Search Results (67)

Sustainable aviation fuels (SAFs) are vitally important for aviation decarbonization. The laminar burning velocity (LBV), a key parameter reflecting the combustion behavior of fuel/oxidizer mixtures, serves as a fundamental metric for evaluating SAF performance. This paper systematically reviews and evaluates the LBV experiment method and the performance of traditional aviation fuel, SAFs produced via different pathways, and individual components (n-alkanes, iso-alkanes, cycloalkanes, and aromatic hydrocarbons, as well as the impacts of isomers and homologues) in aviation fuels. It is found that LBV values of different SAFs exhibit significant fluctuations, approaching or slightly deviating from those of conventional aviation fuels. Carbon number, branching degree, substituent types, and testing methods in the components all affect LBV performance. Specifically, increased branching in iso-alkanes reduces LBV, cyclohexane and benzene show higher LBV than their methylated counterparts (methylcyclohexane and toluene), and n-alkylcyclohexanes/benzenes with short (C1–C3) side chains demonstrate minimal LBV variation. Spherical flame methods yield more consistent (and generally lower) LBV values than stagnation flame techniques. These findings provide insights for optimizing SAF–conventional fuel blends and enhancing drop-in compatibility while ensuring operational safety and usability. Full article

White mulberry (Morus alba L.) is a tree growing up to 15 m in height. It is a plant whose cultivation is historically associated with silk production. Mulberry leaves are the only food source of the mulberry silkworm caterpillars (Bombyx mori L.). The cultivation of this tree has recently gained renewed importance. Due to the content of numerous bioactive substances, mulberry is a valuable raw material for the food, pharmaceutical and herbal industries. This article presents the results of tests on pellets from 1-, 3- and 5-year-old branches, which are waste biomass remaining after pruning mulberry shrubs cultivated to obtain leaves to feed silkworms. Additionally, analyses of pellets from mulberry leaves were also carried out. For the specified mulberry biomass yield, analyses of chemical composition of mulberry biomass (branches and leaves) were carried out, and energy properties (heat of combustion and calorific value) and energy potential were calculated. The heat of combustion of pellet from mulberry branches was, on average, 19,266 MJ∙Mg⁻¹, and the calorific value was 17,726 MJ∙Mg⁻¹. The energy potential, on the other hand, was, on average, 159 GJ∙ha⁻¹ and 44 MWh∙ha⁻¹. The obtained results indicate the possibility of the effective use of mulberry branches after the annual pruning of bushes in plantations for energy purposes. Full article

This study examines the variations of elements in PM_2.5 emitted from biomass burning in urban settings, which raises health concerns among urban dwellers. It specifically focused on how Sodium (Na), Calcium (Ca), Potassium (K), and Phosphorus (P) concentrations in tree combustibles affect their concentrations in PM_2.5 emitted during combustion. Understanding these interactions is critical for evaluating air quality and its public health effects. Urban landscape coniferous and broad-leaf tree species combustibles (branches and leaves) were assessed, and the data were processed using Microsoft Excel, Origin Pro 2024, and R Studio. It was discovered that the species and organs had a common elemental concentration pattern (Ca > K > P > Na) in their combustibles but a different concentration pattern in the emitted PM_2.5. Quantitatively, the concentrations in the combustibles varied, with Ca being the most abundant (69.85 mg/kg) and P the least (3.97 mg/kg). In PM_2.5, the contrary was observed, i.e., Na (which was among the least concentrated elements in the combustibles) became prominent; the highest levels were recorded in PM_2.5 from conifers (Na = 0.86 mg/kg). Among the assessed elements in PM_2.5, P had the lowest concentration in all the tests, having the lowest values from broad-leaf species (P = 0.02 mg/kg). The SEM result further revealed that, quantitatively, the concentration of these elements in the combustibles does not necessarily mean that they will be in higher concentrations in the emitted PM_2.5. These variations highlighted the importance of considering tree species, organ types, and elemental interactions when assessing the impacts of biomass combustion on urban air quality and human health. Full article

The current paradigm of low-T combustion and autoignition of hydrocarbons is based on the sequential two-step oxygenation of fuel radicals. The key chain-branching occurs when the second oxygenation adduct (OOQOOH) is isomerized releasing an OH radical and a key ketohydroperoxide (KHP) intermediate. The subsequent homolytic dissociation of relatively weak O–O bonds in KHP generates two more radicals in the oxidation chain leading to ignition. Based on the recently introduced intramolecular “catalytic hydrogen atom transfer” mechanism (J. Phys. Chem. 2024, 128, 2169), abbreviated here as I-CHAT, we have identified a novel unimolecular decomposition channel for KHPs to form their classical isomers—enol hydroperoxides (EHP). The uncertainty in the contribution of enols is typically due to the high computed barriers for conventional (“direct”) keto–enol tautomerization. Remarkably, the I-CHAT dramatically reduces such barriers. The novel mechanism can be regarded as an intramolecular version of the intermolecular relay transfer of H-atoms mediated by an external molecule following the general classification of such processes (Catal. Rev.-Sci. Eng. 2014, 56, 403). Here, we present a detailed mechanistic and kinetic analysis of the I-CHAT-facilitated pathways applied to n-hexane, n-heptane, and n-pentane models as prototype molecules for gasoline, diesel, and hybrid rocket fuels. We particularly examined the formation kinetics and subsequent dissociation of the γ-enol-hydroperoxide isomer of the most abundant pentane-derived isomer γ-C5-KHP observed experimentally. To gain molecular-level insight into the I-CHAT catalysis, we have also explored the role of the internal catalyst moieties using truncated models. All applied models demonstrated a significant reduction in the isomerization barriers, primarily due to the decreased ring strain in transition states. In addition, the longer-range and sequential H-migration processes were also identified and illustrated via a combined double keto–enol conversion of heptane-2,6-diketo-4-hydroperoxide as a potential chain-branching model. To assess the possible impact of the I-CHAT channels on global fuel combustion characteristics, we performed a detailed kinetic analysis of the isomerization and decomposition of γ-C5-KHP comparing I-CHAT with key alternative reactions—direct dissociation and Korcek channels. Calculated rate parameters were implemented into a modified version of the n-pentane kinetic model developed earlier using RMG automated model generation tools (ACS Omega, 2023, 8, 4908). Simulations of ignition delay times revealed the significant effect of the new pathways, suggesting an important role of the I-CHAT pathways in the low-T combustion of large alkanes. Full article

The process of normal (N) zone propagation in three superconducting YBaCuO thin films with different Pearl length values was theoretically studied. The point appearance of the N zone was found to result from powerful energy release caused by micro-sized magnetic cumulation. Solutions of the heat equation for hot electrons, diffusing to ~15 nm depth into the edge of the Pearl length, were obtained for the two length cases. The hot electron thermalization induced a transition to N state at the aforementioned depth due to fast exceeding of T_c, followed by flash high temperature growth. In the third case, we considered a process of crack branching when the superconducting current concentrated at the tips, followed by the transition to N state caused by exceeding j_c. The superfast reaction of the superconductor allowed it to restore the energy loss at the Pearl length in all cases. This explains the step propagation process of the N zone with velocities up to 2.7 × 10³ and 1.1 × 10³ m/s in the first and second cases. In the third, the propagation can reach the detonation wave velocity of about 1 × 10⁴ m/s. It is concluded that the process of the N zone propagation has the character of a combustion wave. Full article

As a result of the energy crisis due, among other things, to climate change, most developed countries have taken steps with the main aim—among other things—of increasing the use of green energy sources that do not rely on fuels (including primarily liquid fuels) but use renewable energies. Plant biomass is a versatile substrate that can be used in many areas of the economy and production, but also for the production of various types of fuel. These range from rapeseed oil used as a component of biodiesel or maize starch for ethanol production to typically cellulosic plants such as energy willow, which can be used for direct combustion. The floodplain is home to this type of vegetation. It is characterized by great diversity in terms of geometric dimensions and mechanical and morphological properties. In addition, the location (easy access to water and sunlight) influences its potential energy value. Vegetation, thanks to favorable conditions, can achieve large weight gains in a relatively short period of time. Therefore, its properties should be carefully recognized in order to make more efficient use of energy and operating equipment used during harvesting. This paper presents an analysis of the changes in the elasticity of willow branches over a period of 16 days following harvesting. The changes were analyzed for branches taken from three different shrubs at three different plant height levels during the post-growth period. Based on the measurements carried out, the elastic modulus E of the shoots was estimated. The average modulus of elasticity ranged from about 4500 two days after cutting to about 5500 MPa 16 days after cutting and showed high variability, reaching even CV = 37%, both within a given shrub and depending on the measurement date. The results presented here indicate a high natural variability of mechanical parameters even within the same plant. Full article

The combustion of renewable solid fuels, such as biomass, is a reliable option for heat and power production. The availability of biomass resources within urban areas, such as tree leaves, small branches, grass, and other green city waste, creates an opportunity to valorize such resources. The energy densification of such resources using hydrothermal carbonization (HTC) and pelletization of the carbonized material could create a new generation of domestic boiler biofuel. However, combustion efficiency and emission assessments should be carried out for HTC pellets. The primary objective of this study is to assess HTC pellets, provided by a waste upgrade company, in terms of kinetics, combustion efficiency, and emissions, taking as reference base ENplus A1 certified softwood pellets. Therefore, thermogravimetric analysis and combustion tests were conducted for both fuels to achieve this. It was observed that a third peak of the burning rate during the solid carbon oxidation of HTC pellets indicated a high activation energy. Combustion tests showed a 7% increase in boiler efficiency for HTC pellets compared to softwood pellets. However, higher particulate matter (PM), NO_x, and CO emissions were recorded during the HTC pellets test. The results suggest that optimizing the air/fuel ratio could further improve the performance of HTC pellets in domestic boilers. Full article

Ensuring firefighter safety during oil tank fires is paramount, given the substantial risks posed by thermal radiation. This study employs both the Fire Dynamics Simulator (FDS) and Areal Locations of Hazardous Atmospheres (ALOHA) software to simulate a severe oil tank fire scenario at the Zhushan Branch Power Plant, where two heavy oil tanks and multiple light oil tanks are located. The simulation framework divides the combustion scenario into 22.4 million grids with a grid size of 0.5 m, allowing a fine-resolution assessment of thermal radiation. Assuming a worst-case scenario involving n-Heptane combustion, the FDS simulation calculates essential parameters, including temperature, velocity, and soot distribution fields, and suggests a minimum safe firefighting distance of 22 m (equivalent to one tank diameter, 1D) for those equipped with personal protective equipment when exposed to a 5 kW/m² heat flux. Meanwhile, ALOHA modeling extends the safety assessment, recommending a downwind safety distance of 62 m (approximately 2D) to establish a preliminary exclusion zone, crucial in early emergency response when data may be incomplete. Additionally, a grid sensitivity analysis was conducted to validate the accuracy of the numerical results. This study underscores the importance of coupling FDS and ALOHA outputs to develop a balanced, adaptive approach to firefighter safety, optimizing response protocols for high-risk environments. The results provide essential guidance for establishing safety zones, advancing standards within fire protection and emergency response, and supporting strategy development for large-scale oil and petrochemical storage facilities. Full article

The transformation path to electric mobility will have fundamental impacts on the existing value chain and employment structures in the automotive industry. The purpose of this paper is to derive and examine these effects based on two different electric mobility market scenarios for the European (EU27) passenger car as well as truck market 2040 with special focus on the highly export-oriented industrial automotive cluster in Baden-Wuerttemberg. To achieve this, both a moderate and a progressive market scenario were simulated using the scientifically validated DLR VECTOR21 vehicle technology scenario model, based on two different parameter sets derived from actual and possible framework conditions on the European car and truck markets. Based on a detailed analysis of the industrial branch, value creation, and employee structure in Baden-Wuerttemberg and its automotive cluster, the effects resulting from the transformation to electric mobility will be displayed. With detailed Fade-In and Fade-Out analysis, the shifts from internal combustion engine components to electrified components will be derived and illustrated for each employee segment in the automotive cluster in Baden-Wuerttemberg, which leads to completely new and original results at this level of detail. Furthermore, the detailed display of the automotive cluster in this study allows for regionalized statements on employment effects, considering, for the first time, not only the car but also the truck segment. The analysis shows that battery electric vehicles will achieve a share of 34% or 57% for new registrations on the German car market in 2030, depending on the scenario framework conditions. The resulting employment effects for the entire automotive cluster in Baden-Wuerttemberg reach −37,000 (−8%) or −66,000 (−14%) by 2030 with further negative development until 2040 (−155,000, −30%) for the respective scenarios. Employment segments, in particular powertrain-dependent production employees, are at risk, with a potential decline of up to −60%. R&D employees could be also be significantly, affected with a reduction in workforce of about −50%. Full article

The intramolecular H-migration reaction of R^IOR^IIOO· radicals constitute a key class of reactions in the low-temperature combustion mechanism of ethers. Despite this, there is a dearth of direct computations regarding the potential energy surface and rate constants specific to ethers, especially when considering large molecular systems and intricate branched-chain structures. Furthermore, combustion kinetic models for large molecular ethers generally utilize rate constants derived from those of structurally similar alcohols or alkane fuels. Consequently, chemical kinetic studies involve the calculation of energy barriers and rate rules for the intramolecular H-migration reaction class of R^IOR^IIOO· radicals, which are systematically conducted using the isodesmic reaction method (IRM). The geometries of the species participating in these reactions are optimized, and frequency calculations are executed using the M06–X method in tandem with the 6–31+G(d,p) basis set by the Gaussian 16 program. Moreover, the M06–2X/6–31+G(d,p) method acts as the low-level ab initio method, while the CBS–QB3 method is utilized as the high-level ab initio method for calculating single-point energies. Rate constants at the high-pressure-limit are computed based on the reaction class transition state theory (RC-TST) by ChemRate program, incorporating asymmetric Eckart tunneling corrections for intramolecular H-migration reactions across a temperature range of 500 to 2000 K. It was found that the isodesmic reaction method gives accurate energy barriers and rate constants, and the rate constants of the H-migration reaction for R^IOR^IIOO· radicals diverge from those of comparable reactions in alkanes and alcohol fuels. There are significant disparities in energy barriers and rate constants across the entire reaction classes of the H-migration reaction for R^IOR^IIOO· radicals, necessitating the subdivision of the H-migration reaction into subclasses. Rate rules are established by averaging the rate constants of representative reactions for each subclass, which is pivotal for the advancement of accurate low-temperature combustion reaction mechanisms for ethers. Full article

(1) Background: In recent years, forest fires have become increasingly frequent both domestically and internationally. The pollutants emitted from the burning of fuel have exerted considerable environmental stress. To investigate the influence of forest fires on the atmospheric environment, it is crucial to analyze the variations in PM_2.5 emissions from various forest fuels under differing fire conditions. This assessment is essential for evaluating the effects on both the atmospheric environment and human health. (2) Methods: Indoor simulated combustion experiments were conducted on the branches, leaves, and bark of typical tree species in the Liangshui National Natural Reserve, including Pinus koraiensis (PK), Larix gmelinii (LG), Picea koraiensis (PAK), Betula platyphylla (BP), Fraxinus mandshurica (FM), and Populus davidiana (PD). The PM_2.5 concentrations emitted by six tree species under various combustion states were measured and analyzed, reflecting the impact of moisture content on the emission of pollutants from fuel combustion, as indicated by the emission factors for pollutants. (3) Results: Under different fuel loading and moisture content conditions, the mass concentration values of PM_2.5 emitted from the combustion of different organs of various tree species exhibit variability. (4) Conclusions: Among the various tree species, broad-leaved varieties release a greater quantity of PM_2.5 compared to coniferous ones. A positive correlation exists between the moisture content of the fuel and the concentration of PM_2.5; changes in moisture content notably influence PM_2.5 levels. The emission of PM_2.5 from fuel with varying loads increases exponentially. Utilizing the Response Surface Methodology (RSM) model for simulation, it was determined that both moisture content and fuel load exert a significant combined effect on the release of PM_2.5 during combustion. Full article

A small-scale (up to 5 kWe) biogas-solid oxide fuel cell (SOFC) energy system is an envisioned system, which can be used to meet both electrical and thermal energy demand of off-grid settlements. SOFC systems are reported to be more efficient than alternatives like internal combustion engines (ICE). In addition to energy recovery, implementation of biogas-SOFC systems can enhance sanitation among these settlements. However, the capital investment costs and the operation and maintenance costs of a biogas-SOFC energy system are currently higher than the existing alternatives. From previous works, H₂S removal by biochar was proposed as a potential local cost-effective alternative. This research demonstrates the techno-economic potential of locally produced biochars made from cow manure, jackfruit leaves, and jack fruit branches in rural Uganda for purifying the biogas prior to SOFC use. Results revealed that the use of biochar from cow manure and jack fruit leaves can reduce H₂S to below the desired 1 ppm and substitute alternative biogas treatments like activated carbon. These experimental results were then translated to demonstrate how this biochar would improve the economic feasibility for the implementation of biogas-SOFC systems. It is likely that the operation and maintenance cost of a biogas-SOFC energy system can in the long run be reduced by over 80%. Also, the use of internal reforming as opposed to external reforming can greatly reduce the system capital cost by over 25% and hence further increase the chances of system economic feasibility. By applying the proposed cost reduction strategies coupled with subsidies such as tax reduction or exemption, the biogas-SOFC energy system could become economically competitive with the already existing technologies for off-grid electricity generation, like solar photovoltaic systems. Full article

Current global challenges associated with energy security and climate emergency, caused by the combustion of fossil fuels (e.g., jet fuel and diesel), necessitate the accelerated development and deployment of sustainable fuels derived from renewable biomass-based chemical feedstocks. This study focuses on the production of long-chain (straight and branched) ketones by direct α-alkylation of short chain ketones using both homogenous and solid base catalysts in water. Thus, produced long-chain ketones are fuel precursors and can subsequently be hydrogenated to long-chain alkanes suitable for blending in aviation and liquid transportation fuels. Herein, we report a thorough investigation of the catalytic activity of Pd in combination with, (i) homogenous and solid base additives; (ii) screening of different supports using NaOH as a base additive, and (iii) a comparative study of the Ni and Pd metals supported on layered double oxides (LDOs) in α-alkylation of 2-butanone with 1-propanol as an exemplar process. Among these systems, 5%Pd/BaSO₄ with NaOH as a base showed the best results, giving 94% 2-butanone conversion and 84% selectivity to alkylated ketones. These results demonstrated that both metal and base sites are necessary for the selective conversion of 2-butanone to alkylated ketones. Additionally, amongst the solid base additives, Pd/C with 5% Ba/hydrotalcite showed the best result with 51% 2-butanone conversion and 36% selectivity to the alkylated ketones. Further, the screening of heterogenous acid-base catalysts 2.5%Ni/Ba_1.2Mg₃Al₁ exhibited an adequate catalytic activity (21%) and ketone selectivity (47%). Full article

The disorder and disaster evolution characteristics of ascensional airflow fires in mine ventilation systems has been the focus of mine fire research. In this work, through repeated experiments, the variation characteristics of the temperature and air volume in the main and side branches of an ascensional airflow fire were obtained under different ventilation capacities. Using the TF1M(3D) software to solve the problems of mine physical ventilation and combined with the analysis of an example, the variation in the ascensional airflow fire and the process of disordered airflow in the ventilation system in an entire area mine were described in detail. Fire combustion served as the power source for uncontrolled energy release, and its fire pressure interacted with the thermal resistance of the mine ventilation, directly causing airflow disorder. As the fire intensified, the ascensional airflow fire caused the airflow in the side branch to decrease, stagnate, or reverse. Improving the fan supply capacity can not only help reduce the increase in the ventilation thermal resistance of the side branch but also help avoid the airflow reversal of the side branch. From the regular variation characteristics, the theoretical results were found to be in good agreement with the experimental results. Full article

Field studies with the large-stemmed plant Artemisia dubia (A. dubia) have been carried out at the Vėžaičiai Branch of LAMMC since 2018. According to three years of experimental results, annual dry matter (DM) yield varied from 7.94 to 10.14 t ha⁻¹. Growing conditions, nitrogen application level, and harvesting time had statistically significant impacts on A. dubia productivity. The most important tasks of this article were to investigate and determine the factors influencing A. dubia plant biomass productivity and the evaluation of technological, power, and environmental parameters of plant biomass utilization for energy conversion and the production of high-quality solid biofuel pellets. For the experiments, six variants of A. dubia samples were used, which were grown in 2021. Plants were cut three times and two fertilization options were used: (1) no fertilization and (2) fertilization with 180 kg ha⁻¹ of nitrogen fertilizer. These harvested plants were chopped, milled, and pressed into pellets. The physical–mechanical characteristics (moisture content, density, and strength) of the A. dubia pellets were investigated. During this study, it was found that the density in the dry mass (DM) of the pellets ranged from 1119.86 to 1192.44 kg m⁻³. The pellet moisture content ranged from 8.80 to 10.49%. After testing pellet strength, it was found that the pellets which were made from plant biomass PK-1-1 (first harvest without N fertilization) were the most resistant to compression, and they withstood 560.36 N of pressure. The dry fuel lower heating value (LHV) of the pellets was sufficiently high and was very close to that of the pine sawdust pellets; it varied from 17.46 ± 0.25 MJ kg⁻¹ to 18.14 ± 0.28 MJ kg⁻¹. The ash content of the burned pellets ranged from 3.62 ± 0.02% to 6.47 ± 0.09%. Emissions of harmful pollutants—CO₂, CO, NO_x, and unburnt hydrocarbons (C_xH_y)—did not exceed the maximum permissible levels. Summarizing the results for the investigated properties of the combustion and emissions of the A. dubia pellets, it can be concluded that this biofuel can be used for the production of pressed biofuel, and it is characterized by sufficiently high quality, efficient combustion, and permissible emissions to the environment. Full article