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Understanding the ignition and dynamic processes for the combustion of hydrate is crucial for efficient energy utilization. Through reactive force field molecular dynamics simulations, we studied the high-temperature decomposition and combustion processes of methane hydrates in a pure oxygen environment. We found that at an ignition temperature of 2800 K, hydrates decomposed from the interface to the interior, but the layer-by-layer manner was no longer strictly satisfied. At the beginning of combustion, water molecules reacted first to generate OH•, followed by methane oxidation. The combustion pathway of methane is C H 4 → CH 3 • → C H 3 O • → C H 2 O → H C • O → HCO O • → CO (C O 2 ). During the combustion process, a liquid water layer was formed between melted methane and oxygen, which hindered the reaction's progress. When there is no heat resistance, oxygen will transform into radicals such as OH• and O•, which have faster diffusion rates, allowing oxygen to conveniently cross the mass transfer barrier of the liquid water layer and participate in the combustion process. Increasing the amount of OH• may cause a surge in the reaction. On the other hand, when significant heat resistance exists, OH• is difficult to react with low-temperature hydrate components, but it can transform into O• to trigger the oxidation of methane. The H• generated has a sufficient lifetime to contact high-temperature oxygen molecules, converting oxygen into radicals that easily cross the water layer to achieve mass transfer. Therefore, finding ways to convert oxygen into various radicals is the key to solving the incomplete combustion of hydrates. Finally, the reaction pathways and microscopic reaction mechanisms of each species are proposed. [ABSTRACT FROM AUTHOR]

• Rapid cooling is effective for the anti-crystallization of rice husk silica ash. • Cooling pathway patterns are drawn in a uniform temperature-time diagram. • On the diagram, the border zone between the crystalline and amorphous phases is drawn. • The phase diagram is applicable for finding a cooling condition for anti-crystallization. • The border zone is different depending on the inorganic components of rice husk. Rice husk (RH), which is an abundant agricultural waste, consists of ca. 20 % silica (SiO 2 · n H 2 O). Upon RH combustion, a large amount of silica ash is generated. RH silica is originally amorphous; however, the ash is crystalized depending on the conditions of the combustion. Crystallization of RH occurs at a much lower temperature than that of pure SiO 2 due to the eutectic effects of minerals, such as Na and K, that are initially present in RH. Controlling for anti-crystallization is required for expanding the possibility of using RH ash that is abundantly generated by combustion. Here, RH is combusted, followed by a highly thermocontrolled investigation, and the time and temperature dependency of RH ash crystallization are studied. Crystallization is avoidable when the ash is rapidly cooled; for instance, 20 °C/min cooling can avoid crystallization even if the combustion temperature reaches 950 °C. Various pathway patterns for achieving temperature and cooling ratio are plotted on a uniform diagram of temperature vs. time. Furthermore, a border zone, indicating the regions in which RH ash becomes amorphous and crystals, is successfully drawn into the diagram by using the data maintained at a constant temperature. A comparison with a few different types of RH showed that the border zone on the diagram can move depending on their ratios of inorganic elements, causing a eutectic effect. [ABSTRACT FROM AUTHOR]

Oil shale is a critical strategic resource with enormous reserves. In-situ combustion technology offers great potential for the development of oil shale reserves. In this study, the combustion behavior and kinetics of Domanik oil shale were investigated using High Pressure Differential Scanning Calorimetry. Additionally, the thermal behavior of the oil shale during combustion was studied by using a self-designed Porous Medium Thermo-Effect Cell. Furthermore, the stability of the combustion front and the upgrading effect of the combustion process were investigated with Visual Combustion Tube, and the produced oil was analyzed to evaluate its quality. The results showed that the combustion process of oil shale is characterized by two reaction stages. The oil shale was found to form enough coke residue during the oxidation reactions to allow for stable propagation of a combustion front. The produced oil was of better quality compared to the naturally produced bitumen in oil shale, which indicates that the combustion process had a good upgrading effect. The findings of this study provide a better understanding of the in-situ upgrading process of kerogen and provide significant knowledge about the combustion mechanism of oil shale for its potential development using the in-situ combustion technology. [ABSTRACT FROM AUTHOR]

The current research focuses on enhancing oxygenation through titanium dioxide (TiO 2) nanoparticle-doped biofuel-diesel blend and oxy-hydrogen (HHO) gas. Initially, baseline diesel data was collected on conventional diesel engine. A 20% palmyra oil biodiesel (POB) with an 80% diesel blend was formed as POB20 and operated in the next stage. In the successive stages, the diesel engine is retrofitted to work in dual-fuel mode using HHO gas as inducted fuel along with POB20, 50 ppm TiO 2 -doped POB20, and 100 ppm TiO 2 -doped POB20 are used as primary pilot test fuels The minimal hydrocarbon (HC), carbon monoxide (CO), and smoke emissions were noticed with 100 ppm TiO 2 -doped POB20 along with HHO gas about 0.12 g/kWh, 2.25 g/kWh, and 27%, respectively. For the same test fuel operation, brake thermal efficiency (BTE) [by about 5.5%], maximum cylinder pressure (P max) [by about 5.95%], and maximum heat release rate (HRR max) [by about 7.6%] were increased compared with diesel. Due to the promising results of TiO 2 -doped POB20 and HHO gas operation, this research holds promising potential for practical implementations in various fields like agriculture and stationary electric power generation. [Display omitted] • Palmyra oil biodiesel, HHO gas, and TiO 2 nanoparticles are used to run the engine. • Higher ICP and HRR are noticed for TiO 2 -doped biofuel-diesel blend and HHO gas. • TiO 2 -doped biofuel-diesel blend and HHO gas resulted in higher BTE. • Low HC and smoke emissions are noticed with all the oxygenated test fuels. [ABSTRACT FROM AUTHOR]

Ammonia, gaining attention as a carbon-free fuel amid declining fossil fuel reserves, faces challenges like combustion instability and misfiring in its application in internal combustion engines. In this study, polyoxymethylene dimethyl ethers (PODE 3), a clean, renewable, and electrically synthesized fuel with high cetane number and oxygen content, is evaluated as a pilot fuel for ammonia in dual-fuel engines. The study, performed in a dual-fuel optical engine, investigates the use of PODE₃ compared to diesel as direct injection fuels for ammonia combustion, focusing on the impact of PODE 3 injection timing and dwell (the interval between dual-stage injections) on the ignition characteristics of ammonia. The results demonstrate that, compared to diesel, using PODE 3 enhances ammonia combustion in dual-fuel engines. This is evident from increased in-cylinder pressure, higher apparent heat release rate (AHRR), advanced combustion phases, and improved indicated mean effective pressure (IMEP), enhancing overall stability. PODE 3 also effectively minimizes soot generation, evidenced by a 71.5 % reduction in spatially integrated natural luminosity (SINL), accompanied by a 16.9 % increase in peak flame area. Adjusting PODE 3 injection timing is crucial; initial retardation improves combustion performance, marked by higher in-cylinder pressure and AHRR, as well as expanded flame area. However, over-delaying injection timing reduces these gains. The optimal performance is achieved under the SOI-25 condition, balancing combustion and flame development, though some areas remain unburnt. In a dual-stage injection strategy using PODE 3 , where the second injection timing remains fixed at −25 °CA ATDC, the critical adjustment of advancing the first injection timing to −35 °CA ATDC markedly enhances combustion performance compared to a single injection condition. This setting reduces ignition delays, increases peak in-cylinder pressures, and improves stability, which collectively contribute to a significant 20.4 % increase in the peak flame area, particularly between adjacent fuel jets. Expanding upon this, advancing the first injection timing further to −45 °CA ATDC leads to a decrease in peak in-cylinder pressure and AHRR, accompanied by a notable 40.3 % reduction in the peak flame area. This research affirms the advantages of PODE 3 over diesel in ammonia-powered dual-fuel engines, markedly enhancing combustion performance and environmental sustainability, where the injection strategy of PODE 3 emerges as a crucial element. • Research explores PODE 3 as a pilot fuel for NH 3 in dual-fuel engines, focusing on combustion enhancement. • PODE 3 improves ammonia flame propagation, leading to a substantial reduction in soot compared to diesel. • Optimal PODE 3 injection timing (SOI-25) balances combustion and flame development, with some unburnt areas. • Dwell-10 condition in dual PODE 3 injection enhances combustion, increasing peak flame area by 20.4 % and IMEP. [ABSTRACT FROM AUTHOR]

Cocoa Pod Husk (CPH) is biomass waste from plantation activities which have the potential to be used as a companion fuel for low-rank coal (LRC). This study aims to find out the characteristics of combustion using the TGA-DTA testing. This experiment was carried out by testing the crushed CPH and LRC raw materials with a particle size of 40 mesh based on ASTM standards, then CPH was added to the LRC. The composition of adding CPH into the LRC is 10%, 30%, and 50%, respectively. The results of this experiment presented that there is an increase in combustion performance as a result of adding the CPH into the LRC. This is a result of a decrease in the burning temperature of volatile matters and ignition temperature. The optimum amount of addition which gives a significant increase in combustion performance is obtained by adding 10% CPH into the LRC. [ABSTRACT FROM AUTHOR]

High-speed video recordings of slab burner experiments were analyzed using a machine learning approach with convolutional neural networks in order to compute the regression rate of hybrid rocket fuels over time. Combustion tests of paraffin-based fuel grains performed in two different hybrid rocket slab burners were recorded with high-speed video cameras and the resulting image data are analyzed in order to determine the height of the fuel in each frame. To this end, a deep neural network with U-net architecture is trained in a supervised fashion to segment the shape of the fuel slab. It is demonstrated that this approach is more capable to segment combustion images in unsteady flow conditions than classical computer vision methods based on thresholding or edge detection. Furthermore, methods in the area of uncertainty quantification of neural networks are applied to estimate the errors in the neural network prediction to new previously unseen data. Finally, the regression rate of the fuel is computed as the rate of change of this height. This method enables automatic analysis of a large amount of video data, taking full advantage of the optical access capabilities of slab burners. Additionally, the method delivers not only the time and space average values of the fuel regression rate, but also quantifies its variation over time and over the length of the slab, providing deeper insights into the combustion mechanics of hybrid rockets. • Shape of solid fuel detected in images from combustion test using a U-Net. • U-Net applied to a high-speed video enables measurement of the regression rate. • Regression rate can be resolved as time- and space-dependent quantity. • Method is applied to combustion tests performed at two different test facilities. • Tests under both atmospheric and super-critical pressure conditions were evaluated. [ABSTRACT FROM AUTHOR]

To promote the efficient and clean application of low-carbon alcohol fuels in internal combustion engines, this article compares and studies the effects of three internal EGR strategies, including exhaust valve lift strategy (EVVL), exhaust timing advance strategy (EVT), and intake valve timing advance strategy (IVT), on the combustion, performance, and emissions of gasoline, methanol, and ethanol. Under the same internal EGR rate, the internal EGR temperature generated by the three valve strategies is, from highest to lowest, as follows: EVT, EVVL, and IVT. With an increase in internal EGR in the cylinder, the ignition delay and combustion duration under the EVVL and IVT strategies increase progressively, whereas the ignition delay under the EVT strategy tends to first shorten and then lengthen. Methanol has the shortest combustion duration. Furthermore, methanol and ethanol have lower heat transfer and exhaust losses than gasoline. The thermal efficiency of methanol, ethanol, and gasoline can be raised by 7.7%, 7.5%, and 7.2%, respectively, using the IVT strategy; 3.1%, 3.9%, and 4.6% using the EVVL strategy; and 6.82%, 6.85%, and 7% using the EVT strategy. The combination of methanol and ethanol with internal EGR technology greatly reduces NOx emissions, with an 84.5% reduction under the EVVL strategy. [ABSTRACT FROM AUTHOR]

Carbon sequestration and utilization has been proposed as a method for decarbonizing high-efficiency industrial gas turbines operating on natural gas fuels for power generation and industrial markets. To increase the efficiency of the carbon removal process from the exhaust stream of the turbine, exhaust gas recirculation (EGR) can be used. EGR recycles a portion of the engine exhaust into the inlet, increasing the concentration of inert species in the exhaust stream to improve the performance and cost-effectiveness of CO2 separation systems. This strategy can, however, reduce the oxygen concentration in the air, leading to changes in flame stabilization in the combustor. In this study, we investigate the effect of air diluted with inert gases of different compositions and the impact that these mixtures have on flame static and dynamic stability. A swirl-stabilized flame in a single-nozzle, variable-length combustor is used to measure the flame behavior for oxygen concentrations of 15-21% by volume. A constant adiabatic flame temperature test matrix is conducted to mimic operation in an industrial gas turbine. High-speed chemiluminescence imaging is used to determine the change in flame shape and dynamics for each gas composition. As the oxygen concentration decreases, the flame lifts from the centerbody, resulting in an aerodynamically stabilized flame at the lowest O2 concentrations. Different compositions of gases result in different flame shapes, where higher levels of N2 in the diluents result in more flame stabilization in the outer recirculation zone as compared to those with higher levels of CO2. The flame oscillation mechanisms also change with oxygen concentration, where the lifted flames at low O2 levels exhibit an ignition/extinction oscillation mode as compared to a vortex-shedding-coupled oscillation mode at high O2 levels where the flame is stabilized on the centerbody. Companion chemical kinetics simulations are used to explain changes in the flame's shape and behavior. [ABSTRACT FROM AUTHOR]

As alternative fuels are designated for future energy applications, flexible combustor designs require considerable development to ensure stable operation with reduced NOx emissions. A nonpremixed variable swirl burner was used to experimentally appraise changes in NO production pathways, with CH4 NH3 and H2 flames, alongside intermediate fuel blends. Maintaining an equivalent thermal power and flame temperature between fuels, preheated reactants (500 K) were supplied to the burner, with parametric changes made to pressure (1-6 bara) and swirl number (0.8-2.0). NO production was characterized, alongside variations in flame structure and topology, with a correlation demonstrated for exhaust emissions. NO production was shown to be sensitive to combustor pressure, providing an expected increase for CH4 and H2 flames. Emission profiles from both NH3 and H2 flames are shown to be significantly augmented by a change in swirl number. As NH3 fractions were increased in the H2 blend, a decaying trend in NO emissions was observed with an increase in pressure, and as a function of mixture ratio. However, this behavior was markedly augmented by a change in swirl number and suggests that further reductions may be possible at increased pressure. At the low swirl/high pressure condition, the NH3/H2 blend outperformed pure H2, providing lower NO concentrations. Emissions data were normalized using the traditional dry/O2 correction, alongside mass scaled by thermal power, with a comparison provided. The corresponding differences in emission formation pathways were investigated, alongside high-speed OH* chemiluminescence to further elucidate findings. [ABSTRACT FROM AUTHOR]

Studying the relationship between electronic structure and activity helps to understand the catalytic mechanism since the catalytic combustion is a redox reaction dominated by electron transfer. Herein, we regulated the electron energy and O p-band center of La-based perovskite catalysts by a facile method of changing the B-site ion (B = Co, Mn, Fe). The crystal structure, morphology, reducibility, element valence distribution, and catalytic properties of prepared catalysts were characterized. Combining with DFT calculation, it was found that the low electron energy in (110) facets of LaCoO3/SiO2 catalyst contributes to the formation of reactive oxygen species and high-valence Co3+ ions. The highest oxygen adsorption activation capacity of LaCoO3/SiO2 originates from a moderate location of the O p-band center with respect to the Fermi level. As expected, the LaCoO3/SiO2 sample shows higher n-butylamine oxidation activity than that of LaMnO3/SiO2 and LaFeO3/SiO2. This work provides different insights into understanding the activity of La-based perovskite catalysts for oxidation reactions. [ABSTRACT FROM AUTHOR]

Microcombustors are microscale combustion devices that can be used to power microelectromechanical systems. Many combustor configurations are reported in the literature and, among them, combustion in a microscale recirculating heat exchanger is a feasible option. In this work, a simple, double‐channel, recirculating heat exchanger is considered. The novelty of the present work lies in the heat transfer analysis approach to design a microcombustor. A combustor is designed using thermal resistance networks for a premixed fuel containing a methane–air mixture in stoichiometric ratio. The length of the combustor is designed based on the position of the combustion flame. Computational fluid dynamics is utilized to validate the theoretical results. The analysis is carried out for adiabatic and nonadiabatic conditions. The combustor lengths for adiabatic and nonadiabatic (ceramic) combustors vary from 39 to 242 mm and 49 to 276 mm, respectively, for variations in the mass flow rate of the premixed gases from 6 to 10 mg/s. A minimum limiting flow rate of 6 mg/s was identified. The average error in the maximum combustion gas temperatures between the theoretical and CFD results obtained in this work is 4.2%. The theoretical approach presented can be suitably applied to more complex geometries involving multichannels and variations in geometrical properties. [ABSTRACT FROM AUTHOR]

This study provides a chemical mechanism reduction strategy based on entropy production analyses in both auto-ignition and laminar flames, which enhances the predictive accuracy for laminar burning velocities. In addition to chemical reactions, other irreversible sources causing entropy generation, such as mass diffusion and heat conduction, are considered in the modified approach. Specifically, initial skeletal mechanisms are first generated based on important reactions that contribute to entropy production in auto-ignition processes. Mechanism patches are then constructed to include important species and reactions, which contribute to entropy production from mass diffusion and heat conduction in laminar premixed flames beyond the pre-defined thresholds, respectively. Finally, the initial skeletal mechanisms and mechanism patches are combined to establish the final skeletal mechanisms. In this way, two final skeletal mechanisms for n-dodecane, consisting of 162 species and 2276 reactions, and 160 species and 1916 reactions, respectively, are developed from the detailed POLIMI mechanism with 451 species and 17,848 reactions. The two final skeletal mechanisms are proven to accurately predict laminar burning velocities and entropy production in n-dodecane flames with insignificant variations in the simulation results compared to the detailed mechanism, while their accuracy in predicting ignition delay times relies on the initial skeletal mechanisms. Specifically, the reduced mechanism with 160 species and 1916 reactions exhibits less satisfactory performance in predicting ignition delay compared to that with 162 species and 2276 reactions, indicating that a lower threshold is required to generate the initial skeletal mechanism through entropy production analysis of homogeneous auto-ignition processes. Additionally, compared with the reduced mechanisms with similar sizes obtained with other mechanism reduction strategies, the two final skeletal mechanisms accurately capture the characteristics of laminar burning velocities and ignition delay times, with similar calculation time required. [ABSTRACT FROM AUTHOR]

The objective of the present study is to investigate two new formulations of the Conditional Source-term Estimation (CSE) model using Reynolds Averaged Navier Stokes (RANS) calculations applied to Sandia flames D and F. The first method relies on a first-order Tikhonov regularisation and the second approach denoted by CSEBP, includes Bernstein polynomials to approximate the conditional averages. Current predictions for temperature, main product and minor species are consistent with previously published CSE results with a different implementation. However, smoother conditional profiles are obtained with less a priori information. Both formulations have good predictions for flame D with minor discrepancies near the inlet and one position downstream, with occasional small advantages for CSEBP. In contrast to previous RANS-CSE attempts, stable solutions are obtained for flame F in good agreement with the experiments. Considering the RANS and single conditioning limitations to capture transient effects, both formulations predict the changes of conditional averages and Favre averaged quantities from flame D to F well, except at one location where the predicted re-ignition occurs earlier than what is seen in the experiments. Additionally, the computational cost of the CSE routine is decreased significantly from $ 85\% $ 85 % of the total computational cost to only $ 10\% $ 10 % for the first formulation and under $ 3\% $ 3 % for CSEBP by means of using hash tables for storing the results of interpolations from the chemistry tables and avoiding on-the-fly interpolations. [ABSTRACT FROM AUTHOR]

Black carbon, or soot, is one of the highest contributors to global warming. The International Civil Aviation Organization (ICAO) has adopted regulatory standards for soot from aircraft engines, also referred to as a nonvolatile particulate matter (nvPM), to limit or reduce the harmful impacts of nvPM on the environment. Sustainable aviation fuels (SAF) offer advantages to reduce soot emissions and overall environmental impact but require extensive testing and evaluation before wider adoption. Typical measurements of soot produced by combustion of aviation fuels require full-sized jet engines and large volumes of fuel, which can be prohibitively expensive. This study investigates flame spray pyrolysis (FSP) as a simple bench-top tool for comparison of soot emissions from the combustion of different liquid jet fuels. A sampling assembly is designed for soot collection and analysis. Morphological analysis follows from transmission electron microscopy (TEM) image analysis and mobility (differential mobility analyzer) classification. Morphologies are compared to previous measurements from aircraft turbines. Soot agglomerate size distributions and elemental to total carbon ratios (EC/TC) are measured for three liquid fuels and flame conditions with Reynolds numbers and burner equivalence ratios ranging from 6100 to 9100 and 7 to 13, respectively. Day-to-day variations in the dilution ratio resulted in up to 20% variability in the measured total agglomerate number-based concentration and mobility diameter. Geometric mean primary particle and mobility diameter values are below 21 and 104 nm, respectively, in excellent agreement with those emitted from jet engines and prior work using FSP. EC/TC remains > 0.75 for most flame conditions and fuels and increases with burner equivalence ratio, but values as low as 0.63 are measured from SAF combustion. Copyright © 2024 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The results of experimental studies of the cocombustion of coal–water fuel with fuel oil are presented. According to the results of experimental studies, the efficiency of joint ignition of stationary single droplets of coal–water fuel and fuel oil was substantiated. A decrease in the ignition delay times of fuel droplets was found in comparison with the ignition of only coal–water fuel droplets under identical conditions. A significant decrease in the ignition delay times of coal–water fuel droplets is typical for droplets with sizes of 2 and 3 mm in the entire studied temperature range of the oxidizer (from 873 to 1,273 K) and distances (from 2 to 4 mm) between drops of coal–water fuel and fuel oil. It has been experimentally established that the reduction of ignition delay times is 58 and 70%. For droplets of coal–water fuel with a characteristic size of 1 mm, the changes in ignition delay times are ambiguous. The joint combustion of coal–water fuel and fuel oil affects the ignition of droplets of coal–water fuel, and the characteristic size of which is more than 1 mm. With this method of burning coal–water fuel and fuel oil, the latter acts as a catalyst when igniting coal–water fuel, thereby ensuring a stable combustion of such fuel. The combustion of two-component coal–water fuel together with fuel oil can avoid the problems typical of such fuels: reduce the requirements for spraying devices, solve the problem of low reactivity, increase the completeness of combustion of this fuel, and fully use it in the production of thermal and electrical energy. [ABSTRACT FROM AUTHOR]

Blending hydrogen with natural gas is useful for reducing CO 2 emissions, but this alters the flame structure, creating challenges for flame stability. Numerous researches on methane-hydrogen flame structure have been carried out based on two-dimensional combustion diagnostic techniques such as flame chemiluminescence and planar laser-induced fluorescence. In this paper, a low-cost OH* chemiluminescence imaging system consisting of 8 ultraviolet (UV) cameras is proposed to reconstruct the three-dimensional (3D) structure of methane-hydrogen flames, and validated through use of the correlation coefficient. Further experimental investigations of the low-swirl methane-hydrogen flames are performed by this computed tomography of chemiluminescence (CTC) system. The flame properties are determined to evaluate the effects of various fractions of blended hydrogen on the flame structure, including the flame center of mass, flame surface density and fractal dimension. Results showed that the flame initially has bowl-shape structure. The flame height gradually decreases and the flame cross-sectional area increases as the blended hydrogen fraction increases. Meanwhile, the bottom of the flame moves toward the nozzle outlet. Nevertheless, when the blended hydrogen fraction reaches 50%, the flame transforms into a cup-shaped flame and shows a double-layer flame structure. When the flame is bowl-shaped, the flame center of mass moves away from the nozzle center axis with increasing blended hydrogen fraction, but the fractal dimension and flame surface density are not sensitive to the blended hydrogen fraction. In contrast, when the flame is cup-shaped, the flame center of mass moves towards the nozzle center axis, and the flame surface density and fractal dimension increase significantly, indicating the increase of flame wrinkling. These results reveal that blending hydrogen leads to two distinct flame structures and characteristics in low-swirl flame, also demonstrate that the proposed 3D low-cost CTC system based on multiple UV cameras is well-suited for combustion diagnostics. • A low-cost 3D computed tomography of OH* chemiluminescence system is proposed. • Two distinct low-swirl CH 4 –H 2 flame shapes are observed and reconstructed. • The change in flame shape is accompanied by a significant change in flame wrinkling. [ABSTRACT FROM AUTHOR]

To elucidate structure‐reactivity relationship and prepare improved catalysts for soot combustion, a series of CuO/CeO2 with different loadings have been fabricated by the impregnation method. With XRD and XPS extrapolation methods, it is disclosed that CuO disperses finely on the CeO2 support to form a monolayer with a capacity around 1.06 mmol 100 m−2, which equals to 2.9 wt. % CuO loading. Below this capacity, CuO is in a sub‐monolayer state. However, above this capacity, CuO micro‐crystallites are formed, and co‐exist with the monolayer CuO. By increasing CuO loading, soot combustion activity of the catalysts increases as well until it reaches the monolayer dispersion capacity. Further increasing the CuO loading to 5 % decreases the activity slightly, and then remains constant. Therefore, an apparent monolayer dispersion threshold effect is observed for soot combustion on CuO/CeO2 catalysts. It is found that the amount of surface‐active O2− sites plays critical role for the catalytic activity. To obtain the most active CuO/CeO2 catalyst, a monolayer amount of CuO should be loaded on the supports. [ABSTRACT FROM AUTHOR]

The purpose of this work is to investigate the effects of adding hydrogen to the fuel on the combustion induced vortex breakdown flashback phenomenon in a combustion chamber. An atmospheric research burner is selected for studies and the analysis is performed using numerical simulations. In order to model the turbulence-chemistry interactions, the EDC combustion model is utilized and the GRI 2.11 reaction mechanism is used to investigate the combustion process as carefully as possible. The present studies are performed keeping the exit temperature constant. To do this, by adding any amount of hydrogen to the premixed inlet flow, the methane is decreased by using the trial-and-error until the mass averaged exit temperature remains almost constant. The purpose of applying this limitation is to keep the cycle operational condition unchanged that is important for adding hydrogen to the existing combustion chambers especially from technological viewpoint. In addition, the thermal NO x production is controlled. In the following, the effect of hydrogen addition on the flame thickness and flame shape is investigated and finally, the effect of operating pressure on the flashback behavior is analyzed. • Effect of hydrogen addition to the fuel on the combustion induced vortex breakdown flashback is investigated. • The studies are performed keeping the exit temperature constant. • By adding hydrogen and reducing methane, the equivalence ratio decreases but the flame moves upstream. • Adding hydrogen reduces the flame thickness, but at higher hydrogen percentages, flame thickness will no longer depend on hydrogen addition. • It is illustrated that increasing the pressure moves the upstream in both pure methane and hydrogen-methane fuels. [ABSTRACT FROM AUTHOR]

The effects of the vent burst pressure (P v) on the vented explosion of hydrogen-methane-air mixtures are investigated in a cylindrical vessel connected with a duct. The results demonstrate that P v significantly affects the flame behaviors and overpressure inside and outside the venting configuration. The flame front velocity at the vent increases with P v. Two pressure peaks, P a c , caused by the acoustically enhanced combustion, and P s e , caused by the secondary explosion, dominate within the vessel at P v ＜ 132 kPa and P v ≥ 132 kPa, respectively. The maximum overpressure (P max) inside the duct increases with P v. The maximum pressure rise (d P / d t) of the duct is always higher than that of the vessel. As P v increases, increased turbulence of unburned gases within the duct results in higher d P / d t. Exit flame speed increases with P v. When P v ≥ 153 kPa, "Mach disk" appears outside the relief duct. Three pressure peaks, P a , P b , and P e x t , due to vent failure, the secondary explosion, and the external explosion, respectively, occur in the external pressure curve. P b dominates outside the configuration except for P v = 153 kPa. • Initial flame velocity in the duct increased with P v. • P v was positively correlated with P max inside the duct. • "Mach disk" appeared only when P v ≥ 153 kPa. • Both P a and P e x t increased with the increase of P v. [ABSTRACT FROM AUTHOR]

This study investigates the ignition and combustion characteristics of intersecting diesel surrogate (pilot) and hydrogen (H 2 , main) jets under engine-relevant conditions. The experiments, performed in an optically accessible constant-volume combustion chamber (CVCC), utilised two converging single-hole injectors, with the pilot fuel accounting for 12% of the total injected fuel energy. This study investigated the effects of two key parameters on the ignition process: jet interaction angle (12° to 19°) and ambient O 2 concentration (10 to 21 vol.%). The results show that the presence of H 2 either advances or delays pilot ignition depending on whether the pilot n -heptane jet ignites before or after interacting with the H 2 jet, respectively. The pilot-main ignition transition period is influenced by both jet interaction angle and ambient O 2 concentration. Under identical ambient conditions, a smaller jet interaction angle results in a longer transition, while for a constant angle, lower ambient O 2 leads to a more prolonged transition. Under 10 vol.% O 2 conditions, flame kernels emerge upstream of the main flame body, before eventually merging with the reacting jet downstream, with this phenomenon observed to induce variation in heat and flame stabilisation characteristics. An explanation for the upstream kernel formation is offered based on the entrainment of residual pilot n -heptane-jet fuel into the upstream region of the still-injecting main jet, with the relative jet momentum a likely key contributor influencing this entrainment that impacts kernel formation. • Study of main H 2 and pilot diesel jet interactions in engine relevant conditions. • Studies on jet interaction angle, ambient O 2 and relative jet momentum effects. • Main jet interaction and pilot injection duration impact pilot ignition delay. • Jet overlap and ambient reactivity influence pilot-to-main jet ignition transition. • Interaction of H 2 jet and pilot remnants can impact flame stability and heat release. [ABSTRACT FROM AUTHOR]

This study explores the transition in combustion technologies from dry micro-mix hydrogen-air to wet micro-mix hydrogen-oxygen configurations. The investigation involves a comprehensive analysis of the combustion processes currently being considered for converting methane gas turbines to methane-hydrogen mixtures and hydrogen, including wet premixed, dry low emission, sequential combustion, and micro-mix, examining key parameters such as efficiency, emissions, and overall performance. Then, the work considers the shift from utilizing air as an oxidizer to oxygen. Wet micro-mix hydrogen-oxygen combustion is then discussed for its impact on combustion dynamics and the potential for achieving zero emissions, cancelling NOx emissions in addition to CO 2 emissions. The findings contribute valuable insights into the feasibility and advantages of transitioning from conventional hydrogen-air combustion to innovative wet hydrogen-oxygen combustion, paving the way for more sustainable and environmentally friendly combustion technologies. Scheme of a hydrogen energy storage system comprising one electrolyser, two tanks for the hydrogen and the oxygen, and an O 2 /H 2 /H 2 O gas turbine power system. The system could be able to receive non-dispatchable electricity and release dispatchable electricity working as a battery but without any limitation on the amount of energy storable, or the time of the storage. [Display omitted] [ABSTRACT FROM AUTHOR]

Reactivity-controlled compression ignition (RCCI) is a promising new combustion technology for marine applications. It has offered the potential to achieve low NOx emissions and high thermal efficiency, which are both important considerations for marine engines. However, the performance of RCCI engines is sensitive to a number of factors, including the start of injection. This study used computational fluid dynamics (CFD) to investigate the effects of start of ignition (SOI) on the performance of a marine RCCI engine. The CFD model was validated against experimental data, and the results showed that the SOI has a significant impact on the combustion process. In particular, the SOI affected the distribution of fuel and air in the combustion chamber, which in turn affected the rate of heat release and the formation of pollutants. Ten different SOIs were implemented on a validated closed-loop CFD model from 96 to 42 CAD bTDC (crank angle degree before top dead center) at six-degree intervals. A chemical kinetic mechanism of 54 species and 269 reactions tuned and used for simulation of in-cylinder combustion. The results show that in early injection, high-reactivity fuel was distributed close to the liner. This distribution was around the center of late injection angles. A homogeneity study was carried out to investigate the local equivalence ratio. It showed a more homogenous mixture in early injection until 66 CAD bTDC, after which point, earlier injection timing had no effect on homogeneity. Maximum indicated mean effective pressure (IMEP) was achieved at SOI 48 CAD bTDC, and minimum amounts of THC (total hydrocarbons) and NOx were observed with middle injection timing angles around 66 CAD bTDC. [ABSTRACT FROM AUTHOR]

In recent decades, there has been growing interest in the thermal conversion of various alternative fuels, such as biomass and waste-derived fuels. One of the technological solutions for the so-called direct co-combustion of fuels is to create mixtures of various fuels, called mixed secondary fuel. However, mixed secondary fuel has different properties compared to primary fuels. Due to this, by properly selecting the types and proportions of mixtures, it is possible to eliminate their potentially negative impact on both combustion technology and the natural environment. In this paper, we decided to prepare mixed secondary fuel by mixing sunflower husk pellets with RDF (refuse-derived fuel) in a ratio of 1:1 and then analyze the combustion process of the produced fuel in fluidized bed conditions. The results obtained on the basis of the presented research indicate that the mixed secondary fuel eliminated the impact of alkali metal compounds on reducing the melting point of ash and, consequently, on the combustion process of the mixed secondary fuel. An additional benefit is the reduction of emissions of harmful compounds into the atmosphere occurring during the combustion of municipal waste and compliance with the concept of the circular economy. [ABSTRACT FROM AUTHOR]

Pulverized coal pyrolysis based on solid heat carrier has a huge advantage in high tar yield. In this study, pyrolysis experiments on pulverized coal were conducted in a lab-scale fluidized bed reactor at 650 °C, utilizing char as the solid heat carrier. The influence of mass ratio of char to coal (RATIO) was investigated. Results show that the incorporation of solid heat carrier of char significantly enhanced the primary pyrolysis reaction in coal pyrolysis, resulting in increasing yields of tar and gas but reducing one of char. The yield of tar maximally reached 148.80–262.22% of the Gray–King analysis value at the RATIO of 14.52 g/g. As the RATIO increased, the tar contained more light component content, indicating that incorporating solid heat carriers improved the tar quality. These findings offer significant insights for the design of fluidized bed pyrolysis unit utilizing char as solid heat carrier. [ABSTRACT FROM AUTHOR]

In the present study, a multi-nozzle hydrogen burner based on the micromix combustion principle (MCP) and designed to operate under atmospheric pressure and without preheated air was investigated both numerically and experimentally. Previous investigations regarding this type of burner have shown low NO x emissions and no risk of flashback, which are the two main issues when burning pure hydrogen. Numerical models were calculated based on a CFD code, and the burner performance was assessed under various operating conditions, including thermal powers between 5 and 25 kW and excess air ratio between 1.3 and 2. The importance of turbulence-chemistry interaction modelling and differential diffusion effects, particularly for highly diffusive flames such as hydrogen, has been widely addressed. All numerical results were validated with experimental results from a laboratory-scale burner using thermocouple measurements, including the corresponding radiative corrections. An infrared camera was used to detect and study the flame shape under various operating conditions. The turn-down of the multi-nozzle hydrogen burner was extensively analysed, focusing on the penetration depth or, equivalently, the momentum flux ratio as a highly sensitive design parameter. Low Reynolds number flames were also considered, demonstrating a collapse of the MPC under these conditions. These conclusions emphasize the relevance of this parameter in determining the optimal operating conditions and guiding the redesign process. Likewise, the investigation of deviations from optimal settings emphasizes potential applications of this burner design in industrial processes. • Design and characterization of a hydrogen multi-nozzle micromix burner. • Thermography diagnosis of the flame stability: flame merging, shape, size and buoyancy phenomena. • NOx emission assessment for industrial potential application. [ABSTRACT FROM AUTHOR]

Microwave-induced combustion (MIC) was proposed in this study for honey decomposition aiming for As, Cd, Hg, and Pb determination by inductively coupled plasma mass spectrometry (ICP-MS). Sample mass (up to 1.0 g), absorbing solution (0.5 to 14.4 mol L−1 HNO3, and H2O), heating program, and combustion aids were evaluated. The Eurachem guidelines were used for method validation. The proposed method enabled combustion of a high sample mass (0.8 g of honey, with 0.4 g of microcrystalline cellulose and 100 µL of 6 mol L−1 NH4NO3) using 6 mL of an absorbing solution consisting of 1 mol L−1 HNO3, which resulted in low residual carbon in solution (< 25 mg L−1). Honey samples from different geographical origins were analyzed. Results showed no significant difference in comparison to other two microwave decomposition methods, based on microwave-assisted wet digestion with single reaction chamber (MAWD-SRC) and microwave-assisted wet digestion (MAWD). Standard addition experiments resulted in recoveries higher than 98%. The limits of detection ranged from 1.10 (As) to 4.60 ng g−1 (Pb). In addition to using only diluted reagents and resulting in digests virtually free of interferences, the proposed method was faster (< 30 min) than most of those presented in the literature. [ABSTRACT FROM AUTHOR]

The present study focuses on the removal of ineffective hydroxyl surface (B–OH) of the shell of pristine boron (B) particles, followed by its modification using a low-cost, eco-friendly, and non-hazardous ethylene glycol (EG). Subsequently, very small-sized titanium dioxide (TiO 2) particles are coated onto the boron surface by adding titanium tetraisopropoxide (TTIP) precursors at room temperature. Characterization techniques were employed to investigate the structure and morphology of these materials. FTIR, XPS, and TEM analysis reveal that EG effectively removes ineffective boron hydroxyl surfaces and modifies the surface through passivation by its surface functionalities. Furthermore, EG assists in the coating very small-sized TiO 2 particles on the boron surface. Thermal stability tests show that the modified boron surface and TiO 2 -coated boron surface exhibit earlier oxidation of the core boron compared to pristine boron. This enhanced capability for earlier oxidation of core boron was further investigated in the shock tube and bomb calorimeter for measurement of ignition delay time and heat of combustion. The findings demonstrate that room temperature synthesized TiO 2 -coated B particles (ignition delay time of ∼181 μs and heat of combustion of ∼17.3 kJ/g) outperform pristine B particles (ignition delay time of ∼284 μs and heat of combustion of ∼13.2 kJ/g). This improvement is attributed to the removal of ineffective boron hydroxyl surfaces, surface modification, uniform coating with very small TiO 2 particles, the catalytic effect of TiO 2 on oxygen diffusion, and effective oxidation of core boron. This study suggests that efficient energetic material can be achieved at room temperature with no potential harm to the environment. [ABSTRACT FROM AUTHOR]

Gallium (Ga) and germanium (Ge) critical elements have a wide range of applications and market value. Extracting critical elements from coal gangue and combustion products can alleviate pressures on primary mining resources. Understanding the transformation behavior of Ga and Ge during coal gangue combustion processes is significant for resource utilization and environmental protection. Coal gangue from Xing'an League, Inner Mongolia, was chosen to explore how combustion temperatures (600 °C to 1000 °C) and particle sizes (50, 80, 10, 140, and 200 mesh) influence Ga and Ge migration during combustion. Techniques such as ICP-MS, XRD, XRF, SEM, TG-DSC, and sequential chemical extraction were employed to analyze the transformation of minerals and to quantify the contents and occurrence forms of Ga and Ge. Smaller gangue particle sizes were associated with higher concentrations of Ga and Ge. Approximately 99.19% of Ga and Ge in coal gangue were found in the residual, organic/sulfide-bound, and metal-oxide-bound modes. High temperatures promoted element volatilization and changed the reactions and interactions between elements and minerals. As combustion temperatures rose from 600 °C to 1000 °C, Ga and Ge contents in the products declined progressively. Under high temperatures, minerals like kaolinite, illite, and pyrite in gangue converted to silicate glass phases, mullite, and hematite. Minerals like kaolinite, calcite, and pyrite melted, leading to increased cohesion and agglomeration in the products. Over 90% of Ga and Ge in the combustion products existed in the residual, organic/sulfide-bound, and metal-oxide-bound forms. Moreover, Ga was enriched in combustion products, with its content exceeding critical extraction levels. The results may provide a useful reference for developing critical elements enrichment, extraction, and separation technologies from coal gangue. [ABSTRACT FROM AUTHOR]

The present study explores a nano-grained perovskite material for use in an intermediate-temperature solid oxide fuel cell. Electrolytes with the formula Ba1−xCaxCe0.8Nd0.2O3−δ (BCCN), where x = 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05, were synthesized through the sol–gel auto-combustion process. Structural, surface morphology and vibrational analyses were conducted through XRD, SEM, FTIR, and Raman studies. Scherer's formula revealed predicted crystallite sizes for the electrolyte materials ranging from 25.13 to 38.69 nm. Morphological assessments determined grain diameters between 1 to 3 µm. Raman spectroscopy identified the 355 cm−1 vibrational mode associated with CeO6 octahedra, while FT-IR identified bands corresponding to M–O vibrations. Electrical impedance spectroscopy results indicated ionic behavior conducive to electrolytes, with overall conductivities increasing with measurement temperature. Notably, bulk conductivity surpassed grain boundary conductivity, with the highest overall conductivity observed in x = 0.05 compositions among the examined perovskite oxides. [ABSTRACT FROM AUTHOR]

Animal dispersal is often phenotype‐dependent and can exert evolutionary pressures on populations in which it occurs. The evolutionary pressure arising from phenotype‐dependent dispersal is called spatial sorting. We examined the evolutionary pressure arising from spatial sorting (sorting pressure) caused by downstream dispersal in juvenile white‐spotted char Salvelinus leucomaenis under ordinary flow conditions. We conducted outdoor experiments using an artificial channel with 10 steps to investigate the relationship between phenotypic characteristics and the occurrence or distance of downstream dispersal during five daytime hours. Six experiments were conducted using young‐of‐the‐year juveniles collected early in the morning of each experimental day. We focused on two phenotypes, fork length (body size) and station‐holding (SH) behavior, where juveniles remain sedentary on the substrate. Juveniles were assigned to the "SH group" if they exhibited SH behavior for more than 10 s during a 540‐s observation period, and to the "swimming group" if they exhibited SH behavior for less than 10 s. Juveniles in the swimming group had a higher occurrence of downstream dispersal than in the SH group. In addition, large juveniles in the SH group and small juveniles in the swimming group tended to show long dispersal distances. These results suggest an effective sorting pressure against juveniles with active swimming behavior. This sorting pressure may accumulate in isolated char populations located above a tall migration barrier and contribute to the creation and maintenance of the reported interpopulation variation in SH behavior. [ABSTRACT FROM AUTHOR]

The change in the content and composition of polycyclic aromatic hydrocarbons (PAHs) was studied in organic horizons of soils of the boreal zone subjected to combustion under oxygen deficiency conditions. Organic soil horizons from the oligotrophic bog and two types of forest ecosystems (lichen pine and green moss spruce forest) were analyzed. It was found that combustion conditions, the composition of burned organic material, and its flammability influence significantly the content and composition of PAHs. Polyarenes are formed, for the most part, at 300°C. As compared to original samples, their content increases from 2.7 to 9.7 times. The maximum content of PAHs in the samples is reached at 300°C, whereas it falls by 5.8–33.0 times at 500°C. An abrupt decrease in the PAHs content is probably due to the decomposition to simpler substances. The experimentally obtained ratio of low-molecular weight to high-molecular weight polyarenes, which exceeds one, may indicate the pyrogenic origin of PAHs. [ABSTRACT FROM AUTHOR]

Fire risk analysis of electric vehicles and internal combustion vehicles in open car parks: part 2: fire safety and reliability analysis In order to counteract climate change, it is necessary to switch from vehicles with combustion engines to electric vehicles. Consequently, an increasing number of electric vehicles can be observed in Germany. In this context, the question arises whether and if how this development influences the fire risks in open car parks. Answers to this question are the subject of a research project under the leadership of the Institute of Steel Construction of Leibniz University Hannover in cooperation with the iBMB, Division of Fire Safety, of TU Braunschweig. In particular, the project is investigating the influence of a fire scenarios with electric vehicles compared to vehicles with combustion engines on the load‐bearing behaviour structure of an open car park. In this paper, the methodological approach to evaluate the fire risk based on a reliability analysis for the load‐bearing structure of these car parks is explained. By means of the reliability analysis, the fire risk assessment procedure is illustrated for the composite beam using exemplary fire scenarios. As a result, it can be concluded from the fire risk analysis that fire scenarios with electric vehicles do not have a higher fire risk than conventional vehicles with combustion engines and fulfil the required safety level. [ABSTRACT FROM AUTHOR]

Numerical calculations of the innovative flue gas recirculation (FGR) system through an inactive coal pulverizer for a 40% load of the OP 650 boiler at the Jaworzno III Power Plant were carried out. The research was conducted to determine the effect of FGR on the formation of NOx, CO emissions, and low-NOx waterwall corrosion. Using numerical modelling, the influence of the place of injection of recirculated flue gas on the formation of NOx was also investigated. The tests were carried out based on data from the boiler monitoring system and calculation results using a 0-dimensional model. Modelling of the FGR was performed for five variants. FGR equalized the temperature in the furnace, eliminating temperature peaks in the burner belt. Moreover, FGR did not increase the CO content in the flue gas and reduced the O2 concentration in the area zone of pulverized coal combustion. For FGR systems, the emission of NOx below 200 mg/m3n for 6% O2 in dry flue gas was kept. This proves that the recirculation helps to meet the BAT (best available techniques) requirements for NOx emissions. It has also been shown that FGR does not pose a risk of low-NOx corrosion in the next 20 years. [ABSTRACT FROM AUTHOR]

This study investigates the combustion of agricultural biomass rich in alkali elements in the fluidized bed. The experiments were performed with smashed corn cob in a 500 kW fluidized bed combustor which was designed for work under low bed temperatures (650–700 °C). During the experiments, the formed compounds from corn cob combustion were measured by sampling particulate matter, and mineral compositions were determined. Also, the temperature profile of the FBC was established. It was determined that the emissions of K and Na elements from the FBC increased from 4 to 7.3% and from 1.69 to 3%, respectively, changing the bed temperature from 650 to 700 °C. Though alkali emissions are reduced at a 650 °C bed temperature, CO emissions are higher by about 50% compared to the case of 700 °C. The addition of 3% of dolomite reduced the pollutant emissions and alkali emissions as well. Potassium content decreased by about 1% and 4%, respectively, at the bed temperatures of 650 °C and 700 °C. The NOx emissions were less than 300 mg/m3 and did not exceed the limit for medium plants regarding DIRECTIVE (EU) 2015/2193. During extended experiments lasting 8 h, no agglomeration of the fluidized bed was observed. Moreover, the proposed configuration of the FBC and its operational parameters prove suitable for facilitating the efficient combustion of agricultural biomass. [ABSTRACT FROM AUTHOR]

Methane Number (MN) is a fuel rating technique for gaseous fuels analogous to Octane Number. This study establishes and shares a repeatable and reproducible method for MN determination of a gaseous fuel using a modified Cooperative Fuel Research Engine (CFR). Adaptations required to convert a CFR engine for use in the MN test procedure are identified. The investigation includes allowable environmental parameters and operating variation limits. An essential aspect of the MN method involves identifying and quantifying Knock Intensity (KI) during engine operation. CFR engines, originally designed for gasoline testing, come equipped with their own knock measurement systems utilizing a capacitive detonation sensor. The original system is compared with a Fast Fourier Transform (FFT) approach that uses a piezoelectric pressure transducer. Quantification of methane number requires an accurate assessment of the reference fuel blend (CH4 + H2). A comparison is carried out between dynamic blending using mass flow meters and bracketing using certified gas bottles containing various CH4/H2 blends from a gas supplier. [ABSTRACT FROM AUTHOR]

Technologies used in the transport sector have a substantial impact on air pollution and global warming. Due to the immense impact of air pollution on Earth, it is crucial to investigate novel ways to reduce emissions. One way to reduce pollution from ICE is to use alternative fuels. However, blends of alternative fuels in different proportions are known to improve some emissions' parameters, while others remain unchanged or even worsen. It is therefore necessary to find ways of reducing all the main pollutants. For SI engines, mixtures of hydrogen and natural gas can be used as alternative fuels. The use of such fuel mixtures makes it possible to reduce CO, HC, and CO2 emissions from the engine, but the unique properties of hydrogen tend to increase NOx emissions. One way to address this challenge is to use port water injection (PWI). This paper describes studies carried out under laboratory conditions on an SI engine fuelled with CNG and CNG + H2 mixtures (H2 = 5, 10, 15% by volume) and injected with 60 and 120 mL/min of water into the engine. The tests showed that the additional water injection reduced CO and NOx emissions by about 20% and 4–5 times, respectively. But, the results also show that water injection at the rate of 120 mL/min increases fuel consumption by between 2.5% and 7% in all cases. [ABSTRACT FROM AUTHOR]

Different combustion reaction process models were used to numerically study the behavior of the temperature, velocity, and turbulence fields, as well as to gain a better understanding of the differences between the reaction products obtained with each model. Transient-state simulations were conducted for a gasifier under specific operating conditions. The standard K-epsilon (2eq) turbulence model was utilized, along with the incorporation of species transport, volumetric responses, and eddy dissipation. In this study, the impacts of one-, two-, and four-step reaction mechanisms on the mass fraction of the products of the reactions, as well as the maximum values of velocity, turbulence, and temperature, were examined. The findings demonstrated that for all mechanisms, the greater maximum values of velocity and turbulence are attained at early time steps and decrease with subsequent time steps. The temperature rises as much in the early time steps and nearly stays the same in the late time steps. In all situations examined, the species' fraction mass varies slightly in the early time steps but becomes nearly constant in the latter time stages. Similar species mass fraction values were found for both one-step and four-step methods. The results also suggest that the lower half of the gasifier is where the highest mass fraction values are found. [ABSTRACT FROM AUTHOR]

Ammonia serves as an efficient hydrogen energy carrier, holding promise for achieving carbon neutrality in the internal combustion engine (ICE) industry. To boost the thermal efficiency of ammonia ICE, plasma-induced jet ignition (PIJI) is proposed with hydrogen as a combustion promoter. A zero-dimensional model of the PIJI ammonia-hydrogen engine, integrating SENKIN and ZDplaskin, reveals that plasma ignition consumes only 1/10 of the energy of spark ignition (SI) in the jet chamber. Active radicals resulting from the plasma reaction of O2 and NH3 expedite combustion in the jet chamber. By extending discharge duration from 3 ns to 4 ns, increasing discharge frequency from 30 kHz to 100 kHz, and strengthening the electric field from 350 Td to 450 Td, energy consumption is reduced by 80%, 50%, and 95% respectively. A low temperature exothermic phase is observed before the auto-ignition of the main chamber, irrespective of the ignition method. • A novel ignition method, plasma-induced jet ignition(PIJI), is proposed. • 0D plasma-induced ammonia-hydrogen jet ignition engine model is developed. • The ignition energy of plasma ignition is 1/10 of spark ignition. • Active radicals resulting from the collision of O 2 and NH 3 expedite combustion. [ABSTRACT FROM AUTHOR]

The steam-diluted oxyfuel combustion of the hydrogen-enriched fuels is promising to attain zero-emission in the energy system. One critical challenge for this technology is the flame stabilization, which was examined in this work mainly through the flame structure analysis. The burner adopted three swirlers to enhance the mixing, which leads to V-shaped diffusion-like flames. Starting from the purely hydrogen fuel, the CH 4 addition effects with fractions of 20% and 40% were studied. Meanwhile, combustion with different equivalence ratios were also compared, when the volume flowrate ratio of the O 2 and steam was kept constantly at 1:4. For these diffusion-like flames, the reaction zone was obtained using the OH-PLIF. Then, the flame structure statistics, such as the number and area of the broken reaction zone and its thickness, were all examined. Results show that the fuel properties and steam flowrate intensively affect the flame stabilization. With increased CH 4 addition in the hydrogen fuel, the reaction zone tends to be broken seriously. This is characterized by frequently appeared small reaction zone fragments, along with largely decreased reaction zone area. With a larger stream flow rate, the local flame extinction is also increased obviously and the flame branches can be completely distinguished due to the intensive straining effects. The extinction upstream is observed to promote an enveloped reaction zone downstream, due to the unburned fuel leakage. It is found that the mean reaction zone thickness is overall close, which varies from 1 to 2 mm, but can be modified by different factors. An analogical comparison of the reaction thickness to the laminar counter-flame thickness reveals that the CH 4 addition and flow straining can decrease the reaction zone thickness, but the accompanied turbulence effects can broaden it to at least about 1.2 times. These results are beneficial to attain a stable ultra-clean combustion utilizing hydrogen-based flexible fuels. [Display omitted] • Steam-diluted swirling CH 4 /H 2 /O 2 flames are studied. • The flame is a diffusional type and can be unstable. • Extinction is increased with either CH 4 addition or high steam flowrate. • Extinction and fuel leakage lead to enveloped reaction zone downstream. • The reaction zone thickness can be broadened by turbulence. [ABSTRACT FROM AUTHOR]

MILD combustion technology is expected to enable safe and stable low-emission combustion of hydrogen-doped fuels, or pure hydrogen fuels, in gas turbines designed for zero-carbon emissions. To improve combustion stability at high hydrogen content while maintaining low NO x emissions, a MILD model combustor was modified, specifically the upstream fuel/air distribution and mixing method. And the combustion stability of the modified MILD combustor was significantly extended. Here, the combustion characteristics of the modified MILD combustor are experimentally investigated at 0–100% hydrogen contents. The investigation results demonstrate that unlike the combustion stability region at low hydrogen concentrations, a narrow thermoacoustic instability region occurs at 60% hydrogen content. As the hydrogen content increases, the instability region becomes narrower while shifting towards lower equivalence ratios. The change in hydrogen content is accompanied by a significant peak energy migration of the dynamic pressure. The OH* chemiluminescence images showed that the heat release zone became more concentrated with increasing hydrogen content. And the dominance of high-frequency peak energy correlates to lateral motion, whereas the dominance of low-frequency peak energy corresponds to axial motion. This transition in flame dynamics occurs not only for different hydrogen contents but also for different equivalence ratios of pure hydrogen combustion. In contrast, NO x emissions are not sensitive to hydrogen content. At the same time, the MILD model combustor produces low emissions, with NO x emissions of less than 10 ppm@15%O 2 at adiabatic flame temperatures ranging from 1200 K to 2100 K. These results show that the MILD model combustor has favorable fuel suitability. • The high-speed jet-induced MILD model combustor is capable of stable combustion over a wide range of loads with hydrogen content ranging from 0 to 100%. • The energy of the dynamic pressure of the combustion system has migration at different hydrogen contents. • POD analysis of OH* images revealed the phenomenon of transit flame dynamics under various operation conditions. • NO x emissions are within 10 ppm@15%O 2 at adiabatic flame temperatures of 1200 K–2100 K. [ABSTRACT FROM AUTHOR]

Blending hydrogen into methane impacts flame stability, morphology, and pollutant emissions. This study, set against the backdrop of hydrogen-enriched natural gas combustion technology, employs a non-premixed coaxial burner with conical bluff body to create recirculation zones for flame stabilization. Combining EDC and GRI-Mech 3.0, the research fills in the gap of effects of hydrogen blending ratio (0–100%) and equivalence ratio vary (0.4–1.4) within a wide range. Keeping equivalence ratio and fuel volume flow rate as constants, as increasing hydrogen blending ratio, the mean velocity in the chamber decreases, the size of vortex structure located in outer recirculation zones reduces, and the flame length is shortened, illustrating the reaction zone shifts to chamber inlet. Furthermore, when Ф = 1.4, average temperature and temperature uniformity are averagely larger 59.82% and 4.21% than that under Ф = 0.4. The CO 2 emission at X H2 = 80% is 54.70% averagely lower than that at X H2 = 0%, but peak concentration of NO increases. [Display omitted] • Coupled Eddy Dissipation Concept and GRI-Mech 3.0 to CH 4 /H 2 diffusion flame. • Flame shifts toward combustion chamber inlet as hydrogen blending ratio increases. • Flame width of high-temperature zones increases a little when pure hydrogen burns. • Average temperature and temperature uniformity increase with hydrogen addition. • CO 2 and NO emissions firstly increase and then decrease from fuel-lean to fuel-rich. [ABSTRACT FROM AUTHOR]

Ammonia have been attractive as one of the alternative fuels for reducing greenhouse gas (GHG) emissions. However, ammonia combustion has lower combustion performance than common hydrocarbon fuels. Furthermore, it may emit nitrous oxide (N 2 O), which is one of the GHGs. This paper presents the experimental investigations of plasma-assisted ammonia combustion (PAAC) using a rod-electrode-type microwave plasma source (MPS) at atmospheric pressure. The equivalence ratios of premixed ammonia/dry air (NH 3 /Air) gas are set below the stoichiometric combustion of NH 3 to reduce toxic NH 3 in the combustion gas. Under the condition of the equivalence ratios, the experiments are focused on reducing the unburned NH 3 and produced N 2 O concentrations in the combustion gas. In the experiments, the unburned NH 3 , nitrogen oxide (NO x) (the sum of nitric oxide (NO) and nitrogen dioxide (NO 2)), and N 2 O concentrations in the combustion gas are investigated in terms of the flow velocity of premixed NH 3 /Air gas inside the rod-electrode-type MPS and the transmission power to the rod-electrode-type MPS. In conclusion, the rod-electrode-type MPS is identified to be useful for PAAC. The NH 3 and N 2 O concentrations in the combustion gas reach approximately 25 and 4 parts per million (ppm), respectively, under the conditions of the equivalence ratio of 1.0, flow velocity of approximately 0.167 m/s, and transmission power of about 84 W. At that time, the NO x concentration is approximately 4300 ppm, and the power transmission efficiency is approximately 68 %. • Plasma-assisted ammonia combustion (PAAC) was conducted using microwave discharge. • The microwave discharge was generated using a rod-electrode-type microwave plasma source (MPS). • The experiments were conducted without a swirler and below the stoichiometric combustion. • The minimum concentrations of NH 3 and N 2 O in the combustion gas reached 25 and 4 ppm. • The rod-electrode-type MPS was identified to be useful for PAAC. [ABSTRACT FROM AUTHOR]

While ammonia (NH 3) and hydrogen (H 2) are promising carbon-free fuels, there are significant challenges presented by their combustion properties. Blending them can help mitigate some of these issues; however, the fundamental behaviors of these blends need to be well understood. A constant volume combustion chamber (CVCC) is used to study the emissions of nitrogen oxides (NO, NO 2 , N 2 O), laminar burning velocity (LBV), and intrinsic instabilities for H 2 -NH 3 blends across a wide range of equivalence ratios (Φ = 0.5 to 1.5) and volume fractions of H 2 in the blends (0% to 50%). Measurements of LBV are consistent with existing data where available. The largest NO x and N 2 O emissions are found at lean conditions and decrease significantly for rich mixtures. NO x emissions tend to increase with H 2 fractions in fuel for lean mixtures. Intrinsic instabilities are more prominent at lean conditions and heavily influenced by the amount of H 2 in the blend. [Display omitted] • NO x production peaks at Φ =0.7, increases with H 2 content for lean mixtures. • N 2 O production peaks at lowest Φ , no significant variation with H 2 content. • Higher H 2 content results in earlier and more pronounced flame wrinkling. • LBV and emissions data extends available range for mechanism validation. [ABSTRACT FROM AUTHOR]