Combustion Behavior Research Articles

Combustion performance of aluminum modified boron nanoparticles coated with silane coupling agent

Boron (B) powder, with its high mass and volumetric heat values, makes it highly promising in the field of energetic materials. However, the oxide layer on the B surface is the most significant barrier to realizing its full potential as a fuel. How to eliminate or disrupt the oxide layer is currently an urgent problem that needs to be addressed. This study proposes an approach to enhance the combustion of nano-B powder by coating aluminum (Al) onto its surface using a silane coupling agent. The combustion characteristics of Al-modified B powder with different Al contents were investigated through experimental and molecular dynamic simulation methods, and the bidirectional diffusion mechanism on the interfacial layer of modified B particles was revealed. A small amount of Al powder can largely lower the initial oxidation temperature of B powder, increase the maximum flame temperature, and enhance the heat release. However, an excessive amount of Al powder leads to a deterioration in the combustion of B powder but can alter the combustion behavior and suppress the aggregation of B powder during the combustion. Additionally, combination reaction and redox reaction occurring during the combustion of B@Al samples not only reduce the burning time of B powder but also accelerate the flame expansion speed and improve the combustion efficiency. These results lay the foundation for the application of B@Al in the field of energetic materials.

The effect of additives on the co-pelletization of sewage sludge and extraction residue on combustion behavior and off-gas emission reduction

Co-combustion of biomass and sludge is a promising method for waste treatment and power generation. In this study, additives such as ammonium dihydrogen phosphate (ADP), calcium oxide (CaO), attapulgite (AT), and their combinations were added into the co-pelletization of semi-dry sludge (with approximately 50% water content) and extraction residue from vegetable oil processing. The objective of the studies was to examine the pelletization behavior, reduce off-gas emissions during the combustion, and investigate the mechanisms influenced by these additives through the thermogravimetric analysis and the tube furnace combustion experiment. The results of the analysis of variance (ANOVA) indicated an increase in pellet density due to the addition of additives. During the combustion, the addition of AT and compound additives generated more complex compounds with high melting temperatures, thereby mitigating the high slagging tendency. Meanwhile, additives facilitated the conversion of ultrafine particles (PM0.1) to fine particles, leading to a reduction in PM0.1 emissions by 15.60–42.40%. The additives exhibited efficacy in reducing SO2 emissions, with a reduction range of 5.00–23.20%. However, the addition of ADP additives resulted in a 12.00% increase in NO emissions. Consequently, adding additives to pellets could address the slagging issue and reduce the emission of air pollutants during combustion.

Variation of flammability and smoke toxicity of upholstered furniture composites with fire retardant treatment

Since the 1980s, mass market upholstered furniture sold in the United Kingdom has incorporated flame retardant chemicals to meet regulatory flammability requirements. However, UK fire deaths remain comparable with similar European countries which have no such regulations. Quantitative measures of the effect that different chemical flame retardants additives have on the flammability and smoke toxicity of UK regulatory-compliant upholstered furniture remain limited. It has been shown that most fatal fires involve upholstered furniture; most fire deaths result from toxic gas inhalation; gas phase flame retardants increase the toxicity of smoke; and the fall in fire deaths over the last 30 years is the same in countries with and without furniture flammability regulations. Moreover, the presence of certain flame retardants in furniture is a significant obstacle to any meaningful end-of-life processing.The burning behaviour and smoke toxicity of nine upholstered furniture composites using a range of flame retardant technologies were assessed in the cone calorimeter. The total heat release (THR) varied from 46 MJ m−2 to 68 MJ m−2, the time-to-ignition (tti) from 8 s to 105 s, and peak heat release rate (pHRR) from 230 kW m−2 to 430 kW m−2. The composite filled with PET showed the longest tti while the expandable graphite fabric on the FR-foam showed the lowest pHRR. The composite with the Br-FR fabric and the FR-foam had the shortest tti, the greatest smoke, the second highest CO and the highest HCN yield. The composite with the non-FR fabric and the PET filling had the longest tti. For all the fabrics, the transition from non-FR to FR foam resulted in significant increases in the smoke, CO and HCN, except CO of Br-FR and FR-foam was slightly lower than non-FR foam.Smoke toxicity predictions show that the use of gas phase flame retardants in both the fabrics and fillings of upholstered furniture contributes to the high proportion of smoke-related fire casualties. The work shows that the smoke toxicity of upholstered furniture can be reduced by using condensed phase FRs, such as expandable graphite, or less flammable materials, such as polyester wadding. The regulatory component tests which focus on ignitability have been shown to be ineffective at assessing the fire safety of composites representative of furniture as sold. The alternative approach of assessing heat release and smoke toxicity, as described here, would improve the fire safety of furniture while reducing reliance on additive flame retardants acting in the gas phase.

Study on the combustion characteristics of NH3 and the inhibition characteristics of R134a on NH3

NH3 has been considered as an alternative to hydrofluorocarbon (HFC) refrigerants due to its environmentally friendly properties, while it is flammable. Therefore, it is necessary to investigate the flammability of NH3 (R717) and find its matching flame retardant to broaden its application. In this paper, the combustion behaviors of R717 and the inhibition characteristics of flame retardant R134a on R717 were studied experimentally and theoretically. Firstly, the flame propagation pattern, flammability limit, laminar burning velocity, and Markstein length of pure R717 were measured by a constant volume combustion bomb from 300 K to 400 K. Then the flammability characteristics of R134a/R717 mixture were further tested. The results indicated that R134a had a distinct flame retardancy on the flammability limits of R717. Further, the flame retarding mechanism of R134a on R717 was analyzed by density functional theory (DFT) on the 6–311++G(d,p) level. The flame retarding effects of R134a were classified to physical and chemical mechanisms. The physical force mainly depended on the dilution effect of additional R134a. The chemical mechanism was contributed to the newly flame retarding reactions introduced by R134a, which reflected in the dehydrogenation of R717 and the consumption of OH and H active radicals by fluorine-contained radicals (CF3, CF2, and F).

Extension of a Zero-Dimensional Mixing-Controlled Combustion Model for the Development of a NOx–Free System Based on the Oxy-Combustion Concept

Oxy-combustion is a promising concept to achieve an extremely clean combustion, independently of the fuel type, because, on the one hand, it is a NOx-free combustion and, on the other hand, the CO2 produced during combustion can be easily captured once the water vapour is removed from the exhaust gases stream, consequently allowing also carbon neutral operation. An existing zero-dimensional (0D), mixing-controlled combustion model, developed for a standard diesel combustion scenario, has been adapted to the oxy-fuel combustion scenario. Initially, the model over-predicted the heat release at the end of the combustion process. The main model adaptation was to modify the relationship between the average YO2 and the effective YO2 (i.e. the one of the charge actually entrained by the spray), to be consistent with the significant increase in compression ratio needed in the oxy-fuel context. As a result, a model able to correctly predict the combustion behaviour at any operating condition has been obtained, which finally represents a very suitable tool to assist in the concept development.

Combustion Behaviors, Kinetics, and Thermodynamics of Naturally Decomposed and Torrefied Northern Red Oak (Quercus rubra) Forest Logging Residue

Torrefaction and combustion have been applied to naturally decomposed red oak logging residues. The results indicated that four-year natural decomposition would lower the energy density of red oak from 20.14 to 18.85 MJ/kg. Torrefaction reduced the O/C and H/C ratios but improved the energy yield values. Two combustion stages were observed for all samples, and no hemicellulose derivative thermogravimetric peak appeared for torrefied samples. The differential scanning calorimetry exothermic heat flow increased after torrefaction. In addition, the Kissinger–Akahira–Sunose average activation energy of untorrefied samples decreased in the first stage (from 157.77 to 149.52 KJ/mol), while it increased in the second stage (from 131.32 to 181.83 KJ/mol). The ∆H, ∆G, and ∆S values of all samples decreased in the first stage, while they increased when the conversion rate was greater than 0.5 for torrefied samples. These findings can aid in a better understanding of the fuel performance of torrefied and untorrefied naturally decomposed red oak logging residues.

N, P co‐doped carbon quantum dot and ammonium polyphosphate as the synergistic flame retardant for epoxy resin

AbstractAn N, P co‐doped carbon quantum dot (NP‐CQD) was prepared using citric acid as the carbon source and hexachlorotripolyphosphonitrile as the nitrogen and phosphorus source. The structure and morphology of NP‐CQD were characterized. Subsequently, NP‐CQD was blended with ammonium polyphosphate (APP) to come into being a synergistic phosphorus‐nitrogen flame retardant system (SPFRS). The SPFRS was applied in epoxy resin (EP) to enhance the flame retardancy of EP. Thermal stability, flame retardancy, combustion behavior, and char residue morphology of the EP samples were determined by multiple testing methods such as thermogravimetric analysis, vertical burning (UL‐94) and limiting oxygen index (LOI) tests, microscale combustion calorimetry test, and scanning electron microscopy. When the weight ratio of NP‐CQD to APP was kept at 1:9 and 8% SPFRS was added to EP, the obtained flame‐retardant EP (EP/CQD‐APP2:18) passed the UL‐94 V‐0 level and the LOI value of EP/CQD‐APP2:18 reached 33.2%. The MCC test showed that the heat release capacity (HRC) of EP/CQD‐APP2:18 was reduced by 48.7% compared with pure EP. Morphology observation on the char residue of EP/CQD‐APP2:18 after the UL‐94 test indicated that the addition of SPFRS promoted the formation of the dense char residue layer to improve the flame retardancy of EP.Highlight An N, P co‐doped carbon quantum dot (NP‐CQD) was prepared and applied as a flame retardant. NP‐CQD and ammonium polyphosphate (APP) showed synergistic flame retardancy in epoxy resin. The proper weight ratio of NP‐CQD to APP was 1:9.

Thermal Decomposition and Combustion Analysis of Malaysian Peat Soil Samples Using Coats Redfern Model-free Method

This research investigates the thermal decomposition behaviour of Malaysian peat soil through thermogravimetric analysis at varying heating rates. The study aims to analyse the thermal kinetics of decomposition for distinct peat soil types under inert and oxidative atmospheres while considering the role of available oxygen. The investigation encompasses virgin and agricultural peat, employing a non-isothermal thermogravimetric analysis technique to evaluate thermal decomposition characteristics and compute kinetic parameters using the Coats Redfern model-free approach. The pyrolysis profiles reveal three primary stages: moisture evaporation (30–180°C), organic component decomposition (200–500°C), and mineral decomposition (600–800°C). Virgin peat experiences a 43% mass loss during pyrolysis, while agricultural peat shows a 46% mass loss, emphasising insights into thermal behaviour and consistent decomposition patterns across peat types. Combustion profiles exhibit three main stages: dehydration (30–180°C), oxidative pyrolysis transforming organic matter into volatiles and char (200–300°C), and subsequent char oxidation (300–500°C). The study determines average activation energy trends, measuring 14.87 kJ/mol for virgin peat and 5.37 kJ/mol for agricultural peat under an inert atmosphere, and 28.89 kJ/mol for virgin peat and 36.66 kJ/mol for agricultural peat under an oxidative atmosphere. The research introduces an innovative two-step reaction model elucidating peat thermal decomposition kinetics (excluding dehydration), including a discussion on the impact of oxygen availability on kinetic parameters. These findings essential peat fire smouldering modelling, contributing to peat combustion behaviour for effective strategies to reduce peat fire risks.

Development of a surrogate and its comprehensive compact chemical kinetic mechanism for the combustion of Alcohol-To-Jet fuel

This study develops a compact high-fidelity chemical kinetic mechanism for a proposed surrogate of Alcohol-To-Jet fuel, capable of modelling ignition delay time, laminar flame speed, and species concentration. A combination of 85% iso-dodecane and 15% iso-cetane by wt% that is a close approximation to the real fuel composition was selected as the ATJ surrogate to investigate the simulation of the three given combustion properties. A relatively good agreement has been observed for ignition delay, laminar flame speed, and mole fraction of some species, between the simulation by the Chemkin-Pro software package and the available experimental data in the literature. The authors suggest that this proposed surrogate with its compact validated mechanism can be used by researchers to study the combustion behaviour of ATJ fuel including the investigation on the complex geometries of combustion system such as Equivalent Reactor Network Analysis which require a compact accurate chemical kinetic mechanism.

Experimental Research on Moisture Transfer, Burning and Charring Behavior of Glue Laminated Larch Under Fire Heating Using Cone Calorimeter

Experimental Research on Moisture Transfer, Burning and Charring Behavior of Glue Laminated Larch Under Fire Heating Using Cone Calorimeter

The effect of organophosphorus flame retardants on the combustion behavior and performance of poly (methyl methacrylate)

Maintaining transparency poses a challenge in the preparation of flame-retardant poly (methyl methacrylate) (PMMA). The feasibility of preparing flame-retardant transparent PMMA by incorporating oligomeric resorcinol bis(diphenylphosphate) (liquid), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and hexaphenoxycyclotriphosphazene (solid) as additives has been explored. The impact of the flame retardants on the processing performance, thermal stability, combustion behavior and mechanical properties of PMMA has been investigated. The presence of organophosphorus compounds does not impact the transparency of PMMA and has a significant plasticizing effect. The modified PMMA displays a UL94 V-2 rating largely due to the formation of noncombustible droplets. However, the blend exhibits lower heat resistance, modulus and strength than does unmodified PMMA. The presence of organophosphorus compounds induces a higher limiting oxygen index (LOI) and reduced heat release for combustion of the blends than observed for PMMA without relying on charring, among which DOPO has a higher flame retardant efficiency due to its higher phosphorus content and lower decomposition temperature.

Upgrading Carthamus by HTC: Improvement of Combustion Properties

This study investigated the fuel potential and combustion behavior of hydrochars derived from a unique precursor: Carthamus pomace. Initially, the hydrothermal carbonization process of this novel feedstock was examined across various temperature ranges (180–240 °C) and durations (15–180 min). The impact of these processing conditions was analyzed in terms of degradation mechanisms and their correlation with the resulting properties of the hydrochars (HCs) produced. Then, the combustion performance of these materials was studied by means of thermogravimetry, and the differences in reactivity and activation energy were analyzed and associated with preparation processes. Finally, the most promising HTC parameters were identified and a thermoeconomic study on the use of selected HCs on a thermal plant devoted to the production of electricity was evaluated including energy savings associated with the implementation of heat exchangers using the heat of the flue gases to partially supply the energy needs associated with HTC.

Exploring electric field forces and polarization influence on combustion in Fe-additive fuel droplets

The application of electrical techniques such as electric field, polarization, and ionization in the field of combustion makes many positive developments possible. The electric field effect offers significant advantages in controlling flame stability and reducing soot formation during the combustion of fuels. Also, the conditioning effect can improve particle oxidation during combustion for hydrocarbon fuels containing metal particle inclusions with high calorific value. This study focuses on investigating the combustion and atomization behavior of Fe additive diesel fuel droplets at electric field strengths of E = 5 V/m, E = 6.7 V/m, and E = 10 V/m and in positive (↑) and negative (↓) electric field directions. The experiments were carried out by igniting a fuel droplet suspended on a ceramic wire with an arc at the center of the electric field between two conductive plates in a combustion chamber with optical apertures. The combustion processes were recorded with an optical system consisting of a high-speed camera and a thermal camera. Combustion and atomization behavior were characterized by sequential flame and droplet atomization images, respectively. The droplet shape change and flame behavior results were comparatively evaluated according to the d2-law. Ignition delay and extinction times were determined by processing threshold technique and maximum flame temperatures were determined by processing thermal camera images. The results showed that increasing the electric field intensity in the negative electric field direction resulted in improved soot oxidation, and Fe particles burnt efficiently. Ignition delay times showed a decreasing trend with an electric field effect and an increasing trend with the addition of Fe particles. The highest maximum flame temperature and lowest extinction time were recorded as 785 K and ∼ 578.34 ms for Diesel/Fe/100(↓) fuel droplet, respectively and Fe particles did not exhibit microexplosion phenomena at E = 10 V/m. In this study, it has been shown that an effective oxidation can be achieved for Fe particles by increasing the mobility of ionized species in the flame zone under the effect of electric field and a homogeneous thermal field can be created in the flame zone even in fuels with particle addition at increasing electric field intensities.

Theoretical and kinetic study of the hydrogen abstraction reactions of ethyl propionate

Ethyl propionate shows great promise as a biodiesel molecule model. However, the current oxidation kinetic model falls short in accurately predicting its combustion behavior. Therefore, this study employed ab initio quantum chemistry methods to analyze the hydrogen abstraction reactions of ethyl propionate with various reactive radicals, including OH, O, H, CH3, C2H3, C2H5, HO2, CH3O and CH3O2, which play a critical role in refining the oxidation kinetics. Theoretical calculations were conducted to determine the rate constants and branching ratios for these reactions at temperatures ranging from 500 K to 2500 K using transition state theory, quasi-rigid rotor harmonic oscillator model, and tunneling correction. After updating the kinetics of hydrogen abstraction reactions in the oxidation mechanism proposed by Metcalfe et al., the modified model was validated by comparing the simulated mole fraction evolutions of ethyl propionate and major products in a jet-stirred reactor, ignition delay in a closed homogeneous batch reactor, and laminar flame speed with experimental data. The findings indicate that the modified model reliably reproduces the experimental data and significantly improves the prediction accuracy for low-temperature combustion of ethyl propionate when compared to the original model.

The mechanism of the influence of radiation heat flux on the combustion behavior of raw rubbers

Understanding the combustion behavior of rubbers is crucial for predicting their fire hazards. The cone calorimeter experimental results in this study confirm that the combustion behavior of raw rubbers depends on the rubber type and the heat flux. Natural rubber and ethylene-propylene-diene monomer rubber exhibit heat release rate (HRR) curves with only one peak at the end of the burning stage under all tested heat fluxes. At higher heat fluxes, the HRR curves of polybutadiene rubber (BR) and styrene butadiene rubber (SBR) exhibit a single peak; at heat fluxes lower than 20 kWm−2, two HRR peaks were observed. The proposed mechanism model with the crosslink reaction as the key factor can explain the emergence of two-peak HRR curve and has been proved through experiments and simulations. For BR and SBR at 15 kWm−2, the specimens exhibit two upper layers at ignition time. The surface pyrolysis layer seems to be covered by black film or char, with the crosslink degree as high as 84.23–100 %. The second crosslink reaction layer exhibits a higher decomposition temperature Td,5 % than the original rubber. Based on reaction kinetics and thermodynamics data derived from TG/DSC experiments, the novel pyrolysis model taking crosslink reaction and thermal decomposition of crosslinked intermediate into account well predicts the HRR curves obtained at varied heat fluxes. The conversion of raw rubber to the crosslinked intermediate plays an important role in the reduction of HRR immediately after ignition, resulting in the first HRR peak.

Insight into energy release characteristics of TiH2 dust explosion through ignition experiments and molecular dynamic simulations

TiH2 is an efficient hydrogen storage material with high energy density and relatively stable chemical quality, which is commonly used in metal sponge production, hydrogen storage, battery technology, rocket propellants, etc. In this study, TiH2 dust explosion is systematically investigated by integrating ignition experiments with reactive force field molecular dynamics simulation. Findings show that when the TiH2 dust concentration is 750 g·m−3, both the explosion pressure and explosion pressure rise rate reach their maximum values under airtight and venting conditions. There are three stages in the whole combustion process: the combustion development stage, the stable combustion stage, and the decay stage. The flame length (L) and flame propagation velocity (v) grow with the increase of dust concentration. TiH2 dust explosion with different concentrations in macroscopic tests is approximated by simulating the combustion behaviors of the TiH2 system with different densities. The combustion reaction rate of TiH2 grows with an increase in system density, and the simulation results are consistent with experimental findings.

Silica-Containing Phosphorus-Based Sol-Gel Finishing to Improve Flame Retardant Performance of Cotton Fabrics

In this paper, the sol-gel technique was used to design hybrid phosphorus-doped silica structures for improving the thermal stability and flame retardancy of cotton fabrics. To this aim, diethylphosphatoethyltriethoxysilane (DPTS) was employed as phosphate alkoxysilane in a multistep procedure that involved multiple layers (from 1 to 6) depositions. The multi-layer coatings were applied by padding using sols containing appropriate molar ratios of the precursor, anhydrous ethanol, catalyst, and hydrochloric acid. Moreover, the synergism P-N on flame retardancy of cotton was assessed by introducing 3-aminopropyltriethoxysilane (APTES) as an N-donor precursor in DPTS sols. The effects of the catalyst during the alkoxide reaction and the silica amount applied by sol-gel treatment on the thermo-oxidative behavior of the treated fabrics were deeply studied. The creation of the silica skeleton on the cotton surface and the interactions between the cellulosic fibres and the doped layer were investigated using FT-IR ATR spectroscopy. Moreover, thermal and thermo-oxidative stability, flammability properties, and combustion behavior of the sol-gel treated cotton fabrics were also studied, proving the effectiveness of the sol-gel coating in the fire protection of the cellulosic substrate.

Direct numerical simulation of ammonia/n-heptane dual-fuel combustion under high pressure conditions

Ammonia (NH3) combustion has received increasing attention for its carbon-free nature. However, the utilization of ammonia in engines is constrained by its relatively low reactivity. To overcome this shortcoming, ammonia blending with high-reactivity fuels has been used. In the present work, direct numerical simulation (DNS) of ammonia/n-heptane dual-fuel combustion was performed to understand the effects of ammonia addition on the combustion behavior of n-heptane sprays. Three DNS cases with NH3 energy ratios of 0%, 20%, and 40% were considered. Two-stage combustion was observed in all cases. It was found that both the first-stage and second-stage ignition delay times increase with increasing NH3 energy ratio, and the peak of mean heat release rate (HRR) reduces with increasing NH3 energy ratio. For low-temperature combustion, ignition kernels were observed in the case with pure n-heptane while ignition occurs almost volumetrically in the cases with NH3 addition. The reaction zone of the cases with NH3 addition is thicker compared to that of the case with pure n-heptane. The reactions of NH3 involve radicals, such as OH, which affects the low-temperature combustion of n-heptane. In the stage of high-temperature combustion, individual ignition kernels with significant heat release rate were observed in the cases with NH3 addition, where the reaction zones are thin. In contrast, for the case with pure n-heptane, large heat release rate occurs simultaneously over the entire domain with thick reaction zones. Ignition occurs in regions characterized by low scalar dissipation rate for both low-temperature and high-temperature combustion in all cases. It was found that, though the contributions of NH3-related reactions to the total HRR are noticeable, the contributions of important elementary reactions to the total HRR in pure n-heptane combustion still prevail in the cases with NH3 addition, which indicates that n-heptane chemistry dominates that of NH3 in this work.

Property Enhancement of Waste Printed Circuit Boards Powders Reinforced Polypropylene by In Situ Magnesium Hydroxide Impregnation from Waste Lye.

Using alkali pretreatment can effectively remove residual variable-valence metals from non-metallic powder (WPCBP) in waste printed circuit boards. However, substantial amounts of waste lye are generated, which causes secondary pollution. On this basis, this study innovatively utilized waste alkali lye to prepare nano-magnesium hydroxide. When the dispersant polyethylene glycol 6000 was used at a dosage of 3 wt.% of the theoretical yield of magnesium hydroxide, the synthesized nano-magnesium hydroxide exhibited well-defined crystallinity, good thermal stability and uniform particle size distribution, with a median diameter of 197 nm. Furthermore, the in situ method was selected to prepare WPCBP/Mg(OH)2 hybrid filler (MW) and the combustion behavior, thermal and mechanical properties of PP blends filled with MW were evaluated. The combustion behavior of the PP/MW blends increased with the increasing hybrid ratio of Mg(OH)2, and the MW hybrid filler reinforced PP blends showed better thermal and mechanical properties compared to the PP/WPCBP blends. Furthermore, the dynamic mechanical properties of the PP/MW blends were also increased due to the improved interfacial adhesion between the MW fillers and PP matrix. This method demonstrated high economic and environmental value, providing a new direction for the high value-added utilization of WPCBP.

Analyzing Burner Performance and Combustion Phenomenon in an Olefin Plant's Industrial Furnace: A CFD Study.

This work presents a comprehensive study of the combustion performance of an industrial furnace in an olefin plant using computational fluid dynamics (CFD) simulations. The focus was on analyzing the heat release pattern of bottom burners to optimize the furnace efficiency in steam-cracking processes. The study developed an accurate computational fluid dynamics (CFD) model for predicting combustion behavior in a cracking furnace. The computational model was validated by comparing the simulation results with industrial data and was used to investigate the impact of burner clogging and the importance of small holes in the body of burners in the furnace. The results also provided insights into the influence of excess air, temperature distribution, fluid behavior, composition of combustion products, and thermal efficiency of the furnace. The presented results contributed to a better understanding of parameters controlling combustion performance in steam-cracking furnaces.