Fuels

Current research and development to lower the production cost of biodiesel by utilizing feedstock derived from waste motivates the quest for developing catalysts with high performance in transesterification. This study investigates the performance of citric acid as a catalyst and support catalyst in transesterification of oil from black soldier fly (Hermetia illucens) larvae fed on organic kitchen waste. Two catalysts were prepared by synthesizing citric acid with NaOH and CaO by a co-precipitation and an impregnation method, respectively. The design of the experiment adopted response surface methodology for the optimization of biodiesel productivity by varying: the percentage loading weight of citric acid, the impregnation temperature, the calcinating temperature and the calcinating time. The characteristic activity and reuse of the synthesized catalysts in transesterification reactions were investigated. The morphology, chemical composition and structure of the catalysts were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray fluorescence (XRF) and X-ray diffraction (XRD). High citric acid loading on NaOH and a small amount of citric acid on CaO resulted in improved dispersion and refinement of the particle sizes. Increasing citric acid loading on NaOH improved the CaO and SiO₂ composition of the modified catalyst resulting in higher biodiesel yield compared to the modified CaO catalyst. A maximum biodiesel yield of 93.08%, ±1.31, was obtained when NaOH was synthesized with a 130% weight of citric acid at 80 °C and calcinated at 600 °C for 240 min. Comparatively, a maximum biodiesel yield of 90.35%, ±1.99, was obtained when CaO was synthesized with a 3% weight of citric acid, impregnated at 140 °C and calcinated at 900 °C for 240 min. The two modified catalysts could be recycled four times while maintaining a biodiesel yield of more than 70%. Full article

This work covers the impact of varying injector nozzle hole numbers (INHNs) and fuel injection pressures (IPs) on fuel atomization, performance, and exhaust emission characteristics of a diesel engine. The primary goal of this research was to improve fuel characteristics. Increasing INHNs and fuel IPs have a substantial impact on the blended fuel viscosity and density, which leads to increased atomization and mixing rates, as well as combustion and engine efficiency. The fuel atomization was checked by varying the INHNs with an operating diesel fuel using the ANSYS Fluent spray simulation work. The experimental test was performed on the fuel blends of waste cooking oil (WCO)–diesel blends from 10 to 30% (with an increment of 10%) by evaluating the performance and emission parameters. The fuel IPs were altered on four, such as 190, 200 (default), 210, and 220 bar with a modification of INHN of 1 (default), 3, and 4), each 0.84, 0.33, and 0.25 mm in orifice size, respectively. The simulation result shows that the INHN-4 has better fuel atomization. Whereas the experimental test revealed that the increment in blending ratio of WCO was up to 30%, INHNs and fuel IPs enhanced the BSFC and BTE and reduced exhaust emissions. The results indicate that increasing the fuel IP up to 210 bar with a 4-hole INHN for B30 was the optimal combination for the overall enhancement of BSFC and BTE, as well as lower CO and HC emissions with a minor rise in NO_x when compared to the baseline diesel. Full article

This study presents design considerations and an evaluation of a full-scale process chain for methanol and advanced drop-in fuel production derived from lignite/solid recovered fuel (SRF) feedstock. The plant concept consists of a high-temperature Winkler (HTW) gasifier coupled with an air separation unit (ASU), which provides a high-purity (99.55%) gasification oxidant agent. The concept includes the commercially proven acid gas removal (AGR) system based on cold methanol (e.g., Rectisol^® process) for the removal of BTX and naphthalene components. With the involvement of Rectisol^®, an almost pure CO₂ off-gas stream is generated that can be further stored or utilized (CCS/CCU), and a smaller CO₂ stream containing H₂S is recovered and subsequently driven to the sulfur recovery unit (e.g., Claus process). One of the potential uses of methanol is considered, and a methanol upgrading unit is implemented. The overall integrated process model was developed in the commercial software Aspen Plus^TM. Simulations for different feedstock ratios were investigated, ensuring the concept’s adaptability in each case without major changes. A number of parametric studies were performed concerning (a) the oxygen purity and (b) the reformer type, and a comparison against alternative methanol production routes was conducted. Simulations show that the proposed system is able to retain the cold gas efficiency (CGE) in the range of 79–81.1% and the energetic fuel efficiency (EFE) at around 51%. An efficient conversion of approximately 99.5% of the carbon that enters the gasifiers is accomplished, with around 45% of carbon being captured in the form of pure CO₂. Finally, the metrics of EFE and total C for the conversion of methanol to liquid fuels were 40.7% and 32%, respectively, revealing that the proposed pathway is an effective alternative for methanol valorization. Full article

Several cellulose-hydrolysis enzymes are required for eco-friendly utilization of cellulose as renewable biomass, and it would therefore be beneficial if fermenting microbes can provide such enzymes without genetic engineering. Thermotolerant and multisugar-fermenting Kluyveromyces marxianus is one of the promising yeasts for high-temperature fermentation and has genes for putative oligosaccharide-degradation enzymes. Mutants obtained after multiple mutagenesis showed significantly higher activity than that of the parental strain for cellobiose fermentation. The efficient strains were found to have amino acid substitutions and frame-shift mutations in 26-28 genes including 3 genes for glucose transporters. These strains grown in a cellobiose medium showed higher β-glucosidase than that of the parental strain and greatly reduced glucose utilization. The introduction of KTH2 for a glucose transporter into one of the efficient mutants reduced the cellobiose fermentation activity of the mutant. The results suggest that release from glucose repression significantly promotes the uptake of cellobiose. Co-culture of one efficient strain and the parental strain allowed good fermentation of both glucose and cellobiose, suggesting that the efficient strains are useful for conversion of cellulosic biomass to ethanol. Full article

Research Octane Number (RON) is one of the primary indicators for the determination of the resistance of gasoline fuels to autoignition. This parameter is usually determined with a test procedure involving a standardized engine that requires expensive hardware and time-consuming tests. In this work, a set of different methods with which to determine the RON of gasoline fuel surrogates is presented, considering only computer simulations, which allows to reduce both cost and time for the evaluation. A palette of 11 chemical species has been chosen as the basis for the surrogates’ database, which will be investigated in the work, allowing the representation of the complex chemical formulation of fuels in an easier way. A simplified zero-dimensional engine model of the standard variable compression ratio is used to provide pressure and temperature, then employed to calculate RON. This is done first by means of existing methods, and then by introducing new processes concerning a simplified chemical reactor built on kinetic schemes. Finally, these different methodologies are tested against a molar weighted sum of RONs of each chemical specie, allowing to have a criterion for comparison and evaluating their real prediction capabilities. Full article

Bioethanol has great potential to reduce emissions from transportation while improving energy security and developing the economy. Bioethanol has a higher octane-number and a higher enthalpy of vaporisation than gasoline (resulting in charge cooling)—properties that have been used to extend knocking limits. Therefore, bioethanol can be used to substitute gasoline in automotive engine applications. The characteristics of bioethanol spray, such as hydrous bioethanol fuel which consists of 93% bioethanol and 7% water, were investigated under various temperature conditions from sub-zero (−15 °C) to room temperature (17 °C) by means of high-speed direct photography and laser Mie scattering techniques without any seeding materials. The experimental results show that the spray patterns are not significantly changed. In the case of the sub-zero temperature condition, the spray tip penetration decreases while the spray angle keeps almost constant once the spray becomes fully developed. The results show that scaling of the spray tip penetration rate achieves a reasonable collapse of the experimental results. The normalised droplet diameter was also obtained and shows that larger droplets are formed at the sub-zero temperature condition. Full article

The expansion of the research on nanoscale particles demonstrates several advantages in terms of stability and an increased surface area to volume ratio compared to micron-sized particles. Based on this, the present work explores the addition of aluminum particles in hydrotreated vegetable oil (HVO), an alternative jet fuel. To evaluate the influence of particle sizes, nano and micron particles (40 nm and 5 μm) in a particle concentration of 0.5 wt.% were stably suspended in HVO. This study evaluates droplet combustion with an initial diameter of 250 μm in a drop tube furnace under different furnace temperatures (600, 800, 1000 °C). A high magnification lens coupled with a high-speed camera provides qualitative and quantitative data regarding droplet size evolution and micro-explosions. Pure HVO and Jet A-1 were also tested for comparison purposes. The results reveal that the addition of aluminum particles enhances the alternative jet fuel combustion. Furthermore, decreasing the particle size and increasing the furnace temperature enhances the burning rate compared to the pure HVO. Pure HVO presents a burning rate nearly to 1.75 mm²/s until t/D${}_0^2$ = 0.35 s/mm² at T = 1000 °C. When nanoparticles are added to HVO in a particle concentration of 0.5 wt.%, an improvement of 24% in burning rate is noticed. Conventional jet fuel and pure HVO do not present any disruptive burning phenomena. However, when aluminum particles were added to HVO, micro-explosions were detected at the end of droplet lifetime, regardless of the particle size. Full article

There is a growing interest in finding a suitable catalyst for the adsorption and activation of CO₂ molecules to minimize the effect of global warming. In this study, density functional theory-based simulations are employed to examine the adsorption and activation of a CO₂ molecule on the pure, Ti-supported and Ti-doped surfaces of C₆₀. The adsorption on the pure surface is very week. Adsorption becomes significant on the Ti-supported C₆₀ surface together with significant activation. Such strong adsorption is evidenced by the significant charge transfer between Ti and C₆₀. The Ti-doped C₆₀ surface adsorbs weakly, but the activation is not significant. Full article

In this study, wood sawdust as waste residue from wood processing mills was pretreated using torrefaction to improve fuel properties and densified to facilitate transportation. Sawdust was torrefied in a fixed bed reactor using inside temperatures (IT) of 230, 260 and 290 °C for 15, 30 and 45 min, residence time. Due to the low calorific value of the treatments, the outside temperature (OT) of the fixed bed reactor was used instead for a fixed duration of 45 min, which resulted in an increase in energy value by 40% for the most severe conditions. The mechanical strength of the pellets was enhanced by adding 20% binder (steam-treated spruce sawdust) to biochar, which improved the pellet tensile strength by 50%. Liquid by-products from the torrefaction process contained furfural and acetic acid, which can be separated for commercial uses. Thermochemical analysis showed better fuel properties of OT torrefied samples such as high fixed carbon (52%), low volatiles (41%) and lower oxygen contents (27%) compared to IT torrefied samples (18, 77 and 43%, respectively). Low moisture uptake of torrefied pellets compared to raw pellets, along with other attributes such as renewability, make them competent substitutes to fossil-based energy carriers such as coal. Full article

The present work aims to assess the influence of the composition of blends of hydrogen (H₂) and Natural Gas (NG) on Dual Fuel (DF) combustion characteristics, including gaseous emissions. The 3D-CFD study is carried out by means of a customized version of the KIVA-3V code. An automotive 2.8 L, 4-cylinder turbocharged diesel engine was previously modified in order to operate in DF NG–diesel mode, and tested at the dynamometer bench. After validation against experimental results, the numerical model is applied to perform a set of combustion simulations at 3000 rpm–BMEP = 8 bar, in DF H₂/NG-diesel mode. Different H₂–NG blends are considered: as the H₂ mole fraction varies from 0 vol% to 50 vol%, the fuel energy within the premixed charge is kept constant. The influence of the diesel Start Of Injection (SOI) is also investigated. Simulation results demonstrate that H₂ enrichment accelerates the combustion process and promotes its completion, strongly decreasing UHC and CO emissions. Evidently, CO₂ specific emissions are also reduced (up to about 20%, at 50 vol% of H₂). The main drawbacks of the faster combustion include an increase of in-cylinder peak pressure and pressure rate rise, and of NO_x emissions. However, the study demonstrates that the optimization of diesel SOI can eliminate all aforementioned shortcomings. Full article

The embedded immobilized enzymes (Rhizopus-oryzae) on the magnetic nanoparticles (Fe₃O₄-NPs) is a new application for the sustainable production of high-quality biodiesel. In this study, biodiesel is derived from Kapok oil via ultrasonication (US)-assisted catalytic transesterification method. A novel attempt is made to prepare magnetic nanoparticles embedded by an immobilized enzyme to solve the problem of enzyme denaturation. This innovative method resulted in optimum biodiesel conversion of 89 ± 1.17% under reactant molar ratio (methanol: oil) of 6:1, catalyst loading 10 wt% with a reaction time of 4 h at 60 °C. The kinetic and thermal study reveals that conversion of Kapok oil to biodiesel follows a pseudo first-order reaction kinetic with a lower ΔE of 30.79 kJ mol⁻¹. The ΔH was found to be 28.06 kJ mol⁻¹ with a corresponding ΔS of −237.12 J mol⁻¹ K⁻¹ for Fatty Acid Methyl Ester formation. The ΔG was calculated to be from 102.28 to 109.40 kJ mol⁻¹ for temperature from 313 K to 343 K. The positive value of ΔH and ΔG is an indication of endothermic and non-spontaneous reaction. A negative ΔS indicates the reactant in the transition state possesses a higher degree of ordered geometry than in its ground state. The immobilized catalysts provided great advantages towards product separation and efficient biodiesel production. Highlights: 1. Effective catalytic transesterification assisted by the ultrasonication method was used for bi-odiesel production. 2. Magnetite nanoparticles synthesized by the co-precipitation method were used as heteroge-neous catalysts. 3. An immobilized enzyme (Rhizopus-oryzae) was embedded in the heterogeneous catalyst, as it is reusable and cost-effective. 4. The maximum biodiesel yield obtained from Kapok oil was 93 ± 1.04% by catalytic trans-esterification reactions. Full article

The use of renewable biodiesel fuel in diesel engines can reduce the demand for depleting fossil fuels and reduce harmful emissions to the environment. In this research, an engine simulation is conducted using ANSYS Forte software, which allows for visualization of the spray inside the combustion chamber. The results show that biodiesel has higher liquid and vapor penetration lengths, higher droplet mass and diameter, and a longer breakup length. Molecular images of fuel molecules show that the temperature of biodiesel molecules is 141 °C lower than diesel molecules at 709 degree crank angle (°CA). These characteristics result in an extended evaporation time for biodiesel, consequently leading to poorer performance. Additionally, increased penetration length can lead to carbon deposits inside the combustion chamber. Therefore, such inefficiencies of biodiesel spray properties lead to lower combustive performance than diesel. In terms of performance, on average, biodiesel produces 16.9% lower power and 19.9% higher brake specific fuel consumption. On average, the emissions of CO, CO₂, and HC of biodiesel are 17.8%, 3.41%, and 23.5% lower and NOx is 14.39% higher than the corresponding values obtained for pure diesel, respectively. In-cylinder combustion analyses show that the peak pressure of biodiesel is 0.5 MPa lower, the peak cycle temperature is 36 °C lower, the ignition delay is 4 °CA longer, the peak heat release rate is 16.5 J/deg. higher, and the combustion duration is 5.96 °CA longer compared to diesel combustion. Full article

Asphaltenes are the heavy fraction of fossil fuels, whose characterization remains a very difficult and challenging issue due to the still-persisting uncertainties about their structure and/or composition and molecular weight. Asphaltene components are highly condensed aromatic molecules having some heteroatoms and aliphatic functionalities. Their molecular weights distribution spans in a wide range, from hundreds to millions of mass units, depending on the diagnostic used, which is mainly due to the occurrence of self-aggregation. In the present work, mass spectrometry along with size exclusion chromatography and X-ray diffraction analysis have been applied to asphaltenes for giving some further insights into their molecular weight distribution and structural characteristics. Relatively small polycyclic aromatic hydrocarbons (PAHs) with a significant degree of aliphaticity were individuated by applying fast Fourier transform (FFT) and double bond equivalent (DBE) number analysis to the mass spectra. X-ray diffraction (XRD) confirmed some aliphaticity, showing peaks specific of aliphatic functionalities. Size exclusion chromatography indicated higher molecular weight, probably due to the aliphatic substituents. Mass spectrometry at high laser power enabled observing a downward shift of molecular masses corresponding to the loss of about 10 carbon atoms, suggesting the occurrence of aryl-linked core structures assumed to feature asphaltenes along with island and archipelago structures. Full article

Surrogate fuels are composed of a few pure components, mixed together in order to imitate a real fuel’s characteristics regarding its combustion and emission. In this study, four surrogate feeds were synthesized, corresponding to petroleum middle distillates. The desulfurization of the surrogate blends was performed using the hydrogen peroxide–acetic acid oxidative system. Consequently, extractive desulfurization was carried out using imidazolium-based ionic liquids, namely 1-butyl-3-methylimidazolium bromide [BMIM][Br] and 1-butyl-3-methylimidazolium hydrogen sulfate [BMIM][HSO₄], in a multiple extraction cycle procedure. Both ionic liquids were synthesized and characterized with spectroscopic techniques. The influence of the extraction temperature process was studied. In each extraction cycle, the sulfur concentration and the physical properties of the surrogate extraction products were estimated. The used ionic liquids were regenerated with a reasonably effective method. The synthesized and recycled ionic liquids showed high desulfurization efficiency, while [BMIM][Br] prevailed. Additionally, extractive desulfurization in oxidized surrogate LCO using ionic liquids is comparable with that using acetonitrile, since it has an advantage in terms of mass yield. Full article

Catalytic tests to assess the performance of mixed perovskite-type oxides (La_0.9Ca_0.1FeO_3-δ, La_0.6Ca_0.4FeO_3-δ, Nd_0.9Ca_0.1FeO_3-δ, Nd_0.6Ca_0.4FeO_3-δ, Nd_0.6Ca_0.4Fe_0.9Co_0.1O_3-δ, Nd_0.6Ca_0.4Fe_0.97Ni_0.03O_3-δ, and LSF) with respect to CO oxidation are presented as well as characterization of the materials by XRD and SEM. Perovskites are a highly versatile class of materials due to their flexible composition and their ability to incorporate dopants easily. CO oxidation is a widely used “probe reaction” for heterogeneous catalysts. In this study, it is demonstrated how tuning the composition of the catalyst material (choice of A-site cation, A-site and B-site doping) greatly influences the activity. Changing the A-site cation to Nd³⁺ or increasing the concentration of Ca²⁺ as A-site dopant improves the performance of the catalyst. Additional B-site doping (e.g., Co) affects the performance as well—in the case of Co-doping by shifting ignition temperature to lower temperatures. Thus, perovskites offer an interesting approach to intelligent catalyst design and tuning the specific properties towards desired applications. Full article

Due to the popularity of diesel engines, utilization of fossil fuel has increased. However, fossil fuel resources are depleting and their prices are increasing day by day. Additionally, the emissions from the burning of petroleum-derived fuel is harming the global environment. This work covers the performance and emission parameters of a biogas-diesel dual-fuel mode diesel engine and compared them to baseline diesel. The experiment was conducted on a single-cylinder and four-stroke DI diesel engine with a maximum power output of 2.2 kW by varying engine load at a constant speed of 1500 RPM. The diesel was injected as factory setup, whereas biogas mixes with air and then delivered to the combustion chamber through intake manifold at various flow rates of 2, 4, and 6 L/min. At 2 L/min flow rate of biogas, the results were found to have better performance and lower emission, than that of the other flow; with an average reduction in BTE, HC, and NOx by 11.19, 0.52, and 19.91%, respectively, and an average increment in BSFC, CO, and CO₂ by 11.81, 1.05, and 12.8%, respectively, as compared to diesel. The diesel replacement ratio was varied from 19.56 to 7.61% at zero engine load and 80% engine load with biogas energy share of 39.6 and 16.59%, respectively. Full article

Modern gas turbines use combustion chemistry during the design phase to optimize their efficiency and reduce emissions of regulated pollutants such as NOx. The detailed understanding of the interactions during NOx and natural gas during combustion is therefore necessary for this optimization step. To better assess such interactions, NO₂ was used as a sole oxidant during the oxidation of CH₄ and C₂H₆ (the main components of natural gas) in a shock tube. The evolution of the CO mole fraction was followed by laser-absorption spectroscopy from dilute mixtures at around 1.2 atm. The experimental CO profiles were compared to several modern detailed kinetics mechanisms from the literature: models tuned to characterize NOx-hydrocarbons interactions, base-chemistry models (C0–C4) that contain a NOx sub-mechanism, and a nitromethane model. The comparison between the models and the experimental profiles showed that most modern NOx-hydrocarbon detailed kinetics mechanisms are not very accurate, while the base chemistry models were lacking accuracy overall as well. The nitromethane model and one hydrocarbon/NOx model were in relatively good agreement with the data over the entire range of conditions investigated, although there is still room for improvement. The numerical analysis of the results showed that while the models considered predict the same reaction pathways from the fuels to CO, they can be very inconsistent in the selection of the reaction rate coefficients. This variation is especially true for ethane, for which a larger disagreement with the data was generally observed. Full article

This review considers the selective studies on environmentally friendly, combustion-free, allothermal, atmospheric-pressure, noncatalytic, direct H₂O/CO₂ gasification of organic feedstocks like biomass, sewage sludge wastes (SSW) and municipal solid wastes (MSW) to demonstrate the pros and cons of the approaches and provide future perspectives. The environmental friendliness of H₂O/CO₂ gasification is well known as it is accompanied by considerably less harmful emissions into the environment as compared to O₂/air gasification. Comparative analysis of the various gasification technologies includes low-temperature H₂O/CO₂ gasification at temperatures up to 1000 °C, high-temperature plasma- and solar-assisted H₂O/CO₂ gasification at temperatures above 1200 °C, and an innovative gasification technology applying ultra-superheated steam (USS) with temperatures above 2000 °C obtained by pulsed or continuous gaseous detonations. Analysis shows that in terms of such characteristics as the carbon conversion efficiency (CCE), tar and char content, and the content of harmful by-products the plasma and detonation USS gasification technologies are most promising. However, as compared with plasma gasification, detonation USS gasification does not need enormous electric power with unnecessary and energy-consuming gas–plasma transition. Full article