Flame Intensity Research Articles

Effect of upstream injection on local flame intensity in a scramjet combustor fueled with liquid kerosene at Mach 4 flight condition

The intensity of the local flame generated by spark ignition was investigated in a scramjet combustor fueled with liquid kerosene under Ma 4 flight conditions. The study utilized wall pressure evolution and high-speed imaging during experiments to assess the local flame intensity. The rise in wall pressure near the aft edge of the cavity was found to be an indicator of local flame intensity, and the impact of upstream injection on the flame intensity was discussed. The results demonstrated that the dense spray resulting from upstream injection suppressed the local flame intensity. In particular, the spray in close proximity to the shear layer caused weakening of the local flame through evaporation. Additionally, the height of penetration increased with higher upstream injection pressure, leading to the dense spray being located further away from the shear layer flame and thereby strengthening the local flame intensity. Moreover, a larger injection distance marginally decreased the flame intensity due to the presence of additional spray near the wall. Conversely, injections with higher mass rates resulted in a weaker flame intensity as more spray was distributed into the cavity.

Performance study of a central reentrant step pilot-flameholder in a dual-mode combustor

The augmented/ramjet combustion chambers are characterized by wide operating ranges, large flow state variations, and harsh operating conditions. The reliable ignition of these chambers urgently needs to be achieved. To improve the pilot ignition and blowout performance based on the centerbody in augmented/ramjet combustion chambers, a reentrant step flameholder is proposed on the basis of a conventional backward step. In this paper, the flow characteristics, ignition and blowout boundary under the non-premixed inflow, dynamic ignition process and flame stabilization mechanism of the reentrant step flame holder are investigated by using an experimental method with numerical simulation. The results show that the reentrant step flame holder exhibits better ignition and blowout performance than the conventional step flame holder without increasing the flow resistance. The ignition and blowout equivalence ratios of the reentrant step flame holder decrease by 22.86 % and 24.34 %, respectively, compared with those of the conventional step flame holder. The radial reentrant expansion is more effective than the axial reentrant expansion. Analyzing different reentrant structures shows that radial expansion can shorten the ignition delay time and improve the time-averaged integral flame intensity; axial expansion can improve the time-averaged integral flame intensity and reduce the flame pulsation rate; and the structure Da30Dr30 (the conventional step structure expands axially and radially by 30 mm simultaneously within the centerbody.) whose pilot flames are all stabilized in front of the reentrant step flame holder under different incoming flow conditions, exhibits the best ignition and blowout performances.

Radiating biofuel-blended turbulent nonpremixed hydrogen flames on a coaxial spray burner

The low radiant intensity and luminosity of hydrogen flames can be enhanced by the addition of a small portion of sooting biofuels. To achieve higher effectiveness, the impact of blending turbulent nonpremixed hydrogen flames with liquid biofuels, by gas-assist atomisation, is investigated and compared with the introduction methods of prevapourisation and ultrasonic spray. The flame appearance, luminosity, radiant fraction, centreline temperature, and the near-field spray characteristics of four biofuel surrogates (eucalyptol, D-limonene, guaiacol, and anisole) blended into hydrogen flames are measured experimentally. Radiating biofuel/hydrogen flames are achieved on a coaxial needle spray burner by the addition of 0.1–0.3 mol% biofuel surrogates. Compared with the unblended hydrogen flame, the luminosity and radiant fraction are enhanced by 30%–500% and 2%–15%, respectively, with the addition of biofuel surrogates. The results show that adding the biofuel surrogates by gas-assist atomisation is more effective than prevapourisation and ultrasonic atomisation in luminosity and radiant fraction enhancement. It is found that the local fuel-rich conditions, which are beneficial for soot formation, are further facilitated by the larger droplets and spray objects generated by gas-assist atomisation. Of the additives tested, anisole is the most effective for luminosity and radiant fraction enhancement of a hydrogen flame while exhibiting the largest flame temperature drop due to the enthalpy of vapourisation and the radiative loss from the promoted soot formation. The viscosity and surface tension greatly influence the spray characteristics which in turn impacts the flame characteristics. Guaiacol, the representative of lignin, appears to have the lowest effectiveness in radiant fraction enhancement due to the presence of a hydroxy group, a higher bond dissociation enthalpy, and a coarser spray ascribed to higher viscosity and surface tension.

Study on the effect of particle morphology on transient dispersion behavior and ignition of Al[sbnd]Mg alloy powder

Particle morphology has a significant effect on the explosion of energetic dust which includes heat transfer and transient dispersion behavior. This study aimed to investigate the differences in transient dispersion characteristics of Al-Mg alloy powders with different shapes using Particle Image Velocimetry (PIV) and to elucidate their effects on subsequent flame propagation and explosion parameters. The results demonstrated that irregular dust exhibited lower agglomeration and terminal fall velocity (TFV) compared to spherical dust, leading to a higher overall concentration of dust involved in the explosion. In addition, the turbulence intensity in the critical ignition zone of irregular particles was relatively high, resulting in particles having more active motion characteristics during the initial ignition phase. Therefore, irregular dust exhibited more intense flame phenomena and higher explosion parameters. These findings emphasize the importance of considering particle morphology when assessing the risk associated with metal dust explosions.

Combustion enhancement in a model scramjet by a simple pin-to-pin AC arc plasma

A simple pin-to-pin alternative-current (AC) arc plasma located upstream of the cavity was developed to achieve significant combustion enhancement in a Mach 2.52 C2H4-fueled and cavity-based model scramjet. The arc plasma-enhanced combustion process was recorded by high-speed CH⁎ chemiluminescence imaging, optical emission spectroscopy, static pressure measurements, and discharge waveform measurements. In the absence of the arc plasma, the flame heat release intensity was low, and the heat release region was located at the shear layer of the cavity; the flame stayed in a relatively weak combustion state and even appeared in a lower heat release intensity. Once the arc plasma was turned on, the static pressure of the model scramjet at the typical positions was increased by up to 9 %, and the flame area and the flame intensity were significantly enhanced. In the presence of the arc plasma, the position of the flame heat release region moved upstream and even caused the long-scale displacement for the flame with a higher heat release intensity several times. The arc plasma provided a large number of reactive species and Joule heat at the practical influence region of the arc plasma, which contributed to igniting an initial flame upstream of the cavity. The propagation and development of the continuous initial flame generated by the arc plasma can enable the flame to be more frequently transferred into the cavity-assisted jet-wake stabilized combustion mode, leading to significant combustion enhancement.

Local statistics of turbulent spherical expanding flames for NH3/CH4/H2/air measured by 10 kHz PIV

In this paper, we present high-speed particle image velocimetry measurements to quantify combustion-induced turbulence and turbulent stretch rate effects on flame propagation in a fan-stirred constant-volume combustion vessel. Three stoichiometric fuel/air mixtures including methane/air, methane/hydrogen/air and ammonia/methane/air were tested. The expansion rate of flame radius is found to scale with a half-power law of the mean-radius based Reynolds number. Measurements of velocity in the reactant zone show that the gas mean and rms velocity increase within the flame brush then gradually decrease when approaching the detection edge. Combustion enhances the measured non-reacting flow turbulence by ∼64 % within the reactant side of the flame brush of this expanding spherical flame. The evolution of rms velocity is found to be insensitive to pressure but sensitive to initial turbulent intensity and laminar flame speed, scaling with Reynolds number in a similar manner as the rate of expansion of the flame radius. Hydrogen blending shows the largest absolute value of rms velocity increase, but ammonia blending leads to the largest increase in rms velocity relative to laminar flame speed. The pdfs of 2D curvature are broadened as u′ and p increase but gradually saturate at high u′ for all mixtures, those of stretch rate are widened by flame speed. The temporal evolution of statistical flame stretch rates suggests the tangential stretch rate is larger than and anti-correlated with the normal stretch, and that there is a strong positive correlation between instantaneous flame propagation rate and the rms strain rate. Finally, the mean flame curvature and mean stretch rate are found to be near zero as flame propagates outwardly.

A comprehensive study on the design and computational analysis of an air swirl burner

This paper presents a comprehensive study on optimizing the design of a vane-type air swirl burner, along with a computational analysis comparing the combustion of diesel and hydrogen fuel within the same burner. For the combustion simulations, a coupled approach was employed involving a Lagrangian approach with the Discrete Phase Model to track the trajectories of fuel particles providing a comprehensive understanding of the particulate dynamics within the system. This research aimed to analyze hydrogen's potential as a sustainable energy carrier in comparison to its conventional counterparts such as diesel fuel. The results showed that the contours of hydrogen fuel revealed a well-defined and intense flame front whereas it was not the same in the case of diesel fuel which had a less intense flame front.

Application of Fuzzy Neural Networks in Combustion Process Diagnostics

Coal remains one of the key raw materials used in the energy industry to generate electricity and heat. As a result, diagnostics of the combustion process is still an important topic of scientific research. Correct implementation of the process allows the emission of pollutants into the atmosphere to be kept at a compliant level. Therefore, it is important to conduct the process in a manner that will not exceed these standards. A preliminary analysis of the measurement signals was carried out, and signal predictions of flame intensity changes were determined using the autoregressive moving average (ARMA) model. Different fuzzy neural network architectures have been investigated. Binary and multi-class classifications of flame states were conducted. The best results were obtained from the ANFIS_grid partition model, producing an accuracy of 95.46% for binary classification and 79.08% for multi-class classification. The accuracy of the recognition of flame states and the high convergence of the determined predictions with measurement signals validate the application of the proposed approach in diagnosing or controlling the combustion process of pulverized coal and its mixtures with biomass. Expert decisions determine the range of acceptable states.

Flame lift-off detector based on deep learning neural networks

This study evaluates the application of deep learning techniques in real-time flame lift-off detection and lift-off length prediction from flame images. A multi-feed test facility equipped with an optical diagnostic system was used to investigate the flame stability of both liquid and solid fuels. A high-speed camera was used to capture flame images, and image processing techniques were employed to extract the data. In the case of flame detection from images captured by high-speed cameras, the temporal resolution of the images is very high, which is beneficial for detecting rapid changes in the flame dynamics. In the current study, the analysis of 10,000 images by images processing methods takes approximately 60 min. Therefore, traditional methods may not be suitable for real-time monitoring, as they may not be able to capture the detailed variations in the flame appearance and intensity. The objective of this study was to find a fast and computationally efficient way to detect flame lift-off in high-speed online flame monitoring system. Two models were used in this study: a convolutional autoencoder and a regression neural network. The results demonstrate the potential of deep learning techniques in online flame diagnostics. The proposed approach provides a fast and efficient way to process 10,000 images in only 3.5 s, making it suitable for implementation in real-time flame monitoring systems.Novelty and significancePrevious studies in the field of real-time flame diagnostics have predominantly used low sampling rates to capture flame images. However, when high-speed cameras are used, conventional image processing techniques prove inadequate to provide instant results for real-time monitoring systems. This study presents a novel deep learning approach capable of directly detecting flame lift-off from high-speed images without the need for separate segmentation, thereby significantly enhancing the analysis speed. The results obtained in this paper emphasize the advantage of using deep learning techniques to extract flame characteristics at high speed and with excellent quality. These capabilities are particularly crucial in high-speed systems.

Experimental study of the fuel spray and ignition characteristics in an aeroengine afterburner under subatmospheric pressure

The fuel atomization and ignition characteristics of an afterburner under subatmospheric pressure are important foundations for expanding the operating range of the afterburner at high flight altitudes. In this work, the lean ignition limits of the afterburner at subatmospheric pressure were obtained through experiments, and the fuel droplet size distribution and ignition process in the afterburner were acquired using a laser particle sizer and a high-speed camera. The results showed that the ignition equivalence ratio increased as the inlet pressure decreased and was lowest when the flame stabilizer blockage ratio was 0.3. When the inlet pressure of the combustor decreased from high pressure to subatmospheric pressure, the Sauter mean diameter (SMD) range of the fuel droplets increased from 60∼110 μm to 100∼190 μm due to the increase in the ignition equivalence ratio and the deterioration of the fuel atomization characteristics. Under subatmospheric pressure, the flame residence phase time in the ignition process decreases significantly, while the flame intensity fluctuates more dramatically during the flame growth phase due to the decrease in the equivalence ratio of the gaseous phase, the larger fuel droplet size, and the uneven fuel distribution. When the inlet pressure is high pressure, the flame propagates from the ignition position to the trailing edge of the flame stabilizer first and anchors within the shear layer behind the flame stabilizer, whereas under subatmospheric pressure, the flame does not propagate to the anchoring point in the first place, which is one reason for the difficulty of ignition of combustors under high-altitude conditions.

Combined inhibition effect of vacuum chamber and inert gas on LPG explosion

In order to investigate combined inhibition effect of vacuum chamber and inert gas on Liquefied petroleum gas (LPG) explosion, the explosion experiment was carried out on the self-built gas explosion experiment pipe (L/D = 47.5). The flame propagation and explosion pressure characteristics of LPG were investigated at different vacuum degrees and 10% CO2 volume fraction (VF). The results showed that it is feasible to use a photosensitive solenoid valve to open the vacuum chamber. The Photoreceptor Solenoid Valve can open the vacuum chamber in time; Compared to add only 10% CO2, after installing the vacuum chamber, the maximum pressure peaks were all delayed; The pressure drops rapidly and a short period of negative pressure appeared, and the negative pressure duration becomes shorter as the vacuum degree increases; At various vacuum degrees levels, the maximum pressure peak value occurs at 0.06 vacuum degrees, primarily due to the combined influence of residual fuel quantity, Helmholtz oscillation, and turbulence near the flame front. The Pmax in the pipe and the flame intensity at any position is lower than that when only adding 10% CO2; high vacuum is more conducive to extinguish the flame and increase the thickness of the flame; the pumping effect of the vacuum chamber inhibits the rise of explosion pressure and flame propagation velocity. The combined explosion suppression is more effective on LPG explosions compared to add only 10% CO2. When selecting vacuum degree, it is important to consider the impact of the opening time and different vacuum degree within the vacuum chamber on pressure formation and flame propagation.

Transient flameout process of boron-magnesium agglomerates during combustion in oxygen-rich atmospheres

In this study, boron–magnesium agglomerates with varying mass ratios were prepared by drying a micron-sized boron–magnesium mixed suspension, and the combustion process of these agglomerates under different oxygen-rich concentrations were investigated using a laser ignition system. The test results showed that when the mass fraction of magnesium powder in boron-magnesium agglomerates exceeded a certain threshold (between 2% and 5%), flame extinction and reignition occurred after a significant reduction in the agglomerate volume during combustion. This process is referred to as the transient flameout process, which is affected by the magnesium content of the agglomerate and the oxygen concentration in the ambient atmosphere. An increase in the magnesium content or oxygen concentration makes this phenomenon more pronounced. During weakening of the flame intensity, a dark film gradually covered the particle surfaces. X-ray diffraction and elemental analyses of the cross-section and outer surface of the condensed combustion product suggested that the dark film is primarily composed of Mg-B-O ternary oxides. This film prevents direct contact between boron and oxygen, thereby inhibiting surface and gas-phase reactions and leading to the occurrence of the transient flameout phenomenon.

Correlation of wall heat loss with quenching distance for premixed H2/Air flames during unsteady Flame-Wall interaction

Flame-wall interaction (FWI) of a laminar, premixed hydrogen/air flame perturbed by a pulsating inflow with excitation frequency (f) is investigated using fully resolved simulations employing finite-rate chemistry and detailed molecular diffusion. The setup is a two-dimensional (2D) V-shaped flame interacting with an isothermal wall on one side and a freely propagating flame on the other side, exhibiting a side-wall quenching and a freely-propagating mode. The impact of unsteady flame stretch on flame dynamics is characterized by the Damköhler number (Da), which is defined by the ratio of the turnover time of the oscillating inflow to the flame transit time. Da is found to directly describe the degree of flame deformation during flame propagation. During FWI, flame pocket formation is suppressed at conditions with Da close to unity. The correlation between wall heat flux (WHF) and quenching Peclet number (Peq) shows a time delay that depends on Da. A negative linear correlation can be recovered between time-averaged wall heat flux (WHF¯) with the quenching Peclet number (Peq¯), and its slope depends on the fuel equivalence ratio. For the lean hydrogen flame, the flame stretch near the quenching point leads to a decrease in flame intensity during FWI and therefore different slope of the correlation of WHF vs. Peq.

FSDF: A high-performance fire detection framework

Fire detection is crucial in the protection of human life and property. Traditional methodologies and deep learning techniques have been extensively employed in this area, yet they often fall short due to the considerable variability in the shape, size, and intensity of flames. Conventional approaches lean on predefined fire characteristics, failing to adapt sufficiently across a broad spectrum of fire conditions. Simultaneously, deep learning techniques may struggle with managing diverse and unusual flame attributes. In response to these challenges, we introduce a novel framework that synergizes traditional methods with deep learning techniques—the Fire Segmentation-Detection Framework (FSDF). FSDF enhances flame feature detection by extracting color and texture information from images, utilizing Hue, Saturation, and Value (HSV), and the Complete Local Binary Pattern (CLBP). In addition, we weave YOLOv8 and Vector Quantized Variational Autoencoders (VQ-VAE) into the fabric of our framework to facilitate image segmentation and carry out unsupervised fire detection, respectively. To gauge the accuracy and robustness of our proposed method, we implemented a comprehensive assessment using a dataset constructed from real-world forest and urban fires. Experimental results unequivocally demonstrate the competitive edge of our approach over some baseline methods. For instance, in contrast to YOLOv8, our framework has bolstered precision, recall, and F-score by 19.5%, 1.2%, and 11.7% respectively. Finally, we conducted extensive field tests by deploying a robot with the relevant algorithm in an actual fire scenario, further emphasizing our dedication to real-world application. These experiments underline not only the performance of the method, but also its potential for practical deployment.

Investigating the relationship between butanol molecular structure and combustion performance in an optical SIDI engine

Butanol has a high potential as a renewable substitution for gasoline in spark-ignition direct-injection (SIDI) engines. Different butanol isomers showed various flame characteristics that are strongly related to their molecular structure. However, there has been limited research on the implications of the butanol isomer's molecular structure on SIDI engine combustion, performance, and emissions. This study investigated butanol isomers as gasoline substitutes in SIDI range extender engines, with a focus on the effects of isomer molecular structures. This work employed a single-cylinder optical SIDI research engine and a high-speed camera to examine engine performance, flame kernel stability, flame propagation, and particle number (PN) emissions. The investigated blends comprised 70% toluene reference fuel (TRF) and 30% butanol isomers (1-butanol (n), 2-butanol (s), isobutanol (i), and tertbutanol (t)). Experimental tests are carried out at a 1000 rpm engine speed and a load of 5.7 bar IMEP, while the fuel condition is kept stoichiometric.The results elucidate that adding 1-butanol makes the flame kernel more stable and reduces COVimep compared to pure TRF. On the other hand, TRF-i, TRF-s, and TRF-t decrease flame initiation stability and increase COVimep. 1-butanol exhibited the highest apparent flame speed, IMEP, and peak in-cylinder pressure, followed by TRF, TRF-i, TRF-s, and TRF-t. Over half of the TRF-t cycles exhibited either no or a delayed flame kernel. Flame circularity improved with 1-butanol and diminished with the other blends. Diffusion flame intensity and PN emissions were higher for TRF, TRF-n, and TRF-t compared to TRF-s and TRF-i. In conclusion, linear chain butanol isomers with more internal C-H bonds and terminal C-OH bonds provide a more stable flame kernel and superior engine performance than branched isomers featuring internal C-OH bonds. The results from this study can be useful for expanding the practical applications of butanol isomers as a renewable fuel replacement in SIDI engines.

Insight into the Primary and Secondary Particle-Bound Methoxyphenols and Nitroaromatic Compound Emissions from Solid Fuel Combustion and the Updated Source Tracers.

Methoxyphenols and nitroaromatic compounds (NACs) have strong atmospheric radiative forcing effects and adverse effects on human health. They are emitted from the incomplete combustion of solid fuels and are secondarily formed through photochemical reactions. Here, an on-site study was conducted to determine the primary emission and secondary formation of particulate phase products from a variety of solid fuels through a potential aerosol mass-oxidation flow reactor. Emission factors for total quantified methoxyphenols and NACs (i.e., EF∑Methoxyphenols and EF∑NACs) varied by 2 orders of magnitude among different fuels, which were greatly influenced by volatile matter, incomplete combustibility, flame intensity, and combustion temperature. Guaiacol and 4-nitro-2-vinylphenol were used as tracers for primary organic aerosol due to the low aged-to-fresh ratios (0.21-0.97), while 4-methyl-guaiacol, 4-ethyl-guaiacol, eugenol, 4-methyl-syringol, isoeugenol, acetovanillone, syringaldehyde, homovanillin acid, vanillin acid, and syringic acid were identified as secondary organic aerosol (SOA) (aged-to-fresh ratios between 1.90 and 4.20). During simulated aging, the -CHO group reacted with the hydroxyl radical (•OH) to form the -COOH group, but there was no correlation between syringol and 4-nitrosyringol, implying that •OH is the main reactant rather than the nitriate radical (•NO3) in the atmospheric aging processes of methoxyphenols. Aging caused substantially different emission profiles due to variable photochemical reaction properties. The fresh EFs for guaiacol emitted from the biomass burning ranged from 3.80 ± 0.44 to 26.2 ± 5.40 mg·kg-1, which were much higher than those in coal combustions (of 0.03 ± 0.01 to 1.42 ± 0.28 mg·kg-1). However, the aged EFs (EFaged) for guaiacol was 1.02 ± 0.06 to 1.61 ± 0.11 mg·kg-1 in most biomass combustions, which were comparable with those of the bituminous chunk (1.20 ± 0.16 mg·kg-1). Therefore, guaiacol, a traditional biomass marker, is not an ideal tracer for aged PM2.5 emitted from biomass burning. Indeed, the syringol/guaiacol and syringol/4-nitrosyringol ratios were found to be more suitable and efficient to be used in source characterization.

ALGORITHM FOR APPLICATION OF METHODS FOR DETECTING CENTRAL SIGNS OF AN EMERGENCY SITUATION DUE TO FIRE AT CRITICAL INFRASTRUCTURE FACILITIES

The work is devoted to the solution of an actual scientific task in the field of civil protection, namely, the development of an algorithm for the application of the technique of detecting focal signs of an emergency situation due to a fire at critical infrastructure facilities. Recommendations for the practical application of the methodology as the basis of the method of non-destructive control of the processes of preventing emergency situations due to a fire of a terrorist nature at the objects of critical infrastructure of Ukraine are given. the algorithm for the application of the method of detecting focal signs of an emergency situation due to a fire at critical infrastructure facilities consists of three procedures, namely: procedures for conducting measurements at a critical infrastructure facility, procedures for statistical processing of measurement results, fire reconstruction procedures. The received general recommendations of the fire reconstruction procedure can be reduced to the following. In particular, we note that the value of the electrical resistance of soot is related to the mode of combustion in one or another zone. If this value, which was measured directly above the investigated area, exceeds 10101011 Ohm, then this indicates that there was no intense flame burning in this area, but the burning took place in the form of smoldering. Long-term smoldering of a fire load in conditions of insufficient air exchange can lead to the formation of a thick layer of greasy soot on the ceiling and in the upper part of the walls, sometimes with clear drops of the liquid phase or drop-like spots. This can be observed in small rooms and other volumes that are not ventilated. If the combustion moves from such premises to a larger space with better air exchange, and a flaming combustion occurs, then the formed electrical resistance pattern will mainly reflect the development of flaming combustion. The source of the fire may appear in the form of soot burning or extremely low values of its electrical resistance, or vice versa, in a rather thick layer of soot with a high content of extractive substances. Thus, the interpretation of the results of the measurement of electrical resistance must be accompanied by an analysis of the specifics of the volume-planning decisions of the building (room), the conditions of air exchange, and the distribution of the fire load. The obtained results of the soot research can be used within the framework of fire engineering expertise to reconstruct the process of the occurrence and development of combustion, including to establish the center of the fire. Keywords: emergency situation, critical infrastructure object, technique, focal signs, thermal damage.

Adsorption charring flame retardant effect of phosphaphenanthrene derivate intercalated micro-expanded graphite composite system in rigid polyurethane foams

Phosphaphenanthrene derivate molecule (DT) was synthesized by a simple method, and exploring the flame retardant effect of DT, micro-expanded graphite (MEG) with different combination modes compounded dimethyl methylphosphonate (DMMP) in polyurethane foam rigid polyurethane foams (RPUFs). The results showed that the properties of an intercalated DT-MEG system was better than a DT blended MEG system. Specific data of DT-MEG/DMMP were as follows: the LOI value of the 6DT-8MEG/16D sample reached 30.3%, the peak heat release rate (PHRR) value decreased by 70.4%, the total smoke release value decreased by 42.4%, the total heat release (THR) value was the lowest at only 14.9 MJ/m2, and the residue yields reached 31.6%. According to the test results, the flame retardant mechanism of the DT-MEG/DMMP compounded system was also explored. DMMP of DT-MEG/DMMP can exert flame retardant effects by releasing phosphorus free radicals in the gas phase to inhibit flame intensity at the beginning of combustion. Then, when the DT-MEG structure was heated, it expanded to form a caged char layer to exert adsorption charring flame retardant effects to filter and absorb the smoke particles. Meanwhile, the intercalated DT-MEG structure produced stronger adhesion with MEG during combustion, which generated more phosphoric acids to carbonize more RPUF matrix. Therefore, DT-MEG/DMMP compound flame retardant system can endow RPUFs with excellent synergistic flame retardant effects in both the gas and condensed phases. This exerts adsorption charring flame retardant effects in the DT-MEG microscopic form, and decreases the combustion intensity and obtains a compacted char layer.

Characterization of in-cylinder spatiotemporal flame and solid particle emissions for ethanol-gasoline blended in gasoline direct injection engines

Stricter regulations for internal combustion engines have necessitated the inclusion of eco-friendly fuels with conventional ones to reduce gas and solid emissions. Gasoline direct injection (GDI) engines, however, have been found to produce more particle number and mass emissions than port fuel injection engines. To address this, bioethanol fuel has been selected as an additive eco-friendly fuel for gasoline, with the aim of reducing particle emissions. In this study, we quantitatively characterize in-cylinder spatiotemporal flame to feature combustion performance and particle emissions for ethanol fuel in the GDI combustion chamber. We examined three engine combustion modes differed in equivalence ratio and injection strategy to produce various combustion results to quantify combustion performance and particle emission characteristics. Using an eight-channel non-intrusive flame luminosity sensor in one cylinder, we measured the flame front and its propagation direction. At the tailpipe, we measured particulate emissions using an engine exhaust particle sizer and a micro soot sensor coupled with a catalytic stripper that removed semi-volatile compounds. Our study found that increasing ethanol fuel content for different combustion modes resulted in distinct combustion and flame development. The particle size distribution also showed different patterns at each combustion mode, depending on the ethanol content. Lean combustion modes yielded high diffusion flame intensity compared to stoichiometric combustion mode, which resulted in a larger amount of particle formation. The physical properties of ethanol fuel were found to predominantly determine the fuel-air mixture quality, combustion process, and flame development at each combustion mode. An increase in ethanol fuel content at lean-homogeneous mode resulted in higher diffusion flame intensity and larger particle emissions. Our comparative study of flame and solid particles for ethanol fuel content improves the understanding of in-cylinder combustion processes and their correlations.

Experimental and analytical investigation on the thermal runaway propagation characteristics of lithium-ion battery module with NCM pouch cells under various state of charge and spacing

Thermal runaway (TR) has emerged as a critical challenge for the practical implementation of lithium-ion batteries (LIBs) in electric vehicles and energy storage systems. This paper examines thermal runaway propagation (TRP) in NCM pouch LIBs under two operating conditions: different state of charge (SOC) and spacing. Based on the results of various SOC experiments conducted without spacing, it is evident that the TRP time decreases significantly as the SOC increases. Additionally, there is a gradual increase in the maximum temperature and mass loss rate of the module and more intense flame ejection behavior. Furthermore, the TRP interval and duration gradually increase with increasing spacing. In comparison, different SOC has a more pronounced effect on maximum temperature, mass loss, and flame ejection behavior of the module than changes in spacing do. Heat transfer analysis shows that the main source of heat before TR is mainly contributed by the previous cell, which accounts for 35.3 %–72 % of the total heat absorbed by the cell. This study offers guidance for further characterization studies and safety measures of the LIBs TRP.