidative stability and cold flow performance, while CVU showed a higher polyunsaturated fatty acid content. This research highlights the economic viability of using ADE as a low-cost cultivation medium and the potential for scalable thermal pretreatments. Future research should focus on reducing energy demands of pretreatment processes and exploring alternative stress induction methods to further enhance biofuel yields. These findings offer valuable insights for tailoring cultivation and processing strategies to maximize lipid and methane production, supporting sustainable and economically viable dual biofuel production systems. Full article

In this study, Kerogen conversion and oil production laboratory modeling results in Bazhenov formation source rock samples (Western Siberia, Russia) are presented. Two samples from one well with a similar composition and immature type II kerogen, which were accumulated in the same deep-sea conditions, were used for this investigation. Hydrous pyrolysis was performed under 300 °C, with liquid products and a sample portion collected every 12 h to study kerogen parameters via pyrolysis and the synthetic-oil composition via GC–MS. The transformation of pyrolytic parameters was similar to the natural trend previously determined for Bazhenov source rocks with different maturities. The synthetic oils’ normal alkane composition and biomarker parameters transformed with time. Sedimentary conditions and lithology biomarker parameters presumed to be constant (Pr/Ph, Ph/C18, H29/H30, and DBT/Phen) changed depending on the heating duration. The oil maturation increased slightly. Differences between the samples were detected in hydrocarbon generation endurance (5 and 8 days), n-alkane composition, and C27/C29 and DBT/Phen. A hypothesis about the influence of kerogen variability and mineral matrix on oil production was made. This paper provides the basis for more detailed and accurate investigation of the factors affecting kerogen cracking and hydrocarbon formation. Full article

Direct methanol fuel cells (DMFCs) typically operate in passive mode, where methanol is distributed across the membrane electrode assembly through natural diffusion. Usual methanol concentrations range from 1% to 5% by weight (wt.%), although this can vary depending on the specific configuration and application. In this work, the effect of an additional pumping system to supply the methanol has been analyzed by varying the methanol flow rate within the pump’s range. To this end, a parametric experimental study was carried out to study the influence of temperature (25–40 °C), concentration (0.15–6 wt.% methanol in water), and the flow rate of methanol (1.12–8.65 g/s) on the performance of a single mini-direct methanol fuel cell (DMFC) operating in semi-passive mode with a passive cathode and an active anode. Open circuit voltage, maximum power density, and cell efficiency were analyzed. To this purpose, open circuit voltage and current–voltage curves were measured in different experimental conditions. Results indicate that temperature is the most decisive parameter to increase DMFC performance. For all methanol concentrations and flow rates, performance improves with higher operating temperatures. However, the impact of the concentration and flow rate depends on the other parameters. The operating optimal concentration was 1% wt. At this concentration, a maximum power of 14.2 mW was achieved at 40 °C with a methanol flow of 7.6 g/s. Under these same conditions, the cell also reached its maximum efficiency of 23%. The results show that switching from passive to semi-passive mode generally increases open-circuit voltage and maximum power, thus improving fuel cell performance, likely due to the enhanced uniform distribution of the reactant in semi-passive mode. However, further increases in flow rate led to a decrease in performance, probably due to the methanol crossover effect. An optimal methanol flow rate is observed, depending on methanol flow temperature and concentration. Full article