Burning Rate Research Articles

Reactivity Control of Oxidative CL-20@PVDF Composite Microspheres by Using Carbon Nanomaterials as Catalysts.

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is one of the high-energy oxidants, but has limited application due to its high sensitivity. In this work, polyvinylidene fluoride (PVDF) was used as a co-oxidizer, which is expected to increase the safety of CL-20. One kind of novel graphene-based carbohydrazide complex (GCCo and GCNi) was employed to modify the properties of dual-oxidant CL-20@PVDF composites by the spray drying method and compared with traditional nanocarbon materials (CNTs and GO). The properties of these composites were investigated using the TGA/DSC technique and impact test. The results show that GCCo and GCNi could increase the activation energy (Ea) of CL-20@PVDF composites, and change the physical model of CL-20@PVDF, which followed the random chain scission model and then the first-order reaction model. In addition, these nanocarbon materials could reduce the impact sensitivity of CL-20@PVDF by their unique structure. Besides that, a dual-oxidant CL-20@PVDF system was used to improve the combustion property of Boron. GCCo and GCNi with the synergetic effect could increase the flame temperature and control the burn rate of CL-20@PVDF@B compared with CNTs and GO. The energetic nanocarbon catalyst-modified oxidant provides a facile method for stabilizing high-energy but sensitive materials to broaden their application.

Construction of nanoflowers combustion catalyst NiO@g-C3N4 for improving thermal decomposition performance of AP

Thermal decomposition of ammonium perchlorate (AP) typically requires high temperatures and activation energy, but the introduction of combustion catalysts will improve its thermal decomposition performance. Therefore, it is crucial to rationally design combustion catalysts for enhancing the thermal decomposition performance of AP. Herein, 3D NiO nanoflowers@2D graphite-phase carbon nitride (g-C3N4) nanosheets (NiO@x%CN, x = 1, 3, 5, 7, 9) composite catalysts were constructed by solvothermal and calcination methods, and characterized by a series of analyses. NiO@5%CN displayed the best ability to catalyze the thermal decomposition of AP, which reduced the high decomposition temperature of AP by 113.8 °C and the activation energy by 21.67 kJ mol−1. The combustion rate of NiO@5%CN-CSP has increased by 118 % compared to that of composite solid propellants. This work provides a new insight for the design of NiO-based high-efficiency combustion catalysts.

Role of Surface Tension on Heat Feedback and Power from Energetic Composites.

Heat feedback to the unburned reaction interface is an important controlling factor of the velocity of the reaction front and power delivery. In this paper, we investigate the effect of agglomerate surface tension and its relationship to surface residence time and heat feedback on the combustion characteristics by Si addition to an Al/KClO4 composite. Macroscopic imaging demonstrates a significant increase in burn rate with the addition of Si despite the fact that Si/KClO4 has a slightly lower energy density than Al/KClO4. Microscopic imaging coupled with three-color pyrometry reveals that molten liquid forms and evolves into spherical droplets on the burning surface, which are subsequently ejected from the surface. We find that the addition of Si results in a small increase in droplet size and a negligible impact on droplet temperature. However, the droplet formation rate on the surface is slower, leading to a significantly longer surface residence time. This leads to enhanced conductive heat feedback to the unburnt materials, thereby increasing the burn rate and energy release rate. We attribute the decreased droplet growth rate to the lowered surface tension of the liquid mixture with Si addition. This study highlights the crucial role of agglomerate physical property (e.g., surface tension) in influencing the combustion behavior of energetic composites.

Experimental and numerical investigation on oscillatory combustion characteristics of an integrated flameholder

Integrated flameholders are widely used in advanced afterburner. Oscillatory combustion can be easily caused by the complex flow field and non-uniform fuel distribution in advanced afterburner with integrated flameholders. Therefore, the oscillatory combustion characteristics under uniform and non-uniform fuel distribution downstream of integrated flameholder is investigated by using an experimental method with numerical simulation. The results show that oscillatory combustion is more likely to occur under the condition of non-uniform fuel distribution. When oscillatory combustion occurs, the main frequency is approximately 33.99 Hz and the flame variations can be divided into three phases: re-ignition phase, instability pre-transmission phase and extinction phase. Furthermore, three combustion states are observed at equivalence ratio Φ varied between 0.2 and 0.85: steady combustion, quasi-periodic oscillatory combustion and limit-cycle oscillatory combustion. Limit-cycle oscillatory combustion exhibits a relatively simple proper orthogonal decomposition structure and a longer axial motion wavelength than quasi-periodic oscillatory combustion. Notably, during oscillatory combustion, the pressure and heat release rate pulsations are roughly in the same frequency and phase, which shows that the oscillatory combustion is mainly caused by thermoacoustic interaction. These results provide guidance for further investigations of oscillatory combustion in advanced afterburner with integrated flameholders and development measures for its suppression.

Stable aluminum-lithium alloy fuels for solid propellants by facile surface modifying

As a highly reactive metal fuel, aluminum–lithium (Al-Li) alloy is an ideal candidate for replacing Al powders in solid propellants. However, the Li solid solution and AlLi compounds on the surface of Al-Li alloy powders display high reactivity, which can react with a large number of organic and inorganic reagents. Thus, the incompatibility of Al-Li alloy with other components of propellants makes it difficult to be further applied in propellants. In this study, surface-modified Al-Li alloy powders (Li content of 5 wt%) with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (FAS17) were prepared by a facile self-assembly method, which made the alloy powders super-hydrophobic. The results of SEM, XPS and FIB-TEM show that the surface of Al-Li alloy powder is well-coated by an evenly distributed FAS17 layer. Due to the fluoroalkyl on the surface of the powders, the water contact angle increased by 91°and the intensity of the reaction between alloy powders and water is significantly reduced, which results in improved compatibility with other components of propellants.Meanwhile, the propellant grain of surface-modified powders had fewer defects than the sample before coating, and showed original excellent combustion performance. The average combustion pressure and pressurization rate increased by ∼114 kPa and ∼8613 kPa/s, and the steady burning rate increased by 0.24 mm/s. Therefore, the surface-modified Al-Li alloy powders with FAS17 are expected to be an attractive candidate as a highly active and stable fuel in solid propellants.

Understanding the role of methanol as a blended fuel on combustion behavior for rotary engine operations

Methanol, being one of the most promising carbon-neutral fuels, has the potential to enhance the fuel mixture homogeneity of gasoline rotary engines, thereby improving engine performance. This study, based on computational fluid dynamics model, investigates the in-cylinder flow, combustion, and emission characteristics under various methanol blending ratios, ignition timings, and equivalence ratios. At the methanol energy blending ratio of 10 %, a more extensive and efficient operating range is observed across different ignition timings and equivalence ratios, attributed to the higher diffusion and combustion rates. An increase in in-cylinder temperature enhances the complete conversion of HC. However, higher proportions of methanol are disadvantageous for the combustion process due to methanol's lower heat value and higher latent heat of vaporization. Thus, the optimal ignition timing was determined to be 30°EA BTDC. At this optimal ignition timing, the cylinder shows higher average turbulent kinetic energy and radical content compared to the ignition timing at 50° EA BTDC. Specifically, the concentrations of OH, H, and O free radicals increase by 12.40 %, 14.77 %, and 13.91 % respectively, leading to more complete initial flame kernel expansion. It is notable that emissions of CO, HC, and NOx are all reduced. The study further explores the influence of the equivalence ratio on the combustion process. At an equivalence ratio of 0.9, there is an earlier peak in the maximum cylinder pressure rise rate and the highest generation of O and OH, with a shorter main combustion period and concentrated heat release. This achieves economically viable operation for rotary engines, indicating a 2.122 % improvement in thermal efficiency and a reduction in fuel consumption to 375.537 g kW−1 h−1.

Effect on polytropic index, performance and emission of diesel engine using hydrogen as gaseous fuel with additive di-tert butyl peroxide

Diesel engines are commonly used due to its higher reliability and better fuel conversion efficiency. However, it produces exhaust emissions like carbon dioxide (CO2) and particulate matter (PM). Hydrogen gas is regarded as a clean fuel as it is free from carbon. The addition of hydrogen fuel enhances the burning rates and extends the flammability limits of fossil fuels, and therefore has the potential of reduced exhaust emission in diesel engines operating on dual fuel mode. This paper has investigated the effect of hydrogen addition to the performance and emissions of a single-cylinder diesel engine, working in dual fuel mode with additive di-tert butyl peroxide (DTBP). About 25% hydrogen was introduced into the cylinder on a mass basis via the engine intake manifold with the addition of additive di-tert butyl peroxide up to 5% in diesel fuel. In this experimental study, mean gas temperature, indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP), polytropic index, and exhaust emissions were studied at medium (53%) and high (69%) load conditions. The indicated mean effective and brake mean effective pressure was 9.79 bar with a 3% addition of additive and 4.15 bar with the 5% addition of additive as compared with 8.71 bar and 4.11 bar diesel fuel operation. 16% hydrogen addition with 1% di-tert butyl peroxide, IMEP, and BMEP are 10.92 bar, and 4.14 bar respectively.

Properties and combustion characteristics of bioslurry fuels from agricultural waste pyrolysis

ABSTRACT The current research investigates the combustion characteristics of bioslurry fuel derived from the products of agricultural waste pyrolysis. The bioslurry fuel was prepared by mixing biochar and pyrolysis oil. The combustion characteristics of a suspended single droplet of the bioslurry were analysed. The results indicate that an increase in pyrolysis temperature (400–600°C) lead to higher concentrations of fixed carbon (56–60%), increased ash content (16–18%), and higher calorific values (25–32 MJkg−1). As the pyrolysis temperature rises, the biochar surface becomes more porous, lower volatile matter content and particle size. As biochar content increases, the bioslurry’s density, viscosity, and caloric value increase but stability index decreases. Higher biochar content in the bioslurry increases the ignition delay and burnout time while reducing the burning rate. The bioslurry fuel contained 30% biochar achieved a calorific value of 28 MJkg−1 and a viscosity of 600 cP, comparative to conventional fossil fuels. Highlights Up to 30% BC can be added to pyrolysis oil to produce SF. Pyrolysis temperature increased FC, ash, and calorific value of biochar. Biochar surface appears more porous with increasing pyrolysis temperature. Biochar content affects bioslurry combustion characteristics.

Effect of the contact load and rotation speed on the formation of rolling current-carrying arc and the corresponding material damage

The current-carrying arc is a critical factor that affects the electrical contact performance and material damage of contact pairs. In this study, a copper disk–copper disk pair was used to simulate the rolling electrical joint in a conductive rotating joint. Under operating conditions with a current of 2 A, rotation speeds from 4 to 600 r/min, and loads from 40 to 180 N, the dynamic behavior of the current-carrying arc and the surface damage mechanism were investigated. The movement characteristics of the arc at the friction interface were observed, and the arc generation difficulty and intensity were statistically analyzed based on the arc burning rate and arc energy. With increasing load and rotation speed, the generation of current-carrying tribological arcs became easier, and both the arc burning rate and arc energy increased. After the arc was generated, the arc root position was randomly distributed at the contact interface, exhibiting dynamic phenomena such as splitting and merging. Following the generation of the arc, the dominant damage mechanism at the current-carrying friction interface transitioned from mechanical damage to electrical damage. The manifestations of electrical damage included burning, oxidation, and roughening, with the degree of electrical damage positively correlated with the arc burning rate and arc energy. Surface oxidation could reduce the adhesion between metal contact pairs, contributing to a decrease in the current-carrying friction coefficient. Simultaneously, the film resistance caused by oxidation and the contraction resistance caused by roughening could lead to an increase in the average contact resistance.

Optimizing calliandra (Calliandra calothyrsus) biomass pellets: Impact of particle size and bark composition

Calliandra biomass pellets offer a promising alternative energy source to replace fossil fuels. Typically, these pellets are produced by directly processing the stem and bark of the calliandra (Calliandra calothyrsus) plant without separation, aiming for manufacturing efficiency. This study investigated the quality differences between calliandra biomass pellets with and without bark and varying particle sizes. Particle sizes used were 20 mesh, 40 mesh, and 60 mesh. The pellets were made using a 12 mm diameter biomass pellet mold and a manual hydraulic press with a pressure of 3 tons. Characterization involved assessing proximate analysis, calorific value, physical and mechanical properties, and Fourier Transform Infrared analysis. The test results were compared with biomass pellet standards from Indonesia, Japan, Korea, and Germany. Results indicate that bark affects several properties, with higher ash content observed in pellets with bark due to the higher mineral content in bark. Volatile matter decreases with finer particle size, influencing combustion rate. Moisture content is higher in pellets with bark, impacting combustion efficiency and smoke production. Fixed carbon values are influenced by moisture and volatile matter content. Calorific values are generally higher in pellets without bark and smaller particle sizes. Density and compressive strength increase with decreasing particle size. FTIR analysis reveals differences in functional groups between pellets with and without bark, indicating variations in chemical composition. Overall, this research provides insight into the potential of calliandra biomass pellets with bark and without bark along with particle size as a renewable energy source.

Lucky strike: testing the utility of manganese dioxide powder in Neandertal percussive fire making

Late Middle Palaeolithic Neandertals in France are known to have engaged in the collection and grinding of black minerals rich in manganese dioxide (MnO2), generally presumed for symbolic use as powdered pigments. However, lab-based experiments conducted by Heyes and colleagues (Sci Rep 6: 22159, 2016) have shown that the addition of powdered MnO2 to wood turnings both reduces the temperature required for combustion by ca. 80–180 °C and significantly increases the rate of combustion. This special pyrotechnic property of powdered MnO2 may have been observed and leveraged by Neandertals to aid in fire making—a technology known to Neandertals in this region by at least 50,000 years ago. To test this idea, a series of actualistic fire-making experiments were performed to determine the practical applicability of MnO2 as a tinder-enhancing additive. The flint-and-pyrite percussive fire-making method was employed to produce sparks that were directed onto eight different types of tinder common to temperate Northwest Europe to determine if and to what degree the addition of MnO2 powder improved their ability to capture sparks that then propagate into glowing embers. The results show that MnO2 does indeed considerably improve the ignition efficiency of tinder material over untreated tinder, both in terms of the point of first ignition and the total number of ignitions achieved. It was observed, however, that the incidental addition of pyrite dust onto a tinder over the course of an experiment also appeared to improve its ability to capture sparks. Supplemental experiments using tinder pre-mixed with powdered pyrite confirmed this hypothesis, suggesting pyrite powder similarly expedites fire production. While this finding may raise questions regarding the need for collecting MnO2 for this purpose, its potential utility may lie in (1) its relative softness compared to pyrite, making it much easier to grind or scrape into powder, and (2) the greater potential for MnO2-bearing deposits to yield larger quantities of usable raw material compared to pyrite-bearing outcrops, making it relatively more abundant in some areas. Thus, when available, it is clear that adding MnO2 to tinder would have noticeably reduced the time and energy required to produce fire, making it a potentially novel Neandertal innovation complementary to the fire-making process.

Preparation and Characterization of Paving Blocks from Polyethylene-Based Plastic Waste and Natural Fibre

The current methods of managing plastic waste especially in developing countries have become an issue of environmental and public health concern globally. This has led environmentalists and scientists to work on finding day-to-day activities that can help to reduce the plastic waste disposal problem. Recycling and reuse of plastic waste into construction materials is a valid way to reduce the effect of this improper disposal of plastic waste. This will help to reduce the negative impact of the high cost of cement in the construction industry. In this research, polyethylene waste (table water sachet) was used as a replacement for cement in the construction of paving blocks. The sample with a 1:4 mixing ratio was found to have the highest compressive strength among the different mix ratio examined. Paving blocks were then produced with this mixing ratio from plastic-aggregates and plastic-aggregate-fibre and compared with the standard cement-aggregate paving blocks for their compressive and tensile strengths, water absorption, thickness swelling, density, and thermal properties (thermogravimetric analysis (TGA) and horizontal burning rate). Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) was also conducted on the paving blocks to determine the distribution of the particles of the blocks, the compatibility of the matrix, and their elemental composition. The results of the compressive strength test showed 18.1667 Nmm<sup>-2</sup> for plastic-aggregate block, though lower when compared with the cement-aggregate block with a compressive strength of 21.6667 Nmm<sup>-2</sup>. The plastic-aggregate block has the least water absorption value among the three samples. The 0.1350% and 1.8861% water absorption values obtained for the plastic-aggregate and plastic-aggregate-fibre bricks respectively showed an impressive water absorption which falls within the maximum of 5% water absorption for quality paving blocks. The plastic-aggregate and plastic-aggregate-fibre both also recorded lower density when compared with the cement-aggregate block, which gives them a logistic advantage over the cement-aggregate block in the case of transporting them from one location to another. The blocks were found to be stable at low temperatures. The SEM images of the plastic-aggregate and plastic-fibre-aggregate paving blocks clearly showed a consistent dispersion of the plastic waste particles within the aggregate matrix over that of the cement-aggregate paving block. Therefore, plastic-aggregate brick can be recommended for use as paving bricks for low-traffic roads, walkways, parks, and gardens, although there is need to carry out further studies on other material properties of the plastic-based paving block.

Enhancing combustion performance of solid propellants using synergistic effect of energetic metal–organic framework with cage-like [Bi6(µ3-O)3(µ3-OH)5] clusters and copper-iron hetero-metallic compound

This study explores the potential of energetic metal–organic frameworks (E-MOFs) to enhance the combustion performance of solid propellants. A {[Bi6O3(tza)5(NO3)2(OH)5]·H2O}n (Bi-MOF) incorporating the energetic ligand tetrazole-1-acetic acid (Htza) was synthesized and evaluated for structural characteristics and properties. The catalytic thermal decomposition of cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX) by mixed systems was investigated. These systems consisted of Bi-MOF and copper-iron hetero-metallic compound ({[CuFe3O(tza)6(H2O)3]·Cl·(NO3)2·4H2O}n, CuFe-MOF), previously reported by our group in different ratios. The effect of the mixed system with the highest synergy index on the combustion performance of composite modified double-base propellant (RDX-CMDB) and nitrate ester plasticized polyether propellant (HMX-NEPE) was investigated. The impact of varying carbon black (CB) contents on the catalytic performance of the mixed system was also examined. The results showed that Bi-MOF exhibits good thermal stability (Tdec = 226.9 °C) and insensitivity (IS>40 J, FS>360 J). The mixed system, comprising Bi-MOF and CuFe-MOF in a 2:1 ratio (M2), exhibited the highest synergistic indices (3.35 and 3.24) on thermal decomposition for RDX and HMX. RDX-CMDB and HMX-NEPE propellant formulations containing M2 and a small amount of CB exhibited significant improvements in combustion performance. RDX-CMDB propellant exhibited up to an 80.6 % increase in burning rate and up to a 59.6 % reduction in pressure index. The pressure indices of NEPE without and with aluminum were reduced from 0.65 and 0.50 to 0.38 and 0.40, respectively (10–20 MPa, 1–20 MPa). These findings highlight the promise of the mixed system, formed by Bi-MOF and CuFe-MOF, as a potential combustion catalyst for RDX-CMDB and HMX-NEPE propellants.

Self-Propagating High Temperature Synthesis of Composite Material Based on Zirconium and Chromum Oxide

Ceramic composite materials based on stabilized zirconium oxide were obtained by self-propagating high-temperature synthesis. Yttrium oxide was used as a stabilizing additive. The work studied the effect of the content of yttrium oxide additive on the temperature and combustion rate of the materials studied. Also, based on the results of X-ray phase analysis and scanning electron microscopy, the effect of yttrium oxide on the phase composition and microstructure of the synthesized materials was studied.

Enhanced catalytic influence of carbon-supported Ti/Co bimetallic oxide nanocomposites on combustion of AP/HTPB propellants

Development and application of solid rockets have put forward new requirements for the combustion performance of AP/HTPB propellants. Herein, carbon-supported Ti/Co bimetallic oxide (MTiCo) nanocomposites with carbon skeleton and porous structure were proposed to use as catalysts for improving the combustion performance of AP/HTPB propellants. For AP decomposition, MTiCo-2 (2.0 wt%) reduced the AP HD temperature by 93.1 °C and enhanced heat release by about 356.3 %. Simultaneously, MTiCo-2 (2.0 wt%) significantly decreased Ea of AP HD stage by 51.4 %. MTiCo-2 (2.0 wt%) also reduced the ignition delay of AP/HTPB propellant by 78.3 % and enhanced combustion rate by 192.0 %. The synergistic effect of catalysis and combustion support of MTiCo-2 provided by the structure of carbon-supported Ti/Co bimetallic oxide was the main mechanism for improving the combustion performance of AP/HTPB propellants.

Quantitative three-dimensional reconstruction of cellular flame area for spherical hydrogen-air flames

The cellular flame area continues to increase with the development of cells on the spherical flame surface, which will greatly promote the flame burning rate and propagation speed. This work mainly focuses on a new three-dimensional (3D) reconstruction method of the cellular structure on the flame surface, attempting to quantitatively characterize the real flame area. Initially, the visualization investigation of hydrogen-air premixed spherical flames within a constant volume vessel was conducted using the Schlieren optical technique under room temperature and atmospheric pressure conditions. In parallel, the Cellpose 2.0 graphical user interface was used for the preliminary training of the cell segmentation model. Subsequently, this pre-trained model was applied in the image post-processing, enabling the quantitative characteristics extraction of the cellular structure, such as the cells number, area, and the flame radius, etc. Additionally, a concept of peak height h on the flame profile was proposed to characterize the fluctuation degree of flame profile. A new flame equivalent radius ru was defined by the average value of valid distance from flame centroid to flame profile pixel by pixel. Based on the comparison of cell equivalent radius r and average peak height h¯, an innovative 3D reconstruction concept was proposed for the quantitative characterization of flame area. Finally, cellularity factor ξ was introduced to evaluate the cellularization degree on spherical flames surface. Results show that the appearance of secondary cracks marks the formal onset of flame cellularization, accompanied by an increase in the h¯. In the later stages of flame development, cellularization will eventually tend to a stable value of about 0.4, indicating the occurrence of “saturated state”. After 3D reconstruction, the average cell area stable at around 26 mm2 in this stage. The results of this study provide data support for the construction of combustion models in the field of premixed hydrogen-air combustion.

A Comparison Between Conventional and MILD Combustion Processes of Turbulent Stratified Mixtures

ABSTRACT The relative enhancements of volume-integrated burning rate and flame surface area under turbulence and heat release rate contributions due to different combustion and flame propagation modes have been compared between conventional and Moderate or Intense Low Oxygen Dilution (MILD) combustion of stratified mixtures (for a global mean equivalence ratio of 0.8) for the first time using three-dimensional Direct Numerical Simulation (DNS) data. The burning rate enhancement under turbulence is found to be comparable to the enhancement of flame surface area for the conventional stratified flames considered here, whereas the burning rate enhancement is found to be considerably greater than flame area augmentation in the MILD cases analyzed here. It has been found that almost all the heat release rate arises due to the lean-premixed mode of combustion for the conventional stratified flame cases considered here. In contrast, the lean premixed mode of combustion accounts for about 50% of the total heat release rate for the MILD cases where rich-premixed and non-premixed modes of combustion contribute significantly to the overall heat release rate. Under the conditions analyzed here, more than 75% of heat release rate arises from the propagation-dominated regions for both MILD combustion and stratified flame cases, but the trend is stronger in the conventional stratified mixture combustion. More than 80% of heat release rate in the globally lean conventional stratified flame cases considered here originates from back-supported flame propagation, whereas both front and back-supported flame propagation modes have comparable contributions to heat release in the MILD combustion cases. The non-premixed mode of combustion has been found to play a more important role in the MILD combustion cases than in the case of conventional stratified flames. This implies that the closures, which work reasonably well for MILD combustion of homogeneous mixtures, may not be sufficient for modeling of MILD combustion of stratified/inhomogeneous mixtures.

Experimental observation of crack formation on surface of charring timber

Crack formation on the charring surface of burning wood is an important factor increasing the burning rate by offering a passage for heat and oxygen, but it remains a poorly understood process. This work considers crack formation on pyrolyzing Norway spruce, Scots pine and birch timbers. Timber specimens of different sizes were tested under various radiative heat fluxes in nitrogen atmosphere. The cracking process was followed with an infrared camera mounted above the specimen. The obtained recordings were used to determine the formation times and lengths of cracks and to estimate the validity of an existing thermomechanical model for crack formation. The results show that the crack formation time has no significant dependence on the specimen geometry. Further, the inverse of the square root of crack formation time follows grows linearly with external heat flux, which is a similar dependence as with time for ignition, according to the thermal model of ignition. The analytical model predictions were of correct order of magnitude, but not consistently accurate at all experimental conditions. This could be accounted for the simplifying assumptions within the analytical model, and therefore creating a more detailed three-dimensional numerical model for crack formation is suggested as future research.

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.

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.