Staged Combustion Research Articles

Contemporary Approaches to Wound Burn Healing

The World Health Organization (WHO) reports that over 11 million individuals get burns annually, resulting in 180,000 fatalities. A burn is a condition resulting by heat, chemical agents, electrical currents, or other forces that inflict tissue damage. Burns primarily impact the skin, however they may also include deeper structures, including bones and muscles. Upon combustion, the skin forfeits its primary functions, including protection against the external environment, infections, moisture evaporation, and thermal regulation. Based on the burn's stage, the patient's health, and the burn's etiology, it is essential to choose the most suitable therapy. Personalization and interdisciplinary teamwork are essential for the effective therapy of burn victims. This thorough study compiles and examines the existing treatment modalities, emphasizing current advancements in topical therapies, wound debridement, dressings, skin grafting, nutritional support, pain management, and scar tissue therapy.

Combustion efficiency analysis and thermal radiation risk quantification for spill fire in sealed ship cabin

In this study, the authors conducted a series of one-dimensional spill fire experiments in a sealed model-scale ship cabin with different leakage rates to reveal the combustion characteristics. The results showed that a stable combustion stage with a consistent combustion area and flame height appears around the cut-off of the fuel, where the consumption of oxygen increases when the leakage rate increases. And the CO2 concentration increases more rapidly and the upward trend is found to appear earlier. Compared with the film thickness in the open space, that of the spill fire in the sealed ship cabin is slightly thinner because of the ventilation control effect. Using the “oxygen-consumption” method, the η of this stage was calculated and verified with the “mass loss rate” method. With these two methods, the HRR of spill fie when burning steadily is calculated. This work also improved the predicting model for the flame height of rectangular pool fire and developed a predicting model for the flame height of a steadily burning spill fire. The error is 14.35 %. Additionally, a predictive model of thermal radiation risk in ship spill fire is developed, and the death risk and unacceptable risk areas are delimited.

Study on the Characteristics of Combustible Mixed Gas Production during Lignite Oxidation Process

CO, H2, and other combustible gases will be produced during coal oxidation in coal mines, which will increase the risk of explosion when mixed with methane. Therefore, it is very important to understand the production characteristics of combustible gas during coal oxidation. In this paper, a programmed temperature gas test system is built to study the impact of lignite on the production of gases at different particle sizes and temperatures, and the release characteristics of gases are also analyzed. The result shows that the production of combustible gas is influenced by the coal particle size significantly when the temperature is above 200 °C, and it decreases as the particle size increases. CO is the main gas during the early stage of coal spontaneous combustion, and the release of CH4 and H2 increases after 300 °C. The fitted equations of gas generation and temperature are consistent with the experimental results. The research results are helpful in understanding the hazards of coal spontaneous combustion and have a certain guiding significance for coal mine monitoring and prevention of coal spontaneous combustion.

Comparison of identification methods used in Forensic Anthropological services in four distinct institutes in Brazil and the United States

ABSTRACT Identifying unknown deceased individuals, especially those in advanced stages of decomposition, dismemberment, or burning, is a major medico-legal challenge. Forensic anthropologists play a crucial role in these cases due to the numerous characteristics that can be derived from bone remains. Their methods help evaluate the biological profile and individual characteristics, narrowing potential matches. This research investigates the identification methods used by forensic anthropologists in Medicolegal Institutes and Medical Examiner’s Offices in Brazil and the USA. Case reports from forensic anthropology institutes in Vitória, Rio de Janeiro, Porto Velho (Brazil), and New York City (USA) were analysed. In resolved cases, details such as the biological profile, trauma, decomposition extent, and individualization markers were documented. Statistical tests evaluated the association between these variables and identification outcomes. Conventional identification methods included dental analysis, DNA testing, and fingerprint analysis. Additionally, Bayesian methods, visual identification, prosthetics, and X-ray comparison proved useful. This study highlights that forensic anthropologists can employ a variety of methodologies beyond standard practices, enhancing the identification process in complex cases.

Study on the Optimization of Culture Parameters of Oxygen-Consuming Bacterium for Preventing CSC and Its Effect on the Coal Oxidation Characteristic

ABSTRACT Microorganisms can work together to prevent coal spontaneous combustion (CSC) by consuming oxygen and changing coal oxidation characteristics. In order to explore the influence of oxygen-consuming microorganisms on coal spontaneous combustion characteristics, a highly oxygen-consuming bacterium was isolated and identified from the soil near mine drainage, named ZQ-1. The oxygen consumption characteristics of microorganisms were investigated and optimized by single-factor and response surface experiments. Further, the effect of microorganisms on CSC was analyzed from both macroscopic and microscopic perspectives by using programmed warming, simultaneous thermal analysis, and Fourier-transform infrared spectroscopy (FTIR). The results revealed that the isolated bacterium was Pseudomonas aeruginosa. Its optimal culture conditions were pH = 6.98, temperature 28.15°C, and carbon nitrogen ratio (C/N) = 12.94 when the oxygen consumption rate was maximum. After bacterial action, coal showed a decrease in the release of the indicator gas CO during the combustion process, a delay in the cross point temperature (CPT) by 18.63°C, and an increase in the residual mass at the end of combustion. In addition, the average activation energy of the coal samples in the oxidative combustion stage was increased by 2.05721 kJ/mol. Finally, the FTIR results showed that microorganisms were able to destroy the reactive groups in the coal samples, especially hydroxyl, aliphatic hydrocarbon, and oxygen-containing functional groups, which resulted in the inhibition of CSC. This paper has important theoretical research value and practical significance for CSC prevention and control.

Characterization of pressure oscillations and combustion noise of hydrogen reactivity-controlled compression ignition (RCCI)

Knock and combustion noise are the main reasons limiting the increase in hydrogen (H2) replacement rate in H2 reactivity-controlled compression ignition (RCCI). This study aims to identify the knock-dominated mechanism and elucidate the characteristics of knock and combustion noise of H2 RCCI operated at a broad range of parameters through the combined analysis of the heat release profile and pressure oscillations. The results indicated that under inhomogeneous heat release conditions, the onset of pressure oscillations is mainly attributed to the local fast heat release at the initial combustion stage, but for the conditions with relatively homogeneous and high-reactivity mixture, the pressure oscillations are primarily excited by the end-gas autoignition. Compared with the single injection strategy, the double injection strategy with the first and second start of injection of −60 and −15°CA ATDC (SOI1/2 = −60/-15°CA ATDC) can effectively mitigate the pressure oscillations and shorten the propagation period of pressure waves. However, as the SOI2 is advanced to −30°CA ATDC, the pressure oscillations dramatically increase, because the enhanced fuel reactivity of premixed H2 exacerbates the end-gas autoignition. The results of frequency analysis of in-cylinder pressures show that with the increase in inhomogeneous combustion, the first resonance frequency reduces. As the intake pressure (Pin) is raised from 1.2 to 1.6 bar, the first resonance energy increases, since the elevated in-cylinder temperature associated with the piston compression during the compression stroke enhances the propagation and development of pressure waves. The high-order resonance is closely related to the autoignition of end gas with higher fuel reactivity. Overall, the combustion noise shows a good linear correlation with peak heat release rate for all the points investigated in this work, but the linearity of H2/polyoxymethylene dimethyl ethers RCCI is better than that of H2/diesel RCCI. Moreover, with the increase in Pin, the engine noise associated with the piston compression increases.

Effect of ammonia reforming on combustion and emission characteristics of a 4-valve engine with an active pre-chamber

Ammonia (NH3), as a hydrogen carrier and carbon-free fuel, offers an attractive opportunity for engines to achieve carbon neutrality. Turbulent jet ignition (TJI) combined with ammonia reforming shows the great capacity in ammonia-fueled engines. In this study, the effects of reforming strategy in an ammonia-fueled TJI are numerically studied, addressing the reforming ratio and reforming region. The results show that when only using reformate in the pre-chamber, the promoting effect of jet flame is more effective on the initial combustion phase. There are still very high NH3 emissions due to the low reactivity in the main chamber. Further using reformate both in the pre-chamber and the main chamber, all the combustion stages (ST-CA10, CA10-50, CA50-90) can be shortened almost linearly with the increase of reforming ratio. Besides, the unburned NH3 can be reduced to an acceptable level when the reforming ratio reaches 200‰ (hydrogen energy ratio of 18.50%). The main reason is that the jet-induced strong flow field is coincident with the whole combustion stage. Further increasing the reforming ratio (pure hydrogen) in the pre-chamber, a high combustion efficiency and acceptable NH3 emission can be achieved at a low hydrogen energy ratio (7.08%). However, knocking combustion will happen at high reforming ratio with a low knock intensity. The results can provide some guidance for making the best-promoting benefit of the limited hydrogen in ammonia TJI engines with different reforming strategies.

Kinetic analysis of coal oxidative pyrolysis before and after immersion effect

The oxidative pyrolysis kinetics of coal before and after immersion effect was studied by thermogravimetric experiments. Non-isothermal thermogravimetric analysis data were analyzed at four heating rates of 5, 10, 20 and 30 K/min. Furthermore, temperature-programmed experiments and Fourier-transform infrared (FTIR) spectroscopy were employed to understand the oxidation activity and chemical structure of raw coal and soaked coal. After coal immersion effect, the increase in the content of active functional groups, the increase in the concentration of gaseous products, and the decrease in crossing point temperature during oxidation process all indicate that soaked coal is easier to oxidize and spontaneously combust. Lastly, four model-free methods such as Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Friedman and Kissinger methods are employed to calculate the activation energy (Eα). Kinetic analysis reveals that Eα value obtained by the former three methods significantly depends on the conversion of coal oxidative pyrolysis process, and the average Eα value of soaked coal obtained by four methods is lower than that of raw coal. For the kinetic analysis of coal oxygen adsorption and combustion stages, it is more reliable to adopt the FWO and KAS methods in turn. This research helps to better understand the mechanism of enhanced oxidation activity of soaked coal and optimizes the calculation method of kinetic parameters in different oxidation stages of coal.

Evaluation of the reactivity of co-combustion of wheat straw and waste rubber thermolysis char

The co-combustion of wheat straw (WS) and waste rubber thermolysis char (WRTC) was examined with the perspective of utilizing WRTC as a high-calorific value fuel addition to agricultural biomass. The study investigated the effect of different proportions of WS-WRTC blends (10/15/25/49 wt% WRTC) and a maximum of 4 wt% binders, including potato starch and calcium oxide, on the reactivity of co-combustion and the distribution of products during the process. Thermogravimetric analysis with Fourier Transform Infrared Spectroscopy (TGA-FTIR) analyses was employed at a temperature range of 25–1000 ° C with a heating rate of 10 ° C/min. The kinetics of co-combustion were analyzed using the Fraser-Suzuki (FS) deconvolution method and a model-based kinetic modeling. The results indicate that a 10% addition of WRTC char reduces the intensity and rate of combustion and prolongs the combustion time. It was observed that the optimal addition to the blend is 25% WRCT, and it resulting in a reduction in activation energy and combustion indexes. However, it remains with no significant impact on process stability and efficiency. Kinetics of the decomposition of the WRTC25 mixture modeled by the deconvolution method indicates a 5-step reaction course, which is a combination of the characteristic combustion stages of both fuels. The main denoted functional group observed in the FTIR absorption spectra were C=O, C-O, O-H, and C-H related to the release of CO2, CO, H2O, CH4, aromatic compounds, and hydrocarbons.

Numerical investigation of NOx emission characteristics in air-staged combustion system fueled by premixed ammonia/methane

For the purpose of achieving global CO2 reduction, decarbonization at the source of fuels is a practical approach. The transition phase of blending fossil fuels with carbon-free fuels for combustion is a hot topic in the current carbon emission reduction process. In order to achieve efficient and low-pollution combustion of NH3/CH4, the combustion and emission characteristics of NH3/CH4 under single-stage and air-staged combustion methods were numerically investigated in this work. The emissions were compared for different equivalence ratios and different ammonia content conditions. rate of production (ROP) and sensitivity analysis were performed for NOx, and the reaction path of NH3/CH4 was analyzed. The results indicate that the C-N interaction of the NH3/CH4 mixed combustion process is not significant and turns weaker in the lean flames. HNO intermediate is an important specie for NO generation, and HCN together with HNO intermediate, are essential species for NO generation. NH2 and NH almost dominate the promotion and inhibition of NO generation. Given that the contrasting NOx and CO emission behavior of NH3/CH4 in rich and lean flames, the single-stage combustion approach is not suitable. Air-staged combustion achieves both ensuring complete burning of NH3 and CH4 while reducing NOx and CO emissions. Moreover, the results suggest that Φpri=1.2/Φtotal=0.6 is the optimal NH3/CH4 combustion staging method for controlling NOx emissions.

Oxidation progress and inner structure during single micron-sized iron particles combustion in a hot oxidizing atmosphere

The present experimental study focuses on the determination of the oxidation progress and internal structures during the combustion of single iron particles using combined in-situ optical measurements and ex-situ material examination of rapidly quenched particles. Narrowly sieved iron particles with a mean diameter of 49µm are ignited and burn in the hot exhaust of a premixed CH4/O2/N2 flat flame with remaining 20vol% O2, provided by a laminar flow reactor with well-defined thermal and flow boundary conditions. During particle combustion, key parameters of oxidation progress are determined optically in a time-resolved manner, such as the time-resolved particle surface temperature and the reaction time relative to the instant of the particle peak temperature. Furthermore, individually burning particles are rapidly quenched at different combustion stages and then extracted from the exhaust gas using an isokinetic extraction probe. The bulk composition of the quenched particles with respect to α-Fe and its three oxides FeO, Fe3O4, and Fe2O3 is determined using Wide-angle X-ray Scattering and 57Fe Mössbauer Spectroscopy. Combining the information obtained from in-situ and ex-situ measurements, it is shown that iron particles oxidize rapidly to FeO during the initial stage of combustion, followed by a much slower oxidation to Fe3O4 as the particles cool down. The peak particle temperatures are measured during the fast initial oxidation. Finally, particles sampled from representative positions of the oxidation process are analyzed by Energy-Dispersive X-ray Spectroscopy and Focused Ion Beam Scanning Electron Microscopy, revealing different particle morphology and internal structures. For the first time, the clear presence of an oxide shell and iron-core structure in quenched particles suggests that liquid iron and liquid iron oxide are layered during liquid phase combustion, if the particle remains within the miscible gap.

Finite element analysis of thermal barrier properties under relevance vector machine in coated pistons and blades

Internal Combustion (IC) engines require Thermal Barrier Coatings (TBCs) to preserve their effectiveness and performance. By coating engine parts with TBCs, thermal fatigue and environmental heat loss may be minimised. To reduce heat loss in IC engines during the combustion stage, piston thermal barrier coating is extremely beneficial. Additionally, it is well known that power plants with higher energy efficiency tend to operate their gas turbines at higher operating temperatures. To produce TBCs for the thermal design of gas turbines and diesel engines with higher performance, an in-depth study on the thermophysical properties of TBCs is required. This article presents an experimental investigation into the combined effect of gas turbine blades and diesel engine pistons coated with a heat barrier, utilising two distinct Thermal Barrier Coatings. Initially, numerical calculations are used to assess the wall heat transfer model’s ability to control temperature and density. The piston and blade top surfaces received plasma-sprayed, Yttria-Stabilised Zirconia (YSZ) with different material combinations on the piston and blades are evaluated. The Finite Element Method is developed for the coating of the ideal thickness to analyse the failure mechanism of the TBC sample. To evaluate the fatigue residual lifespan of TBC pistons, as well as blades in high-power engines, the authors also created a relevant vector Machine-based lifetime prediction model. The CO, HC and NOx emissions, as well as the fuel depletion and braking thermal efficiency, are used to calculate the performance analysis of the coated piston and blades. The results demonstrated improved thermal process endurance and decreased thermal conductivity by 28% when compared to YSZ using the RVM method respectively.

Investigation of Al-Li particle ignition dynamics with different Li content

Promoting the ignition of aluminum powder is considered an effective method to inhibit the agglomeration of aluminum powder in propellants and enhance combustion efficiency. This study utilizes laser ignition technology and high-speed photography to investigate the ignition and combustion processes of single aluminum particles and aluminum-lithium alloy particles. The focus is on comparing the effects of the diameter of micron-sized metal particles and the lithium content in aluminum-lithium alloy particles on the ignition and combustion processes of metal particles. The results show that the ignition delay time is directly proportional to the diameter of the metal particles and inversely proportional to the lithium content. For the aluminum-lithium alloy particle with a lithium content of 3.5 %, even if the diameter is close to 300 μm, the ignition delay time is only 125.5 ms, which is much smaller than that of the pure aluminum particle with a diameter of 208 μm. Compared to aluminum particles and aluminum-lithium alloy particles, there is basically no difference between the two during the combustion stage. However, in the ignition stage, aluminum-lithium alloy particles sequentially exhibit a red gas-phase flame corresponding to lithium and a yellow gas-phase flame corresponding to aluminum. This indicates that during the ignition process of aluminum-lithium alloy particles, lithium first reacts with the oxidative atmosphere and releases heat, providing a heat source for the subsequent ignition of aluminum particles. This also explains why the ignition delay time of metal particles is inversely proportional to the lithium content. An ignition model for aluminum particles in a multi-component atmosphere is established, which further considers the chemical reactions between lithium and oxidative gases, making the model applicable to aluminum-lithium alloy particles. This ignition model effectively describes the impact of particle diameter and lithium content on the ignition process of metal particles. The model is further verified, and the results show that the calculated ignition delay is in good agreement with the experimental data. Overall, this study provides deeper experimental and theoretical insights into the ignition and combustion processes of aluminum-lithium alloys, and the findings can guide the application of aluminum-lithium alloys in propellants.

Speed Effects on the Performance of a Gasoline Engine Using a Mixture of Gasoline-Ethanol Fuels

In recent years, to quantify the quality, energy called "exergy" has been widely used in designs, simulations, and evaluation of the performance of various thermal-chemical systems. The main goal of this project is to evaluate the quality of gasoline engines and the efficiency of a gasoline engine using a mixture of gasoline and ethanol. Furthermore, the effects of 2500 rpm and 4500 rpm on analyzing the second law of thermodynamics were investigated with different fuels. The methods examined in this research include efficiency through heat transfer, irreversibility, total efficiency, and efficiency of burned fuel. The results showed that the performance parameters for gasoline and different ethanol compounds increase until the combustion stage then decrease with the beginning of the expansion phase. For fuel E85, 32.323% of the input energy is converted into indicative exergy and this value for E0, E20, E40, and E60 fuels was 26.27%, 28.5%, 30.3%, and 31.8% respectively. By increasing the amount of ethanol, the efficiency of the second law of thermodynamics increases. The second law efficiency at 4500 rpm for E0, E20, E40, E60, and E85 fuels was, 32%, 35.7% 39.8%, 42.8%, and 50% respectively. Furthermore, by reducing the speed to 2500 rpm, the efficiency for E0, E20, E40, E60, and E85 fuels reduced to 26.7%, 30.4%, 31%, 34%, and 36%, respectively.

Investigation on Nitrogen Chemistry Modeling in Coal Combustion Process with CPD Calculation

ABSTRACT This paper presents a model that combines the CPD model to predict coal pyrolysis and a nitrogen chemistry model to calculate NOx emissions from coal combustion process. The model saves the need to obtain the pyrolysis components of coal by experimental means while ensuring the accuracy of the calculation results to a certain extent. The model is validated by comparison with experimental results from the literature on coal pyrolysis cases and coal combustion cases with non-staging, fuel staging, as well as air staging. In general, the modeling results for the three combustion cases are satisfactory, except for the deviation of the results for NO in the case of some small air ratios at air staging combustion, which leads to some limitations of the model. While according to the reported studies, in the actual process, the small air ratio values are not in the optimal conditions for air staging combustion, making the model of some practical significance. In the future, more work is needed in solving the calculations of coal combustion processes at low air ratios to further refine the model.

Prediction of combustion pressure with deep learning using flame images

Deep learning methods provide data-driven techniques for handling large amounts of combustion data, thus finding the hidden patterns underlying these data. This study aims to predict combustion pressure from flame images, which provide more comprehensive information about the combustion process than traditional pressure sensors. The flame images were captured from a single-cylinder 4-stroke optical gasoline direct injection (GDI) engine at 1000 rpm, 5.7 bar IMEP, and stoichiometric combustion conditions using a high-speed camera. To achieve this prediction, we employed five different models: EfficientNetB4, ResNet50, Ensemble Adversarial Inception ResNet, convolutional neural network (CNN), and CNN-XGBoost. The training dataset comprised 1350 flame images captured from a single-cylinder optical GDI engine across different combustion stages. To ensure robustness, 150 images were used for validation. The models were subjected to a testing set of 4500 flame images obtained from different cycles, to evaluate how well they could perform on new, unseen data. The results showed that EfficientNetB4 achieved an impressive R2 of 0.94 and a low RMSE of 0.70 compared to other tested models. Saliency analysis revealed that the model focuses on subtle flame characteristics and areas without intense flames, which suggests that it detects features invisible to the human eye. Additionally, the proposed deep learning approach is applied for the sake of monitoring cycle-to-cycle variations based on in-cylinder flame propagation where it is found that it produces high accuracy compared to those obtained through pressure sensors. Our findings are intended to advance the adoption of machine learning approaches for assisting in engine design and optimization.

Natural gas-fueled HCCI engine performance and emission analysis and comparison with SI and spark-assisted operations

ABSTRACT The homogeneous charge compression ignition (HCCI) engine is a promising technology in terms of both soot and NOx emission. Natural gas (NG) is advantageous especially for HCCI engines with its single stage combustion, low C/H ratio, and high octane number. Since the main challenge of HCCI technology is stability and transient operations, using HCCI for constant speed operations may be advantageous. In this study, a CI diesel engine, which is used as a generator at constant speed, was modified and converted into an NG-fuelled, SI engine. Then, the engine was supplied with NG for SI, HCCI, and spark-assisted HCCI experiments. Spark-assisted operations were executed by using 3, 5, and 7 degree ignition advance values to assist HCCI combustion. In-cylinder pressure variations, exhaust temperature, specific fuel consumption, and emission values were investigated for comparison of different strategies. Experimental results showed that using the HCCI strategy and retardation of ignition advance of spark-assisted HCCI operations reduced maximum pressure. Therefore, these strategies improved NOx emissions, while HC emissions were slightly increased. The spark-assisted HCCI strategy improves the stability of operation while increasing CO emission. The specific fuel consumption value of HCCI was slightly higher than that of SI operation, while it was lower than spark-assisted strategies.

Study on fuel-N conversion mechanism of ammonia-coal co-firing at different combustion stages

The co-combustion of ammonia and pulverized coal can effectively reduce the carbon emission of thermal power generation. However, ammonia, as a carbon-free fuel, is rich in large amounts of nitrogen, which increases the risk of high NOx emissions. Therefore, it is important to clarify the influence mechanism of ammonia on the NO formation of coal volatile-N and coal char-N in the co-combustion, and to reveal the N oxidation pathway in different combustion stages.In this study, simulations were carried out on the CHEMKIN software to investigate the generation characteristics of NO and the transformation mechanism of fuel-N at different combustion stages of ammonia-coal co-firing. The study showed that ammonia-blending combustion promoted the release of coal volatiles and the oxidation to NO. In the total NO generation during the ammonia-coal co-firing, the proportion of NO produced by ammonia-coupled coal char combustion was very low. Compared with ammonia-coupled coal combustion, the amount of NO produced in ammonia-coupled coal volatile combustion was significantly reduced. Sensitivity analysis and rate of production (ROP) analysis indicated that the increase of H, OH, and O free radicals promoted the NO formation, and that NHi free radicals played an important role in the NO reduction. By analyzing the elementary path of NO generated from ammonia-coupled pulverized coal, coal volatiles and coal char combustion at 1400 °C and 10 % ammonia ratio, it can be seen that the main path of NO formation during ammonia-coupled coal volatiles combustion is VOL→HCN→NCO→NO, CHAR→NO, NH2→HNO→NO, compared with ammonia-coupled coal combustion. The proportion of NH2→NH→NO reaction paths decreased, while the proportion of NH2→N2, NCN→NCO→N2, and NH2→NNH→N2 reaction paths increased respectively, indicating that separation combustion promoted the reduction of NO by NHi free radicals while inhibiting the oxidation of N-containing components.

Study on multi-field coupling characteristics of underground coal combustion and nitrogen injection parameter optimization

Underground coal fires, which are widely distributed and cause serious resource waste and environmental hazards, have become a common concern of the international community. This paper aims to reveal the mechanism of coal spontaneous combustion and the expansion law of underground coal fires. A void rate model from the goaf to the ground surface and a multi-field coupling model for underground coal fires were established. Based on which, the combustion process from the beginning of oxidation to the formation of large-scale fire of the remaining coal in goaf was analyzed. Furthermore, the evolution law of underground coal fire after nitrogen injection and the influence of different nitrogen injection parameters were analyzed. The results show that the coal spontaneous combustion can be divided into three stages: slow reaction stage (stage Ⅰ), violent combustion stage (stage Ⅱ), and stable combustion stage (stage Ⅲ), and the transformation of different stages is mainly controlled by the oxidation reaction rate of coal. To obtain the optimal parameters for nitrogen injection for fire suppression, the fire extinguishing efficiency concerning nitrogen injection time, nitrogen injection amount and nitrogen injection position, as well as the distribution law of nitrogen in rock strata were analyzed. Through range analysis, it is determined that the most effective fire extinguishing occurs with the injection rate of 0.15 m3/s in stage I, and the injection position has little influence on the fire extinguishing effect. This understanding contributes to a deeper understanding of the multi-field coupling mechanism of underground coal fires and provides a guidance for extinguishing and preventing underground coal fires.

The Technical and Economic Aspects of Integrating Energy Sectors for Climate Neutrality

With the development of an energy sector based on renewable primary sources, structural changes are emerging for the entire national energy system. Initially, it was estimated that energy generation based on fossil fuels would decrease until its disappearance. However, the evolution of CO2 capture capacity leads to a possible coexistence for a certain period with the renewable energy sector. The paper develops this concept of the coexistence of the two systems, with the positioning of green hydrogen not only within the renewable energy sector but also as a transformation vector for carbon dioxide captured in the form of synthetic fuels, such as CH4 and CH3OH. The authors conducted pilot-scale research on CO2 capture with green H2, both for pure (captured) CO2 and for CO2 found in combustion gases. The positive results led to the respective recommendation. The research conducted by the authors meets the strict requirements of the current energy phase, with the authors considering that wind and solar energy alone are not sufficient to meet current energy demand. The paper also analyzes the economic aspects related to price differences for energy produced in the two sectors, as well as their interconnection. The technical aspect, as well as the economic aspect, of storage through various other solutions besides hydrogen has been highlighted. The development of the renewable energy sector and its demarcation from the fossil fuel energy sector, even with the transcendent vector represented by green hydrogen, leads to the deepening of dispersion aspects between the electricity sector and the thermal energy sector, a less commonly mentioned aspect in current works, but of great importance. The purpose of this paper is to highlight energy challenges during the current transition period towards climate neutrality, along with solutions proposed by the authors to be implemented in this phase. The current stage of combustion of the CH4−H2 mixture imposes requirements for the capture of the resulting CO2.