Combustion Research Articles

First applications of ultrasound technology in solid rocket propellant combustion promotion

The regulation of propellant combustion using ultrasonic waves is proposed. Under ultrasonic frequencies of 25–40 kHz, we systematically examined the combustion characteristics of Al particles, ammonium perchlorate (AP)/hydroxyl-terminated polybutadiene (HTPB) propellants, and Al-containing Al/AP/HTPB propellants. Ultrasonic treatment increased the ignition delay time of the Al particles by 48.3 %. However, it increased the burning rate of the AP/HTPB propellants by up to 26.1 % and decreased their ignition delay by 39.3 %. As the ultrasonic frequency increased, the burning rate of the solid Al/AP/HTPB propellants increased by 22.5 %, and the degree of Al agglomeration decreased, resulting in a 24 % decrease in the size of the condensed-phase combustion products. The action mechanism was analyzed in terms of the effects of ultrasonic waves on Al droplets and combustion flames. The introduction of ultrasonic waves split the Al droplets near the burning surface into smaller particles, which affected combustion efficiency. Bringing the diffusion flame closer to the burning surface affected the burning rate. These findings demonstrate that the combustion and agglomeration characteristics of solid propellants can be modified using ultrasonic techniques, providing a new method for controlling the thrust of solid rocket motors.

A new low NOx emission technique for NH3/H2 blends in a flameless combustor through offset injection

The application of ammonia (NH3) as a possible future fuel presents a plausible solution for green energy storage. It helps provide a carbon-neutral fuel alternative for industrial power generation and transportation. However, the combustion of NH3 presents a formidable challenge due to its low reactivity, inadequate flame stability, sluggish flame propagation, and high NOx emissions. Consequently, its integration into combustion systems necessitates substantial system and strategy modification to enable its deployment to industrial systems. The current study presents a novel fuel/air injection technique, which emphasizes the high recirculation of hot combustion products and the extended residence time of fuel/air mixtures. A comprehensive experimental and numerical investigation is conducted using a swirl air injection and offset fuel injection to achieve the flameless combustion mode for optimized NH3/H2 fuel blends. A range of mixture conditions (ϕ = 0.5–1.2) and NH3/H2 compositions (50/50–70/30) are experimentally examined. The investigations helped elucidate the effect of residence time and recirculation on NOx emissions through kinetic simulations using a reactor network model. Subsequently, 3-D numerical simulations helped identify regions of high recirculation, quantified through reactant dilution ratios and uniform temperature distribution. These aspects are determined using a new parameter, the temperature uniformity index along the axial direction of the combustor. The emissions of NOx, unburnt NH3, and unburnt H2 are quantified for different equivalence ratios and NH3 mole fractions in the fuel mixture. The investigations reveal that NOx emissions reached their minimum (450–654 ppm) and (344-211 ppm), when the burner operated at lean (ϕ = 0.5–0.8) and rich (ϕ = 1.0–1.2) conditions, respectively, for 70/30 NH3/H2 blend. The emissions of unburnt NH3 and H2 species remain minimal for lean conditions. Both lean and rich operational regimes demonstrated similar or superior emission characteristics in flameless combustion mode when compared to the conventional combustion mode.

Improving used Lubricant Oil Burner Performance: Effect of Swirled Flow of Internally Distributor Type on the Combustion and Flue Gas Temperature and Emission

This study aimed to experimentally investigate the combustion characteristics of used lubricant oil (ULO). A simple cylindrical burner of the natural draft vaporizing type, equipped with an internal air distributor, was designed and fabricated to achieve this objective. The burner’s efficiency was evaluated based on combustion temperature, flue gas temperature, and concentration levels. The key feature of this burner lies in the swirled flow of air combustion and ULO vapor within the combustion chamber, facilitated by the swirled flow air distributor type. Various air-fuel ratios (ϕ), ranging from 0.5 to 4, were considered in characterizing the burner’s performance. The results revealed increased combustion and flue gas temperatures in the radial airflow types. The highest temperatures achieved using the radial flow type are 930 oC and 410 oC for combustion and exhaust gas temperature, respectively. In contrast, the combustion chamber and exhaust gas temperatures are 980 oC and 465 oC for the swirled flow type, respectively. It was found that there is a decrease in the emission of CO and CO2 by volume under optimum conditions. This decrement was attributed to the swirled flow effects, which promoted a better mixture of air combustion and ULO vapor during combustion.

CFD Simulation of the Influence of the Type of Gas Distribution in the Burners on Thermal Aerodynamic Processes in the DKVR 10-13 Boiler

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power stations. However, in Asian countries, the ease of using natural gas as the main fuel and its environmental friendliness compared to coal made it possible to widely use natural gas in industry and energy sector. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion that it has the most attractive characteristics for its use in industry, including energy facilities, can be drawn. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy sector in the near future. The paper is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal one and at 60% capacity. The study was carried out using numerical methods with the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single-row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NOx generation in jet-niche systems was obtained. The authors of the paper believe that replacing the regular burners of the DKVR-10-13 water heating boiler with a jet-niche ones can contribute to better mixing of fuel and air and ensure more complete combustion. In this paper, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of combustion products spraying. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NOx. Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

SIMULATION HEATING PROCESS FOR WEAKLY REACTIVE COAL IN THE HORIZONTAL REACTOR

In this study results of the active medium parameters influence formed by hot air on the thermal heating process of weakly reactive coal from the formation «Maikubensk 3B» for the extraction of additional heat are represented. In the course of the research the regularities of the hygroscopic moisture and volatile combustible substances release for the obtaining additional heat have been determined. Optimal temperature ranges of the stage heating taking into account thermal destruction of coal in the temperature range from 20 C to 600 C, the main steps of the insulated heating process, the moisture content gradient propagation lines and dependence of the heat transfer and mass transfer coefficients on the temperature and the humidity during the thermal heating process in the horizontal coal heating reactor. The results show that it is possible to release volatile combustible gases with a gradual increase of temperatures in the obtained mode. The heating mode comprises a pre-heating stage with hydroscopic moisture release, in the temperature range from 20 C to 105 C, the stage of isothermal heating in the temperature range from 105 C to 400 C and the phase of flame-free combustion in the temperature range from 400 C to 600 C with the temperature rise above the set value. Process simulation was carried out in the Comsol Multiphisics software environment for the weakly reactive coal real-world heating conditions. Keywords: coal heating, weakly reactive coal, isothermal heating, step-by-step heating, Lagrange method, non-liner equation, non-stationary process.

Comparison of DeNOx additives in SNCR fluidized bed boiler system

Due to decreasing BAT emission limits of NOx the owners of heating plant are looking for DeNOx solution, especially by solid fuel firing boilers. Fluidized-bed boil-ers combustion temperature is generally lower, and some primary precautions were sufficient. Nowadays lots of plants install secondary precautions (especially SNCR) into their boilers due to increasing periods of exceeding emission NOx limits. The article is about comparison of water solution of urea (41 % wt.), ammonium sulfate (33 % wt.) and am-monia (22 % wt.) and their utilization in SNCR technol-ogy. Laboratory determination specified exact content of functional substance and content of redox nitrogen. Also, significant content of heavy metals was not detected. Operational tests were realized in CFB coal-biomass boiler (steam parameters: 140 t·h-1, 525 °C, 12.5 MPa). Dosing of DeNOx additives were only during boiler per-formance higher than 92 %, for lower performance pri-mary precautions were sufficient. There was higher tem-perature through the combustion chamber during active SNCR dosing (877 °C, standard temperature 850 °C), alt-hough the amount of combustion air was increased. Com-plication connected with high emission of NH3 was not detected. Lower emission of CO was also detected. All three additives are suitable for application in SNCR technology. To reach emission limits were needed 3.7 l·h-1 of ammonia solution, 5.04 l·h-1 of urea solution and 5.74 l·h-1 of ammonium sulfate solution. After recal-culation it means 0.65 kg·h-1 (ammonia), 1.1 kg·h-1 (urea) and 0,38 kg·h-1 (ammonium sulfate) of redox nitrogen content.

Determination of the effect of low concentration titanium dioxide nano fuel additive in biodiesel on performance and emissions

In this study, the effect of nanoparticle addition into rapeseed methyl ester (R0) produced by the transesterification method on engine performance and emissions was experimentally investigated. Titanium dioxide was used as a nano fuel additive and was added to the test fuels at rates of 50 ppm (RTi50) and 75 ppm (RTi75) using an ultrasonic mixer. The effect of titanium dioxide on engine performance and exhaust emissions was experimentally determined by taking advantage of its photocatalysis effect and chemical reaction accelerator properties. Additionally, titanium dioxide additive reduced the viscosity and density of biodiesel fuel, resulting in higher micro explosion. According to the test results carried out at 4 different engine loads, brake specific fuel consumption decreased by 7.51% and 8.62% in RTi50 and RTi75 fuels compared to R0 fuel. Brake thermal efficiency increased by 2.47% and 6.21%, respectively. The improvement in combustion achieved by the nano additive increased the conversion of CO emissions into CO2, increased NOX emissions, reduced smoke emissions and caused more complete combustion products to come out of the exhaust.

Modeling the stability of air flows in inclined workings in case of fire

Purpose. Development of a mathematical model and study of the processes occurring during conveyor belt fires in inclined mines to determine the mechanism of air flow distribution under appropriate conditions. Methods. Practical measurements of the distribution of air flows in an inclined conveyor operated at the mining and processing plant of PJSC ArcelorMittal Kryvyi Rih were carried out. Based on the obtained data, a mathematical model was crea-ted, which was then used to perform Computational Fluid Dynamics (CFD) modeling of gas flows in the mine under normal conditions and in the event of a fire with a thermal capacity of 9 MW. Findings. The study reveals the peculiarities of gas flows during the combustion of a conveyor belt in inclined workings, as well as the influence of turbulence on the flow, changes in the density of gases during heating, and the impact of gravity on the distribution of gases in the cross-section and along the length of the workings. A fire centre with a heat output of 9 MW has a significant impact on the distribution of air flows. The phenomenon of thermal expansion results in a 59.2% increase in the volume of gases behind the fire. The thermal expansion of gases and their low density have a significant impact on the formation of gas flows in inclined workings. As the jet moves away from the centre of the fire, the velocity of the jet gradually increases, reaching a value of 12.4 m/s. This results in a notable alteration in the distribution of total pressure across adjacent workings, accompanied by an increase in flow turbulence. Consequently, the mass of air exiting the right branch is observed to have a five-fold increase in comparison to the pre-fire state. The overturning of the jet from the left branch of the workings gives rise to the exclusive distribution of combustion products along the right branch. Originality. The study helps to understand the mechanism of jet overturning and the peculiarities of the distribution of combustion products in case of fire in inclined conveyor workings. Practical implications. The results of the research allow us to predict the probability of fire, identify the most dangerous areas for fire, and plan the most rational actions for firefighting in specific unique conditions.

Predicting critical flame quenching thickness using machine learning approach with ResNet and ANN

In the study of flame quenching, quenching thickness is one of the important parameters to determine the design of a flame arrester, and often determines the flame quenching performance of the arrester. In the study, residual network (ResNet) and artificial neural network (ANN) are used to predict the critical quench thickness of combustible gas in pipelines. The critical quench thickness is influenced by fuel concentration and density, pipeline size, inert gas type and concentration, porous media porosity, and thermal conductivity. The influence of different combinations of hyper-parameters on the prediction performance of the two models is explored. The results show that the prediction performance of both models reaches the best after hyper-parameter optimization. Compared with ANN, the ResNet model shows more stable and better prediction ability, and its optimal evaluation parameters are: MAE is 1.4679, MSE is 91.7431, R2 is 0.9216. The prediction errors of the two models on the same dataset are subjected to analysis, and the impact of the use of normalized data on the performance of the two models is compared. It is determined that the ResNet model demonstrated superior robustness and generalization ability in predicting the critical quenching thickness of combustible gases. The study is helpful for the safety protection of combustible gas and the safety design of pipeline arresters.

Numerical investigation of lean methane flame response to NRP discharges actuation

This study investigates the response of a laminar methane-air flame to Nanosecond Repetitively Pulsed (NRP) discharges in a canonical wall-stabilized burner using a combined experimental and numerical approach. The flow and flame behaviors were modeled using Direct Numerical Simulation (DNS) with an Analytically Reduced Chemistry for a precise chemical description. A phenomenological model incorporating detailed plasma kinetics and experimental observations was developed to simulate plasma effects. Zero-dimensional plasma reactor simulations were used to build up a reduced-order model describing discharge energy distribution in the specific conditions studied. Experimental measurements of electrical profiles identified two discharge regimes: a low-energy Corona discharge and a higher-energy Glow discharge, characterized by distinct spatial energy distributions. Experimental flame response analysis revealed three major phases: marginal response up to 100 pulses, a downstream shift of the flame tip, and stabilization after 400 pulses. Numerical simulations indicated that the Corona regime is crucial for explaining initial flame responses, while the Glow regime influences later stages. Adjustments in the Vibrational-Translational (VT) energy relaxation time and energy deposition ratios between fresh and burnt gases were necessary to match experimental observations. Additionally, an accurate modeling of the transient and steady-state flame responses requires integrating both the specificity of the Corona and the Glow discharge regimes. Future work should focus on measuring or theoretically calculating N2(v) relaxation times in CH4-H2O-CO2 mixtures and analyzing the spatial energy distribution of discharges interacting with flames to enhance plasma-combustion coupled models.Novelty and significanceIn this work, a phenomenological plasma-assisted combustion model has been developed, to investigate a laminar premixed stagnation plate burner, focusing on VT energy relaxation time and spatio-temporal energy distribution modeling. For the first time, not only O2, N2 and O but also the fuel and combustion intermediates and products have been considered in the VT relaxation model. It revealed their strong influence on the overall flame response in a case where the discharge crosses a flame front, highlighting the strong beneficial effect of energy deposited in vibrational form. The study questions and investigates the energy distribution from fresh to burnt gases, challenging the conventional uniform energy distribution assumption. The experimental identification of two specific plasma regimes was necessary to predict the transient flame response. Additionally, energy deposited downstream of the flame, in fresh gases, was found to more efficient than in hot gases to enhance combustion.

Modeling of thermo-aerodynamic and environmental parameters on the example of a two-pipe water heating boiler that has worked out the park resource

Topics related to fuel combustion and its impact on the environment will never lose their relevance, as the issues of efficient combustion and emission reduction are key in power generation and environmental protection. The countries of the European Union are massively abandoning the use of natural gas as a fuel for thermal power station. However, in Asian countries, the ease of using natural gas in industry as the main fuel, its environmental friendliness compared to coal, made it possible to widely use natural gas in industry and energy. Comparing natural gas with alternative combustible gases (generator, blast furnace, mine, biogas), the main conclusion can be drawn that it has the most attractive characteristics for its use in industry, including energy. Therefore, it is impossible to replace it with alternative fuels in the chemical, heavy industry and energy industry in the near future. The presented work is devoted to CFD modeling of stabilized combustion without premixing in a burner with low swirl for two operating modes of the boiler unit - nominal and at 60% capacity. The study was carried out using numerical methods using the ANSYS-Fluent application program package. The object of the study is a burner built according to the technology based on the use of jet-niche systems with gas distribution of fuel by circular jets fed perpendicularly into the flow of the oxidizer through a single- row system of holes. Hydrodynamics and heat exchange processes were chosen as the subject of research, based on the analysis of which a model of NO x generation in SNS was obtained. In this work, two types of burners are considered. In one of the burners, fuel is supplied through rectangular slits, in the other – through round holes arranged in a row. Air is supplied to both burners through rectangular slits. It was determined that gas distribution through round holes increases the spraying of the mixture and increases the area of spraying of combustion products. Visualization of the distribution of pressure, temperature, kinetic energy profiles of turbulent pulsations and vorticity was carried out. The obtained results indicate that there are no changes in the flow regime, flame displacement or its instability. It was determined that both the axial velocity and the tangential velocity of the flow affect the distribution of combustion products and harmful impurities such as NO x . Gas distribution in circular jets stabilizes combustion and reduces flame expansion.

Potential impact of the 2023 Lahaina wildfire on the marine environment: Modeling the transport of ash-laden benzo[a]pyrene and pentachlorophenol

The Lahaina urban/wildland fire event is considered the deadliest wildfire in the past century of U.S. history. This fire resulted in over 2200 building structures destroyed or damaged, approximately 4000 automobiles were incinerated and between 450 and 878 ha of grassland burned in areas adjoining the town of Lahaina, Maui County, State of Hawaii, U.S.A. One of the most abundant contaminants of both wildland and urban fires is the incomplete combustion product, benzo[a]pyrene. Pentachlorophenol from burned and unburned utility poles/residential burn sites enter into navigable waters, thus posing a serious risk to the water quality of coastal waters. The Risk Quotient Plumes for benzo[a]pyrene and pentachlorophenol, mobilized from Lahaina into coastal waters were calculated based on a hydrodynamic analysis and an integrated ecological risk assessment. This plume was simulated using rainfall events in November 2022 as a proxy for the first major rainfall event expected in Lahaina in 2024. The models indicated that the estimated levels of benzo[a]pyrene and pentachlorophenol posed a risk to near shore habitants within 2 km of Lahaina. The levels of pentachlorophenol were more widespread than benzo[a]pyrene and were predicted to pose a hazard to marine life as far away as Molokini Shoal Marine Life Conservation District and ʻĀhihi-Kīnaʻu Natural Area Reserve. Fisheries species captured near these areas should be tested for consumption safety.

Microwave plasma conversion of food waste using carbon foam: Production of heteroatom-doped graphene and combustible gas

The mass production of food waste (FW) has a terrible impact on the environment, but with proper treatment, FW can be transformed into a new resource. Currently, thermal conversion (especially incineration) has been the most common and efficient means of handling FW, but it also entails negative impacts, such as high carbon emissions and lower added value. In this study, a new high-efficiency thermal conversion process is proposed that uses carbon foams to induce the formation of microwave plasma (MP), which generates very high final temperatures to enable the direct conversion of FW into combustible gases and high-value-added heteroatom-doped microwave plasma graphene (HMPG) in 5–20 s. This work investigated the optimal carbonization temperature of the melamine sponge (carbon foam precursor) and the effect of microwave plasma reaction duration on the distribution of the gas products and the properties of HMPG, and HMPG was characterized in detail by Raman spectroscopy, X-ray diffraction, scanning electron microscope, etc. Ultimately, HMPG was tested in potassium ion battery anodes for evaluation of its energy storage potential, and the results showed that the capacities were able to reach ∼270 mAh g−1 at 50 mA g−1 after 60 cycles.

Technical Analysis of the Possibility of Burning Hydrogen in Furnaces of the Metallurgical Sector

This article analyses the possibility of using hydrogen as fuel in furnaces used in the metallurgical industry. The research was conducted for a selected continuous furnace. For this purpose, based on actual measurements, a heat balance of the furnace was prepared to determine its energy indicators. These values were used to verify the developed numerical model in IPSEpro 7.0 software. Numerical calculations were performed for three variants: pure natural gas; 30% hydrogen, 70% natural gas; and 100% hydrogen. The determined values of gas and combustion air streams allowed for achieving the assumed charge temperature in the heating technology. Calculations of the impact of the excess combustion air ratio on process parameters were also carried out. It was found that no changes are required in the exhaust gas removal system, but verification of the fan supplying air to cool the exhaust gases before the recuperator is necessary. The amount of hydrogen required to fuel the continuous furnace also increases significantly (nearly threefold), which may also affect operating costs. At the same time, the emission of carbon dioxide into the atmosphere is completely reduced, which may be an important criterion when considering modernization options for heating furnaces in the metallurgical industry.

Study on Fast Temporal Prediction Method of Flame Propagation Velocity in Methane Gas Deflagration Experiment Based on Neural Network

To address the challenges of high experimental costs, complexity, and time consumption associated with pre-mixed combustible gas deflagration experiments under semi-open space obstacle conditions, a rapid temporal prediction method for flame propagation velocity based on Ranger-GRU neural networks is proposed. The deflagration experiment data are employed as the training dataset for the neural network, with the coefficient of determination (R2) and mean squared error (MSE) used as evaluation metrics to assess the predictive performance of the network. First, 108 sets of pre-mixed methane gas deflagration experiments were conducted, varying obstacle parameters to investigate methane deflagration mechanisms under different conditions. The experimental results demonstrate that obstacle-to-ignition source distance, obstacle shape, obstacle length, obstacle quantity, and thick and fine wire mesh obstacles all significantly influence flame propagation velocity. Subsequently, the GRU neural network was trained, and different activation functions (Sigmoid, Relu, PReLU) and optimizers (Lookahead, RAdam, Adam, Ranger) were incorporated into the backpropagation updating process of the network. The training results show that the Ranger-GRU neural network based on the PReLU activation function achieves the highest mean R2 value of 0.96 and the lowest mean MSE value of 7.16759. Therefore, the Ranger-GRU neural network with PReLU activation function can be a viable rapid prediction method for flame propagation velocity in pre-mixed methane gas deflagration experiments under semi-open space obstacle conditions.

Rare elements and non-ferrous metals in the paleogene brown-coal deposits of the Zeya-Bureya sedimentary basin (Amur Region, Far East): accumulation models, enrichment conditions and criteria for assessment of resource potential (a review)

A model has been developed for deposition of rare earth elements with yttrium, trace elements, and non-ferrous metals in platform and activated structures of the Upper Amur region. Genetic types of lanthanide enrichment are considered; lanthanides are shown to concentrate non-uniformly in coal seams and in coal combustion products. Light rare earth elements predominate in coals. The capacity of peat and coal for metal extraction from aqueous solutions was proven. Criteria for a preliminary assessment of coal as a raw material for lanthanides were considered and prospects for their identification were analyzed.

Enhancing prediction of elemental composition through machine learning decision tree models for biomass gasification optimization

Abstract The worldwide transition to cleaner, sustainable energy sources, prompted by population growth and industrialization, responds to uncertain fossil fuel prices and environmental concerns, highlighting the substantial benefits of renewable energy in reducing greenhouse gas emissions and addressing climate change. Derived from non-fossilized organic materials, biomass emerges as a significant and sustainable contributor to renewable energy. Its diverse nature is complemented by a range of conversion technologies, encompassing combustion, pyrolysis, gasification, and liquefaction, providing versatile avenues for biomass energy transformation. Gasification, the transformative process of converting organic matter into combustible gases under controlled oxygen levels, is accomplished through direct oxygen supply or pyrolysis. This method yields a dependable gaseous fuel versatile for heating, industrial processes, power generation, and liquid fuel production. Machine learning employs advanced statistical techniques for modeling across diverse industries, showcasing particular efficacy in optimizing thermochemical processes by precisely identifying the optimal operating conditions required for achieving desired product properties. These models utilize proximate biomass data to predict the elemental compositions of N2 and H2. Assessment of both single and two hybrid models indicated that the introduced optimizers significantly enhanced the estimation of N2 and H2 when combined with Decision Tree (DT), with Decision Tree Coupled with Artificial Hummingbird Algorithm (DTAH) proving particularly effective. Notably, DTAH demonstrated outstanding performance with remarkable R 2 values of 0.990 for N2 and 0.992 for H2. Additionally, the minimal Root Mean Square Error (RMSE) values of 1.291 and 1.550 for N2 and H2 predictions respectively underscore the precision of DTAH, establishing it as a suitable choice for practical real-world applications.

Chronic and Periodic Effects of Smoke from Crop Residue Combustion on Soil Enzymatic Activity

Wildfires lead to the emission of large volumes of toxic smoke, which is transported hundreds of kilometres away from the fires and can have a negative impact on soil, biota and humans. A series of modelling experiments on pyrogenic fumigation of soil were carried out to assess the effects of gaseous products from wildfires on soil biochemical parameters. The effects of chronic exposure to gaseous substances and periodic, repetitive effects of smoke exposure on soil were determined. The results were compared with a single intensive smoke exposure. It was found that pyrogenic impact significantly affected the change of enzymatic activity of ordinary chernozem. The degree of influence depended on the duration and periodicity of smoke exposure. In all experiments enzymes of oxidoreductase class (catalase, peroxidase, polyphenol oxidase) were more sensitive to fumigation than invertase from hydrolase class. The reason of suppression of enzymatic activity of soils is high concentrations of toxic gases. The following concentrations exceeded the maximum permissible concentrations for atmospheric air: CO 714 times, phenol (hydroxybenzene) 441 times, acetaldehyde 24100 times, formaldehyde 190 times. Accumulation of polycyclic aromatic hydrocarbons (PAHs) in soil after fumigation was revealed, the total content of PAHs was 377 ng/g. The highest values were recorded for naphthalene, where the concentration was 4.4 times higher than the maximum permissible and phenanthrene 2.8 times higher than the maximum permissible. It was found that 60-minute intensive smoke affects the soil to a lesser extent than chronic and periodic. Indicators of enzymatic activity of chernozem after such fumigation decreased by 15-33% depending on the enzyme, in chronic and periodic by 41-84 and 31-78%, respectively. The obtained data indicate a significant effect of smoke on enzymatic activity of soils under chronic and periodic exposure to gaseous products of combustion.

Sustainable organic waste valorisation: A zero-waste approach

The annual increase in global organic waste generation emphasises the need to develop a sustainable management platform to address environmental concerns. This study aims to explore sustainable treatments for the conversion of organic waste into energy in pursuit of zero-waste. The organic waste generated from the animal feed industry (referred to as WF) was used for the model compound in this study. 8.5 wt% of lipids were extracted from the WF, which contained unidentified impurities. Acid-catalysed transesterification yielded less than 80 wt% biodiesel might be due to the reversible reaction. In contrast, non-catalytic transesterification resulted in a significantly higher biodiesel yield (95.6 wt%), suggesting that this method was more effective at converting impure lipids into biodiesel compared to acid-catalysed transesterification. These results indicate the potential advantages of the non-catalytic approach, particularly when dealing with impure lipid sources. To minimise the generation of waste in the process, the WF residue produced after lipid extraction was converted into combustible gas (syngas) through pyrolysis. CO2 was used as a reactive medium in pyrolysis. In one-stage pyrolysis, the gas yield under CO2 was comparable to that under N2, indicating that CO2 did not react effectively with the volatiles derived from the WF residue. Enhanced CO2 reactivity was achieved via catalytic pyrolysis using a nickel-impregnated catalyst. Consequently, the combustible gas yield under CO2 was much higher than that under N2. This approach might contribute to maximising the efficiency of converting organic waste into renewable energy while simultaneously consuming CO2 during pyrolysis, thereby enhancing the sustainability of this approach.

Mineralogical characterization of magnesium-based nanoparticles recovered from a swirl-stabilized magnesium flame by analytical and scanning/transmission electron microscopy

Abstract. The current climate emergency and the related energy transition require the development of technology producing zero-carbon energy. One viable option entails the utilization of recyclable metal fuels. The primary energy stored by the reduction in metal oxides can be transported and later released by metal combustion. Mg is among the most promising metal as a regenerable energetic vector, having an energy density of 25 MJ kg−1. The exploitation of the Mg oxidation and reduction loop has recently been demonstrated, and the loop combustion products are made of metal oxides. The mineralogical characterization of the MgO crystals generated by the Mg combustion is of utter importance for the optimization of the particle trapping capacity in the combustion system during the closed oxidation and reduction loop. In this paper we characterize MgO particles generated in a swirl-stabilized Mg flame by using powder X-ray diffraction, transmission electron microscopy and selected area electron diffraction, and atomic-resolution microscopy combined with energy-dispersive X-ray spectroscopy and dual-electron energy-loss spectroscopy. The MgO combustion products were chemically homogeneous at this level of investigation. Three representative morphologies (cubic, truncated octahedron, and spherical) and two isostructural phases were identified in the MgO combustion product. These findings may contribute to the optimization of system development, particularly in terms of the collection efficiency of the combustion end product.