Combustion Devices Research Articles

Predicting oxidation‐limited lifetime of Ni‐Al‐Cr porous radiant burners made by combustion synthesis

Ni-Al intermetallic alloys have superior high-temperature properties such as excellent oxidation resistance and high yield strength, making them particularly attractive as materials for the fabrication of porous components of energy conversion and combustion devices. In this study, the cyclic oxidation resistance of highly permeable Ni-Al-Cr alloys has been investigated. The porous alloys with a structure of irregular porous scaffold comprised of welded mm-sized spheroidal strut elements forming a net of mm-sized interconnected pore channels (porosity of 0.55–0.60, specific surface area below 10−3 m2/g) were manufactured by the combustion synthesis method using μm-sized Ni, Al, and Cr powders of commercial purity as starting reagents. The surface area of alloys exposed to oxidation was calculated with an accuracy of 6% using quantitative 2D stereology. The cyclic oxidation tests were conducted in dry artificial air at 1150 ℃ for 100 h. The Ni‐Al‐Cr alloys, compared to Ni‐Al alloys, exhibited a twofold increased oxidation resistance because of decreased scale spallation. The porous alloys were also tested in a combustion environment. The lifetime prediction showed that Ni‐Al‐Cr radiant burners could be used for > 10,000 h at a temperature of 1000 ℃, which makes them relevant for application in domestic combustion appliances such as water heating boilers.

Study on condition analysis and temperature prediction of coal spontaneous combustion based on improved genetic algorithm

For major coal mine spontaneous combustion caused by major disasters every year, various scholars have studied and analyzed the conditions of coal mine spontaneous combustion and predicted the coal temperature. Coal mine spontaneous combustion is an inevitable disaster, but studying the coal mine surface covering to damp coal mine spontaneous combustion can greatly reduce the occurrence of coal mine spontaneous combustion. We analyzed the oxygen absorption in the pores of coal and the tendency of its own water content for spontaneous combustion of coal. The model experiment was carried out, and the correlation between different gas concentrations and coal temperature produced during spontaneous combustion of mixed coal samples was analyzed. The coal temperature was predicted in coal mines with different water contents and oxygen absorption levels, the coal temperature was predicted four times, and the performance evaluation and comparison of the correct prediction of coal temperature under different algorithm models were carried out. Finally, in the contrast experiment, the curve of the fitting function and minimum error value is further compared, and it can be seen that the combined model of the genetic algorithm and neural network algorithm has more accurate prediction accuracy than the single model. Through the analysis of the coal spontaneous combustion phenomenon and the study of anti-coal spontaneous combustion devices and the oxidation process, we have reduced the risk of spontaneous combustion in coal mining areas.

Transported JPDF modelling and measurements of soot at elevated pressures

Accurate measurements and modelling of soot formation in turbulent flames at elevated pressures form a crucial step towards design methods that can support the development of practical combustion devices. A mass and number density preserving sectional model is here combined with a transported joint-scalar probability density function (JDPF) method that enables a fully coupled scalar space of soot, gas-phase species and enthalpy. The approach is extended to the KAUST turbulent non-premixed ethylene-nitrogen flames at pressures from 1 to 5 bar via an updated global bimolecular (second order) nucleation step from acetylene to pyrene. The latter accounts for pressure-induced density effects with the rate fitted using comparisons with full detailed chemistry up to 20 bar pressure and with experimental data from a WSR/PFR configuration and laminar premixed flames. Soot surface growth is treated via a PAH analogy and soot oxidation is considered via O, OH and O2 using a Hertz-Knudsen approach. The impact of differential diffusion between soot and gas-phase particles is included by a gradual decline of diffusivity among soot sections. Comparisons with normalised experimental OH-PLIF and PAH-PLIF signals suggest good predictions of the evolution of the flame structure. Good agreement was also found for predicted soot volume statistics at all pressures. The importance of differential diffusion between soot and gas-phase species intensifies with pressure with the impact on PSDs more evident for larger particles which tend to be transported towards the fuel rich centreline leading to reduced soot oxidation.

Reducing Emissions from Combustion of Grape Residues in Mixtures with Herbaceous Biomass.

The use of grape residues as a renewable energy source for combustion presents various problems. One of these is the excessive production of carbon monoxide and nitrogen oxides. Analyses and combustion tests were performed on white and red grape pomace as well as grape stems. To verify the possibility of a reduction in emissions, straw of Miscanthus sinensis was added to mixtures with red grape pomace. Emission concentrations of carbon monoxide and nitrogen oxides were determined on a grate combustion device with a nominal thermal output of 8 kW under steady-state conditions. In addition to these emission concentrations, the excess air factor and the flue gas temperature were monitored. The results show a high energy content in grape residues. In red grape pomace, the gross calorific value of dry matter reached 22.17 MJ kg−1. Unfavourable properties included high ash and nitrogen contents. During combustion tests on all types of grape residue, the emission concentrations of carbon monoxide were above the legal limit for the combustion of solid fuels. The addition of Miscanthus straw improved the behaviour during combustion. The maximum content of grape pomace in the mixture capable of meeting legislative emission requirements was 50% wt.

The effects of flame orientation and mean shear on flame stretch in highly turbulent premixed flames using DNS

In the present work, direct numerical simulation data of a laboratory-scale high Karlovitz number (Ka) jet flame with a strong mean shear and a high Ka freely propagating planar flame without a mean shear were analyzed to explore the influence of flame orientation and mean shear on flame stretch in highly turbulent flames. Three flame fronts, i.e. the leading, in-plane and trailing front, were identified for the jet flame. The leading and trailing front is defined as the flame normal being facing the downstream and upstream regions, respectively, while the flame normal of the in-plane front is near the cross-stream plane. It was found that the flame stretch is positive in the leading front, and is negative in the trailing front of the jet flame. As for the planar flame, the statistics of the flame stretch are similar in various flame fronts. The components of the flame stretch are analyzed. The normal vector of the leading front is aligned with the most compressive strain rate in the jet flame, resulting in a large tangential strain rate, while the tangential strain rate of the trailing front is significantly lower. In contrast, the alignment characteristics and the strain rates of the planar flame are not sensitive to the flame orientation. The value of the stretch due to curved propagating flame front is large and negative in the trailing front of the jet flame due to the negative correlation between the displacement velocity and curvature, which is weak in the leading and in-plane front. The correlation between the displacement velocity and curvature is, however, similar in various fronts of the planar flame. Overall, it is suggested that the effects of flame orientation and mean shear should be accounted for in understanding turbulence-flame interactions in practical combustion devices.

Study on statistical invariance of probability processing and fluctuation characteristics of consecutive images of horizontal spray flame under low-pressure

With the development of the plateau environment, to make better use of the heat energy and safety of combustion devices, the structure and stability evaluation of horizontal jet flame and other related issues have attracted more and more people's attention. Consecutive image processing of flame is one of the emerging methods to evaluate the flame structure. In this paper, the statistical invariance of horizontal spray flame under low pressure is investigated experimentally and photographically, especially the characteristic of flame terminal fluctuation. A consecutive flame image of 0.05 MPa atmospheric pressure taken by conventional 25 frames per second in a low-pressure chamber was processed with probabilistic statistics, and the probability statistical contours were obtained by binarization statistics for the consecutive 100 to 1000 frames. The results show that different flame characteristic parameters have a different minimum statistical threshold, but most of them are between 300 and 400. The most reasonable statistical interval is determined by combining it with the flame stability evaluation index. The variation mechanism and feasibility of using statistical invariance to characterize flame stability are illustrated from the viewpoint of flame fluctuation characteristics. This is of great significance to the integrity of probabilistic processing of horizontal jet flame and lays a theoretical foundation for flame stability evaluation.

Flame stabilization in narrow channels by a highly conductive wall segment: Application to small-scale combustion devices

The structure and dynamics of premixed flames in narrow channels in the presence of a highly conductive wall segment are investigated in this work. It is shown that these systems present a multiple steady-state regimes. A linear stability analysis applied to these steady solutions reveals that several steady-state solutions may be simultaneously stable. The stability analysis results are confirmed by time-dependent simulations, that show that the actual realization of one or another stable regime depends on the initial conditions. Finally, we show that nonlinear periodic and chaotic dynamics may appear under certain conditions in these system.

The effects of air staging and combustion air control on black carbon and other particulate and gaseous emissions from a sauna stove

The combustion of wood in small-scale appliances emits significant amounts of particulate and gaseous pollutants into the atmosphere, leading to impaired air quality and adverse health and climate effects. Simple and easily implemented reduction techniques are needed to address this issue. In this study, different air staging strategies in a sauna stove were investigated with high temporal resolution, and the relationships between combustion air settings, combustion parameters, and different emission components were examined. Air staging was found to decrease PM1 and BC emissions by 43 and 41 %, and CO and OGC emissions by 23 and 42 %, respectively, when the stove was used in its standard configuration. Reducing and redistributing primary air decreased emissions further. BC emissions were lowest when the sauna stove was operated with an air-to-fuel ratio of 1.5. BC correlated weakly with gaseous emissions, with the exception of acetylene, highlighting the role of C2H2 as a precursor gas in soot formation. High OC/EC ratios during experiments with inefficient combustion conditions led to high average AAE values, which ranged from 1.23 to 1.41. Instantaneous AAE values correlated with concentrations of carbonyl compounds, especially acetaldehyde, suggesting that carbonyls may be indicative of BrC in wood smoke. The results show that significant emission reductions can be achieved in a simple combustion device with small, easily implemented modifications. In addition, the highly time-resolved data revealed relationships between various emission components, combustion conditions and the formation and properties of soot.

PEAT IS AN EFFECTIVE ALTERNATIVE FUEL

The article considers peat as an effective alternative fuel. Its reserves and directions of use in the world and in Ukraine presented and analyzed. The analysis showed that the geological reserves of peat in Ukraine are equivalent to 600 billion cubic meters of natural gas. The main reserves of peat are concentrated in the districts of Polissia. Industrial peat extraction can take place in 12 regions: Volyn, Rivne, Zhytomyr, Kyiv, Cherkasy, Poltava, Sumy, Chernihiv, Khmelnytskyi, Ternopil, Lviv, and Ivano-Frankivsk. It has been shown that, compared to traditional energy carriers, peat fuel has a lower heat of combustion and a fairly high ash content, but during combustion it emits almost no toxic substances and, accordingly, pollutes the environment much less. In home furnaces, peat fuel burned with a higher efficiency than coal, and the ash used as fertilizer. The estimated cost of 1Gj of lower heat of combustion of various types of fuel according to the data of recent years shows a noticeable advantage of peat fuels. The cost of thermal energy obtained from burning 1 ton of peat briquettes is 2 times cheaper than when using coal, 3 times cheaper than gas, and 4 times cheaper than fuel oil. Peat fuel is suitable for use in all types of modern solid fuel combustion devices, which increases the prospect of its implementation on the domestic and foreign fuel markets. The technology for using plant biomass as a filler in peat briquettes and granules developed. Special attention paid to wood, buckwheat husk, sunflower and other grain crops, which have a lower ash content and a higher heat of combustion, the potential of which waste is significant, and the fuel characteristics are able to increase the heat of combustion of composite peat briquettes or peat granules and reduce their ash content. Taking into account that peat used in large quantities as fertilizer for agriculture, a technology developed according to which humic substances first removed from peat for fertilizer, and then biomass added to this peat and a composite peat fuel obtained. This technology involves the integration of technology and extraction of humic substances into the production cycle of a peat briquette plant for the production of composite fuel. The wide implementation of the developed technology of composite peat briquettes at peat briquette factories will allow to increase the production of briquettes by almost 2 times without increasing the consumption of peat raw materials and to produce peat fuel in the range of 0.18-0.2% of geological reserves, which is equivalent to the replacement of more than 1 billion m3 of natural gas. All this allows us to draw a conclusion about the positioning of peat fuel as an effective local type of fuel, which is an alternative to gas and coal.

Recent developments in DNS of turbulent combustion

The simulation of turbulent flames fully resolving the smallest flow scales and the thinnest reaction zones goes along with specific requirements, which are discussed from dimensionless numbers useful to introduce the generic context in which direct numerical simulation (DNS) of turbulent flames is performed. Starting from this basis, the evolution of the DNS landscape over the past five years is reviewed. It is found that the flow geometries, the focus of the studies and the overall motivations for performing DNS have broadened, making DNS a standard tool in numerical turbulent combustion. Along these lines, the emerging DNS of laboratory burners for turbulent flame modeling development is discussed and illustrated from DNS imbedded in Large Eddy Simulation (LES) and flow resolved simulation of bluff-body flames. The literature shows that DNS generated databases constitute a fantastic playground for developing and testing a large spectrum of promising machine learning methods for the control and the optimisation of combustion systems, including novel numerical approaches based on the training of neural networks and which can be evaluated in DNS free from sub-model artefacts. The so-called quasi-DNS is also progressively entering the optimisation loop of combustion systems, with the application of techniques to downsize real combustion devices in order to perform fully resolved simulations of their complex geometries. An example of such study leading to the improvement of an incinerator efficiency is reported. Finally, numbers are given relative to the carbon footprint of the generation of DNS databases, motivating the crucial need for community building around database sharing.

Replacing the greater evil: Can legalizing decentralized waste burning in improved devices reduce waste burning emissions for improved air quality?

Open waste burning emissions constitute a significant source of air pollution affecting human health in India. In regions where cleaner fuels have displaced solid biofuel usage, open waste burning is rapidly becoming one of the largest sources of airborne human class-I-carcinogens and particulate matter. As the establishment of waste management infrastructure in rural India is likely to take years, we explore whether health-relevant emissions can be reduced by legalizing the burning of dry non-biodegradable waste in improved devices. We measure the emission factors of 76 VOCs, CH4, CO, and CO2 from different types of waste burned in two different improved devices, a burn basket and a local water heater. Based on our experiments, we create four “what-if” intervention scenarios to assess the improvement of air quality due to the emission reductions that can be accomplished by four management strategies. We find that substituting the traditional, more polluting water heating fuels with dry plastic waste across rural India can reduce primary emissions (e.g., −29 Ggy−1 for benzene) and ozone formation potential (−2960 Ggy−1) from open waste burning. When dry waste is used in lieu of more polluting fuels, and its burning serves a purpose, the net class-I-carcinogen benzene emissions, would be halved compared to the present. The change in emissions for the class-I carcinogen 1,3-butadiene would become net negative. This happens because the emissions avoided when part of the solid biofuel currently used in rural India is replaced by plastic waste (4.1 (1.2–4.1) Ggy−1) exceed the waste burning emissions of this compound (3 (1.2–3.7) Ggy−1) by so much, that residential sector emission reductions offset all waste burning emissions including those of landfill fires. Our study demonstrates that India's air quality can be improved by permitting and promoting the use of dry packaging waste in lieu of traditional biofuels and by promoting improved burning devices.

Study Of Soot Aggregate Formation And Oxidation In A Swirled Stratified Premixed Ethylene/Air Flame

Soot particles are one of the main causes of today's pollution because of their negative contribution to global warming and human health. Aviation is one of the domains dealing with soot reduction as the new engine concepts are developed to reduce fuel consumption and global emissions. Despite the fact that most combustion devices used for air transportation operate at high pressure (e.g., aircraft gas turbines up to 40 bar), our understanding of soot formation and oxidation in such conditions is not yet at an appropriate level, as there is still a fundamental lack of experimental data and corresponding predictive models in the literature. Thus, the objective of the current study is to evaluate soot formation and oxidation processes in stratified, swirled, premixed ethylene/air flames examined with a variety of laser diagnostics designed to simultaneously measure soot particle and soot precursor 2D-distributions, as well as the flame structure and the aerodynamic field. For that, the SIRIUS burner was selected because of its ability to produce flames with topologies similar to those encountered in aircraft combustors. Soot particle distributions are measured by Planar Laser-induced incandescence (PLII) diagnostic. The flame structure is obtained by detecting the hydroxyl radicals (OH) with Planar laser-induced fluorescence (PLIF). A second PLIF diagnostic is also used to investigate the production of polycyclic aromatic hydrocarbons (PAH) with the detection of two benzene rings molecules which are recognized as good precursors of soot nucleation and growth. Finally, the particle Image Velocimetry (PIV) diagnostic is used for measuring the velocity distributions. These laser diagnostics are coupled together in order to obtain cross-correlations between several scalar parameters playing a determining role in the soot formation/consumption processes. The experimental results collected at atmospheric pressure are reviewed and critically assessed. A scenario describing the link between the soot inception, growth, aggregation and oxidation processes is proposed by analyzing velocity, OH, PAHs and soot distributions. In particular, the data reveal the presence of distinct regions for these processes. Incipient soot production zone is strongly function of specific local conditions of velocity, PAH concentration, and strain rate encountered at the interface of the internal recirculation zone and the fuel/air jet. The central part of the inner recirculation zone in which large structures move at low velocities provides suitable conditions for the aggregation of nascent soot particles while an oxidation region located in the upper zone of the internal recirculation zone favors the consumption of soot.

Trace gas emissions from laboratory combustion of leaves typically consumed in forest fires in Southwest China

Forest fires are becoming increasingly severe and frequent due to global climate change. Trace gases emitted from forest fires significantly affect atmospheric chemistry and climate change on a regional and global scale. Forest fires occur frequently in Southwest China, but systematic studies on trace gas emissions from forest fires in Southwest China are rare. Leaves of seven typical vegetation fuels based on their prominence in forest fires consumption in Southwest China were burned in a self-designed combustion device and the emission factors of eighteen trace gases (greenhouse gases, non-methane organic gases, nitrogenous gases, hydrogen chloride, and sulfur dioxide) at specific combustion stages (flaming and smoldering) were determined by using Fourier transform infrared spectroscopy, respectively. The emission factors data presented were compared with previous studies and can aid in the construction of an emission inventory. Pine needle combustion released a greater amount of methane in the smoldering stage than other broadleaf combustion. Peak values of emission factors for methane and non-methane organic gas are emitted by the smoldering of vegetation (Pinus kesiya and Pinus yunnanensis), which is endemic to forest fires in Southwest China. The emission factor for oxygenated volatile organic compounds (OVOCs) in the smoldering stage is greater than the flaming stage. This work established the relationship between modified combustion efficiency (MCE) with emission factors of hydrocarbons (except acetylene) and OVOCs. The results show that exponential fitting is more suitable than linear fitting for the seven leaf fuels (four broadleaf and three coniferous). However, the emission factors from the combustion of three coniferous fuels relative to all fuels are linear with MCE. Findings demonstrated that different combustion stages and fuel types have significant impacts on the emission factors, which also highlighted the importance of studying regional emissions.

Detailed kinetics for anisole oxidation under various range of operating conditions

Biofuels produced from biomass are considered a potential source of renewable energy that can be used as an alternative to fossil fuels. Lignocellulosic biomass produces phenolic compounds like anisole which is a promising source of biofuel. Anisole (methoxybenzene) is an aromatic compound and has advantageous features as a drop-in fuel in combustion devices. In this work, a detailed mechanism of anisole is generated to numerically study the oxidation of this fuel at engine-relevant conditions. The comprehensive model is developed using the reaction mechanism generator (RMG). The mechanism is used for calculating laminar burning speed (LBS), ignition delay time (IDT), and species concentration, to compare with experimental data. Sensitivity and reaction path flux analyses are considered in evaluating the mechanism. Important reactions are identified which have a very significant effect on the prediction of the model. The rate of these important reactions is studied from the literature to make the mechanism perform well for a wide range of conditions. The final mechanism named PCRL-Mech3 contains 466 species and 3691 reactions. PCRL-Mech3 shows a successful validation of IDT at both rapid compression machine (RCM) and shock tube (ST) experiment which cover temperatures of 800–1600 K and pressures of 10–40 atm. Validation of LBS is performed using recently published work by the same group. This data enables the opportunity to evaluate and improve PCRL-Mech3 for a wider range of LBS conditions (i.e., 0.5–5.5 atm, 460–550 K, and 0.8–1.4 equivalence ratio). Species concentration of anisole and stable intermediates of final mechanism match reasonably well with different jet stirred reactor experiments. Compared with the literature, the mechanism can show improved prediction over a larger span of engine-relevant conditions that also helps to identify the regimes where more experimental and numerical improvement is required.

Applying the Random Forest Method to Improve Burner Efficiency

Fuel power plants are one of the main sources of pollutant emissions, so special attention should be paid to improving the efficiency of the fuel combustion process. The mathematical modeling of processes in the combustion chamber makes it possible to reliably predict and find the best dynamic characteristics of the operation of a power plant, in order to quantify the emission of harmful substances, as well as the environmental and technical and economic efficiency of various regime control actions and measures, and the use of new types of composite fuels. The main purpose of this article is to illustrate how machine learning methods can play an important role in modeling and predicting the performance and control of the combustion process. The paper proposes a mathematical model of an unsteady turbulent combustion process, presents a model of a combustion chamber with a combined burner, and performs a numerical study using the STAR-CCM+ multidisciplinary platform. The influence of various input indicators on the efficiency of burner devices, which is evaluated by several parameters at the output, is investigated. In this case, three possible states of the burners are assumed: optimal, satisfactory and unsatisfactory.

Numerical analysis of oil combustion in a small combustion device

This paper focuses on the numerical analysis of the combustion of the liquid fuel Extra Light Fuel Oil (ELFO) in a small combustion device. The calculation was performed by ANSYS CFX computer code for experimental optimal air-fuel ratio (λopt) and the middle power of the oil burner Weishaupt WL5/1-A (37 kW). The goal of the numerical analysis was to establish, whether the experimentally determined λopt ensured the conditions for a complete combustion in each point of the combustion chamber. The comparison of numerical results and measured values confirm the suitability of the chosen numerical model.

Analysis of gaseous polycyclic aromatic hydrocarbon emissions from cooking devices in selected rural and urban kitchens in Bomet and Narok counties of Kenya.

Traditional combustion devices and fuels such as charcoal, wood and biomass, are widely utilised in rural and urban households in Africa. Incomplete combustion can generate air pollutants which are of human toxicological importance, including polycyclic aromatic hydrocarbons (PAHs). In this study, portable multi-channel polydimethylsiloxane rubber traps were used to sample gas phase emissions from cooking devices used in urban and rural households in Bomet and Narok counties of Kenya. A wide range of total PAH concentrations was found in samples collected (0.82 - 173.69 µg/m3), which could be attributed to the differences in fuel type, combustion device, climate, and nature of households. Wood combustion using the 3-stone device had the highest average total PAH concentration of ~71 µg/m3. Narok had higher indoor total gas phase PAH concentrations averaging 35.88 µg/m3 in urban and 70.84 µg/m3 in rural households, compared to Bomet county (2.91 µg/m3 in urban and 9.09 µg/m3 in rural households). Ambient total gas phase PAH concentrations were more similar (Narok: 1.26 - 6.28 µg/m3 and Bomet: 2.44 - 6.30 µg/m3). Although the 3-stone device and burning of wood accounted for higher PAH emissions, the charcoal burning jiko stove produced the highest toxic equivalence quotient. Monitoring of PAHs emitted by these cooking devices and fuels is critical to public health and sustainable pollution mitigation.

Investigations on cellularization instability of 2-ethylfuran

2-ethylfuran (2 EF) has potential as a biofuel for combustion devices. To apply it efficiently in combustion devices, it is necessary to study the combustion characteristics such as the intrinsic flame instability of 2 EF. The intrinsic flame instabilities of 2 EF outwardly propagating spherical premixed flames were theoretically and experimentally studied at initial temperatures of 373, 403, and 433 K, pressures of 1, 2, and 4 bar, and equivalence ratios of 0.7–1.4. The flame topography at different stages of flame development was examined. When large cracks appeared on the flame front surface, resulting in small cracks and new cell generation, the flame became unstable. Linear stability theory was used to investigate the effects of hydrodynamic instability and thermal-diffusion instability on the flame. The critical stability curves were plotted, and the theoretical calculations were consistent with the experimental results. The results showed that the best fits for the theoretical and experimental results were n = 2πPe/48 and n = 2πPe/80, respectively. The critical radius and Peclet number are calculated and discussed. The critical Peclet number decreased as the equivalence ratio increased.

On the generalized Beltramian motion of the bidirectional vortex in a right-cylindrical cyclone with a hollow core

In this work, an exact inviscid solution is developed for the incompressible Euler equations in the context of a bidirectional, cyclonic flowfield in a right-cylindrical chamber with a hollow core. The presence of a hollow core confines the flow domain to an annular swirling region that extends into a toroid in three-dimensional space. The procedure that we follow is based on the Bragg–Hawthorne framework and a judicious assortment of boundary conditions that correspond to a wall-bounded cyclonic motion with a cylindrical core. At the outset, a self-similar stream function is obtained directly from the Bragg–Hawthorne equation under the premises of steady, axisymmetric, and inviscid conditions. The resulting formulation enables us to describe the bidirectional evolution of the so-called inner and outer vortex motions, including their fundamental properties, such as the interfacial layer known as the mantle; it also unravels compact analytical expressions for the velocity, pressure, and vorticity fields, with particular attention being devoted to their peak values and spatial excursions that accompany successive expansions of the core radius. By way of confirmation, it is shown that removal of the hollow core restores the well-established solution for a fully flowing cylindrical cyclone. Immediate applications of cyclonic flows include liquid and hybrid rocket engines, swirl-driven combustion devices, as well as a multitude of heat exchangers, centrifuges, cyclone separators, and flow separation devices that offer distinct advantages over conventional, non-swirling systems.

Modelling of turbulent hydrogen-blended premixed flames using algebraic flame surface wrinkling closure for the Lewis numbers and mean local burning velocity

Hydrogen-blended fuel is of fundamental interest due to difficulties in modelling and its practical significance for the development of high-performance hydrogen combustion devices and safety technologies for the prediction and prevention of fire or explosion. In this analytical study, we validate an algebraic premixed turbulent model [13] for molecular transport effects in both spherical expanding methane flames enriched with hydrogen and Bunsen burner flames. Experiment comparisons are supported with theoretical ideas. Bunsen flames are measured at varied turbulence, equivalence ratios, temperatures, and pressures. We also consider other, very recent, experimental data [32] of similar fuel mixtures to support the trends.In the study of outwardly evolving spherical expanding flames, we present three variants of this model, with two functions based on the Lewis number Le, and one based on the experimentally measured mean local flame burning velocity SFm. The Lewis number is significant in understanding the role of the diffusion of deficient reactants, which is particularly noticeable in blended fuels. The utilitarian part of this work is to demonstrate that the Le-based premixed turbulent models take into account the preferential diffusion effect, and to embed a term that quantifies turbulent flame speed explicitly for mixtures, for example, having the same unstretched burning velocity as the model input. We show that in the modelling of turbulent burning velocity, the use of SFm avoids the use of input parameters the unstretched laminar flame speed and the Lewis number. Moreover, we validate high-pressure experiments by Bagdanavicius [12] to show that the pressure has less significant impact on the Bunsen flames and, therefore, we model without the pressure term. The model correlates well with most of the data.