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The overpressure propagation characteristics of gas cloud explosion are analyzed. The spatial propagation of pressure wave appears to be self-similar. Due to the acoustic property, the absolute values of overpressure peak and impulse peak all decrease in inverse proportion rule. The built-in obstacle could cause the remarkable increase of positive overpressure peak and the absolute value of negative overpressure peak is always lower than that of positive parameter. With pressure wave propagating, the time reaching the positive overpressure peak decreases gradually. The time τ and the distance δ to form a shock front decrease with the increase of pressure wave intensity. However, τ remains constant and δ turns to rise as the pressure intensity increases continually. The positive overpressure duration time remains constant during propagation. For unconfined gas cloud explosion, the integral of overpressure against time is equal to zero and I max and I min basically share the same absolute value. • The overpressure propagation characteristics of gas cloud explosion are analyzed. • The spatial propagation of pressure wave appears to be self-similar. • The pressure wave tends to form a shock front. • Positive overpressure duration time keeps constant during propagation. • Positive and negative overpressure impulse peak share the same absolute value. [ABSTRACT FROM AUTHOR]

27 m3 unconfined hydrogen explosion experiments are conducted to investigate the effect of barrier wall on explosion characteristics. The results show that the flame propagation velocity is highly related with the development of the flame instability, not only dependent on the laminar burning velocity. In front of the wall, due to the wave reflection, the overpressure peak P max and positive overpressure impulse I P increase while the positive overpressure duration time t dur decreases. In the rear of the wall, due to the wave diffraction, P max and I P decrease while t dur increases. The time reaching overpressure peak t peak increases on both sides of the wall. P max is about twice the incident overpressure on the wall surface because of the pressure reflection. The enhancement or mitigation effect of the barrier wall only works in a certain range. The mitigation effect is highly related with the relative height between gas cloud and barrier wall. [Display omitted] • The effect of a barrier wall is analyzed in 27 m3 hydrogen cloud explosion. • The explosion intensity is enhanced before the wall and mitigated behind the wall. • Positive overpressure duration time rises before the wall and drops behind the wall. • The times reaching overpressure peak are delayed on both sides of the wall. • The mitigation effect of the barrier wall with different height is discussed. [ABSTRACT FROM AUTHOR]

In this research, unconfined hydrogen experiments are performed in 1 m3 and 27 m3 gas scale with gas concentration varying from lean-burn to rich burn. The results show that the flame travels fastest upwards and slowest downwards, which makes the flame shape irregularly spherical. The critical flame scales for the extra acceleration in the upward direction and for the deceleration in the downward direction are both smaller in 1 m3 gas scale. The acceleration exponent α is higher in the upward direction. With the gas scale increasing, the value of α increases gradually. For φ = 0.8, 1.0 and 1.5, the equivalent flame radius and the explosion overpressure in different gas scales overlap before the film rupture. According to the wrinkled laminar flame assumption and the self-similar theory, an overpressure prediction model is proposed based on the wrinkling factor Ξ Δ. The predicted results agree well with the experimental data before the film rupture. [Display omitted] • Unconfined hydrogen explosions are studied with 1 m3 and 27 m3 gas cloud. • Flame propagation behaviors in different directions are analyzed. • The explosion overpressure characteristics are discussed. • An overpressure prediction model is proposed based on the flame wrinkling factor. • The wrinkling factor fitted in 1 m3 obtained good overpressure prediction in 27 m3. [ABSTRACT FROM AUTHOR]

Experimental research is performed to investigate the effects of ignition height on explosion characteristics in a 27 m3 hydrogen/air cloud. With the ignition height decreasing, the flame propagation velocity increases gradually. The flame travels in oscillating mode and the average oscillating frequency lies between 145Hz and 155Hz. An original parameter τ, which involves flame scale and flame propagation velocity, is proposed to measure the effect of buoyancy. The higher the value of τ, the more obvious the buoyancy effect. As the ignition height increases, the critical flame scale for flame deceleration increases. The middle ignition height in the gas cloud causes the highest overpressure peak, overpressure impulse, overpressure rising and decreasing rate. As the ignition point approaches the initial gas boundary, the explosion intensity would decrease gradually. For the open space outside the flame, overpressure peak for the lower space is higher, while, the middle space experiences higher overpressure impulse. • The effect of ignition height is studied in a 27 m3 hydrogen cloud. • The onset of buoyancy effect and pressure wave interaction is investigated. • The overpressure characteristics with different ignition height are investigated. [ABSTRACT FROM AUTHOR]

Dempster–Shafer evidence theory is an effective method to deal with information fusion. However, how to deal with the fusion paradoxes while using the Dempster's combination rule is still an open issue. To address this issue, a new basic probability assignment (BPA) generation method based on the cosine similarity and the belief entropy was proposed in this paper. Firstly, Mahalanobis distance was used to measure the similarity between the test sample and BPA of each focal element in the frame of discernment. Then, cosine similarity and belief entropy were used respectively to measure the reliability and uncertainty of each BPA to make adjustments and generate a standard BPA. Finally, Dempster's combination rule was used for the fusion of new BPAs. Numerical examples were used to prove the effectiveness of the proposed method in solving the classical fusion paradoxes. Besides, the accuracy rates of the classification experiments on datasets were also calculated to verify the rationality and efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

This work is to experimentally and theoretically explore the hydrogen cloud explosion subjected to external turbulence. In the experiments, the flame characteristics and explosion pressure are obtained using high-speed camera and pressure sensor. In the theoretical calculation, the peak explosion pressure is obtained using LM, LMIET and TM method. The results indicated that most flame characteristics in the experiments are located in the zone of wrinkled flamelets. The explosion-related parameters including flame propagation velocity, peak explosion pressure and peak rate of pressure rise continue to increase as the gear level increases from G0 to G3, increase firstly and then decrease as the equivalence ratio increases from Φ = 0.5 to Φ = 3.0. Due to ignoring flame acceleration propagation induced by flame instabilities, external turbulence and flame-induced turbulence, the peak explosion pressure obtained using experimental method is significantly larger than that obtained using LM method. Owing to considering the limit value of flame wrinkling level induced flame instabilities and flame-induced turbulence, the peak explosion pressure obtained using experimental method is significantly lower than that obtained using LMIET and TM method. • Effects of external turbulence on flame acceleration is analyzed. • Peak explosion pressure and peak rate of pressure rise are obtained. • Peak explosion pressure is calculated using LM, LMIET and TM method. [ABSTRACT FROM AUTHOR]

Failure mode and effects analysis (FMEA) is a proactive risk management approach. Risk management under uncertainty with the FMEA method has attracted a lot of attention. The Dempster–Shafer (D-S) evidence theory is a popular approximate reasoning theory for addressing uncertain information and it can be adopted in FMEA for uncertain information processing because of its flexibility and superiority in coping with uncertain and subjective assessments. The assessments coming from FMEA experts may include highly conflicting evidence for information fusion in the framework of D-S evidence theory. Therefore, in this paper, we propose an improved FMEA method based on the Gaussian model and D-S evidence theory to handle the subjective assessments of FMEA experts and apply it to deal with FMEA in the air system of an aero turbofan engine. First, we define three kinds of generalized scaling by Gaussian distribution characteristics to deal with potential highly conflicting evidence in the assessments. Then, we fuse expert assessments with the Dempster combination rule. Finally, we obtain the risk priority number to rank the risk level of the FMEA items. The experimental results show that the method is effective and reasonable in dealing with risk analysis in the air system of an aero turbofan engine. [ABSTRACT FROM AUTHOR]

This paper presents a novel reconstruction method based on multi-refraction to remedy the non-linear refraction, which recovers 3D geometry from 2D images. To simplify calibration, this paper prove that air calibration can replace underwater calibration. Finally, a multi-line rotating structured is designed to improve the measurement efficiency without additional equipment. The results of the clean water experiment show that the measurement accuracy is 1.91 mm within the 1000–2000 mm depth of field. The qualitative analysis demonstrates our method can reconstruct the surface topography of underwater U and N letter boards. In different Nephelometric Turbidity Unit (NTU) (as NTU = 0.156 mg/ml) environment, a circular plate with a diameter of 220 mm is measured, the shape reconstruction error (whether the reconstructed shape is a circular, square, or other) is 1.74 mm; the diameter measurement result is 218 mm, so the size error of the circular plate is 2 mm. [ABSTRACT FROM AUTHOR]

The strong pressure wave in gas explosion accident could cause great casualties and property loss, which has become the main threat to safety of chemical process and further popularization of clean energy. In this research, unconfined explosion experiments under different methane concentrations at 27 m3 scale were performed with internal and external obstacles. The results showed that the flame buoyant effect was more obvious for the rich-fuel flame due to the excess methane accumulation. The reflection of the pressure wave could cause higher overpressure near the ground and the external obstacle enhanced the overpressure in the neighborhood. For 27 m3 scale explosion, the critical flame radius for the flame acceleration was larger than 1 m3 scale, because of the longer travelling distance for the reflection wave from the bottom. In addition, the acceleration exponent rose to 1.5 due to the full development of the hydrodynamic instability. The flame radius for peak overpressure, R M , was found to be at a certain distance from the outer obstacle bar center, which was 1.8 for N b = 6, 1.35 for N b = 4 and 0.9 for N b = 2. The predicted results of peak overpressure agreed well with the experimental results, which extended the prediction model to the larger scale. [ABSTRACT FROM AUTHOR]

• The under-sampling problem with folded frequencies in multi-surface WPI is analyzed. • Using active frequency folding undersampling, the correct frequency can be obtained as a solid basis for phase demodulation. • The spectral lines near the frequency peaks are redivided, and the frequencies can be accurately solved. • Based on the solved frequency of each harmonic, extended measurement distances can be reached, and efficient phase demodulation is achieved. The difficulty in multi-surface measurements comes from that each measured surface contributes harmonics to the fringe patterns, and the wavelength-shifting technique is an efficient technique that allows the harmonics to have different frequencies. When under-sampling in multi-surface measurements occurs, harmonic frequencies can not be detected by the spectrum directly. As a typical case in under-sampling, the problem of harmonic frequencies folded in the obtained spectrum as false frequencies are addressed in this paper. This contribution demonstrates an efficient algorithm enabling the detection of real and accurate harmonic frequencies, whereby the wavefronts can also be correctly reconstructed. Then the frequency detection accuracy is improved by redividing a smaller spectral interval of the selected frequency bands. Comparative studies based on the Zernike polynomials verify the effectiveness of the proposed method. Experiments for a transparent flat were performed, and the maximum PV Q , PV, and maximum RMS errors for repeatable measurements verified the effectiveness of the proposed algorithm in practical application. [ABSTRACT FROM AUTHOR]

The explosion venting experiments of 150 nm polymethyl methacrylate (PMMA) dust with different lengths (L) and diameters (D) of the vent tube are conducted. The effect of tube size on overpressure and flame propagation behavior is explored. High-frequency and low-frequency Helmholtz oscillations are observed on the overpressure curves in the chamber. The (d P /dt) max in the chamber is increased with high-frequency oscillations, while the maximum flame width is also visible with low-frequency Helmholtz oscillations. As the L increases from 0 m to 2 m, the P red,max increases by 29.2–145.1% and the (d P /dt) max increases by 38.4% − 127.7%. With the increase of the D , the P red,max in the chamber and vent tube decreases, and the flame transforms from an under-expansion jet flame to a subsonic jet flame. Due to the interaction between the external flow field and the concentration of unburned particles, the maximum external overpressure increases alongside with the incease of the tube length and diameter. In addition, the maximum calculation error of EN14491 is 1100%, while NFPA68 seriously underestimates the explosion venting pressure. A modified prediction model is established to provide a design method for a safe vent through the vent tube of the nano-dust explosion. [Display omitted] [ABSTRACT FROM AUTHOR]

The primary purpose of this paper is to reveal the mechanism of suppressing hydrogen cloud explosion by micron-size water mist. On the basis of experimentally obtaining the characteristics of flame behavior and explosion pressure by changing equivalence ratio and water mist density, the physical and chemical mechanism of suppressing hydrogen cloud explosion is analyzed. The results indicated that with the increase of micron-size water mist density, the explosion-related parameters (including mean flame front speed, peak explosion pressure, peak rate of pressure rise and positive pressure impulse) of ER = 0.8 and ER = 1.0 decrease monotonously, the explosion-related parameters of ER = 2.0 increases firstly and then decreases which peak value is appeared at 26.73 g/m3. A considerable part of micron-size water mist is difficult to be completely evaporated in the reaction region, the temperature of combustion products region will be reduced due to subsequent continuous evaporation. In addition, the gasified micron-size water mist mainly interacts with H radicals through the elementary reactions of R3, R38 and R84. Due to incompletely evaporated micron-size water mist, the mist-induced turbulence is generated, which is the reason of enhancing hydrogen cloud explosion at lower micron-size water mist density of ER = 2.0. • Fine flame structure under micron-size water mist is captured. • Explosion pressure characteristics are obtained. • Physical and chemical mechanism of micron-size water mist is revealed. [ABSTRACT FROM AUTHOR]

Fully understanding the coupling mechanism between the enhancement of explosion overpressure and flame acceleration is a prerequisite for assessing hydrogen cloud explosion overpressure. In this research, unconfined fan-stirred hydrogen explosion experiments were performed to study the effects of flame instability and external turbulence on flame propagation and overpressure characteristics. The results showed that the combination of the external turbulence and the flame instability could result in great flame acceleration and explosion overpressure enhancement. For the intensity of external turbulence considered in this study, the combustion regimes were all in the flamelet zone. With the increase of the external turbulence intensity, the flame gradually got accelerated, and the explosion overpressure got enhanced. A theoretical prediction model for the upper and lower limit of the maximum overpressure was proposed, which fully accounted for flame instability, external turbulence, and flame-induced turbulence. It provides a conservative evaluation for hydrogen cloud explosion. • Fan-stirred hydrogen explosion experiment was performed in unconfined cubic space. • Flame acceleration due to flame instability and external turbulence were analyzed. • Explosion characteristics with and without external turbulence were analyzed. • Theoretical prediction model of limit of peak explosion overpressure was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] The main task of this work is to study the hydrogen-ammonia-air cloud explosion characteristics. The flame behavior and explosion pressure are obtained experimentally by changing equivalence ratio (ER) and ammonia fraction (AF). Then the correlation between flame behavior and maximum explosion pressure is revealed. Finally, the thermal, diffusion and chemical factors affecting laminar burning velocity (LBV) are analyzed. The results indicated that averaged flame propagation velocity (AFPV) and maximum explosion pressure (MEP), become decreased continuously with increasing AF, become increased firstly and then decreased with increasing ER. Maximum value of both AFPV and MEP of AF = 0.1, AF = 0.3, AF = 0.5 and AF = 0.7 is reached at ER = 1.4, ER = 1.2, ER = 1.0 and ER = 1.0. the MEP could be underestimated and overestimated by laminar and turbulent flame model. The MEP is largely affected by LBV especially when the flame instabilities are ignored. With increasing AF, the reduction of adiabatic flame temperature and thermal diffusivilty contributes to the LBV reduction. With increasing ER, the main factor affecting LBV is the generation and consumption of H radical. [ABSTRACT FROM AUTHOR]

This work is aimed at evaluating unrestricted duct-vented explosion of hydrogen-air mixture and hydrogen-methane-air mixture. The flame behavior in the venting zone and explosion pressure inside explosion chamber are obtained in the experiments. On the assumption of only fresh mixture venting or only combustion product venting, a mathematical model of unrestricted duct-vented explosion is established by considering chocked venting. The results indicated that the chocked venting could be achieved for unrestricted hydrogen and hydrogen-methane explosion venting due to the fact that the Mach disc structure is appeared in venting zone. Maximum explosion pressure and maximum pressure rise rate could be reduced significantly by unrestricted duct-venting. For the unrestricted hydrogen explosion venting, maximum explosion pressure and maximum pressure rise rate increases until Φ = 1.5, then decreases monotonously with the increase of equivalence ratio. For the unrestricted hydrogen-methane explosion, maximum explosion pressure and maximum pressure rise rate continue to decrease with the increase of methane addition. Maximum explosion pressure in the experiment is between theoretical values of fresh mixture venting and combustion product venting. Maximum explosion pressure and pressure rise rate are increased with increasing burning velocity whether it is fresh mixture venting or combustion product venting. Maximum explosion pressure is increased linearly with increasing nondimensional vent coefficient. • Flame behavior and explosion pressure of duct-vented explosion are analyzed. • The mathematical model of duct-vented explosion is established. • Maximum explosion pressure of duct-vented explosion is evaluated. [ABSTRACT FROM AUTHOR]

This work is aimed at evaluating hydrogen cloud explosion with built-in obstacles experimentally and theoretically. The flame front evolution is captured using infrared filtering technology and the explosion overpressure at four monitoring points is measured using free-field sound pressure sensor. The laminar flame model and turbulent flame model are established to theoretically predict maximum explosion overpressure in advance. The results demonstrated that the flame acceleration of hydrogen cloud explosion with built-in obstacles is attributed to mutual promotion of flame instabilities and obstacle-induced turbulence. The effects of built-in obstacles on maximum flame front velocity is relatively limited and maximum value of flame wrinkling factor is Ξ Δ,max = 3.64. As the distance between pressure sensor and ignition source increases, the maximum explosion overpressure, positive overpressure impulse and absolute value of negative overpressure impulse are decreased monotonously. The positive overpressure and negative overpressure are mainly affected by steel pipe number in vertical and horizontal direction, rather than length of steel pipe cross-section. The velocity of explosion overpressure propagating in the air is c = 350.88 m/s. The maximum explosion overpressure should be significantly underestimated by laminar flame model, the turbulent flame model could be used to satisfactorily predict maximum explosion overpressure at four monitoring points. • Flame acceleration mechanism of hydrogen cloud explosion is revealed. • Effects of built-in obstacles on explosion overpressure are analyzed. • Maximum explosion overpressure is theoretically predicted. [ABSTRACT FROM AUTHOR]

• Flame suppression mechanism of nano PMMA dust explosion by KHCO 3 was investigated. • The effect of KHCO 3 particle size on the physical suppression mechanism was analyzed. • A numerical model was established to reveal chemical suppression mechanism. Flame suppression mechanism of KHCO 3 for 100 nm PMMA dust explosions was investigated experimentally and computationally. The effect of KHCO 3 particle size on the suppression efficiency was examined. The study revealed that the larger the proportion of added KHCO 3 , the more significant the suppression effect on flame, for KHCO 3 particles with a fixed particle size distribution. The suppression effects were significantly increased with the decreasing of KHCO 3 particle size distributions. For endothermic mechanism, when the KHCO 3 particles with three particle sizes were mixed with 100 nm PMMA, the heat absorption peaks exhibited at the initial stage, in which the heat absorption values were 28 J/g, 26 J/g and 21 J/g, respectively. A kinetics model was established to reveal the chemical suppression mechanism. It was presented that the mole fractions of key flame radicals (H and OH) were obviously reduced during the chain reaction processes with the addition of KHCO 3. For KHCO 3 particles, the formation of catalytic cycle K ⇔ KOH converted H and OH radicals into a stable combustion product H 2 O, resulting in a lower flame speed and flame temperature. [ABSTRACT FROM AUTHOR]

The purpose of this work is to evaluate the characteristics of hydrogen-blend methane explosion. The explosion characteristics without initial turbulence or with initial turbulence are firstly explored. Then the factors affecting laminar burning velocity and turbulent flame regime are revealed. Finally, the different prediction models are developed to evaluate peak explosion pressure of hydrogen-blended methane fuel. The results indicated that the MFFV, PEP, PRPR and laminar burning velocity of MR = 10% and MR = 30% continue to increase with the increase of ER, the peak value of MFFV, PEP, PRPR and laminar burning velocity of other MRs is arrived at ER = 1.0. The MFFV, PEP and PRPR increase gradually with increasing root-mean-square velocity. Regardless of initial turbulence, the MFFV, PEP and PRPR continue to decrease with increasing MR, the PEP and PRPR decrease obviously with increasing distance from ignition location. The turbulent flame regime is highly sensitive to MR, not root-mean-square velocity. The predicted value of laminar model, wrinkled model and turbulent model is relatively conservative, maximum wrinkling coefficient induced by flame instabilities and flame front itself needs to accurately evaluated. • Characteristics of hydrogen-blended methane explosion are explored. • Laminar burning velocity and turbulent flame regime are revealed. • Different theoretical models of predicting PEP are established. [ABSTRACT FROM AUTHOR]

The flame behavior and pressure characteristics of vented propane-air explosions at elevated static activation pressures (P stat) were investigated in a duct with a length-to-diameter (L/D) ratio of 7. The impact of the discharge traction and the coupling effect of the internal flame front and pressure waves on the flame propagation behavior were captured. The effect of increasing P stat on the vented flame length and width under a fixed vent was weak. The influences of P stat on the pressure profiles and maximum reduced pressure (P red) were investigated. The increase of P stat mitigated the blocking effect of external explosion on P red and further promoted the discharge pressure drop rate to be controlled within the limit of the discharge capacity of the vent. The formation mechanisms of the two main external pressure peaks were analyzed. For the larger D v conditions, the sensitivity of high P stat to the increase of maximum external pressure was higher than that of low P stat. A modified model of P red was developed considering the effects of elevated P stat and vent coefficient K V , which is proved to have a good performance in vented explosion ducts with a large L/D ratio. [ABSTRACT FROM AUTHOR]

On March 15, 2024, a wildfire occurred in Yajiang County, Sichuan Province, China, burned an area of 278.8 km2 and influenced 250 catchments in the burned area. On April 23 and May 10–11, 2024, two rainfall events struck the burned area, inducing 8 and 54 post-fire debris flows, respectively. This news investigates the characteristics of the burned area, involving the burn severity mapping, and geometry analysis on the burned catchments. Then, the characteristics of the debris flows following the fire are unravelled based on preliminary field investigations. It is expected that the debris flows after the wildfire, particularly in the first rainy season, with the high susceptibility and low rainfall threshold, will attract researchers’ interest in monitoring and mitigating such unique debris flow disasters. [ABSTRACT FROM AUTHOR]

[Display omitted] • The front surface, rear surface, thickness variation, and refractive index inhomogeneity information of the transparent multi-surface optics to be tested can be reconstructed simultaneously from a set of interferograms; • Two convolutional fitted windows have been redesigned which have explicit function expressions and better window performance, they can be stretched to free lengths; • The factors which affect the performance of multi-surface reconstruction are fully analyzed, which provides a solid foundation for the analysis of sampling validity during multi-surface interferometry; • A phase-shift matching method without strict limitation of cavity lengths is developed, and four-surface detection in flexible positions is realized. Consisting of the front and rear surfaces of the measured optics and two reference surfaces, the four-surface interferometry system can obtain parameters of the measured surface profiles and refractive index inhomogeneity by acquiring and decoding the fringe patterns of the measured plate and the rear reference plate respectively. However, the difficulty of such measurement comes from the complex superposition of at least six interference sub-signals, and the setting of the phase-shift interval determines whether the harmonics can be reconstructed or not. To improve the measurement accuracy, two kinds of convolutional fitting window functions are redesigned based on the Hanning window to enhance the function performance. Then, by analyzing the reconstruction errors of each wavefront under different combinations of sampling intervals and cavity lengths during four-surface measurements, an error quantization matrix obtained by triple iteration is constructed. By setting a threshold condition, the optimal phase-shifts under different cavity lengths can be matched adaptively. The multi-surface measurement accuracy and reliability of adaptive phase-shift matching are verified in the simulation. The interferogram acquisition and phase demodulation of two transparent flats were performed using a Fizeau wavelength-tuning interferometer, and the reconstruction errors of the surfaces in the repetitive measurements further verified the reliability of the proposed method. [ABSTRACT FROM AUTHOR]

• In-depth insights into post-fire hillslope erosion using multi-source data. • Strong correlation between erosion and vegetation regeneration revealed. • Post-fire hillslope erosion recovery requires more than three years. • InSAR technology shows promise for monitoring post-fire hillslope erosion. Wildfires often exacerbate hillslope erosion and lead to severe secondary disasters. Accurate monitoring of post-fire hillslope erosion is crucial for land managers. However, current monitoring methods in burned areas are often time and capital intensive, posing challenges for large-scale and long-term observations. This study explores the potential of using multi-source data, including field investigations, optical remote sensing interpretation, and Interferometric Synthetic Aperture Radar (InSAR), to accurately estimate post-fire hillslope erosion. Particularly, quantitative analysis of C-band Sentinel-1 SAR data acquired one year before and three years after fire unraveled ground deformation in the areas burned on March 30, 2020, in Southwest China. Results show that in the first year following the wildfire, vegetation recovered rapidly, however, complete restoration to pre-fire levels requires more than three years. Hillslope erosion was found to be closely correlated with vegetation regeneration, peaking in the first post-fire year and declining as vegetation recovered. Nevertheless, it did not return to pre-fire levels within our observation period, indicating a recovery duration of over three years. Moreover, significant hillslope erosion variations were observed even within the same rainy season, with higher erosion rates during the early stages of rainfall, followed by stabilization in the later stages. Despite certain limitations associated with InSAR technology in burned areas, its potential for monitoring hillslope erosion presents a promising research approach for monitoring and modelling. [ABSTRACT FROM AUTHOR]

The research proposes arbitrary shaped aperture wavefront fitting (ASAWF) for arbitrary shaped aperture wavefront fitting and aberration removing. It departs from the traditional Zernike polynomials only ideal for wavefront reconstruction of circular wavefronts but not non-circular wavefronts. The approach preserves the orthogonality of the Zernike polynomials in arbitrary shaped aperture wavefronts and addresses the coefficient coupling problems of the non-circular shaped aperture wavefront fitting known adversely affecting aberration removal. The ASAWF method is used to fit non-circular regions with an orthogonal matrix using the modified Gram–Schmidt orthogonalization technique with QR decomposition and point cloud. The ASAWF method is employed to fit the arbitrary shaped aperture wavefront, including elliptical, square, and irregular shape wavefronts. The proposed method is confirmed through numerical simulation and experimental data demonstrating the effectiveness of wavefront reconstruction and aberration removal. [ABSTRACT FROM AUTHOR]

In this research, the effect of ignition, initial pressure (50–250 kPa) and temperature (20–100 °C) on the lower flammability limit (LFL) of hydrogen/air mixture are investigated experimentally and numerically. The results show that with the ignition energy increases, the LFL of hydrogen decreases. When high voltage direct current power supply (HVDC) is used, the time for the flame to propagate to the edge of the window is much shorter than that of 15 kV high voltage transformer (15 kV HVT) ignition. As the initial pressure increases, the LFL of hydrogen increases. When HVDC is used, the time to reach the peak deflagration overpressure increases with the increase of initial pressure. However, when 15 kV HVT is used, the time to reach the peak deflagration overpressure is almost the same. As the initial temperature increases, the LFL of hydrogen decreases. The change of the LFL of hydrogen with 15 kV HVT ignition is greater than that of HVDC. Through the analysis of chemical kinetic factors, the effect of OH radical generation when the LFL of hydrogen increases with the increase of initial pressure is revealed. • Eleven ignition energies under two ignition modes are measured. • LFL are obtained under different ignition, initial pressure and temperature. • Chemical kinetic factors at LFL of hydrogen are analyzed. [ABSTRACT FROM AUTHOR]

• Automatic sampling matching and simultaneous full-aperture multi-surface measurement at flexible cavities can be realized. • Semi-blind multi-surface wavelength-shifting algorithm without prior and whole cavity length determinations is devised. • A DTFT-based global spectrum modulation algorithm is applied to obtain accurate harmonic frequencies. • A thorough sampling performance analysis and experiment are performed. The core issue of multi-surface wavelength-shifting interferometry at free cavity lengths is mainly centered on adaptively matching the tuning step. To avoid harmonic aliasing and undersampling, the discrete-time Fourier transform method with global spectrum densification is used to comprehensively analyze the spectral characteristics under different sampling cases and cavity lengths, then a composite multi-surface wavelength-shifting interferometry algorithm is proposed accordingly. The proposed method includes a preprocessing algorithm and three spectral criteria to identify and avoid undesirable sampling problems for in-situ measurements. The algorithm performance is quantitatively evaluated from several aspects of the simulation analysis. A flat plate with an average thickness of 20 mm was repeatedly measured using a Fizeau wavelength-shifting interferometer in the experiments, and the PV Q and RMS errors at different measurement distances were less than 5 mm and 1 mm, respectively. [ABSTRACT FROM AUTHOR]

Taking maximum flame propagation velocity, maximum explosion pressure, maximum rate of pressure rise and time-average of rising pressure impulse as index, this paper is aimed at evaluating the inerting effects of carbon dioxide on confined hydrogen explosion by varying initial pressure, carbon dioxide addition and equivalence ratio. The results indicated that under enhancing hydrodynamic instability, the stronger flame destabilization occurs with the increase of initial pressure. At Φ = 0.8 and Φ = 1.0, the destabilization effect of thermodiffusive instability continues to increase with the increase of carbon dioxide addition. At all equivalence ratios, the destabilization effect of hydrodynamic instability decreases monotonously with the increase of carbon dioxide addition. All of maximum flame propagation velocity, maximum explosion pressure, maximum rate of pressure rise and time-average of rising pressure impulse reach the peak value at Φ = 1.5, and decrease significantly with increasing carbon dioxide addition. The inerting effect of carbon dioxide could be attributed to the reduction of thermal diffusivity, flame temperature and active radicals. The chemical effect of carbon dioxide reaches the peak value at Φ = 1.0. With the increase of carbon dioxide addition, the chemical effect continues to decrease at Φ = 0.8 and Φ = 1.0, and increase monotonously at Φ = 2.5. • Effects of carbon dioxide addition on flame characteristics are analyzed. • Inerting effect of carbon dioxide is assessed using four evaluation parameters. • Inerting mechanism of carbon dioxide on hydrogen explosion is revealed. [ABSTRACT FROM AUTHOR]

Methane/hydrogen fuels are widely applied in the internal combustion engine and gas turbine due to enhanced laminar burning velocity and extended flammability limits. In order to ensure energy utilization in safety, the flame characteristics and explosion pressure in the lean, stoichiometric and rich mixture are investigated systematically by varying hydrogen addition and initial pressure. In the lean and stoichiometric mixture, effects of the diffusional-thermal and hydrodynamic instability on flame destabilization are enhanced with hydrogen addition. As initial pressure increase, the diffusional-thermal instability has a limited effect on flame destabilization while effects of the hydrodynamic instability continue to enhance. In the rich mixture, effects of the diffusional-thermal instability on the flame stabilization and effects of the hydrodynamic instability on the flame destabilization enhance significantly with hydrogen addition. As initial pressure increase, effects of the diffusional-thermal instability on the flame stabilization are very limited and effects of the hydrodynamic instability on the flame destabilization are enhanced. The variation in maximum explosion pressure could be neglected with hydrogen addition due to decreasing heat loss, and maximum pressure rise rate increases with hydrogen addition. Besides, explosion pressure evolution could be evaluated accurately by considering the flame instabilities. And by varying equivalence ratio, hydrogen addition and initial pressure, the most enhancing and inhibiting reactions to laminar flame velocity are H + O 2  = O + OH and H + CH 3 (+M) = CH 4 (+M), respectively. [ABSTRACT FROM AUTHOR]

Due to low ignition energy and wide range of flammability limit, explosion hazard of hydrogen/ammonia fuel must be evaluated to ensure safety application. In this work, effects of equivalence ratio, ammonia addition and initial pressure on the flame morphology and explosion pressure are revealed. The results demonstrate that effects of three factors on explosion hazard are ranked from the most important to the least important as initial pressure, equivalence ratio and ammonia hydrogen. The cellular flame formation by varying the equivalence ratio could be mainly attributed to the diffusional-thermal instability. The expanding flame of Φ = 0.8, 1.0 and 1.5 tends to be stable with ammonia addition. As initial pressure increases, there exists a joint and competitive effect of the diffusional-thermal instability and hydrodynamic instability. Maximum explosion pressure of Φ = 0.8, 1.0 and 1.5 decreases monotonously with ammonia addition and increases linearly with initial pressure. The explosion pressure prediction is underestimated using the smooth flame model and reproduced satisfactorily using the wrinkled flame model. By varying equivalence ratio, ammonia addition and initial pressure, the most elementary reaction that enhances laminar flame velocity is R9 and the first two inhibiting reactions to laminar burning velocity are R10 and R168. [ABSTRACT FROM AUTHOR]

• Glycerol addition promoted the devolatilization and char formation in tobacco pyrolysis. • Glycerol addition inhibited the formation of aromatics at high temperature. • The yields of ketones and aldehydes increased with glycerol addition. Glycerol is a main by-product in the biodiesel refining process and its blending with waste tobacco for pyrolysis can effectively improve the quality of tobacco pyrolysis products. In-depth study on the mechanism of glycerol influence on the tobacco pyrolysis process is of great significance for the pyrolytic conversion of waste tobacco to high-value chemicals. In this work, tobacco pyrolysis with different glycerol contents (0%, 5%, 10%, 15%, 20% and 25%) were studied by TG-FTIR firstly. It was found that the addition of glycerol was beneficial to the generation of volatiles from tobacco pyrolysis and the yield of tobacco pyrolytic char was increased simultaneously. The pyrolysis kinetics of tobacco with different amount of glycerol addition were then analyzed using the distributed activation energy model with double combined Gaussian functions. The results showed that the activation energy of both the devolatilization and coke formation during pyrolysis decreased significantly with the increase of glycerol addition. In addition, the distribution of pyrolysis products under 250 °C and 650 °C were compared by Py-GC-FID/MS study for both the original tobacco and the one with typical addition of glycerol. The results showed that the addition of glycerol had little impact on the pyrolysis of tobacco at low temperature, while could promote the production of ketones, aldehydes, hydrocarbons and carboxylic acids and helped to inhibit the formation of aromatic hydrocarbons at high temperature. [ABSTRACT FROM AUTHOR]