Explosive Fireballs Research Articles

Fireball distribution characteristics and thermal radiation effects in the explosion of aviation kerosene storage tank

Aviation kerosene acts as the main fuel for civil and military aircrafts. In order to study the explosion fireball distribution and thermal radiation effects of aviation kerosene storage tank, the dynamic explosion test system was established. The development law of explosion fireball and the thermal radiation characteristics in the presence of various oil volumes (empty, bottom, half and full oil) under the dynamic impact of projectile were studied. The dynamic explosion process was divided into four stages: projectile explosion, aviation kerosene jet flow, aviation kerosene deflagration and pool fire. The evaluation model (Y=aXb) for maximum diameter, maximum height, duration of fireball and oil mass was established. The fireball temperature showed a trend of ‘rise-fall-rise-oscillation attenuation’. The maximum fireball temperature and average temperature increased first and then decreased as increasing the oil volumes, with the maximum values at 1534.67 K and 1285.78 K, respectively. Based on the fireball dynamic model, the damage effect of fireball thermal radiation on personnel was analyzed, the safety radius and injury probability were obtained, and the dynamic explosion fireball thermal radiation field was constructed.

Study on the influence of different initial environmental pressures on explosion fireball and thermal damage of thermobaric explosive

Study on the influence of different initial environmental pressures on explosion fireball and thermal damage of thermobaric explosive

Effects of typical MH2 (M= Ti, Mg, Zr) on the detonation energy release characteristics of composite charge containing Al/PTFE reactive materials and RDX

To explore the effects of three typical metal hydride powders (TiH2, MgH2, ZrH2) on the detonation energy release characteristics of composite charge containing Al/PTFE reactive materials and RDX, a variety of composite charges containing Al/PTFE/MH2 ternary active materials and RDX were prepared. The effects of metal hydrides on detonation parameters of composite charges were studied by air blast experiments and the temperature distributions of explosion fireball were mapped using colorimetric thermometry technique. The experimental results indicated that the addition of metal hydrides had significantly positive effects on afterburning effect and detonation performance of composite charges, and the enhancement effect of MgH2 was superior to that of TiH2 and ZrH2. The fireball duration, maximum average temperature and shock wave parameters of the composite charges in air blast experiments all changed with the order of Al/PTFE/MgH2+RDX > Al/PTFE/TiH2+RDX > Al/PTFE/ZrH2+RDX > Al/PTFE + RDX. The results could offer theoretical references for the formulation design of high-power explosives.

Effects of vacuum degree on the detonation characteristics and energy release laws of RDX explosive

To explore the detonation characteristics and energy release laws of RDX explosives under varying degrees of vacuum, the influence of vacuum degree on the fireball characteristic parameters, shock wave propagation laws and detonation performance of columnar RDX charges were studied using the air-blast experiments and AUTODYN simulations, and the fireball temperature distributions were mapped with the colorimetric thermometry technique. The experimental results indicated that as the degree of vacuum increased, the combustion duration and zone area size of the explosive fireball were both extended, while its temperature decay rate was slowed down, making the afterburning effect more pronounced. Furthermore, the peak overpressure and positive impulse of the explosion shock wave showed a downward trend, with the reductions of 56.1 % and 53.5 %, respectively, with the increasing vacuum degree. Numerical simulation was also used to reveal the energy release laws of RDX explosive, and the comparison between the experimental and numerical results showed a good degree of concordance with an average error of 6.45 %. The results of the study could provide a reference for expanding the explosion theory of explosives in plateau environment and improving the performance of explosion-proof equipment.

Effect of AP distribution on energy release characteristics and functional force of HMX/AP/Al explosives

AbstractIn order to understand the reaction kinetics of HMX/AP/Al ternary system, the different distribution of AP in HMX/AP/Al explosives was realized by two different preparation techniques. Detonation test results show that the detonation velocity, explosion heat and detonation pressure of HAP samples are higher than those of HAl samples, but the extent of improvement is not high, not more than 5 %. The results of scanning electron microscopy showed that AP in HAP samples was distributed on the surface of HMX crystal. AP were dispersed around HMX crystals in HAl samples. The experimental results of explosive fireball performance show that the fireball expansion speed of HAP samples is better than that of HAl samples, demonstrating a good fireball effect. Underwater test results show that the shock wave peak pressure and bubble pulsation period of HAP samples increase by 3.06 % and 7.95 % respectively, and shock wave energy and bubble energy increase by 9.8 % and 25.42 % compared with bubble energy. The experimental results show that HAP samples are superior to HAl samples in accelerating ability of Al flies. The dispersion of AP on the HMX crystal surface promotes the energy release of HMX/AP/Al explosives more.

Analysis method of explosive electromagnetic radiation energy

AbstractThe energy of electromagnetic radiation from explosions is coupled to electronic equipment circuits, disrupting the initiation sequence or causing failure in an increasing number of cases, which seriously affects the stability of weapon systems. There is a significant difference between the characteristics of the explosive electromagnetic radiation signals and modulated electromagnetic signals. The electric field intensity and signal power cannot directly represent the magnitude of the explosive electromagnetic radiation energy, and traditional electromagnetic signal analysis methods are unsuitable for explosion electromagnetic signal analysis. To solve this problem, the mechanism of explosive electromagnetic radiation was first analyzed. Through verification experiments of the explosion electromagnetic intensity and temperature, it was concluded that there is a strong correlation between the explosion plasma temperature and electromagnetic intensity. The temperature of the explosive plasma is derived based on the measured surface temperature of the explosive fireball, a functional relationship is established between the energy of the explosive plasma and the temperature of the plasma, and plasma energy is introduced as a parameter for electric field intensity correction. The interference signal analysis method based on eye diagram is used to calibrate the electromagnetic radiation damage ability, achieving quantitative analysis of the interference degree of electromagnetic radiation energy on the signal, and providing a new approach for the analysis of explosive electromagnetic radiation energy.

Advancing thermochemical diagnostics in kilogram-scale explosive fireballs via laser absorption spectroscopy

This article presents methodological advances in the state-of-the-art for making time-dependent, thermochemical measurements within kilogram-scale explosive post-detonation fireballs utilizing tunable laser absorption spectroscopy. This measurement capability is critical for validating multi-scale, multi-physics models of post-detonation dynamics. The technique is based on hardened gauges built around rapidly-tunable lasers and custom post-processing algorithms that provide quantitative thermochemical data interior to large and opaque explosive fireballs. The authors present a holistic overview of the technique including gauge design, the laser absorption diagnostic, and the custom data processing algorithms. Additionally, fielding high-bandwidth laser absorption probes at stand-off ranges presents new challenges in data processing that must compensate for long distance signal transmission effects. We highlight representative data from a hardened gauge measurement at 0.81 m stand-off from a 2.78 kg LX-14 explosive charge detonated in an outdoor test arena. We discuss progress in all-optical measurement of temperature, pressure, and water vapor number density at a 100 kHz repetition rate during the first 10 ms of the fireball evolution. We conclude the article with a brief discussion on our current approach for comparing hardened gauge measurements with computational fluid dynamic simulations.

Research on the Dynamic Model of Fireball Thermal Dose Based on the Effective Band Integral Method.

In the brief combustion process of an explosive fireball, the fireball can release considerable radiant energy. Aiming at the problem that the Stephen-Boltzmann formula calculates the fireball surface radiant energy (full band), it does not match the working bands of most infrared thermal imagers. So, in this paper, we obtain dynamic parameters such as the temperature, diameter, and height of the fireball from the infrared thermal image of the thermobaric explosive fireball, achieve on-site atmospheric transmittance by the temperature calibration target, and integrate within the effective wavelength band of the infrared thermal imager, and a precise dynamic model of the fireball's thermal radiation dose was finally established. According to the fireball test data of the infrared thermal imaging camera in the 2-5 μm band, the heat dose of the fireball at different distances is calculated, which is about 1/2.5 of the calculation result of the Stephen-Boltzmann full-band integral formula. The calculations in this paper are more accurate than measurements from existing static models and provide a better assessment of the thermal damage performance of various types of munitions.

Enhancement of explosive effect of thermobaric explosive by metal reactive material

AbstractReactive materials have mechanical properties comparable to metal materials and also have the reaction‐release energy characteristics of energetic materials. The calorific value of reactive materials is even higher than that of explosives. They can react under high pressure/high temperature and release a large amount of chemical energy. Therefore, reactive materials have a wide range of potential applications in aviation and national defense fields. This study examines the energy release characteristics of the metal reactive material casing (MRMC) under thermobaric explosives and compares them to traditional steel casing. The test specimens had the same casing‐charge mass ratio and size, with the only difference being the casing material: reactive material (with reactive elements Zr and Al) and AISI 1020 steel. The physical and chemical properties of the reactive materials were tested and analyzed using ICP‐MS, oxygen bomb calorimeter, and SHPB. Through explosion tests, the characteristic parameters of explosion fireball and ground shock wave overpressure were measured. And the reactive fragments recovered from the experiment were subjected to XRD testing. The results show that MRMC can significantly increase the diameter, duration, and temperature of the explosion fireball compared to steel casing data. The maximum fireball diameter of the MRMC specimen increased by 31.9 %, while the duration before attenuation increased by 47.3 %. MRMC can increase the area ratio of high‐temperature areas (greater than 1300 °C) in the fireball. MRMC increases the overall temperature of the fireball, not just in specific local areas. Additionally, MRMC significantly enhances far‐field shock waves. At a scaled distance of 2.54, the peak overpressure and positive impulse of the MRMC specimen were 50 % and 52 % higher than those of the steel specimen, respectively. This study provides new insights into the application, design, and energy release research of MRMC.

Dynamic Process and Damage Evaluation Subject to Explosion Consequences Resulting from a LPG Tank Trailer Accident

The involvement of liquefied petroleum gas (LPG), which is highly combustible and explosive, greatly increases risk in road transport. A 3D numerical model was conducted in FLACS, which depicts the dynamic process and variation of combined effects along the multi-directions of LPG explosion under an actual case. With the simulation of scenarios, power-law explosion and fireball models were used to reproduce the results, and the dynamic evolution of specific parameters during the LPG explosion process was analyzed. The results reveal that the LPG explosion’s expansion around the expressway moved along the spaces between obstacles, while conditions at the site of the accident had an enhancement effect on LPG/air mixture accumulation. The propagation trajectory of the shock wave in the horizontal direction presented a regular circle within 623.73 ms, and the overpressure was enough to lead to extensive damage to surrounding structures. Further, shock wave-driven overpressure brought hazards to buildings further afield with multiple peak values. The influence of the LPG explosive fireball evolution is significantly reflected in the injury range of the heat flux; the maximum diameter of the on-site fireball eventually extended to 148.19 m. In addition, the physical effect indicated that the turbulence intensity induced by the surrounding buildings in the accident site significantly promoted the interaction between the shock wave and flame propagation. This research proposes a detailed analysis of damage coupling characteristics caused by an LPG tank trailer explosion integrated with a FLACS-mirrored model, which are useful for blast-resistant design and disposal planning under similar accidental circumstances.

A high throughput rapid scanning dispersive spectrometer for longwave infrared absorption spectroscopy

A rapid-scanning spectrometer was constructed to capture several hundred wavenumber wide spectral scans at greater than 1 kHz repetition rate in the longwave infrared. The system, made from commercial-off-the-shelf components, exceeds scan width and repetition rate limitations present in other infrared diagnostics while maintaining better than 10 cm−1 spectral resolution through its high throughput (f/2) design. Instrument design and construction is discussed in detail, and validation of the spectrometer’s ability to capture time resolved spectra in the 800–1400 cm−1 region at 1.2 kHz was demonstrated through the measurement of organophosphorus chemical nerve agent simulant destruction inside high explosive fireballs.

High-Speed Infrared Radiation Thermometer for the Investigation of Early Stage Explosive Development and Fireball Expansion.

The understanding of blast loads is critical for the development of infrastructure that protects against explosions. However, the lack of high-quality experimental work on the characterisation of such loads prevents a better understanding of many scenarios. Blast loads are typically characterised by use of some form of pressure gauge, from which the temperature can be inferred from a pressure measurement. However, such an approach to temperature measurement is limited; it assumes ideal gas laws apply throughout, which may not be the case for high temperature and pressure scenarios. In contrast, infrared radiation thermometers (IRTs) perform a measurement of temperature based upon the emitted radiance from the target object. The IRTs can measure fast changes in transient temperature, making them seemingly ideal for the measurement of a fireball’s temperature. In this work, we present the use of a high-speed IRT for the measurement of early-stage explosive development and fireball expansion within a confined blast, with the temperature of the explosive fireball measured from its emitted radiance. The temperature measured by the IRT was corroborated against the temperature inferred from a pressure gauge measurement; both instruments measured the same temperature from the quasi-static pressure (QSP) point onwards. Before the QSP point, it is deduced that the IRT measures the average temperature of the fireball over a wide field-of-view (FOV), as opposed to that inferred from the singular shocks detected by the pressure gauge. Therefore, use of an IRT, in tandem with a pressure gauge, provides a potential invaluable measurement technique for the characterisation the early stages of a fireball as it develops and expands.

An image processing method for an explosion field fireball based on edge recursion

To overcome the limitations caused by the complex fireball geometry in an explosion field and the smoke interference of fireball contours, a pre-processing strategy for fireball images in an explosion field, combining threshold segmentation, rectangular filtering, nearest-neighbor clustering and morphological processing, as well as an edge-recursive fireball image segmentation algorithm based on the polar coordinate system, is proposed. The overlap rate was used to compare and evaluate the segmentation effect of the proposed method and traditional image-processing methods on the measured explosion fireball image. The results demonstrate that the edge-recursive fireball image segmentation algorithm based on the polar coordinate system is excellent for identifying fireball image segmentation and fireball damage contour recognition under different smoke-obscured conditions in an explosion field, thereby facilitating the accurate recognition and measurement of the fireball image and contour under a smoke plume. This method improves the accuracy of measuring explosive fireball damage power and provides a method for effectively extracting the distribution information of explosive fireball damage.

Emission spectroscopy with coded apertures for enhanced dimensionality

A coded aperture is used to demonstrate emission spectroscopy from multiple one-dimensional measurement locations simultaneously with a single camera. The coded aperture mask has several columns of periodic apertures, each with a unique spatial frequency. Light transmitted through all mask columns is detected through an imaging spectrometer. Dispersed light from the various mask columns overlaps on the spectrometer camera but is separated using Fourier-domain filtering using the known spatial frequencies of the mask. As the coded aperture is placed at an image plane, each Fourier-filtered spectrogram comes from a unique one-dimensional measurement location. This technique represents a significant increase in the amount of spatially and spectrally resolved emission data available using a single emission spectrometer and camera at the expense of some spatial resolution due to the Fourier filtering. This instrument is particularly useful for studying transient, non-repeating events. Megahertz-rate emission spectroscopy from five one-dimensional measurement locations is demonstrated with explosive fireballs using a single camera. Optical design parameters and instrument performance characteristics are discussed.

Synergistic response of steel columns to explosive thermal and long duration blast loading

This paper investigates the response of steel columns to combined pre-cursor thermal and long duration blast loads. Blast waves are the primary damage mechanism from explosive events. However, explosive events also emit thermal loads. Depending upon the explosive size and standoff distance, the effective thermal load can reach a structure prior to the arrival of the blast. An effective thermal load can damage steel structures such that total damage from the combined thermal and blast load is different to, or greater than the blast load alone. There is limited research to date investigating the synergistic response of steel structures to explosive thermal and blast loading. This paper specifically focuses on the numerical and computational methods appropriate to predict the response of steel columns subject to focused thermal and long duration blast loads (positive pressure phase exceeding 100 ms). Results from a substantive study are presented, showing a synergistic response within a sensitivity envelope of load cases. Computational methods are verified with a novel series of explosive fireball trials and a series of combined thermal, compression and long duration blast trials.

Numerical study of external explosion characteristics induced by indoor natural gas vented explosion

PurposeThe purpose of this paper is to ascertain the harm to personnel and equipment caused by an external explosion during natural gas explosion venting. The external explosion characteristics induced by the indoor natural gas explosion are the focal points of the investigation.Design/methodology/approachComputational fluid dynamics technology was used to investigate the large-scale explosion venting process of natural gas in a 6 × 3 × 2.5 m room, and the characteristics of external explosion under different scaled vent size (Kv = Av/V2/3, 0.05, 0.08, 0.13, 0.18) were numerically analyzed.FindingsWhen Kv = 0.08, the length and duration of the explosion fireball are 13.39 and 450 ms, respectively, which significantly expands the degree and range of high-temperature hazards. The suitable flow-field structure causes the external explosion overpressure to be more than twice that indoors, i.e. the natural gas explosion venting overpressure may be considerably more hazardous in an outdoor environment than inside a room. A specific range for the Kv can promote the superposition of outdoor rupture waves and explosion shock waves, thereby creating a new overpressure hazard.Originality/valueLittle attention has been devoted to investigating systematically the external explosion hazards. Based on the numerical simulation and the analysis, the external explosion characteristics induced by the indoor large-scale gas explosion were obtained. The research results are theoretically significant for mitigating the effects of external gas explosions on personnel and equipment.

Study on energy release characteristics of reactive material casings under explosive loading

Reactive Materials (RMs), a new material with structural and energy release characteristics under shock-induced chemical reactions, are promising in extensive applications in national defense and military fields. They can increase the lethality of warheads due to their dual functionality. This paper focuses on the energy release characteristics of RM casings prepared by alloy melting and casting process under explosive loading. Explosion experiments of RM and conventional 2A12 aluminum alloy casings were conducted in free field to capture the explosive fireballs, temperature distribution, peak overpressure of the air shock wave and the fracture morphology of fragments of reactive material (RM) warhead casings by using high-speed camera, infrared thermal imager temperature and peak overpressure testing and scanning electron microscope. Results showed that an increase of both the fireball temperature and air shock wave were observed in all RM casings compared to conventional 2A12 aluminum ally casings. The RM casings can improve the peak overpressure of the air shock wave under explosion loading, though the results are different with different charge ratios. According to the energy release characteristics of the RM, increasing the thickness of RM casings will increase the peak overpressure of the near-field air shock wave, while reducing the thickness will increase the peak overpressure of the far-field air shock wave.

Three-Dimensional Thermal Field Induced by Gas Pipeline Explosion Fireball Based on Predicted Algorithm and Experimental Validation

Thermal radiation hazards of fireballs induced by gas pipeline leakage and explosion have increasingly contributed to the occurrence of accidental disasters. To reveal the mechanism of fireball’s thermal hazards, the temperature characteristics and propagation behaviors were theoretically and experimentally studied in real scenario. This study proposed an optimization method based on optical computerized tomography (OCT) and reconstruction algorithm. The results of the new OCT algorithm were simulated by using MATLAB, which can realize the visualization of 3D temperature field of the fireball. Moreover, a full-scale gas pipeline leakage and explosion experiment was undertaken, and a series of testing data from the explosion fireball’s thermal radiation were collected by using infrared thermography technique. The simulated accuracy of 3D temperature field by the optimized OCT algorithm was verified by comparing with experimental data, it found that the relative error between the two results ranged from 10.54 to 14.67%, while the average error was less than 11%. This comparative investigation can provide a new practical application of 3D analytical method for thermal radiation damage of fireballs under gas explosion in both steady and dynamic states.

Reflected Near-field Blast Pressure Measurements Using High Speed Video

Background: The design and analysis of protective systems requires a detailed understanding of, and the ability to accurately predict, the distribution of pressure loads acting on an obstacle following an explosive detonation. In particular, there is a pressing need for accurate characterisation of blast loads in the region very close to a detonation, where even small improvised devices can produce serious structural or material damage. Objective: Accurate experimental measurement of these near-field blast events, using intrusive methods, is demanding owing to the high magnitudes (> 100 MPa) and short durations (< 1 ms) of loading. The objective of this article is to develop a non-intrusive method for measuring reflected blast pressure distributions using image analysis. Methods: This article presents results from high speed video analysis of near-field spherical PE4 explosive blasts. The Canny edge detection algorithm is used to track the outer surface of the explosive fireball, with the results used to derive a velocity-radius relationship. Reflected pressure distributions are calculated using this velocity-radius relationship in conjunction with the Rankine-Hugoniot jump conditions. Results: The indirectly measured pressure distributions from high speed video are compared with directly measured pressure distributions and are shown to be in good qualitative agreement with respect to distribution of reflected pressures, and in good quantitative agreement with peak reflected pressures (within 10% of the maximum recorded value). Conclusions: The results indicate that it is possible to accurately measure blast loads in the order of 100s MPa using techniques which do not require sensitive recording equipment to be located close to the source of the explosion.

Experimental studies on blast mitigation capabilities of conventional dry aqueous foam

Aqueous foam provides a dispersion of the gaseous phase in the liquid phase. The commercially available aqueous foam (Denim shaving foam-original) has been investigated for its stability and capability for reducing the extreme thermal and blast effects associated with an energetic material detonation. The dry aqueous foam has evenly distributed bubbles with an average initial size of 15 µm. Different amounts of the C4 explosive were detonated while immersed in the dry aqueous foam having a density 60 kg/m3. The blast wave parameters were measured in the field for scaled distances ranging from 0.39 m/kg1/3 to 1.80 m/kg1/3 based on the cube root law. The dry aqueous foam confinement suppressed the explosion fireball radius up to 80% and quenched the afterburning reactions. An average peak pressure reduction of 70% and positive impulse reduction of ∼62% were observed for hemi-spherical confinement of the dry aqueous foam weighing 1.0 kg–2.75 kg against C4 charges of 82 g–250 g. The shock propagation is attenuated due to the high compressibility of gas bubbles. The dry aqueous foam may be used in emergency circumstances such as against energetic material detonation and lighter improvised explosive device threats to reduce the devastating blast effects. The numerical simulation results using ANSYS AUTODYN for bare charges are in fair agreement with the experimental findings.