Combustion Temperature Research Articles

Influences of ultra-low load operation strategies on performance of a 300 MW subcritical bituminous coal boiler

To reveal the operational characteristics of subcritical boilers under ultra-low loads, numerical simulations were conducted based on a 300 MW subcritical bituminous coal boiler. The impacts of boiler load and low-load operation strategies on coal combustion behavior, heat transfer process, and NOx emission were thoroughly examined. Results indicate that acceptable aerodynamic and temperature fields can still be formed at 25 % ultra-low load, but the boiler performance is significantly reduced, with the maximum cross-sectional average combustion temperature being reduced by 225.98 K compared with the full-load condition. At 25 % load, the use of only two layers of burners results in a substantial increase in NOx emission from 290.32 mg/m3 to 445.56 mg/m3. The position of in-service burners affects the region where the intense coal combustion and heat release process occurs, and using the middle three layers of burners helps to maintain heat absorption by the suspended heating surfaces and to minimize NOx emissions. Furthermore, increasing primary air velocity at ultra-low loads can promote coal combustion and heat transfer processes in the lower furnace, but increase NOx emission by 14.23 % when primary air velocity is increased from 14.90 m/s to 23.00 m/s at 25 % load. These findings provide valuable insights for optimizing the ultra-low load operation of subcritical boilers engaged in deep peak-shaving processes under the carbon neutrality goal.

Optimization on manifold injection in DI diesel engine fuelled with acetylene

Researchers demonstrated that implementing new combustion technology and optimising fuel quantity results in a significant reduction in traditional fossil fuel usage and emission levels. The Reactivity Controlled Compression Ignition (RCCI) combustion strategy is one of the low temperature combustion technologies, and it is used to reduce the overall combustion temperature while also providing better combustion control. This study looks into RCCI combustion technology, which uses conventional diesel fuel as the high reactivity fuel (HRF) injected through the injector and acetylene gas as the low reactivity fuel (LRF) injected into the cylinder via a modified inlet manifold alongside air. The modified engine setup was tested for performance, emissions, and combustion under various load conditions, as well as different mass flow rates of acetylene gas, a low reactivity fuel that is injected with air. The flow field of the low reactivity fuel at the inlet manifold is analysed using the Computational Fluid Dynamics principle, which is used to determine the best flow rate for improving combustion quality. According to the simulation results, the optimal acetylene flow rate is 3 Litres Per Minute (LPM), and experimentation shows that at 3 LPM acetylene injection, the brake thermal efficiency (BTE) improves by about 3.2%, and emissions such as carbon monoxide (CO), hydrocarbon (HC), smoke intensity, and oxides of nitrogen (NOx) are reduced by about 35%, 17%, 10%, and 21%, respectively.

Tuning the textural properties of biomass-derived nanocrystallized BEA for acetyl functionalization of anisole

The synthesis of a highly active zeolite beta catalyst for acetyl functionalization of anisole by utilizing the silica precursor obtained from rice husk is a promising approach for the mitigation of agricultural waste. The influence of combustion temperature (CT) (300, 500, 700, and 900 °C) on the characteristics of rice husk ash was investigated. The C52H obtained at a medium CT (500 °C) has a high surface area compared to the C72H indicates that, merging of smaller crystals of amorphous silica to form crystalline silica with larger crystallites by applying more thermal energy when CT ≥ 700 °C. The PS-5 catalyst derived from C52H possess high surface area (332 m2/g) and a smaller crystallite size (14.8 nm) compared to the PS-7 obtained from C72H, which shown the lower surface area (131.5 m2/g) with a larger crystallite size (25.6 nm). Solid-state NMR and NH3-TPD analysis reveals that PS-5 catalyst possessing higher acidity compare to both PS and PS-7. The activity studies confirms that the PS-5 catalyst exhibited superior catalytic activity (>98%) compared to PS (conventional) and PS-7 catalysts, making it a potential candidate for continuous production of aromatic ketones. acylation reactions.

Numerical study of the combustion process and NOx evolution mechanism of ammonia-hydrogen compound fuel engine under different intake conditions

To explore the distinction between generation atmosphere of fuel NOx and thermal NOx in an ammonia-hydrogen compound fuel engine, a numerical calculation model was established based on a detailed ammonia-hydrogen oxidation mechanism. The combustion process and NOx evolution mechanism of the ammonia-hydrogen compound fuel engine under different intake conditions were studied. The researchresults for different equivalence ratios show that the in-cylinder hydrogen volume is the primary factor influencing the initial heat release. When the equivalence ratio is between 0.89 and 1.14, the mixture exhibits a higher combustion rate, leading to a shorter CD and an earlier CA50. At this point, the heat release process closer to TDC contributes improving engine combustion efficiency and indicated efficiency. Therefore, when the equivalence ratio is between 0.89 and 1.00, combustion efficiency is higher than 98 % and indicated efficiency is higher than 43 %, the ammonia-hydrogen compound fuel engine achieves relatively higher economy. Both over-rich and over-dilute mixtures induce an enhancement of fuel NOx, while the higher in-cylinder temperature caused by stoichiometric combustion leads to a boom of thermal NOx. Consequently, the total NOx emission from the ammonia-hydrogen compound fuel engine is higher at equivalence ratios between 0.80 and 1.00, and the NOx emission reaches its peak at an equivalence ratio of 0.89. Analysis of the evolution process of key N components in the cylinder shows that incomplete combustion plays a significant role in fuel NOx emissions, while thermal NOx emissions are mainly influenced by the distribution of in-cylinder components and combustion temperature. Specifically, thermal NOx emissions primarily depend on the in-cylinder components distribution in the narrow equivalence ratio range around stoichiometric ratio, and are significantly affected by in-cylinder temperature under other conditions. The in-cylinder oxygen concentration significantly affects fuel NOx emissions under most operating conditions. Further optimization of intake temperature shows that combustion efficiency exceeds 90 % when the intake temperature is above 280 K. When the intake temperature reaches 310 K, the combustion efficiency reaches up to 98 %, thus an intake temperature of about 310 K is sufficient to meet the need for improving the combustion efficiency of ammonia-hydrogen compound fuel engine. To achieve high efficiency and lower NOx emissions, appropriate lean combustion combined with an intake temperature slightly above room temperature is recommended.

Combustion synthesis of TiC- high entropy alloy CoCrFeNiMn composites from granular mixtures

The advantage of combustion synthesis is the ability to produce composites from powders in a single technological step, using the heat of an exothermic reaction, in a fast and energy-efficient manner. Ceramic-metal composites TiC–High-Entropy Alloy (HEA) CoCrFeNiMn were fabricated by combustion synthesis from granular mixtures. The content of the metal binder components varied from 10 to 30 wt% and the combustion velocity and temperature gradually decreased as the binder content increased. Scaling up synthesis requires clarification of the parametric range for implementing a safe combustion mode. The impurity gas content and the range of safe conductive combustion were determined from known theoretical models and experimental combustion velocities of samples of granules of 0.6 and 1.1 mm size. The main phases of the product were titanium carbide with up to 3 at. % Cr and HEA CrCoFeNiMn with a reduced Mn content compared to the equimolar composition. The content of secondary phases Cr7C3 and carbon did not exceed 5 wt%. The use of granular mixtures solved the problem of significant sintering of exothermic powder mixtures containing metal binder during combustion. After synthesis, the granules retain their size and do not sinter together, making it easy to grind the sample and obtain a TiC-HEA composite powder.

THE EFFECT OF VARIOUS MOLOTOV COCKTAILS ON DIFFERENT SURFACES AND EVALUATION OF FIRE CHANGES

Objective:Molotov cocktails are a classic homemade weapon used over the past 80 years; also known as gasoline bombs. However, there is not enough research in the literature. Molotov cocktail is classified as a mildly explosive substance. But a Molotov cocktail is not an explosive. This is a handmade lighter. It is used to set fire to targets in terrorist attacks. Methods:In our study, classic homemade Molotov cocktails were used. Oil, diluent, sugar, cologne, epoxy resin, paraffin, egg white, liquid and solid detergent, bleach, wood glue were added to the mixture. Parameters such as burning temperature, burning time, glass and nail spreading diameter, and residues of the Molotov cocktail were investigated. The prepared molotov cocktails were broken on 5 different floors, and the effect of changing the floor on the parameters was investigated. Results:In our study, 51 (59.3%) of 86 molotov cocktails were broken. Most of the destruction occurred in the wall. According to the results we obtained, a relationship was found between the content of the Molotov cocktail, the burning temperature and the time. It was found that the damage was increased with the addition of substances to the mixture. Conclusion: In addition, in our study, it was noticed that the Molotov cocktail did not explode by itself and did not cause damage to the environment by throwing nails.

Flame intensity sensor based on the resistive and memory properties of spintronic memristor

A flame intensity sensor based on the resistive and memory properties of spintronic memristor is proposed. The sensor circuit mainly consists of the infrared radiation conversion module, the spintronic memristor array module, the amplifier and current limiting resistor. In order to verify the designed sensor, experiments were conducted under no flame, constant and gradually increasing flame combustion temperature, and the effects of the number of parallel memristor arrays, current limiting resistors, measurement distance and radiation wavelength on the sensor were analyzed. The experiments results demonstrate that the designed flame intensity sensor based on the resistive and memory properties of spintronic memristor can quantitatively measure the flame intensity. When the temperature change rate of flame combustion is 1℃/s, the sensor measurement range is 0–3.1 mW/cm2, and the sensitivity is 4.516kΩ/(mW/cm2). The rate of change in the resistance of the spintronic memristor array may be affected by the changes in flame intensity, but this does not affect the measurement range of the sensor.

A Dynamic Testing Approach for Particulate Erosion–Corrosion for Gas Turbine Coatings

Abstract Particle interactions in engines can be complex phenomena leading to degradation of thermal (TBCs) and environmental barrier coatings (EBCs) meant to protect engine components. Ingestion of particles into the engine can lead to recession of coatings due to particle erosion. Similarly, these particles can become molten, adhere to coatings, and result in thermochemical corrosion of coating materials. Erosion testing is often carried out where particles are injected into a gas stream, accelerated within a nozzle, and impinge on samples. Conversely, most molten particle corrosion testing is often done in static furnaces, which does not capture the dynamic nature of deposition. Nevertheless, these damage mechanisms are often tested separately, and no standard exists to test both erosive/corrosive particle interactions with coating materials under relevant turbine operating conditions. Understanding the synergies of particle interactions is crucial in determining operating lifetimes of potential coating materials. Such considerations emphasize the need for realistic approaches in standardizing particle interaction testing in combustion environments. This study outlines efforts at NASA Glenn's Erosion Burner Rig Facility in improving dynamic erosion/corrosion testing methods by assessing the durability of state-of-the-art (SOA) TBC 7 wt % yttria-stabilized zirconia (7YSZ) as a function of particle deposition rate, burner temperature, and particle size. Calibration data to determine particle deposition rate will be presented, and mass and optical profilometry measurements were utilized to estimate mass/volume loss versus deposition per increment of particulate used. Electron microscopy analyses were then carried out to assess coating damage after testing.

Co-combustion of municipal sewage sludge and food wastes-derived anerobic digestates: Combustion characteristics, HCl/NO/SO2 emission and ash behaviors

Co-combustion of sewage sludge (SS) and food wastes-derived anerobic digestate (AD) is a promising way of waste-to-energy. Therefore, it is crucial to examine their combustion performance, ash behaviors, and gaseous pollutants emissions during the combustion of AD-SS blends using a thermogravimetric analyzer and a tube furnace combustion system. Results show that obvious interactions between AD and SS are observed in their co-combustion process. In terms of comprehensive combustion index, co-combustion can improve their combustion performance with the decrement of burnout temperature and enhanced combustion reactivity. Higher blending ratio of AD favors the increment of their ash fusion temperature, i.e., from 1109 to 1403 °C for deformation temperature due to the formation of high melting point minerals (i.e., Ca9Fe(PO4)7, 2CaO·Al2O3·SiO2). Significant in-situ reduction of NO and HCl as well as self-desulfurization is observed during the combustion of AD-SS blends. Compared to the theoretical values, the emission amount of HCl, NO, and SO2 is reduced by 0.13, 1.39, and 0.35 mg·g−1, respectively at 850 °C and blending ratio of AD to SS = 0.75:0.25. These phenomena are associated with the reducing environment and reducing substances by their high volatiles as well as the abundant minerals such as CaCO3 and Fe2O3 in AD and SS. However, high combustion temperature is unfavorable for chlorine fixation. This work provides a better understanding of their thermal behaviors, ash characteristics, and gaseous pollutants emission characteristics to realize their stable and clean incineration.

Casting light in the shadows: Exploring the influence of biological sex and age-at-death on heat-induced shrinkage in experimentally burned patellae

Burned human remains have been studied by both forensic anthropologists and bioarchaeologists to understand how fire impacts and alters bone in different scenarios. Heat-induced changes can occur including differences in colour and shrinkage, where the extent of the latter varies in different studies. The current study aimed to bring information regarding this topic and to observe how the individual’s biological sex and age at death impact shrinkage. The variability of shrinkage was analysed, relating to temperature and duration of burning. The sample comprised of the patellae of 32 individuals (18 [56.3 %] females and 14 [43.8 %] males) with age at death between 60 and 93 (age grouped in decades) from the sub-collection of experimentally burned skeletons, part of the 21st Century Identified Skeletal Collection (ISC/XXI). The right patellae were subjected to experimental burning at different temperatures and durations using an electric muffle furnace. Both the right and left patellae had three measurements taken, maximum height, maximum thickness and maximum width, with a digital calliper. The shrinkage percentage was higher in males and among the younger individuals (60–79 years old of both sexes). The values of standard deviation were high which indicates high variability. Shrinkage occurred at every temperature with bigger values observed in the patellae that had been subjected to temperatures over 800ºC. However, three patellae showed an increase in size at temperature under 800ºC. These findings align with previous studies where a non-linear correlation between shrinkage and exposure duration was found. It is essential to underscore that the percentage of shrinkage exhibits substantial variability even under identical temperature and duration conditions, highlighting the critical significance of meticulous experimental design and thorough analysis.

Soot evolution in ethylene combustion catalyzed by electric field: experimental and ReaxFF molecular dynamics studies

In this study, an electric field (E-field) was used to regulate the formation and oxidation of soot in combustion. In the procedure, an E-field is applied to the ethylene non-premixed flame, the flame is stretched horizontally and the flame height is reduced. By comparing the partially premixed flame to eliminate the effect of the E-field on the increase of combustion temperature caused by premixing, transmission electron microscope (TEM) detection revealed that the soot particles were more dispersed in the action of E-field, the “core-shell” structure of soot disappeared, and the markedly improved oxidation rate of soot in the flame. The evolution process of soot in ethylene combustion was studied by reactive molecular dynamics. The 9 ns simulation was performed at E-field strengths of 0, 0.001, and 0.1 V/Å by three successive modelings. The results showed that the E-field reduced the growth of the largest molecule in the system and increased the coagulation time of the initial soot particles. With increasing E-field strength, the “core-shell” structure of soot gradually broke. An increased hydrogen-carbon ratio and decreased number of six-membered rings are the internal factors for the more scattered structure of soot, which allows the soot to be more easily oxidized.

In situ preparation of aluminum-copper pentafluorobenzoate energy microspheres: Enhancing aluminum combustion properties in composite propellants

Aluminum powder is the main metal fuel in composite propellants, and upgrading the proportion of aluminum powder loaded in solid propellants is currently one of the most effective means of increasing propellant energy. Nonetheless, the substantial disparity in boiling points between the core aluminum particles and the alumina layer enveloping their surfaces often results in reduced reactivity, inadequate combustion, and combustion agglomeration during the combustion process of the aluminum powder. Herein, copper pentafluorobenzoate (CuPF) interfacial layer was established on the surface of aluminum powder through the self-assembly coordination reaction between pentafluorobenzoic acid and copper ions, and Al-CuPF energy microspheres were successfully prepared. A comprehensive examination was carried out to scrutinize the surface morphology, elemental composition, and distribution of the Al-CuPF energy microspheres. Furthermore, meticulous studies were conducted on the ignition and combustion properties of these Al-CuPF energy microspheres under various atmospheric conditions. It was found that the Al-CuPF interfacial layer within the Al-CuPF energy microspheres plays a pivotal role in enhancing ignition initiation and acting as a catalyst to facilitate the more efficient combustion of aluminum powder. Moreover, the combustion behavior of Al-CuPF energy microspheres when integrated into composite propellants has been exhaustively researched. Notably, composite propellants incorporating Al-CuPF energy microspheres exhibit heightened burning temperatures and an increased burning rate. Additionally, the combustion and agglomeration dynamics of Al-CuPF energy microspheres on the propellant burning surface were meticulously documented using a high-speed camera. The findings revealed that Al-CuPF energy microspheres spend a significantly shorter duration on the propellant burning surface and notably mitigate the occurrence of aluminum agglomeration issues thereon. This research contributes fresh insights into the application of innovative aluminum-based fuels within the realm of composite propellants.

Combustion of single micron-sized magnesium particles in carbon dioxide

An experimental system integrating micro-sized single particle generation, ignition, and observation was proposed and constructed for investigating the combustion characteristics of magnesium single particles in carbon dioxide. Defining the onset of combustion using the boiling point temperature allows for precise measurement of combustion time without artificial interference. Results revealed four modes of combustion for magnesium particles (Vapor-phase combustion, surface reaction, Micro explosion and flash-out mode) in carbon dioxide. Vapor-phase combustion is diffusion-controlled (with a D01.76 scaling, where D0 is the initial particle diameter). Additionally, the micro-explosion mode primarily occurs in particles with diameters exceeding 70 μm, and the combustion time is rather insensitive to the particle size (Typically 0.5 ∼ 2.2 ms in this study). The characteristic temperatures of the particles were determined using two-color pyrometry, indicating that the particle combustion temperature decreases with increasing particle size. Magnesium particles typically reach temperatures approximately 800 K higher than normal vapor-phase combustion temperatures before experiencing micro-explosions. Analysis of combustion products shows that the oxide shell formed by the combustion of magnesium particles has a three-layer structure. Both the outer and inner layers are mixed layers of magnesium oxide and solid carbon produced during combustion reactions, and the middle layer is the initial oxidation layer of the particles.

Effects of air to fuel ratio on parameters of combustor used for gas turbine engines: Applications of turbojet, turbofan, turboprop and turboshaft

Combustors of gas turbine engines have generally the highest irreversibility due to the combustion process. Therefore, to observe influence of air to fuel ratio (AFR) on combustor performance is of high importance. In this study, thermodynamic laws are employed to separately determine adiabatic flame temperature (AFT), entropy production, exergy destruction and exergy efficiency of combustor for turbojet (TJ), turbofan (TF), turboprop (TP) and turboshaft (TS) where variables are AFR, combustor inlet temperature (CIT) and combustor pressure ratio (CPR). In this regard, the higher the AFR, the lower the adiabatic flame temperature, however the higher the entropy production for related combustor. Similarly, increasing AFR leads to raise exergy destruction, thereby lowering exergy efficiency. On the other hand, as CIT increases, exergy efficiency of the combustor improves whereas slight effects of CPR on the combustor metrics are observed. Namely, due to variation of AFR, exergy destruction of combustor changes between 0.512 MW and 0.825 MW for TJ, between 1.807 MW and 2.735 MW for TS, between 28.38 MW and 40.49 MW for TF and between 3.102 MW and 4.564 MW for TP. Moreover, exergy efficiency of combustor changes between 59% and 73% for TJ, between 70% and 77% for TS, between 78% and 81% for TF and between 75% and 79% for TP engine through the determined AFR and CIT ranges. These findings indicate that combustor of each gas turbine engine demonstrates different behavior according to the mentioned variables and exergy efficiency of combustor depends on finding the optimum points of combustor variables.

Temporal and spatial evolution of wildfires during the Jurassic: From regional to global scale

With ongoing global warming, the frequency of wildfires has increased in many regions worldwide. To fully understand the manifold interactions between warming climates and wildfires it is necessary to study wildfires during Earth's history, preferably during periods characterized by warm climates. The Jurassic was a significant greenhouse period in Earth's history, and although evidence of combustion has been widely reported from deposits of Jurassic age, the spatio-temporal patterns and processes of Jurassic wildfires have not been studied on a global scale. In this study, evidence for wildfires occurring in deposits of the Early Jurassic Sangonghe Formation within the Junggar Basin is reported for the first time. It was found that the range of burning temperatures of these wildfires decreased from the late Early Jurassic to the early Middle Jurassic. Additionally, a comprehensive database, consisting of 196 published records, of Jurassic combustion products, including fossil charcoal, pyrogenic inertinite (fossil charcoal in coal deposits), and pyrogenic polycyclic aromatic hydrocarbons (PAHs), was compiled from the literature and analyzed for this study. Spatially, the database shows a high concentration of published evidence for Jurassic wildfire records in warm temperate climate zones in the mid-latitudes of the Northern Hemisphere. Temporally, trends in the Jurassic wildfires may be related to changes in atmospheric oxygen levels, climate change and fuels. However, like other global compilations on this topic for different periods of Earth's history, these results have to be seen with some care, as various taphonomic biases, including researcher bias and preservation issues, cannot be ruled as complicating factors.

Estimation of soot refractive index from its nanostructural parameters with the dispersion model

Particles derived from combustion processes, mainly composed of soot agglomerates, are acknowledged to be among the main contributors to climate change. Their effects depend mostly on their size, shape, and internal structure. Specifically, the latter has a significant effect on their optical properties, mainly through the refractive index. This index has been widely evaluated, but scarcely correlated with the soot internal characteristics. In this work, relationships between the nanostructural parameters (such as the degree of graphitization, among others) obtained with conventional analytical techniques and the input parameters of the dispersion model (a representation of the electromagnetic radiation through the Lorentz-Drude approach) are proposed with the aim to determine the refractive index. From experiments in a chassis dynamometer, it has been observed that as the vehicle speed increases, the soot samples have, in general, higher degree of graphitization, due to increased combustion temperature. The method proposed allows quantifying how both the real and imaginary parts of the complex refractive index increase as the degree of graphitization increases. Much lower dependence on the average crystal length has been observed. Different combinations of techniques can be used to determine the nanostructural parameters, depending on the analytical technique used. As far as the resulting parameters are reliable, the effect of the technique selected is minor, thus providing flexibility to the application of the method.

The Influence of Powering a Compression Ignition Engine with HVO Fuel on the Specific Emissions of Selected Toxic Exhaust Components

The aim of the research was to determine the potential of hydrotreated vegetable oil (HVO) in reducing nitrogen oxides and particulate matter emissions from the Perkins 854E-E34TA compression ignition engine. The concentrations of these toxic exhaust gas components were measured using the following analyzers: AVL CEB II (for NOx concentration measurement) and Horiba Mexa 1230 PM (for PM measurement). The measurements were carried out in the ESC test on a compression ignition engine with direct fuel injection and a turbocharger. The engine had a common rail fuel supply system and met the Stage IIIB/Tier 4 exhaust emission standard. Two fuels were used in the tests: diesel fuel (DF) and hydrotreated vegetable oil (HVO). As part of the experiment, the basic indicators of engine operation were also determined (torque, effective power, and fuel consumption) and selected parameters of the combustion process, such as the instantaneous pressure of the working medium in the combustion chamber, maximum pressures and temperatures in the combustion chamber, and the heat release rate (HRR), were calculated. The tests were carried out in accordance with the ESC test because the authors wanted to determine how the new generation HVO fuel, powering a modern combustion engine with a common rail fuel system, would perform in a stationary emission test. Based on the obtained research results, the authors concluded that HVO fuel can replace diesel fuel in diesel engines even without major modifications or changes in engine settings.

Study on the influencing factors of gas-liquid two-phase explosions of hybrid methane/isoprene on the basis of bush fires

To evaluate the explosion hazard of hybrid isoprene/biogas in a primary forest environment, a 20 L spherical explosion vessel combining with a colorimetric thermometry was used to study the explosion parameters, flame structures and temperature distributions of hybrid isoprene/methane at different methane content and initial temperatures. Furthermore, the relationships between the explosion gas products and explosibility of hybrid isoprene/methane were analyzed. Experimental results showed that when the mass concentration of isoprene was 272.4 g m−3, the explosion pressure, the pressure rising rate, and the average combustion temperature reached their peak values of 0.89 MPa, 63.9 MPa s−1 and 2216 K, respectively. When the mass concentration was fixed at 272.4 g m−3, the explosibility of hybrid isoprene/methane initially enhanced and then decreased with the increasing methane volume fraction, and got the maximum values at 5 vol% methane. It was worth noting that the explosibility of hybrid methane/isoprene weakened continuously as the initial temperature increased, and it exhibited a stronger explosion power at a lower temperature. The research results would be helpful for understanding the deflagration processes and mechanisms of bush fires under various conditions, providing scientific basis for the formulation of its prevention and control measures.

Hiding the evidence: Preliminary investigation of heat-induced alterations to pre-existing saw mark trauma

Dismemberment and subsequent burning are common methods employed in an attempt to conceal or destroy evidence. While kerf characteristics can be utilised to identify tool(s) used for dismemberment, further research is necessary to assess the effect of burning on these characteristics. In this study, a back (tenon) saw (13 teeth per inch) was used to manually inflict trauma on Ovis aries de-fleshed femur bones (n = 18). Three different cut marks (shallow false start, incomplete cut and complete transection) were made on the mid-shaft of each bone. Subsequently, the bones were burned for 20 minutes in a muffle furnace. Three burn temperatures were assessed: 400 °C, 600 °C and 800 °C. Saw mark characteristics of each cut type were assessed and compared pre- and post-burning. All pre-existing trauma was recognisable post-burning; however, metric and morphological alterations were apparent. An increase in kerf width was observed at 600 °C in false start lesions and 800 °C in incomplete cuts. Breakaway spur thickness decreased post-burning (at 400 °C and 800 °C) but length was not significantly affected. Mean inter-striation distance decreased post burning at all temperature groups. Saw marks were distinguishable from heat-related fractures across all temperature groups. One false start lesion was obliterated at 800 °C. Exit chipping, pull-out striae as well as striation regularity appeared to be more enhanced after heat exposure. These alterations indicate a temperature-dependent impact on these characteristics. Further research is necessary to assess the role of burn duration.

Theory-driven design of graphene schiff base iron nanocomplex as catalyst for composite propellant

New graphene Schiff base iron nanocomplexes (S-792-Fe, S-550-Fe, and S-590-Fe) were designed and fabricated based on investigations of reactions mechanisms of AP pyrolysis, structural analysis of new materials and simulation results of quantum mechanics to deal with the long-standing contradiction between safety and performance for composite propellent combustion catalyst. By taking traditional catalyst Catocene as the benchmark, the S-550-Fe nanocomplexes exhibited competitive catalytic performances, much better anti-migration properties and significantly reduced impact and electrostatic sensitivities. After adding S-550-Fe, the burning rate of propellant enhanced from 13.87 to 19.77 mm s−1 at 15 MPa, and the impact and electrostatic sensitivities are improved to 50.2 cm and 172.12 mJ, respectively. The excellent catalytic performance of S-550-Fe is closely related to its molecular structure, which is manifested by an increase in charge density and a decrease in NH3 oxidation energy barriers. The promotion effects of S-550-Fe on desorption and oxidation of NH3 from the surface of AP is conducive to the rapid and complete pyrolysis of AP, which is reflected in the improvement of combustion rate and temperature gradient. The theory-driven design mode of this work may provide new pathways to tune combustion behaviors of composite propellants from the view of molecular-level insights.