Combustion Behavior Research Articles

Informal settlements ablaze: decoding the combustible nature of building materials used in Bangladesh through experiments and numerical analysis

ABSTRACT Fire outbreaks in informal settlements pose severe threats to residents and their properties. Despite the frequent occurrence of fire events in Bangladesh, detailed studies on fire propagation behaviour remain limited. This study addresses this critical issue by comprehensive investigations into the ignitability and burning behaviour of different materials such as cardboard, polyurethane foam, plastic bags, wood, and structural timber that are commonly found in informal settlements. Additionally, an advanced numerical model based on the finite volume method was developed in Fire Dynamics Simulator and then employed to accurately predict the fire-reaction properties of materials under the cone calorimeter environment. The results revealed that cardboard ignites quickly, burns moderately, and does not produce flaming droplets or ignite the filter paper. PU foam burns vigorously, with a high burning rate, and emits dense black smoke and a toxic odour. Plastic bags ignite rapidly, burn intensely, and are greatly influenced by the presence of airflow. The numerical model successfully quantified fire-reaction properties such as ignition time, heat release rate (HRR), and flame spread characteristics. Notably, wood and structural timber demonstrate a distinct combustion pattern with a sharp HRR peak, while PU foam exhibits the highest peak HRR values followed by timber masonite.

Unveiling the low‐temperature oxidation chemistry of dipropyl carbonate

AbstractDialkyl carbonates (DACs) own an environmentally friendly synthesis route, making them potential candidates as alternative fuels. However, for DACs to be widely accepted as an alternative fuel, a comprehensive understanding of their combustion behavior is essential. Dipropyl carbonate (DPrC) represents a transition from short‐chain to mid‐chain carbonates, understanding its combustion behaviors holds significance in unraveling the combustion chemistry of carbonates. In this study, the oxidation of DPrC was investigated with the initial fuel mole fraction of 0.5% at three equivalence ratios of 0.5, 1.0, and 2.0 within a temperature range of 550–1100 K in a jet‐stirred reactor for the first time. Gas chromatography was utilized for the quantitative detection of reactants, intermediates, and products. A detailed DPrC mechanism was first developed, and good agreements between measurements and simulations were obtained. A notable negative temperature coefficient (NTC) behavior was first observed in the oxidation of DACs. Such NTC phenomenon occurred at fuel‐lean conditions in the temperature range of 620–660 K, while only a weak low‐temperature consumption was observed at the stoichiometric condition. Kinetic modeling studies showed that this unique low‐temperature chemistry of DPrC can be attributed to the differences in the RO2 isomerization reactions between DPrC and short‐chain DACs. The RO2 isomerization via a six‐member ring transition state could happen in DPrC oxidation but not in dimethyl carbonate and diethyl carbonate oxidation, due to the different fuel molecular structure. Therefore, the subsequent reaction pathways via QOOH → O2QOOH → HO2Q = O + OH → OQ = O + OH were promoted and two OH radicals were released in this process. Moreover, it is conceivable that mid or long‐chain DACs could also exhibit an NTC phenomenon due to the increased potential for RO2 isomerization via a six‐ or seven‐member ring transition state, thereby increasing the likelihood of RO2 isomerization occurrence.

Motion and Combustion Behavior of Single Char Particle in Oxy-Fuel Fluidized Bed: Experimental and Modeling Studies

Motion and Combustion Behavior of Single Char Particle in Oxy-Fuel Fluidized Bed: Experimental and Modeling Studies

Catalytic hydrothermal reaction of biomass and its application in blast furnace injection: Physicochemical, conversion mechanism, combustion behavior

This study employs a combination of experimental research and computational fluid dynamics (CFD) simulation to evaluate the optimal conditions for catalytic hydrothermal carbonization suitable for blast furnace injection. Through FTIR spectroscopy, Raman spectroscopy, ICP analysis, and combustion kinetics analysis, the physical and chemical properties of the hydrochar were determined. Subsequently, these properties along with kinetic parameters were applied to an improved CFD model to compare the flow patterns and combustion performance of hydrochar with PCI coal in blast furnaces. The results indicate that the optimal HTC conditions are identified at 300 °C with FeCl3 catalysis, yielding hydrochar (HTC-300-FeCl3) characterized by a calorific value of 32.10 MJ/kg, 98 % K element removal, and enhanced carbonaceous structure ordering. This is attributed to the addition of FeCl3 effectively enhances the generation of hydroxyl radicals in the aqueous phase and promotes deoxygenation and hydrogenation reactions in the solid phase, improving the quality of hydrochars. In addition, CFD model shows that the HTC-300 FeCl3 exhibits a higher burnout (86.2 %) and average gas temperature (2383.1 K) compared to PCI coal, indicating its greater potential as a PCI coal substitute in BF injection.

Development of a chemical mechanism for ammonia/hydrogen blends for engines

ABSTRACT Ammonia/hydrogen blend fuels have been extensively used as alternative fuel for engines. The combustion and emissions characteristics of ammonia/hydrogen engines have been investigated utilising a CFD model. Developing a robust and accurate chemical reaction mechanism for ammonia/hydrogen blend fuels is of utmost importance. In this paper, a chemical mechanism has been developed and validated for the combustion characteristics of ammonia/hydrogen, which includes 31 species and 223 reactions. Extensive validation has been conducted using experimental data as the basis. The obtained data indicate that the simulated values for the ignition delay times of the shock tube and the concentration of the main components in the stirred jet reactor align well with the measured values. The simulated laminar flame speed under turbulent flow conditions shows a remarkable agreement with the corresponding experimental data. The study compared simulated flame evolution values with experimental data from a constant volume combustion bomb. The results indicate that the proposed mechanism is able to produce favourable flame evolution and combustion characteristics. The presented detailed mechanism demonstrates credible overall performance in terms of combustion behaviours, indicating its suitability for effectively modelling ammonia/hydrogen combustion in real engines.

Combustion behavior and effluent liquid properties in extra-heavy crude oil reservoirs developed by steam huff and puff

In recent years, interest in in-situ combustion (ISC) as an alternative technique for extra-heavy crude oil reservoirs subjected to steam huff and puff has grown significantly; however, the ISC behavior and effluent liquid properties in such oil reservoirs remain under-explored. In this work, the combustion tube (CT) was used to investigate the combustion behavior of extra-heavy crude oil. Also, the effluent liquid properties during ISC were analyzed comprehensively. The results revealed that when the secondary water bodies (SWB) were present at the injection end of CT, a stable combustion front advanced, causing a gradual temperature rise and a CO2 concentration above 12 % in the effluent gas. This suggested that steam injection wells in these reservoirs were suitable candidates for subsequent air injection after steam huff and puff. Conversely, when the SWB was located at the production end of CT, the peak temperature of combustion decreased, indicating a transition to medium-temperature combustion and unstable combustion front advancement, making steam injection wells unsuitable for ISC as production ones. Three key criteria for evaluating ISC effectiveness in extra-heavy crude oil were: (1) the intensity of –CH2 and –CH3 peaks, (2) the C-O absorption peak between 1100 and 1000 cm−1, and (3) the distribution of characteristic peaks around 750 cm−1. A significant decrease in these peaks indicated high-temperature combustion and substantial oil upgrading. Also, the presence of alkynes suggested extensive thermal cracking and a stable combustion front. The anion concentration of effluent water increased compared to crude water, but the relationship between water ion concentration and combustion state was weak, without a discernible pattern.

Evaluation of Current and Future Aviation Fuels at High-Pressure Rich-Quench-Lean-Type Combustor Conditions

Abstract Decarbonizing the aviation sector is one of the biggest challenges to minimize climate change effects associated with carbon dioxide emission. Sustainable aviation fuels will play a major role in this context especially for long-distance flights where hydrogen or all-electric propulsion systems do not present a feasible alternative. In addition, aromatic-free sustainable aviation fuels offer a promising solution to lower soot emissions of aeroengines. Jet A-1 as reference fuel, two blends, and two neat synthesized paraffinic kerosenes (SPKs) from hydroprocessed esters and fatty acids (HEFA) were tested to characterize the combustion behavior of drop-in/near drop-in fuels. Experiments in an optically accessible high-pressure rich-quench-lean (RQL)-type combustor at typical aeroengine conditions were performed using optical diagnostics, exhaust gas, and particle sampling measurements to delineate the fuel effects on spray, flame, and emission characteristics. Measurements were performed at pressures up to 10 bar, air preheating temperatures up to 773 K and primary zone equivalence ratios up to 1.66. Liquid fuel distribution and fuel placement were found to be sensitive to fuel properties. By contrast, no pronounced influence on flame position and shape were observed. As a consequence, NOx and CO emissions of the tested fuels differed only moderately. However, particulate matter measurements at the fuel richest operating condition showed a clear fuel ranking with the lowest particle emissions evident for the two neat HEFA-SPK samples. Moreover, the particle volume concentration at the fuel richest condition followed the expected trend with fuel H-content.

The emission of pollutants from ornamental shrubs during forest fires

AbstractThis study investigates the combustion behavior, emissions, and aerosol production of four plant species: Laurus nobilis, Cistus monspeliensis, Photinia fraseri, and Cupressus sempervirens. The Heat Release Rate (HRR) and Smoke Production Rate (SPR) were measured, revealing that Cupressus sempervirens had the highest HRR and longest flame duration due to its higher bulk density. Emission Factors (EFs) for key compounds such as CO₂, CO, NO, and aerosols showed significant variation by species. Aerosol analysis indicated that the combustion of all plants primarily emitted fine particles, with the majority being ultrafine particles (PM0.1), particularly in the 25–130‐nm range. Particle size distributions were bimodal in number but monomodal in volume. These findings highlight the impact of plant characteristics on fire behavior and emissions, with significant implications for understanding fire dynamics in wildland–urban interfaces.

Combustion reactivity of sewage sludge hydrochar derived from hydrothermal carbonization via thermogravimetric analysis

Wastewater treatment plant sludge contains a high concentration of organic compounds that can be used to produce fuel viahydrothermal carbonization (HTC). This study investigated the combustion reactivity and kinetic parameters of hydrochars produced to understand the combustion behavior of the solid fuel derived from HTC. The hydrochar was produced at various temperatures ranging from 150 to 300 °C, reaction times ranging from 30 to 150 min, and solid loadings ranging from 10% to 30%. The combustion behavior of sewage sludge (SS) and hydrochar was evaluated using thermogravimetric analysis with a constant air flow rate (100 mL/min) and heating rate (10 °C/min) from ambient temperature to 900 °C. It was observed that the HTC temperature, reaction time, and solid loading influenced the combustion characteristics and kinetics of the hydrochar. Additionally, the hydrochar exhibited higher ignition and burnout temperatures and a lower peak temperature than SS, indicating superior performance and reactivity in combustion. The combustion kinetic analysis also revealed that the hydrochar had a range of lower activation energy (29.12–41.60 kJ/mol) than SS (52.95 kJ/mol). Therefore, hydrochar derived from SS has the potential to be used as a substrate for solid fuel production for future renewable energy sources.

An evaluation of the combustion temperature profile of Ba(NO3)2-based composition

The study examined both theoretical and experimental combustion temperatures of Ba(NO3)2-based samples of composition with an oxidizer excess coefficient of α~0.72 under various pressures. The results indicate that at low pressures, the combustion temperature of the samples is significantly lower than the calculated value. The temperature profile in the combustion wave at atmospheric pressure was determined, revealing that the samples exhibit a high surface combustion temperature. The majority of the heat required for the propagation of the sample's combustion is released in the condensed phase. These findings underscore the influence of pressure on combustion characteristics and emphasize the importance of considering phase interactions in understanding combustion behaviors.

Electrocombustion Characteristics of Iron Particle-Laden Methanol and Ethanol Droplets in a Direct Current Field

ABSTRACT This study investigates the electrocombustion and atomization behavior of single droplets (2.5 wt.% Fe) of ethanol (EtOH) and methanol (MeOH) fuels at the droplet scale. The experiments utilize a system with two opposing plate electrodes of varying distances (200, 150, and 100 mm) and both negative (↓) and positive (↑) polarizations within a vertical direct current (DC) electric field. The results show that for EtOH and EtOH/Fe droplets, the flame envelope changes to a spherical form at (↓) and (↑) polarizations at 100 mm plate spacing, while for MeOH and MeOH/Fe droplets, the flame envelope changes to a spherical form at (↓) and (↑) polarizations at 200, 150 and 100 mm plate spacing. Increasing electric field strength reduced the micro-explosion tendency of Fe particles in the flame region and the micro-explosion intensity of Fe particles was found to be higher in ethanol droplets than in methanol. No systematic relationship could be established between the electric field effect and the presence of Fe particles. The MeOH/Fe/150(↑) droplet exhibited the lowest extinction time of 1050 ms. The electric field fundamentally alters the secondary atomization process of the fuel droplets. Notably, the diameter regression of all MeOH-based fuel droplets deviates significantly from a linear relationship. The investigation into the combustion behavior of pure EtOH, MeOH, and their Fe-blended counterparts within an electric field environment suggests that MeOH and MeOH/Fe fuels exhibit superior combustion characteristics. However, further research is necessary to fully elucidate these findings.

Numerical Study on Flame Geometric Characteristics of Ammonia-Fueled Small Boiler

Amidst global efforts to cut carbon emissions, the carbon-neutral fuel sector is at a crossroads of opportunity and challenge. The pursuit of clean, sustainable energy alternatives is critical. Ammonia, with its zero-carbon and hydrogen-rich profile, is emerging as a promising clean fuel, yet its combustion behavior in industrial boilers demands further study. This paper presents a numerical analysis of the flame geometry characteristics of ammonia combustion at an equivalence ratio of 1. The study delineates the dimensions of the flame, specifically its diameter and length, offering valuable insights that can inform the design of industrial boilers. This research contributes to the broader understanding of ammonia's role in the transition towards more sustainable energy solutions in industrial settings.

Preparation of high transparency, thermal stability, flame retardant polymethyl methacrylate nanocomposite via gamma-radiation polymerization

Achieving flame retardancy and thermal stability in poly(methyl methacrylate) (PMMA) while maintaining its inherent high transparency presents a significant challenge. In this work, we successfully fabricated an exceptional composite (P-SiO2-PMMA) with high transparency, flame retardancy, and thermal stability using 60Co γ-ray irradiation-induced copolymerization of methyl methacrylate (MMA), 2-hydroxyethyl 2-methyl-2-propenoate phosphate (HEMAP), and nano-silica (SiO2). The impact of the HEMAP on the crystal, optical, thermal stability, and combustion behavior properties of P-SiO2-PMMA has been investigated. P-SiO2/PMMA forms a three-dimensional network cross-linked molecular chain structure, enhancing the thermal decomposition temperature (Tdi), maximum thermal decomposition temperature (Tmax), glass transition temperature (Tg), and reducing the coefficient of thermal expansion (CTE). HEMAP and SiO2 significantly enhance the flame retardancy of the material. The limiting oxygen index (LOI) value of transparent flame-retardant 20-P-SiO2/PMMA composite material increased from 17.5% for PMMA to 23.2%, with a 47.3% decrease in peak heat release rate (PHRR). The flame retardant mechanism was also investigated. This study offers a novel approach for the industrial application of high transparency, thermal stability, and halogen-free flame-retardant PMMA composite.

Cofiring of hydrogen and pulverized coal in rotary kilns using one integrated burner

The grate-kiln process for iron-ore pellet induration utilizes pulverized coal fired burners. In a developed infrastructure for H2, it might be desirable to heat the existing rotary kilns with renewably produced H2. Technical challenges of H2 heating of grate-kilns include high emissions of NOX and maintaining sufficient heat transfer to the pellet bed. This article examined cofiring (70% coal/30% H2) in 130 kW experiments using two different integrated burner concepts. Compared to pure coal combustion, cofiring creates a more intense, smaller flame with earlier ignition and less fluctuations. The process temperature and heat transfer are enhanced in the beginning of the kiln. The co-fired flames emit 32% and 78% less NOX emissions compared to pure coal and H2 combustion, respectively. We can affect the combustion behavior and NOX emissions by the burner design. H2/coal cofiring using integrated burners is probably an attractive solution for emission minimization in rotary kilns.

Physiochemical View of Fuel Jet Impingement and Ignition Upon Contact with a Cylindrical Hot Surface

This study delves into ignition and flame dynamics involving a cylindrical hot surface impact. Previous studies have focused on the flat-wall hot surface interacting with fuel spray, leaving gaps in understanding the effects of cylindrical hot surfaces on fuel-air mixing and ignition. Using high-fidelity large-eddy simulations (LES), this study investigates how fluid elements, upon contacting an electronically activated glow plug structure, exhibit mixing and thermochemical properties. The analysis examines how this type of structure enhances fuel-air mixing and subsequently influences the thermochemistry behavior in conjunction with the fuel-specific combustion behavior. The study includes scenarios with free spray and non-thermal deposit cases to assess their mixing impact, alongside testing five different electric voltage inputs to study the thermally assisted ignition process. Results demonstrate that the cylindrical structure hinders flow, reducing its inertia and increasing flow residence time. Moreover, a significant Coandă effect due to the circular wall structure is identified, potentially serving as a mechanism for enhancing flame-holding. Furthermore, varying the input voltage notably affects ignition timing, revealing a non-monotonic ignition delay pattern with lower voltages. Detailed analysis highlights the critical role of negative temperature coefficient (NTC)-driven low-temperature chemistry (LTC) in the ignition process.

Synchronously enhanced flame retardancy and mechanical properties of polylactic acid via in-situ assembly of polyphosphazene nanoparticles on ammonium polyphosphate

Polylactic acid (PLA) exhibits wide potential applications in many fields ranging from textile, packaging material to biomedical devices. However, the relatively low mechanical properties and inflammability are obstacles to the expansion of its application. Here, a kind of polyphosphazene nanoparticles with tannic acid (TA) as template, hexachlorocyclotriphosphazene (HCCP) and 4,4′-Sulfonyldiphenol (BPS) as comonomers were prepared (named as HTB), and then combined with ammonium polyphosphate (APP) to enhance the comprehensive properties of PLA composites. The introduction of HTB strengthened the interfacial adhesion of composites via constructing the hydrogen bond interaction between PLA and APP, promoting the homogenous dispersion of APP in the composite and the formation of APP network. The flame retardant measurements presented that incorporating 10 wt% APP and 5 wt% HTB in PLA increased the limit oxygen index (LOI) value to 31.0% and endowed the composite with the V-0 rating of UL-94 test and simultaneously, the peak of heat release rate (PHRR) and total heat release (THR) of the composite decreased by 14.2% and 13.2% compared with pure PLA. Specially, there was almost no melt drip appeared during the combustion process, which was distinctly different from the combustion behavior of the composite containing only 20 wt% APP with the V-2 rating of UL-94 test. The uniform dispersion of APP in the PLA matrix and the strong interfacial adhesion between APP and the PLA matrix contribute to the enhancement of the mechanical properties of composites, and the elongation at break, Young’s modulus and impact strength of the composite were increased by 52.9%, 7.6% and 24.2%, respectively. The present study offers novel insights for the trade-off between flame retardancy and mechanical properties with PLA composites.

Fuel blend combustion for decarbonization

The utilization of fossil fuels is currently transforming to low-carbon or zero-carbon fuels, which is one of the solutions to global warming. Hydrogen and ammonia are regarded as promising zero-carbon fuels in power supply and transportation scenarios but the availability of hydrogen and their distinctly different chemical activity constrain their large-scale direct utilizations. Fuel blends with physical and chemical complementary are considered as the effective approaches in the utilization of hydrogen and ammonia because no significant modification to the existing end-user infrastructures is needed. This paper reports recent progress in the fundamental combustion behaviors of fuel blends, focusing on hydrogen-hydrocarbon blends and ammonia-hydrocarbon blends. Firstly, laminar flame behaviors, auto- and forced-ignition characteristics, and pollutant emissions of binary fuels containing hydrogen are reviewed, all of which are supplemented with a discussion on the governing hydrogen-enriched combustion chemistry. Subsequently, the hydrogen-enriched flame responses to the flow conditions are discussed, including the turbulent burning velocity and statistical structures, the flashback swirl flames, thermoacoustic instabilities, and the jet ignition characteristics; Furthermore, with the increasing concern over ammonia as a zero carbon fuel and its extremely weak reactivity, recent progress on combustion of fuel blends containing ammonia are also reviewed. The fundamental combustion chemistry studies including laminar burning velocity, the ignition delay times data collection, as well as the attempts for chemical kinetic modeling development for fuel blend with ammonia are presented. The literature reported ammonia containing blends of turbulent flame characteristics are presented. Finally, from an engineering point of view, examples using hydrogen blends in practical internal combustion engines and in gas turbines are introduced, including the topic of engine efficiency performance and pollutant emissions and different combustors for gas turbines. It is suggested that fuel blends with hydrogen or ammonia that potentially monitors the overall reactivity will be one realistic solution to de-carbonization, on the basis of current transportation and power generation systems.

Self-exothermic reaction behavior and pore structures of Ni-Al intermetallics with more than 70% porosity

Abstract In this study, high-porosity Ni-Al alloys with complete shape and controllable pore structures were prepared by combining the self-exothermic reaction with the space holder method. The observations show that porous Ni-Al sintered discs appeared to melt and deform after a violent reaction without adding space holder particles. The link between the volume content of urea particles and macroscopic morphology, combustion behavior, phase composition and pore structures of porous Ni-Al compounds were studied. The space holder pores acts as a heat absorber, greatly increasing the open porosity to 76.0% when adding 50 vol% urea particles. This leachable space holder method can be an effective strategy to regulate the sample shape and pore characteristics of porous Al-containing intermetallics.

Parametric study of combustion characteristics of diesel/methanol dual fuel engine using global sensitivity analysis and multi-objective optimization

The pursuit of clean and efficient internal combustion engine power necessitates the substitution of fossil fuels with methanol and the adoption of advanced combustion strategies. This study examines the combustion and emission characteristics of methanol/diesel dual-fuel compression ignition engines. To understand the intricate interplay between critical parameters and engine performance, the global sensitivity analysis (GSA) method is employed, utilizing Sobol sensitivity as the quantitative metric. The investigated parameters include methanol substitution rate, diesel injection parameters, and five thermodynamics parameters concerning in-cylinder conditions. A validated computational fluid dynamics (CFD) model, coupled with a chemical kinetic mechanism, is developed to predict the combustion behavior of the dual-fuel engine accurately. This predictive capability forms the basis for utilizing the tree-based process optimization (TPOT) algorithm. By implementing TPOT, a significant reduction in the mean square error (MSE) of the predicted characteristics model is achieved, averaging a decrease of 73.59%. Subsequently, a multi-objective optimization is conducted, exploring the impact of varying target weights on the optimal outcomes. Results show the initial pressure significantly impacts the engine's economy, power and emission characteristics, and NOx formation should be carefully considered in the combustion optimization of dual-fuel engines.

Ab initio molecular dynamics simulations on the combustion mechanism of Al/Fe2O3 nanothermite at various temperatures

Acquiring a comprehensive understanding of the combustion mechanism of nanothermites is crucial for elucidating phenomena and enhancing performance. The ab initio molecular dynamics method was employed to investigate the reaction process of the Al/Fe2O3 nanothermite at various temperatures. The complex combustion behavior and reaction mechanism were qualitatively described in terms of dynamic morphologies, potential energy, atomic density distribution, etc. Results suggest the initial reaction of Al/Fe2O3 is initiated by the migration of interfacial O atoms and the dissociation of Fe-O bonds, subsequently leading to the formation of alumina at the interface, which impedes the further progression of the thermite reaction. The increase in temperature enhances atomic diffusion and provides sufficient energy for the reaction. The interfacial metal Al layer undergoes melting and diffuses into the iron oxide layer, while vacancies generated during the reaction process sustain the continuous migration of internal oxygen atoms. At 2000 K and 3200 K, the initial structures completely collapse, facilitating the inward propagation of the thermite reaction, which subsequently results in the formation of alumina, iron clusters, and intermetallic compounds (AlFe, AlFe3, and Al6Fe). These findings offer significant insights into the combustion reaction mechanisms of nanothermites.