Ignition Performance Research Articles

Significantly different inhibition mechanisms of graphene oxide in laser-ignited combustion of micro and nano CL-20

Because of its high energy density, hexanitrohexaazaisowurtzitane(CL-20) has been widely used in propellants in place of conventional oxidizers. The adjustable burning rate of the CL-20 is a key factor in adapting the propellant to various environments. In this work, the effects of graphene oxide(GO) content on the thermal release, ignition and combustion characteristics of micro and nano CL-20 were thoroughly conducted based on the differential scanning calorimetry measurements (DSC), laser ignition, burning rate test and condensed combustion products collection. The results show GO has a positive effect on micro and nano CL-20 in ignition performance and a negative effect on combustion rate. Owing to the addition of GO, the original flameless combustion of CL-20 changes to flaming combustion. With increasing GO content, the burning rates of micro and nano CL-20 show completely different descending laws. Furthermore, the combustion mechanism of nano and micro CL-20/GO has been studied in detail. The burning rate of micro CL-20/GO is primarily determined by the condensed phase, and that of nano composite is controlled by both of the condensed and gas phases. This work provides a deeply insight into the influence mechanism of GO on the properties of nano and micro CL-20.

Experimental study on the characteristics of a novel aerodynamic wake width flameholder

In this study, a novel flameholder named aerodynamic wake width flameholder (AWF) was proposed. The AWF optimized the sidewall profile of conventional bluff body flameholders and widened the downstream recirculation zone through aerodynamic force, while maintaining the same trailing edge width as conventional flameholders. Consequently, the combustion properties were impacted. To investigate the flow field structure, flame stability limits, and flame evolution of the novel flameholder, an aerodynamic wake width evaporating flame holder (AWEF) was designed and compared with a normal evaporating flameholder (EF). Comparative analysis of the downstream flow field structure revealed that the AWEF exhibited a wider zero-velocity contour and a higher reflux rate. Furthermore, the AWEF demonstrated a larger velocity gradient near the trailing edge, indicating the presence of a thicker shear layer. Within the inlet Ma range of 0.1 to 0.17, the AWEF exhibited wider flame stability limits compared to the EF. The ignition fuel-air ratio (FAR) of the AWEF remained relatively constant within this range, suggesting that the novel flameholder could withstand the deterioration of ignition performance caused by an increase in the inlet Ma. Moreover, the AWEF achieved a larger flame projection area and flame width downstream compared to the EF. Finally, by combining the flow field characteristics and flame stability properties of the AWEF, the mechanisms underlying the changes in flame stability characteristics were analyzed. The results of this study can serve as valuable references for enhancing flame stability in current and future advanced augmentor systems.

Experimental study of the effect of structural differences in the composition of kerosene-like blended fuels on low-temperature autoignition in a constant volume combustion chamber

The cold start performance of compression ignition engines at high altitudes is expected to be improved by means of fuel design involving kerosene-like blended fuels. In this study, the autoignition characteristics of ten blended fuels with different chemical compositions and physical properties were investigated in a constant volume combustion chamber. Steady-state conditions in a low thermal atmosphere are considered at varying temperatures (723, 773, 823 K), pressures (2.2, 2.8, 4 MPa), injection pressures (40, 60, 80 MPa), and injection pulse widths (1.5, 2.5, 5 ms). The relative importance and relevance of the physical and chemical properties of the fuel to the ignition delay were evaluated based on characteristic parameters e.g. total ignition delay, physical delay, chemical delay, combustion delay, pressure and heat release rate evolution. It was found that adding ether-oxygenated component content to kerosene-like significantly shortened the ignition delay, followed by chain alkanes, naphthenes, and aromatics, in that order. The effect of oxidation chemistry changes on the ignition performance of fuels in low-temperature-pressure environments is more significant than physical properties. As the thermal atmosphere or fuel activity intensifies, the percentage of physical delay in the total ignition delay gradually exceeds that of chemical delay as the main part, and the variability in the ignition qualities of fuels with different physicochemical properties diminishes. There is a good linear correlation between ignition delay and cetane number (ranging from 44 to 60), density, viscosity, and recovery temperature, whilst the role of cetane number and density is more prominent.

Effects of using a novel fuel vaporizer on partially premixed charge compression ignition (PPCCI) engine emissions, performance, and combustion characteristics

Environmental concerns of toxic emissions and depleting of fossil fuel supplies due to their excessive usage as the main source of energy have raised interests in the creation of novel combustion modes that result in reduction of combustion temperatures and produce low emissions. In comparison to conventional diesel engines, the partially pre-mixed charged compression ignition (PPCCI) combustion strategy has demonstrated its ability to significantly reduce emissions carbon monoxide (CO), unburned hydrocarbon (HC), oxides of nitrogen (NOX), carbon dioxide (CO2) and smoke opacity. In order to compare the results with those of conventional engines, the current experimental work’s objective is to investigate the combustion, performance, and exhaust emissions characteristics of PPCCI engines. A single-cylinder, air-cooled, 4-stroke, direct-injection diesel engine that had been modified to run in PPCCI mode was used for the experiments. An external mixture formation technique with a fuel vaporizer is added to create the homogeneous mixture for PPCCI combustion. After being heated to the point of vaporization, liquid diesel fuel vapor was mixed with some fresh air and then the mixture directed to the intake manifold, where it was mixed with the remaining fresh air to create an external homogenous mixture that filled the combustion chamber. The tests were conducted at different premixed ratios of diesel fuel proportions of 15%, 20%, and 30% in the intake port. However, the fuel vaporizer chamber was kept at fixed temperature of 100 °C, 105 °C, 110 °C, 115 °C, and 120 °C. The PPCCI engine results were compared with the conventional engine data. Results from the PCCI technique at various premixed ratios indicate a certain decrement for HC, CO, NOX, and smoke emissions, rising in BTE “brake thermal efficiency”. At 30% premixed ratio of the fuel vapour inducted at 110 °C in PCCI mode give the best results as the brake thermal efficiency raised from 28.8% for CDC mode to 34.2% for PCCI mode at full load. Additionally, NOX emissions decreased from 615 PPM to 550 PPM, HC emission decreased to 30 PPM, CO emission decreased from 0.09% to 0.06% and a decrease in smoke opacity from 38% to 19.3%.

Metal‐Free Hybrid Energetic Composites Based on Donor–Acceptor π‐Conjugated Organic Energetic Catalysts with Enlightening the Laser Ignition Performance of Multi‐Scale Ammonium Perchlorate (Small 46/2023)

Metal‐Free Hybrid Energetic Composites Based on Donor–Acceptor π‐Conjugated Organic Energetic Catalysts with Enlightening the Laser Ignition Performance of Multi‐Scale Ammonium Perchlorate (Small 46/2023)

Investigation on jet controlled diffusion combustion (JCDC) mode applied on a marine large-bore two-stroke engine

Ships with large-bore marine engines are essential for international trade and transportation. However, a large number of fuel energy consumption and waste emissions are produced. Future lower fuel consumption and cleaner marine natural gas engines needs technological innovation. One approach is the use of a prechamber, providing high ignition energy. In this study, diesel injected into the prechamber and the prechamber jet controlled diffusion combustion (JCDC) mode was applied to a marine two-stroke natural gas/diesel engine. A three-dimensional simulation method was employed to optimize the combustion control parameters and compare the performance of JCDC mode with the traditional pilot controlled diffusion combustion mode (PCDC). The diesel compression ignition in the prechamber generated turbulent jet in the main chamber, which ignited the direct-injection natural gas. The key parameters influencing the JCDC mode, including the direct-injection interval and diesel energy percentage, were optimized in this study. A small direct-injection interval of 0.15°CA between diesel and natural gas was achieved, resulting in good ignition performance. By utilizing a 1.8% diesel energy percentage in the prechamber, a high indicated thermal efficiency (ITE) of 53.6% was obtained. Compared to the PCDC mode, the JCDC mode demonstrated a maximum reduction of approximately 1.4g/kWh in equivalent indicated specific fuel consumption (EISFC), indicating very large improved fuel economy for the marine two-stroke engine. Furthermore, the JCDC mode exhibited notable reductions of greenhouse gas in CO2 and unburned CH4 emissions, with a maximum decrease of 1.6% and 89%, respectively. The JCDC mode indicates a cleaner marine natural gas engine.

Experimental Studies on Thermal Oxidation and Laser Ignition Properties of Al-Mg-Li Powders.

Powder ramjets are a kind of vehicle propulsion system with high specific impulse and efficiency. They provide significant benefits in terms of extended propulsion and thrust adjustment. The pursuit of a highly reactive fuel appropriate for powder ramjets is likely to stimulate advancements in innovative propulsion systems, which are crucial for deep space exploration and long-term space missions. This work presents experimental studies on the thermal oxidation and laser ignition performance of aluminum-magnesium-lithium powders at atmospheric pressure. TG-DSC curves of powders in three heating rates were obtained. The ignition processes and ignition delay times were recorded by a CO2 laser ignition experiment system at a laser power of 10~60 W. The results show that at a lower heating rate of 10 K/min, the powder's thermal hysteresis is less, and the powder energy released in stage I is more concentrated. However, the degree of heat release concentration approached a similar level at heating rates of 30 K and 50 K. The ignition delay time decreased as the laser flux density increased. When the laser flux density exceeds 80 W/cm2, the effect of laser power on the ignition delay time decreases. At atmospheric pressure, the mathematical relationship between ignition delay time and laser flux density is given. Finally, the powder ignition processes at different laser powers are represented graphically.

Insights into the enhanced performance of ignition and self-sustained combustion of n-decane over Co3O4-based catalysts

Aiming to achieve efficient utilization of high-energy–density fuels in the promising portable power systems, self-sustained combustion of n-decane over Co3O4-based catalysts in a narrow quartz reactor was investigated. Chemiluminescence, gas chromatography and various physicochemical characterization methods were used in this study. The evidences suggest that Co3O4-based catalysts can significantly reduce the ignition temperature and broaden the flammability limits of n-decane. The heat release stored in the catalyst bed can help improve the flame stability, delay the flame extinction, and achieve auto-ignition without forced heating. Besides, great promotion of the catalytic performance of Co3O4 spinel is achieved by doping with 6 wt% PdO. PdO/Co3O4 catalysts exhibit higher activity and enhanced ability in effectual resistance toward deactivate than pure Co3O4. Furthermore, the coupling of heterogeneous and homogeneous reactions of n-decane has been analyzed. It can be revealed that both the adsorbed and gaseous OH* radicals play greatly different roles when using different catalysts. These findings promote the use of heavy hydrocarbon fuels for energy supply and contribute to designing efficient Co3O4-based catalysts rationally.

The combined effect of hydrogen enrichment and exhaust gas recirculation on the combustion stability, performance and emissions of CI engine energized by algae biodiesel

The scarcity of fossil fuels, the rising cost of liquid fuels, and the wide pollution footprint of conventional fuels all motivate scientists to seek out new approaches. This experimental study aims to explore the performance and emissions of compression ignition (CI) engines by introducing hydrogen into a biodiesel blend derived from algae. According to this study, the superior thermal properties of hydrogen associated with algal biodiesel have a significant impact on the performance and emissions of dual-fuel engines. The effect of hydrogen substitution rates of 10.4, 21.6, 32.4, 43.2, and 54 g per hour (g/h) on pure algae biodiesel was investigated. In comparison to diesel, the algae biodiesel reduces unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions by 4.1% and 8.82%, respectively, while nitrogen oxide (NOx) emissions increase by 18%. Diesel was found to have increased brake thermal efficiency (BTE) and decreased brake specific energy consumption (BSEC) compared to biodiesel. With the addition of pure biodiesel, the 43.2 g/h H2 substitution rate produces a maximum thermal efficiency of 1.92% and a 9.5% decrease in brake-specific energy consumption compared to diesel at maximum load. Compared to diesel, the emission attributes of UHC, CO, and smoke opacity decreased by about 45%, 48%, and 41%, respectively. However, NOx emissions increase by about 36% compared to diesel due to the higher flame temperature and carbon-free fuel of hydrogen and oxygenated biodiesel. The induction of 15% exhaust gas with B100 + 43.2 g/h H2 reduces NOx by about 31% in comparison to B100 + 43.2 g/h H2 without exhaust gas recirculation (EGR). This is primarily attributable to the high oxygen dilution and specific heat capacity of burned gases, which result in a decrease in peak cycle temperature. Compared to diesel, B100 + 43.2 g/h H2 increased the cylinder pressure and heat release rate by about 1.86 and 4.29%, respectively. As a result of its high energy density, hydrogen improves overall energy utilization and engine performance. Hydrogen's rapid flame speed and wide flammability range contribute to the efficient and complete combustion of the algae fueling the CI engine. As well as showing outstanding performance, dual fuel CI engines have the potential to significantly contribute to lowering emissions. Finally, it was determined that using algae biodiesel and exhaust gas recirculation with hydrogen substitution in diesel engines can significantly reduce emissions while increasing efficiency.

Performance evaluation of a diesel engine fueled with Chlorella Protothecoides microalgal biodiesel

The main objective of the current study is to determine the engine performance, combustion, and emission analysis of compression ignition engines fuelled with Chlorella Protothecoides microalgal biodiesel (CPMB). The biodiesel was derived from Chlorella Protothecoides microalgal oil (CPMO) through transesterification. Under the specified conditions, which included a methanol-to-oil molar ratio of 7.41 (vol/vol), a reaction time of 105.6 min, a reaction temperature of 65 °C, and a catalyst concentration of 1.024 (% wt/vol) and achieved a biodiesel yield of 98.1%. The fuel properties were determined using standard methods, revealing that the density and kinematic viscosity of CPMB were significantly higher than those of diesel. However, CPMB still exhibits satisfactory fuel properties that meet most biodiesel specifications. CPMB boasts a low cloud point (CP) and pour point (PP) of 0 and -3 °C, respectively, indicating its effective usability in cold climates. The oxidation stability of CPMB, determined by the modified Rancimat method, was found to be 4.6 h, satisfying ASTM specifications. The fuel tested in this study was 20% biodiesel with diesel, 100% biodiesel, and neat diesel. These fuels had been tested on a CI engine in which the engine speed and compression ratio were fixed at 1500 rpm and 18:1, respectively. Based on the results, it is found that the indicated thermal efficiency decreases up to 3.68% and 8.22% with B20 and B100 as compared to diesel. However, mechanical efficiency, volumetric efficiency, and indicated power were estimated to be higher at peak engine load conditions when correlated with neat diesel. Furthermore, the mean effective pressure for B20 and B100 was estimated to be decreasing while the mass fraction of fuel burnt and the rate of pressure rise increased compared to diesel at peak load conditions. For exhaust emission analysis, a significant reduction was recorded in CO and UHC emissions, while NOX emission increases at peak engine loads. From the above results, it is accomplished that the performance of B20 blends is nearly identical to diesel, and it can be recommended to be used in engines without any modification.

Performance and emission characteristics of a CI engine with post-treated plastic pyrolysis oil and diesel blend

Conversion of waste plastics into energy products is an effective waste management technique as they constitute a considerable portion of solid waste at present. In this study, distilled diesel fraction of Plastic Pyrolysis Oil (PPO) named Distilled Plastic Diesel (DPD) was hydrotreated named hydrotreated plastic diesel (HPD) and blended with commercial diesel fuel by 15:85 ratio (wt%), defined as HPD15, to experimentally investigate the performance and emission characteristics of a compression ignition (CI) engine. The experiment was done in 4-cylinder, 4-stroke diesel engine with an eddy current dynamometer testbed at full load (100 % engine load) and an engine speed of 1200–2400 rpm with 300 rpm intervals. The results are compared with neat diesel fuel data at the same operating conditions. This study found that HPD15 performed better or comparable with diesel fuel. Overall, the brake power (BP) and brake thermal efficiency (BTE) of HPD15 were higher than diesel fuel by a maximum of about 4.77 % and 3.77 %, respectively. Brake specific fuel consumption (BSFC) of HPD15 was lower at all operating speeds (by a maximum of about 4.66 %) and brake specific energy consumption (BSEC) was lower in most of the operating speeds (by a maximum of about 3.77 %). This study also revealed that CO2 at some operating speeds and NOx emission at all operating speeds for HPD15 are lower than diesel fuel. However, CO and unburnt hydrocarbon (UHC) emission are slightly higher for HPD15 than diesel at all speeds. Overall, HPD15 can be recommended as a suitable alternative for diesel fuel without any engine modification.

Effect of oleic acid on the stability and the combustion of nanoaluminium/JP-10 bi-phase system: Experimental and molecular dynamics studies

Aluminum-containing hydrocarbon fuels cannot fully release their energy due to the poor dispersion and easy agglomeration of aluminum nanoparticles (ANPs). To solve the issues, oleic acid (OA) was used to modify the surface of ANPs, and then Al@OA particles were incorporated into exo-tetrahydrodicyclopentadiene (JP-10) to form Al/JP-10 bi-phase system. Experimental and molecular simulation methods were used to analyze the stability, ignition, and combustion performance of the Al/JP-10 bi-phase system. The results show that at low temperatures, OA can improve the antioxidant and hydrophobic performance of Al@OA particles, which can effectively protect the ANPs from deep oxidation. At high temperatures, OA can accelerate the oxidative exothermic process of ANPs, and the Al@OA particles can shorten the ignition delay time of JP-10 droplets and intensify the combustion. Notably, when the ratio of Al and OA is 10:3 in the Al@OA particles, the Al/JP-10 droplet exhibits the shortest ignition delay.

Development of a Skeletal Mechanism of a Four-Component Diesel Surrogate Fuel Using the Decoupling Method.

Alkylcyclohexanes with a long alkyl chain account for more than 30% of diesel fuel but seldom used in the oxidation mechanism of diesel surrogate fuel due to the lack of a reduced skeletal mechanism. Hence, a four-component diesel surrogate fuel was developed with n-butylcyclohexane (NBCH) as the representative of alkylcyclohexanes with a long alkyl chain in real diesel. The surrogate fuel can reproduce the physicochemical characteristics of real diesel, especially the distillation range. The reduced mechanism of NBCH was developed, and the skeletal mechanism of the surrogate fuel was formulated including 80 species and 251 reactions based on the decoupling method. The mechanism was validated under a wide range of conditions with the experimental results of ignition delay time (IDT), laminar flame speed, and species concentrations of both pure components and diesel. The accuracy of the mechanism on the spray and ignition performance was further validated against the experimental data obtained in a constant volume combustion chamber system. The calculated results showed a satisfactory agreement, in which the maximum error of flame lift-off length is 7.82 mm and that of IDTs is 0.16 ms. It was proven that the mechanism is suitable to reproduce the physicochemical properties of diesel and further predict the diesel spray and ignition performance.

Methylcellulose as a non-bonding gelling agent for calcium chloride methanol fuel gels

Carbohydrate-based fuel gels find diverse applications across industries ranging from renewable energy and transportation to military and emergency preparedness. This study investigates the thermal properties, gel characteristics, combustion performance, micro-, and nano-scale structure of methylcellulose (MC) in methanol and the effect of calcium chloride (CaCl2) addition. The results show that MC exhibits viscoelastic phase separation due to the lower critical solution temperature, resulting in gelation at the 22 wt%. Thermogravimetric analysis reveals good thermal stability of MC in methanol, with a single decomposition stage. Adding CaCl2 modifies rheological behavior and enhances the thermal properties of the MC/methanol gel, with improved combustion and ignition performance due to the formation of CaCl2-methanolates. Small-angle X-ray scattering analysis indicates changes in nanoscale aggregates, correlation length, and fractal dimension with increasing CaCl2 content. This study provides valuable insights into the properties of MC-based fuel gels and their potential applications.

Effect of primary hole position and ignition position on the ignition performance of a reverse flow combustor

The purpose of this paper is to analyze the influence of the primary hole position and ignition position on the flow field and ignition performance of the reverse flow combustor. Igniters of two schemes are located on the side wall, and the other two are in the outer liner. The lower primary hole with the axial distance value of 29.2 and 24.7 mm are employed for each type of scheme. These four schemes are experimentally studied by particle image velocimeter (PIV) and high-speed camera. The differences of ignition performance between the four schemes are analyzed from the flow field structure and ignition process. The results show that the propagation mode of flame kernel will change with the change of ignition position. When the flame kernel forms in the central region of the combustor, both upper and lower recirculation vortices are ignited simultaneously, resulting in a shorter ignition time. However, when the flame kernel is formed near the outer liner, the upper recirculation vortex ignites first, and then the lower recirculation vortex is ignited, resulting in a relatively longer ignition time. Ignition performance is mainly determined by the flow velocity near the flame kernel. There is a negative correlation between ignition performance and the local flow velocity. Increasing the transverse flow velocity near the flame kernel, the ignition performance will decrease. The overall ignition time is significantly influenced by the propagation path of the flame kernel. In a reverse flow combustor, changes in the position of the primary hole result in two typical flow fields, the ignition time mainly depends on the distance between the flame kernel and the recirculation vortices.

Enhancing Performance and Emission Characteristics of Biodiesel-Operated Compression Ignition Engines through Low Heat Rejection Mode and Antioxidant Additives: A Review.

Depending on the heat content and compression ignition (CI) engine combustion, biodiesel is a viable substitute fuel. Biodiesel is an oxygenated, safe, sulfur-free, biodegradable, and renewable fuel. It may be utilized in CI engines in any combination with diesel fuel without requiring the engine to be significantly modified. Many research studies have been made with several biodiesels as diesel substitutes, including Pongamia pinnata, Jatropha curcas, Mangifera indica, and Madhuca longifolia. The topic of the current review is the potential of renewable fuels to outperform diesel fuel in terms of performance, combustion, and emission characteristics. In the present study, CI engines are fueled with biodiesels made from Man. indica, Mad. longifolia, and pongamia seed oil. Adopting low heat rejection (LHR) mode CI engines and adding an antioxidant agent in addition to the biodiesel blends may resolve the issue of these biodiesels' poorer performance and increased NO emission. Both these additions may provide positive approaches in both performance and emission.

Experimental Investigation of Compression Ignition Engine Combustion, Performance, and Emission Characteristics of Ternary Blends with Higher Alcohols (1-Heptanol and n-Octanol)

Concerns about the depletion of petroleum reserves and rising pollution led researchers to search for alternate and environmentally compatible fuels for compression ignition engines. As an excellent alternative fuel additive to biodiesel–diesel blends, higher alcohol exhibits outstanding fuel properties (such as high energy content and cetane number) and can operate in diesel engines without requiring engine changes. This study focuses on investigating the ternary blends comprising higher alcohols, namely 1-heptanol and n-octanol, in hybrid biodiesel (animal fat oil–rice bran oil–cottonseed oil) and diesel on compression ignition engine characteristics. The performance, combustion, and emissions of a diesel engine fuelled with mono (D100), binary (B20), and ternary fuel blends (B20H10, B20H20, B20O10, and B20O20) were analysed at a constant engine speed of 1500 rpm. The test fuels met the American Society for Testing and Materials standards for fuel properties and exhibited stable behaviour during testing. Experimental results showed that at 100% load, the least brake-specific fuel consumptions for diesel fuel, B20, B20H10, B20H20, B20O10, and B20O20 were 254.1 g/kWh, 302.14 g/kWh, 281.25 g/kWh, 310.94 g/kWh, 292.8 g/kWh, and 313.80 g/kWh, respectively. Meanwhile, the maximum brake thermal efficiency values were obtained as 38.65%, 37.01%, 37.76%, 36.84%, 37.12%, and 36.38%, respectively. At 100% load, the peak heat release rates for diesel, B20, B20H10, B20H20, B20O10, and B20O20 were found to be 64.65 J/deg, 59.07 J/deg, 62.34 J/deg, 56.12 J/deg, 57.95 J/deg, and 51.9 J/deg, respectively. The addition of 1-heptanol and n-octanol as oxygenated additives into the ternary blend resulted in decreased carbon monoxide and unburned hydrocarbon emissions while increasing carbon dioxide and nitrous oxide emissions compared to diesel fuel. Overall, the study concludes that ternary blends with 1-heptanol and n-octanol as additives improve performance and combustion behaviour and reduce exhaust emissions compared to binary blends.

Quality of moxa with different leaf-to-moxa ratios based on correlation analysis of thermogravimetric properties, cellulose content, and microscopic characteristics of non-secretory trichomes

The quality of moxa is a key factor affecting the efficacy of moxibustion. Traditional moxa grades are evaluated by the leaf-to-moxa ratio, but there is a lack of support from scientific data. Scanning electron microscopy(SEM), Image Pro Plus, Van Soest method, and stimultaneous thermal analysis(TGA/DSC) were used to characterize the scientific implication of the combustion differences between moxa with different leaf-to-moxa ratios(processed by crusher). The results showed that the median lengths from non-secretory trichomes(NSTs) of natural NSTs and moxa with leaf-to-moxa ratios of 3∶1, 5∶1, 10∶1, and 15∶1 were 542.46, 303.24, 291.18, 220.69, and 170.61 μm, respectively. The cellulose content of moxa increased significantly(P<0.05) with the increase in leaf-to-moxa ratio and the combustion parameters(T_i, t_i, D_i, C,-R_p,-R_v, S, D_b, and J_(total)) all showed an increasing trend. The correlation results showed that the burning properties of moxa(T_i,-R_v, t_i, and J_2) were significantly and positively correlated with cellulose content. NSTs with a length of 1-200 μm were significantly and positively correlated with J_2. NSTs with a length of 200-600 μm were significantly and positively correlated with J_1, T_(peak2), T_(peak1), and-R_v, and negatively correlated with J_(total), T_b, and t_b. As the leaf-to-moxa ratio increases, the NSTs in the moxa become shorter and the cellulose content increases, which is more conducive to ignition performance, heat release, and a milder, longer-lasting burn. The "NSTs-cellulose-TGA/DSC" quantitative evaluation method scientifically reveals the scientific connotation of the combustion of moxa with different leaf-to-moxa ratios and provides a scientific basis for the establishment of quality evaluation methods for moxa with different leaf-to-moxa ratios.

Molecular dynamic simulations of Ti-6Al and Fe-12Cr alloys for their heat transfer and oxygen transport behaviors

The heat transfer and oxygen transport behaviors of Ti-6Al and Fe-12Cr alloys directly affect their aeronautical material application. In order to investigate the flame retardant mechanism in atomic scale, molecular dynamic (MD) simulations were performed to study the heat transfer and oxygen transport performances of Ti-6Al and Fe-12Cr alloys in the linear and uniform heating treatment. Next, the ignition performances of Ti-6Al and Fe-12Cr alloys were further verified by the frictional ignition tests. Therefore, this is a multi-scale research with a novel combination of MD simulations and ignition tests. Those obtained results show that the heat is more concentrated at the heating edge of Ti-6Al alloy while at the same heating rate. This leads to the intensification of atomic motion at the heating edge, and reduces the structural thermal stability of Ti-6Al alloy’s heating edge. Therefore, the heat transfer performance of Fe-12Cr alloy at the same state is better than that of Ti-6Al alloy. When there is an oxide layer on the surface of these two alloys, Fe-12Cr alloy can inhibit the oxygen transfer more effectively than Ti-6Al alloy, and further improve its flame retardant property. In addition, the frictional ignition tests with Ti alloy rotor under the same airflow environment show that the critical airflow velocity of the Fe-12Cr alloy stator is about 114[Formula: see text]m/s higher than that of Ti-6Al-4V alloy stator at 384∘. Generally, according to MD simulations and frictional ignition tests, it could be concluded that the flame retardancy of Fe-12Cr alloy is higher than Ti-6Al alloy.

Metal Salts of 4-Chloro-3,5-dinitropyrazole for Promising Eco-Friendly Primary Colors Pyrotechnics.

The construction and design of pyrotechnics with superior performance is not only a task of great significance but also a tremendous challenge. In this regard, we present the syntheses of novel green primary colors pyrotechnics (red, green, and blue light-generating pyrotechnics) by employing 4-chloro-3,5-dinitropyrazole (CDNP) as a multifunctional raw material. CDNP contains a flame enhancer, oxygen-rich functional group, and nitrogen heterocyclic combustibles, which contribute to the high performance of the pyrotechnics. The characteristic elements (strontium, barium, and copper) that impart color to the flame are combined with the CDNP to synthesize the primary colors pyrotechnics by an "all-in-one" strategy. The structures of three energetic metal salts (EMS-1, EMS-2, and EMS-3) are completely characterized, and their thermal stability, sensitivity, ignition performance, and color purity are systematically evaluated. All EMSs show excellent thermal stability and low mechanical sensitivities (>330 °C, >40 J, >360 N). Moreover, the EMSs demonstrate successful ignition and combustion under laser conditions and roasting test conditions, producing bright characteristic flames. Chromaticity analysis reveals that the three EMSs possess good color purities of 91, 80, and 70%, respectively. Consequently, the three integrated pyrotechnics exhibit exceptional combustion properties, highlighting their potential for use in various pyrotechnic applications.