Explosive Behavior Research Articles

Effects of H2/CO ratio and CO2 dilution on the explosion behavior and flame evolution of syngas/air mixtures

Syngas, which is used as both a fuel and a raw material, presents numerous safety risks during its utilization. In this paper, the effects of H2/CO ratio (R = 0%, 30%, 50%, 70% and 100%) and CO2 dilution ([CO2] = 0%–20%) on the explosion behaviors of syngas/air mixtures with different equivalence ratios (φ = 0.8, 1.0, 1.6, and 2.5) are examined via experiments and numerical calculations. The results show that the peaks of explosion pressure and OH* spectral intensity are significantly influenced by the H2 percentage in the syngas. The introduction of CO2 notably decreases these parameters in oxygen-rich and severe oxygen-poor states. Additionally, the flame propagation speed noticeably increases with increasing H2 proportion in the syngas. The influence of CO2 on the buoyancy instability of the spherical flame of syngas is considered negligible when compared to that of other combustible gases, such as CH4. Nevertheless, the presence of CO2 decreases the density ratio between the unburned gas and burned gas and increases the flame thickness of syngas/air mixtures. This trend reduces the cellular instability of the spherical flame, particularly in severe oxygen-poor states. Notably, there is a definite correlation between the formation of cellular flames and the rise rate of explosion pressure. The cellular structure on the flame surface becomes more pronounced when the rise rate of explosion pressure increases. Conversely, it develops later or is noticeably inhibited. Furthermore, the main reaction pathways are H2 → ∙OH → H2O2 → H2O and H2 → ∙OH → CO → CO2 during the syngas explosion process. ∙OH is critical in the entire chain reaction because it promotes the conversion of H2 to H2O and acts as a vital connection between the reactants H2 and CO in the explosion process.

Verification and validation of detonation-shock-dynamics relations for explosives described by general equation of state and chemical reaction models

Detonation shock dynamics is a powerful method to model the behaviour of High Explosives (HE). However in order to use this method, the underlying relationship between the local radius of curvature and the detonation speed must be known. Previous work has developed methods to calculate this effect using simple, single-step Arrhenius and polytropic gas, models for the chemical reaction and the equation of state, respectively. In recent years, more complex models for both reaction rates and equations of state have been developed which show better agreement with experimental data than these simple models, especially when considering condensed phase explosives.. This work presents the governing equations for solving these problems in a way that is generalised to use arbitrary equations of state as well as reaction models which may have more than a single step and multiple product species. This implementation is verified against exact solutions, demonstrating that the equations were implemented properly. The verified algorithm is then validated against experimental data and high fidelity simulations, showing that it is able to make accurate predictions in a regime where the underlying assumptions of the governing equations are valid. This approach has many applications: from creating equivalent detonation shock dynamics models for existing reactive burn calibrations for HE; to developing new functional forms and calibrations of reactive burn models for condensed phase high explosives.

Real-time X-ray diffraction measurement on laser shock-loaded hexanitrostilbene (HNS)

Understanding the lattice evolution of hexanitrostilbene (HNS) is crucial for ensuring its safety and reliability under shock loading. However, the lack of in situ, real-time diagnostics has limited the availability of lattice parameters for shock-loaded explosives. In this study, we utilized dynamic X-ray diffraction technology to obtain the diffraction spectrum of laser shock-loaded HNS and to determine its temporal evolution. Additionally, by improving the laser energy, we initiated HNS and obtained the diffraction spectrum of detonation products during the detonation process. The experimental results showed the presence of a diamond structure in the detonation product, suggesting the existence of either diamond or diamond-like carbon. Our research not only elucidates the crystal structure of shock-loaded HNS and its detonation products but also provides an avenue for laboratory-scale investigations into dynamically loaded explosives, which furnishing an opportunity to unveil the underlying mechanism governing explosive dynamic response behavior.

Experimental and theoretical investigations into overpressure during confined space explosions of methane-hydrogen mixture

This study aimed to deeply explore combustion and explosion behaviors within confined spaces fueled by methane-hydrogen blends. By experimenting in a 55 m³ chamber, it examined how different hydrogen mixing ratios (5%, 10%, 15%, and 30%) affect flame spread and overpressure buildup at an equivalence ratio of 1.1. Results showed that two main flame patterns emerge during venting: mushroom clouds and jet flames. Higher hydrogen percentages cause mushroom clouds to form earlier and grow larger; notably, a 30% blend produces a cloud 12% quicker than a 10% blend, reaching a maximum radius of about 2.7 m. Three types of overpressure were identified: Popen (venting structure opening), Pext (external explosion), and Phel (Helmholtz oscillations). Both Pext and Phel rise with increasing hydrogen content. At each blend level, Pext peaks at 1.87–6.42 kPa, while Phel ranges from 5.86 to 20.65 kPa. Pext plays a crucial role in peak overpressure during venting, particularly relevant for ventilation design considerations. To predict Pext, the study tested three engineering models and found that Taylor's spherical piston theory provided the closest match to experimental data, with a maximum error under 30% compared to other models. In summary, this research offers essential theoretical knowledge and practical evidence for designing safer ventilation and explosion relief systems for facilities handling methane-hydrogen mixtures in the process industry.

Explosion behavior of nonuniform hydrogen/methane/air mixtures in the presence of copper foam

The effect of copper foam on the explosion characteristics of nonuniform hydrogen/methane/air mixtures with different hydrogen volume fractions (φ) and diffusion times (DT) was investigated in a closed duct. Copper foams with different PPIs (pores per inch): 0 PPI, 20 PPI, 40 PPI, and 60 PPI were used, where 0 PPI refers to the case where there is no copper foam in the duct. The results show that a triple flame is observed in nonuniformly mixed hydrogen/methane/air mixtures after the hemispherical flame and finger flame stage, rather than the traditional plane flame and successive tulip flames. Upstream of the copper foam, the presence of the copper foam has no effect on the flame evolution process in uniformly mixed hydrogen/methane/air mixtures but affects the shape of the triple flame in nonuniformly mixed gas. The flame front develops numerous folds and cellular structures after it through the copper foam, and the flame velocity and overpressure increase rapidly. When the PPI of the copper foam is increased, the flame downstream of the copper foam becomes more disordered and irregular, and the maximum flame velocity and maximum overpressure initially increase and then decrease with increasing PPI. The maximum flame velocity and maximum overpressure are obtained in uniform and nonuniform hydrogen/methane/air mixtures when copper foams with 20 PPI and 40 PPI are used, respectively. The results provide experimental evidence for preventing and controlling hydrogen/methane fuel explosions.

Experimental study on the explosion behavior of nonuniform hydrogen/methane/air mixtures in a duct

An experimental study is performed on the explosion behavior of a nonuniform hydrogen/methane/air mixture with varying hydrogen volume fractions (α(H2)) in the fuel used and different mixing levels of the fuel/air mixture (characterized by the diffusion time (td) of the hydrogen/methane mixture). Results show that both α(H2) and td considerably impact the explosion behavior of the nonuniform hydrogen/methane/air mixture. Increasing α(H2) and td can increase the uniformity of the hydrogen/methane/air mixture. A triple flame is observed in highly nonuniform mixtures instead of the finger- and tulip-shaped flames seen in more uniform mixtures. The shape of the flame front varies with the degree of fuel/air mixing. As α(H2) and td increase, the propagating flame gradually transitions from a triple flame to a tulip-shaped flame. The flame tip velocity and overpressure increase with α(H2) and td. For a fixed td, the flame tip velocity and overpressure increase slightly as the α(H2) rises from 0 to 40% and rapidly for a large α(H2). These findings suggest that improving the uniformity of hydrogen/methane/air mixtures could increase the severity of explosions for fuels with high hydrogen contents.

Numerical simulation of leakage, dispersion and explosion behavior of LPG in kitchen

ABSTRACT The frequent occurrence of kitchen gas explosion accidents has raised widespread attention to gas safety. This article takes kitchen as the research object, and explores the dispersion law of LPG leakage in kitchens and the influence of ignition at different leakage time on explosion consequences by establishing LPG leakage and explosion models. The results show that the process of LPG leakage in a closed kitchen can be divided into three stages: initial kinetic energy dominant stage, gravity expansion stage, and passive dispersion stage. Propane forms a non-uniform concentration field in the kitchen that gradually decreases from bottom to top, filling the entire kitchen in 583 s. When an explosion occurred in the kitchen center, the initial burst of flame spreads around in a fireball. After 115 ms and 122 ms, the explosion overpressure causes the door and window to be destroyed respectively, and the flames stretch toward the door and window. The flames are then concentrated mainly in the lower area where the fuel is more adequate. In the later stage of the deflagration reaction, the flame propagates toward the upper area of the kitchen under buoyancy. The explosion consequences of LPG non-uniform gas clouds show a pattern of first intensifying and then weakening with the leakage time. The explosion consequences are most severe when ignited about 300 s after the leakage. The maximum explosion overpressures at the center of the kitchen, door, and window were 67.15 kPa, 28.12 kPa, and 27.92 kPa, respectively. The research results can provide reference for emergency response, consequence assessment, and kitchen safety design for kitchen LPG leakage and explosion accidents..

Filtering induced explosive death in coupled FitzHugh–Nagumo neurons: Theory and experiment

Explosive emergent behavior governed by discontinuous and irreversible phase transition is in the center of recent research. In this paper we show that explosive amplitude death (AD) can be induced in a system of coupled oscillators if diffusion is accompanied by low-pass filtering in the mutual coupling path. Here we consider a ring network of diffusively coupled FitzHugh–Nagumo oscillators, and through theoretical and experimental investigations explore how the low-pass filter induces and controls the transition to explosive AD state. We derive the conditions of getting AD in the network through linear stability analysis. Using one and two parameter bifurcation analysis we find the explicit parametric zone of explosive death in the limiting case of two neurons, which reveals that the explosive death arises through the saddle–node bifurcation of limit cycle. In the strong coupling limit, we observe an interesting semi-explosive death scenario, where both continuous and discontinuous transitions are present. Finally, using electronic hardware circuits, we demonstrate the first experimental observation of explosive amplitude death that establishes the robustness of the scenario in a practical setup.

Bursting the bitcoin bubble: Do market prices reflect fundamental bitcoin value?

This paper develops a theoretical model of the bitcoin market and demonstrates that the bitcoin’s volatile and explosive price path is a consequence of the Bitcoin protocol’s system of supply management. The model implies that the marginal cost of mining the target supply of bitcoins is the fundamental value of the bitcoin since it corresponds to an equilibrium in the Bitcoin protocol and the rent-seeking tournament among miners. The data provide strong empirical evidence of cointegration between the bitcoin’s price and the marginal cost of mining the target supply of bitcoins, demonstrating the existence of their long-run equilibrium relationship. Current bubble detection techniques indicate that there is no evidence of explosive departures in the price of the bitcoin from its model-implied fundamental value. Since the raw price data exhibit explosive behavior, the apparent bubbles in the price of the bitcoin can be attributed to its nonstationary market fundamentals.

Natural disasters, deforestation, and emissions affect economic growth in Somalia

This study ascertains the effect of natural disasters, deforestation, and emissions on economic growth in Somalia using annual time series spanning 1990–2018. Contrary to previous attempts, this study utilized the kernel regularized least squares (KRLS) technique, robust Granger causality in the presence of instabilities, and novel supremum right-tail Augment Dickey-Fuller unit root to test explosive behaviors in data series. While two date-stamped explosive behaviors are detected in economic growth (2003–2012, 2014–2016) and FDI (2004, 2016–2018), one explosive behavior is observed in capital formation (2010–2018) and population density (2010–2018). Moreover, time-varying granger causalities among sampled variables are observed. The empirical results show natural disasters and deforestation significantly undermine economic growth, whereas GHG emissions stimulate economic growth. Besides, while GHG emissions have increasing marginal effects, natural disasters and deforestation have decreasing marginal effects. The marginal effect of the interaction between natural disasters and temperature change is close to zero, implying that temperature changes do not mediate the disaster-growth nexus. Nevertheless, the study underscores the need for the implementation of environmental and economic policy reforms related to natural disaster preparedness, eliminating deforestation for charcoal exports while implementing a paradigm shift from domestic charcoal and firewood energy consumption to clean and renewable energy.

High-temperature effect on the mechanical behavior of recycled fiber-reinforced concrete containing volcanic pumice powder: An experimental assessment combined with machine learning (ML)-based prediction

The increasing volume of waste generated by various activities has increased interest in using waste to create sustainable construction materials to achieve possible benefits. In addition, using recycled materials to produce fresh concrete is a desirable option because of its low cost, lower landfill space requirement, and the completed concrete quality. Therefore, an experimental inquiry is undertaken to ascertain the impacts of up to 20 wt% cement displaced by Volcanic Pumice Powder (VPP) with the incorporation of 1% and 2% Recycled Nylon Fiber (RNF) on the mechanical properties of concrete composites following room temperature to high-temperature (600 °C) exposure. Fresh concrete characteristics tests were performed, including slump, compacting factor, Kelly ball penetration, and density. The heat resistance of the concrete was then measured by calculating the percentage decrease in weight, the splitting tensile strength, and the compressive strength of the specimens. Heating mainly raised VPP's pozzolanic reactivity and lowered high vapor pressure through melting RNF. Therefore, VPP and RNF-treated concrete had superior mechanical performance than control concrete even when exposed to elevated temperatures. Further, the microstructural modifications brought on by RNF and VPP additions were also explored by deploying Scanning Electron Microscopy (SEM). The use of VPP in concrete led to an improvement in fresh properties, while RNF demonstrated deterioration in the same qualities. Despite this, supervised machine learning techniques are a central focus of this investigation because of their potential to predict concrete characteristics accurately. To predict the fresh and mechanical characteristics of concrete, both the Random Forest (RF) and the K-Nearest Neighbors (KNN) algorithm, along with their ensemble model counterparts, were explored. The outcomes revealed that RNF and VPP considerably improved the concrete's heat resilience and mechanical characteristics and halted the concrete composites' explosive spalling behavior at 600 °C temperatures. To prevent strength loss at high temperatures, it was discovered that adding 1% RNF content to concrete with 10% VPP was the best combination. In addition, the high coefficient correlation (R2) value of the RF and the ensemble model indicates great accuracy in outcome prediction, while the low R2 value of the KNN model indicates that the KNN model is less accurate.

Global uncertainties, geopolitical risks and price exuberance: Evidence from international energy market

AbstractThe interaction of global uncertainty and geopolitical risks with energy price fluctuations has remained a critical global issue. This interaction can impact several regions' macroeconomic performance and welfare by making fundamental energy price forecasting more difficult, which may lead to exuberant behaviour. To help producers, consumers, and regulators make informed decisions in the face of volatile and uncertain energy markets, it is critical to highlight how these uncertainties influence price exuberance. In this light, this study examines the impact of global uncertainty and geopolitical risks on international energy price exuberance using monthly data from January 1990 to October 2022. The study employs supremum augmented Dickey–Fuller (SADF) and generalised augmented Dickey–Fuller (GSADF) tests to identify energy price exuberance. Firstly, consistent with exuberant behaviour, the tests identify seven episodes of explosive behaviour in the international energy prices within the sample. Secondly, this study applies the Logit model to estimate the impact of global uncertainty and geopolitical risks on price exuberance. The estimates suggest that the heightening of global uncertainty may deflate the price exuberance. This study also observes that adverse geopolitical risks (threats and acts) in the world and Ukraine amplify the likelihood of price exuberance in the market. However, adverse geopolitical risk (GPR) in Russia negatively impacted the formation of price exuberance. This finding implies that policymakers can use global uncertainty and geopolitical risks as early warning indicators of probable price exuberance in the international energy market. The findings also indicate the need for a buffer system and safe passage for the flow of energy supply in a geopolitical conflict or a major global event. The study further shows the need for a coordinated effort in innovation, research, and development to enhance energy efficiency and minimise reliance on fossil fuels, which these uncertainties may not significantly influence.

Public debt dynamics and fiscal sustainability in selected North African countries: new evidence from recurrent explosive behavior tests and quantile unit root analysis

Public debt dynamics and fiscal sustainability in selected North African countries: new evidence from recurrent explosive behavior tests and quantile unit root analysis

Experimental analysis and multi-scale simulation of the fracture behavior of polymer-bonded explosives based on the dynamic notched semi-circular bend method

Polymer-bonded explosives (PBXs) are extensively utilized in both military and civilian applications. Therefore, an accurate measurement of their dynamic fracture properties is critical for ensuring the safety and stability in engineering applications. In this study, a split Hopkinson pressure bar (SHPB) loading system is utilized to conduct dynamic fracture tests on a notched semi-circular bend (NSCB) specimen. A crack propagation gauge (CPG) and a strain gauge (SG) are employed for capturing the transient crack propagation velocity, crack initiation, and unstable propagation at a specific moment. The dynamic fracture behavior of PBX-9001 can be categorized into three stages. To acquire the damage evolution data during loading, a finite element model based on the real crystal morphology, with a cohesive zone model (CZM) for describing the damage, is developed. Additionally, a multi-scale simulation model has been established to investigate the microscopic damage and degree of damage in PBX-9001. The microstructure of PBX-9001 exhibits toughening effects, and the initiation toughness and extension toughness are positively correlated with the loading rate. The multi-scale model effectively simulates the expansion behavior and damage evolution of PBX-9001. Overall, the findings of this study provide useful insights on the nonlinear fracture behavior and the influence of loading rate on the mesoscopic fracture mechanisms of PBXs.

Time and frequency dynamics between NFT coins and economic uncertainty

Non-fungible tokens (NFTs) are one-of-a-kind digital assets that are stored on a blockchain. Examples of NFTs include art (e.g., image, video, animation), collectables (e.g., autographs), and objects from games (e.g., weapons and poisons). NFTs provide content creators and artists a way to promote and sell their unique digital material online. NFT coins underpin the ecosystems that support NFTs and are a new and emerging asset class and, as a new and emerging asset class, NFT coins are not immune to economic uncertainty. This research seeks to address the following questions. What is the time and frequency relationship between economic uncertainty and NFT coins? Is the relationship similar across different NFT coins? As an emerging asset, do NFT coins exhibit explosive behavior and if so, what role does economic uncertainty play in their formation? Using a new Twitter-based economic uncertainty index and a related equity market uncertainty index it is found that wavelet coherence between NFT coin prices (ENJ, MANA, THETA, XTZ) and economic uncertainty or market uncertainty is strongest during the periods January 2020 to July 2020 and January 2022 to July 2022. Periods of high significance are centered around the 64-day scale. During periods of high coherence, economic and market uncertainty exhibit an out of phase relationship with NFT coin prices. Network connectedness shows that the highest connectedness occurred during 2020 and 2022 which is consistent with the findings from wavelet analysis. Infectious disease outbreaks (COVID-19), NFT coin price volatility, and Twitter-based economic uncertainty determine bubbles in NFT coin prices.

Investigation of marginally explosible dusts

“Marginally explosible dusts (MEDs)” are a group of combustible dusts that are distinguished by relatively low volume-normalized maximum rate of pressure rise (KSt) and maximum explosion pressure (Pmax) values. Earlier studies have suggested that dusts with KSt values less than 45 bar m/s in the laboratory-scale 20-L chamber would not explode in the 1-m3 chamber and therefore not on an industrial scale. Conversely, for some metallic dusts, significantly higher KSt values are generated in the 1-m3 chamber. Industries that handle MEDs continue to search for answers to the questions “are they explosible or not?” and “should we protect or not protect against potential explosions of these dusts?“. To answer these questions, four well-characterized materials namely, carbon black, oat grain flour, urea, and zinc were tested in the current study. These materials were selected because they exhibit different combustion behaviors and also cover a range of industries. Five ignition energies (i.e., 0.5, 1, 2.5, 5, and 10 kJ) were used in the 20-L chamber tests. The results show a clear case of overdriving (as a result of the high ignition energy density in the 20-L chamber) with respect to urea and carbon black dusts. Nevertheless, the urea dust is non-explosible. The data also suggests that the choice of test chamber to generate suitable explosion data is strongly dictated by the combustion path of MEDs. However, there are exceptions. The study also establishes the importance of both chemico-physical and thermal analyses to understanding the explosion behavior of MEDs. With reference to urea dust, a new definition for MEDs has been suggested as dusts having Pmax < 3.0 bar(g), KSt < 20 bar m/s (in the 20-L chamber), MEC >1000 g/m3, MIE >1000 mJ, and MIT >600 °C. This work provides guidelines to industries that handle MEDs on the explosibility classification of these dusts, thus addressing the existing difficulty, and informing industry on the safety strategies required when handling this group of dusts.

Cellular instabilities of outwardly propagating spherical hydrogen-oxygen flames using a soap bubble method

Explosion hazards associated with hydrogen-oxygen mixtures remain a significant challenge for the energy industry, despite hydrogen garnering attention as a carbon emissions-free alternative energy source. While several studies have been conducted on hydrogen-air explosions, research on hydrogen-oxygen explosions has been limited. In the current study, we employed a spherical soap bubble method to experimentally investigate the flame propagation behavior of an unconfined hydrogen-oxygen explosion. The experimental values of the laminar burning velocity were in agreement with its calculated values and were notably higher than those observed hydrogen-air mixtures. In the case of hydrogen-oxygen mixtures, a spherical expanding flame is accelerated due to the presence of Darrieus-Landau and diffusive-thermal instabilities. Furthermore, we compared the correlation between the critical Pѐclet number and the critical Karlovitz number with the Markstein number for hydrogen-oxygen mixtures to results obtained with propane-oxygen and methane-oxygen mixtures.

Explosive Behavior in COVID-19 and Policy Responses: Lessons Learned for Public Health Management

Since the first case of COVID-19 in Turkey, there has been a lingering question as elsewhere in the world: “When will or should the government impose severe restrictions to protect public health?” From a public health perspective, there is value in developing a model to support proactive implementation of social policies. This study aimed to show the benefits of using a novel econometric test (the Generalized Supremum Augmented Dickey-Fuller Test) to detect explosive behavior (bubbles) in Turkey’s daily COVID-19 cases and deaths. Results from the analysis demonstrated a link between identified explosive episodes and critical public health decisions, especially in the case of daily new deaths. They also showed a negative relationship between the formation of exuberant behavior during the pandemic and the vaccination rate. Public health policymakers can incorporate this method into their arsenal to evaluate the overall health situation in combating the pandemic and respond accordingly. Furthermore, among the lessons learned from the Turkish experience is the importance of having a coronavirus scientific advisory board in the decision-making process and the ability to promptly implement policy measures. JEL Codes: C22, C58, I10, I18

The quest for explosive bubbles in the Indonesian Rupiah/US exchange rate: Does the uncertainty trinity matter?

The Generalized Supremum Augmented Dickey-Fuller (GSADF) technique is performed to resolve whether the Indonesian Rupiah/US exchange rate has experienced multiple explosive bubbles. The GSADF uncovers that the Indonesian Rupiah/US exchange rate deviates from the fundamental values by six times from January 1985 to September 2023, periodically indicating the presence of numerous explosive behaviors. Once the full-sample period separates into the managed-floating regime and the free-floating regime, the GSADF still detects multiple bubbles. Of particular curiosity on uncertainty trinity, this study underlines that global geopolitical risk negatively drives explosive actions in the ratio of exchange rates for non-traded and traded goods. The global economic policy uncertainty negatively affects speculative bubbles in the exchange rate and the ratio of exchange rates for non-traded. The country's geopolitical risks negatively strike only speculative bubbles in the exchange rate. Further, we find heterogeneity in our results by examining different exchange rate systems. The robustness checks further firmly ascertain across baseline empirical findings.

MULTIPLE-BUBBLE TESTING IN THE CRYPTOCURRENCY MARKET: A CASE STUDY OF BITCOIN

Economic periods and financial crises have highlighted the importance of evaluating financial markets to investors and researchers in recent decades. The asset price fluctuation is an innate quality of the market. However, fluctuations sometimes become abnormal and turn into unbridled spikes and sudden declines, causing irreversible damage to an economy and the trust of investors. In recent years, there have been severe price fluctuations in the cryptocurrency market. Some analysts have defined these fluctuations as price bubbles (i.e., economic bubbles). However, no specific definitions have yet been proposed for these price bubbles. The right-tail augmented Dickey–Fuller (RTADF) test was conducted on the time series data of 13 years (2008–2021) to analyze the presence of bubbles in the Bitcoin market. The RTADF results rejected the null hypothesis and confirmed the alternative hypothesis indicating the presence of bubbles in the Bitcoin market. In other words, there is some evidence of explosive behavior in a bubble. Moreover, the results of GSADF and SADF tests confirmed the presence of multiple bubbles in the Bitcoin market within 2008–2021.