Ignition Mechanism Research Articles

Research on the ignition mechanism and structural optimization of turbulent jet pre-chamber in GDI engines

Turbulent jet ignition has been widely studied, but it is mainly focused on gas engines, the igniting mechanisms of pre-chamber (PC) on GDI engines and the contributions of heat and radicals of the jet in inhomogeneous charge still remain to be clarified. Thus, 3-D simulations with comprehensive spray mixing process were performed under variable structural parameters. The decoupling results of thermal and chemical effects show that the influence of jet temperature on the heat release rate (HRR) inside main chamber (MC) is greater than that of free radicals. The mechanism of hot jet ignition containing free radicals in MC is flame propagation without ignition delay. However, compared to jet temperature, the free radicals in the jet have less effects on HRR in MC after the ignition. The nozzle diameter significantly affects fuel entry into the PC, influencing the pressure difference between PC and MC, and thus the jet velocity and duration. The optimal diameter in this study is 1.0 mm, and the jet duration is prolonged for too small or too large diameters. The nozzle angle is constrained by combustion chamber geometry, with the optimal angle being 140° to avoid jet impingement on cylinder head or piston.

Spray combustion characteristics and soot formation potential of Nano-Al2O3 diesel at low ambient temperatures

Nanoparticle additives have the potential to enhance combustion efficiency and reduce emissions in liquid combustion processes. This study thoroughly investigates the spray evaporation, ignition, and combustion characteristics of nanoparticle/fuel blends, especially under challenging environmental conditions, to improve combustion efficiency and reduce emissions. Employing diffused background illumination, shadowgraph, Mie scattering, high-speed natural luminosity, and two-color method, the spray combustion dynamics of thermally stable nano-Al2O3/diesel (NAD) blends were examined within a constant volume combustion chamber. Diesel, a prevalent primary or auxiliary fuel, represents other highly volatile renewable fuels, while Al2O3, a significant component in combustion fly ash, is noted for its specific catalytic properties and ability to re-burn, eliminating organic toxic elements. The results indicated that NAD blends exhibit a faster evolution rate for both liquid and vapor sprays compared to pure diesel, attributed to the increased kinetic energy of breakup droplets. Under most experimental conditions, incorporation of nano-Al2O3 slightly reduced the ignition delay time due to enhanced heat transfer. Notably, nano-Al2O3 altered the ignition mechanism of the diesel spray, transitioning it from partially premixed to diffusion combustion and relocating the ignition point nearer to the injector. The combustion flame of NAD blends demonstrated increased luminosity, a shorter flame lift-off length, and variations in start-of-injection and total-injection-nozzle-lift-off. However, due to a high equivalence ratio mixture between the liquid phase spray and combustion region, the soot concentration in NAD blends was higher than that in diesel. Additionally, the elevated flame temperature in NAD blends significantly increased the soot concentration. Overall, nano-Al2O3 markedly enhances diesel combustion, especially in low ambient temperatures, suggesting its impressive potential for the high-efficiency and low-emission utilization of renewable fuels or the combustion of recycled waste solvents.

Research on the underground ignition mechanism of ignition fuel and ground simulation experiments

Abstract In the increasingly severe environment of the “dual carbon” situation and the urgent objective demand for national energy transformation and upgrading, the development and use of clean energy have become a new research field and direction. Underground coal gasification technology (UCG) is a clean coal technology that completely bypasses the traditional coal combustion process by converting coal underground into gas and then classifying and recycling it. This method removes sulfur before fuel combustion Nitrogen compounds and particles make it clean like natural gas. The most commonly used ignition method in this technology is chemical ignition. A certain proportion of ignition fuel and main fuel is injected into the underground through pipelines, and then combustion supporting gas is introduced to cause a chemical reaction and generate an open flame to ignite the coal. However, due to the complex internal environment of the pipeline, uneven bending of the pipeline column, and the length of the pipeline exceeding one kilometer, the concentration threshold of the ignition fuel when it reaches the underground igniter cannot be accurately controlled, resulting in ignition failure. In response to the above difficulties, this article has conducted research on the ignition mechanism of ignition fuel, and developed a dedicated ground simulation test bench to conduct ground simulation experiments. The research has strong support for the on-site pilot testing and engineering services of underground coal gasification technology.

Ignition performance and mechanism of Ti/CuFe2O4 composites with high microwave sensitivity

The microwave ignition holds potential in the ignition of weapons due to its simple structure, non-contact property, and simultaneous ignitions of large area. However, the long ignition delay time of the current ignition agents cannot meet the microwave weaponry advancements. To address the issues, a microwave sensitive oxide-CuFe2O4 (CUFO) which was firstly discovered to be easily ignited by microwaves compared many ferrites, was coupled with Ti nanoparticles (n-Ti) to form Ti/CUFO microwave ignition agents by electrostatic spray granulation. The characterization of microwave ignition, volumetric combustion, burning rate and DSC were used to determine its ignition delay time and the energy release properties. It indicates that the microwave sensitivity, maximum peak pressure and pressure pressurization rate of Ti/CUFO first increases and then decreases with the promoting content of n-Ti. The Ti/CUFO at Φ = 3.5 exhibits the lowest ignition delay time by 79.24 ms compared to the 98.7 ms of n-Ti, meanwhile, its maximum peak pressure and pressurization rate reach the highest by 338.54 kPa and 8.57 kPa/ms, respectively. The DSC results indicate that Ti/CUFO exhibits much lower reaction peak temperature by 320–335 °C compared to 488 °C of n-Ti, which suggests Ti-CUFO reaction maybe much easier be activated. The dielectric loss of n-Ti and CUFO under strong electric field transfer the energy of microwaves to heat, reaching to its reaction temperature. The XPS and XRD results of CUFO after microwave radiation disclosing the crystal transition, formation of divalent iron and oxygen vacancies, as well as the released bright light under microwave radiation, suggest the thermal breakdown mechanism of CUFO. When Ti/CUFO exposes into microwaves, CUFO generates oxygen vacancies due to heat loss and n-Ti is dielectric heated, followed by the generated oxygen reacting with n-Ti, improving the combustion performance of n-Ti. This result provides new insight for the designing of microwave ignition.

Analysis of the Role of Lightning Activity in Triggering Forest Fires in Nepal

Forest fires have emerged as a significant and pressing issue in Nepal, jeopardizing its natural ecosystems, biodiversity, and communities. While human activities have been traditionally linked to these fires, this study explores the potential impact of lightning strikes, a natural factor that could contribute significantly to the problem. Using data from Vaisala's Global Lightning Dataset (GLD 360) and the Moderate Resolution Imaging Spectroradiometer (MODIS) dataset, we investigate the relationship between lightning strikes and forest fires over the five years’ period from 2015 to 2019. Advanced tools like ARC GIS and Python are employed for analysis. Preliminary findings indicate a noteworthy correlation, particularly during the pre-monsoon season. This investigation shows an interesting fact that positive lightning strokes are more likely to initiate forest fire as compared to their negative counter parts. This research offers a fresh perspective on lightning-induced forest fires in Nepal, paving the way for targeted fire management strategies and further investigation into lightning ignition mechanisms.

Analysis of Unburned Methane Emission Mechanisms in Large-Bore Natural Gas Engines With Prechamber Ignition

Abstract Although precombustion chambers, or prechambers, have long been employed for improving large-bore two-stroke natural gas engine ignition and combustion stability, their design predates modern analysis techniques. Employing the latest computational fluid dynamics (CFD) modeling techniques, this study investigates the importance of temperature and chemistry for ignition of the main chamber, with an emphasis on eliminating unburned methane. The sensitivity of the ignition and complete combustion to main chamber air/fuel mixture homogeneity was also explored. This study compares the effect of purely thermal ignition, purely chemical ignition, and how their interplay can influence the complete combustion of methane in typical mixtures and in homogeneous distributions of fuel in the combustion chamber. The CFD results demonstrated that temperature and chemistry are equally important in the ignition mechanism, and combining the two phenomena is effective at igniting the main chamber. Reduction of residual methane in the main combustion chamber (MCC) is most effective when chemical intermediates and thermal ignition are combined. A rudimentary analysis of the effect of fuel/air stratification was also conducted, and it demonstrated that a dramatic reduction in methane emissions is observed for homogeneous mixtures. The flow field in the main combustion chamber was shown to create detrimental stratification of the fuel/air mixture, which inhibited complete combustion of the methane in the main chamber. By contrast, in the extreme case of a perfectly homogeneous distribution of both chemical intermediates and fuel in the combustion chamber, it is possible to completely eliminate unburned methane in the main combustion chamber.

Study on ignition mechanism of turbulent jet pre-chamber of H2/CO mixture

Jet flow pre-chamber ignition is used to increase the thermal efficiency of lean-burn engines, but the ignition mechanism in the main chamber remains unclear. Therefore, the ignition mechanism of the jet pre-chamber was investigated experimentally and numerically. The results show that the flame in the pre-chamber can indeed propagate to the main chamber through a 2-mm-diameter nozzle without extinguishing. This occurs because at the very start the flame is located in the center of the nozzle and maintains a certain distance from the wall, preserving both temperature and free radicals. Next the flame in the nozzle will be extinguished due to fuel depletion, leading to a significant reduction in the concentration of free radicals. The free radicals pass through the nozzle, and compared with only the hot ignition, the ignition in the main chamber is one preparation period earlier, indicating a more concentrated heat release and higher thermal conversion ability in real engines.

Discharge and ignition mechanism of high-entropy alloy induced by crack propagation under quasi-static compressive load

In order to reveal the discharge and ignition mechanism of high-entropy alloy under quasi-static compression load, the stress, potential and ignition evolution process of high-entropy alloy with prefabricated cracks were tested. The atomic structure and dislocation evolution of high-entropy alloy during crack propagation and compression were determined by molecular dynamics simulation, and the discharge mechanism of crack tip was analyzed at the micro level. Based on the calculation of Gibbs free energy, the products in the ignition reaction process were predicted. The results of mechanical/thermal/electrical characteristics induced by compressive load show that the discharge usually occurs near the ignition moment of specimen fracture, and the maximum potential signal can reach 34.2 V. The formation of crack group, crack propagation, local stress concentration, charge accumulation and release at the crack tip jointly induce the generation of discharge signals. With the propagation of cracks, a large number of stacking faults appear and a diamond-shaped failure zone is formed. The increase of disordered atoms leads to fracture. During the compression process, a large number of dislocations induce the separation of charges, which aggravates the discharge at the crack tip. In the Hf-Zr-Ti-Ta-Nb-Cu high-entropy alloy system, the reaction product Ta2O5 is preferentially generated, while in the Ti–Zr-Hf-Cu system, Ti2O3 is preferentially generated. The tip discharge and chemical bond fracture during crack propagation induce ignition, and the chemical bond recombines with energy release.

Fundamental insights on turbulence characterization, vortex motion and ignition mechanism of sub/supersonic turbulent jet flames

This paper presents turbulence characterization and vortex behavior measurements of sub/supersonic jet flames subjected to extreme levels of turbulence. Specifically, sub/supersonic CH4/O2/N2 premixed jet flames were studied under calculated Reynolds (Re) number and measured jet tip velocity (Vtip) of around 20,000 and 100 m/s or greater, respectively. The vortex motion on the flame surface was measured by Schlieren image velocimetry (SIV), and ignition mechanisms of sub/supersonic jets are discussed by analyzing vortex motion and free radical reactions, respectively. Results show that the maximum vortex motion is maintained in the jet top edge region. In contrast, the velocity of vortex motion in the middle of the jet, i.e., near the side of the jet orifice, is reduced by a factor of 4–5, which visually shows a “mild” velocity gradient on the jet surface. The direction turning points of X/D = 7.25, X/D = 6.06, X/D = 6.06 and X/D = 3.40 were found in the flow direction (Y-direction) for four typical cases of supersonic jets with top primary swirling motion, supersonic jets with top secondary swirling motion, supersonic jets with weak top swirling motion and subsonic jets without top flame vortex motion. It is speculated that the ignition location is strongly correlated with the direction turning point of the vortex movement along the Y-direction. The vortex propagating along the flow direction disperses many small-scale vortices moving in the X-direction, the X-direction being perpendicular to the flow direction. Moreover, the ignition mechanisms of sub/supersonic jet were explored separately.

Ionization Processes of Negative Corona Discharge Part 1. Review and Experiment

The purpose of the research is an experimental study of physical processes in the near-electrode zones of negative point electrodes in an electronegative gas (air) under the condition of a high-voltage field.Methods. Video image analysis, current-voltage characteristics measurements, and spectroscopy are used. The current-voltage characteristics of the corona discharge ignition voltage in the environment are measured, the problem of experimental identification of surface charges, the mechanism of negative corona discharge ignition, and the ionic structure of streamers is studied, degradation of electrodes during negative corona discharge, spectrum of corona discharge creation and electromagnetic sound.Results. It is shown that at small radii of curvature of needle electrodes, the development of a negative corona discharge is due to the cold emission of electrons, and on flat and slightly curved negative electrodes, due to the capture of surface electrons by electron-withdrawing molecules. The mechanism of ignition of a corona discharge in an electronegative gas with a negative needle, the structure of streamers from negative needles, the emission spectrum and ethonic degradation of electrodes have been studied.Conclusions. The ignition of a negative corona discharge at small radii of the tips of the pointed needles (ro less than tens of microns) is due to the cold emission of electrons followed by impact ionization of neutral molecules. With slightly curved electrodes, the appearance of a negative corona discharge is due to the capture of surface electrons by electronegative gas molecules with subsequent plasma-chemical reactions. The formation of surface electrons depends on many factors: the presence and structure of oxide films (roughness, defects, etc.), which determine the electron work function and form local fields at the tips of microtips. The appearance of a corona discharge leads to degradation of the corona electrodes, expressed in the spraying of the tips of the points and the melting of the needles. In the dark region of the negative corona discharge (U < U*), photons in the in the ultraviolet spectrum (UV spectrum) are emitted, and when U > U*, in addition to UV photons, photons in the visible region of the spectrum are emitted. Glow fluctuations are caused by the chaotic dynamics of the formation of injection centers (melted tubercles - ectons) on the surface of the corona electrode. The ignition of a corona discharge is accompanied by sound emission with a frequency of about 300 Hz.

Features of the Mechanism of Gas-phase Ignition of Wood Biomass Particles

ABSTRACT Use of woody biomass instead of coal as fuel for thermal power plants (TPP) is considered a promising direction for reducing emissions of anthropogenic substances during the operation of coal-fired thermal power plants. But the process of replacing coal with wood in the thermal power industry is happening very slowly due to objective reasons. The main one is the deposition of particles that have not fully passed the pyrolysis stage (in this case, a layer of substance in a resinous state is retained in the wood particle) on heating surfaces (for example, superheaters) and a decrease in the efficiency of using the heat of combustion of fuel as a result of contamination of the heating surfaces. Therefore, when developing technologies for burning dispersed wood in the furnaces of boiler units, reliable experimental data are required on the characteristic times of ignition and combustion of woody biomass particles, taking into account the time of transition from local (focal) gas-phase ignition to the combustion of volatiles in the entire vicinity of the particle (tsf). The article presents the results of experimental studies of flame propagation processes in the small vicinity of a particle during the ignition period. The experiments made it possible to establish that the flame propagation velocity in the small vicinity of the particle significantly depends on the ambient temperature. It is shown that under conditions of low-temperature heating (air temperature Tg = 873 K), the propagation velocity of the combustion (flame) is minimal. An increase in Tg values (from 873 K to 1273 K) leads to a significant (4–5 times) increase in the time of complete flame coverage of the particle. According to the results of the experiments, two heating modes were identified: high-temperature and low-temperature with a conditional interface Tg = 873 K. At Tg = 873 K, the characteristic particle size of wood biomass has no significant effect on the characteristics and conditions of flame propagation in a small vicinity of the particle. An increase in the ambient temperature (up to 1273 K) leads to an increase in the influence of particle size on the characteristics and conditions of flame propagation. A hypothesis describing the process of flame propagation has been developed.

Lightning-Induced Wildfires: An Overview

Wildfire causes environmental, economic, and human problems or losses. This study reviewed wildfires induced by lightning strikes. This review focuses on the investigations of lightning mechanisms in the laboratory. Also, the paper aims to discuss some of the modeling studies on lightning-induced wildfires at different geographical locations using satellite-recorded lightning data and different statistical analyses. This review established that irrespective of the different models used to predict lightning wildfires, there is still a lack of understanding of the lightning-strike ignition mechanism; few experiments have been modeled to establish the dynamics of lightning-strike ignition. Therefore, further research needs to be carried out in this area to understand lightning ignition. It was ascertained from the various statistical modeling that lightning-induced wildfires are exacerbated by the abundant availability of fuel with a lower moisture content and high lightning efficiency. Moreover, because of changes in the climate and weather conditions, i.e., harsh weather and climate conditions due to anthropogenic activities, lightning-induced ignition wildfires have increased over the years, and they are expected to increase in the future if the climate and weather conditions continue to aggravate. Although various modeling studies have identified that lightning-induced wildfires have increased recently, no preventive measures have been conclusively proposed to reduce lightning-caused wildfires. Hence, this aspect of research has to be given critical attention. This review presents information that gives a profound understanding of lightning-induced wildfires, especially factors that influence lightning wildfires, and the state-of-the-art research that has been completed to understand lightning-induced wildfires.

Experimental study on the combustion of NH3/H2/air based on the passive turbulent jet ignition

The mixture of ammonia (NH3) and hydrogen (H2) is the potential alternative fuel for internal combustion engines (ICEs). The turbulent jet ignition (TJI) system can provide high ignition energy and turbulent disturbance to promote the combustion of the mixture for NH3/H2 ICEs. Therefore, the combustion characteristics of NH3/H2/air under passive TJI conditions were experimentally studied in the present study. The experiment was conducted in a constant volume combustion bomb, and the effect of fuel composition and equivalence ratio was investigated. The experimental results show that compared to spark ignition, the combustion of NH3/H2 can be effectively improved by using TJI, especially under high NH3 fraction conditions. The addition of H2 has a significant positive effect on the ignition and combustion performance. With the addition of H2, the ignition delay and combustion duration decrease evidently. And the H2 addition is beneficial for improving the ignition mechanism and achieving flame ignition. In addition, poor ignition performance may occur under rich conditions due to the fluid-dynamic quenching of the jet. However, the high flame propagation rate on the rich side still leads to lower combustion duration. Moreover, increasing the orifices number appropriately can enhance the ignition and combustion performance. The jet strength is weakened by the increased total orifice area and the ignition of NH3/H2 can be improved.

Numerical investigation of nanosecond plasma-assisted ignition in blast furnace gas

The ignition delay of blast furnace gas (BFG) and air mixtures is numerically investigated in a constant-pressure reactor employing plasma-assisted ignition. Given the absence of a well-established chemical kinetic mechanism for plasma-assisted ignition in BFG and air mixtures, this study develops a mechanism by integrating well-validated plasma kinetics reactions involving CO2 with CO and H2, along with pre-existing plasma kinetics for air. The study explores the influence of various factors on ignition delay time, including the reduced electric field, the number of nanosecond pulses, equivalence ratio, and molar fraction of hydrogen. It is found that the utilization of nanosecond pulsed plasma results in a notable enhancement of the ignition delay time in BFG. Under lower reduced electric field conditions, the vibrational states of N2 predominantly contribute to the generation of O radicals. Increasing the number of nanosecond pulses facilitates the ignition in BFG and air mixtures while maintaining the same overall deposition energy. Ignition occurs more rapidly in fuel-rich mixtures due to the elevated accumulation of O, H, OH radicals during the final nanosecond pulse in rich mixtures. When the H2 concentration is elevated to 3 %, the electron impact reaction H2 + e → e + H + H becomes a more significant source of H radicals during the nanosecond pulse, in contrast to the 1 % H2 case. Additionally, this study investigate the effect of species at the last nanosecond pulse on ignition delay time of BFG. The results indicate that the impact of nanosecond plasma on the ignition delay time of BFG can be captured by considering the concentration of the primitive BFG/air species (CO, CO2, H2, O2, N2) and key radicals (O, H, OH) at the last nanosecond pulse.

Experimental investigation on the combustion characteristics of ultra-lean premixed hydrogen/air using turbulent jet ignition

Amid growing environmental concerns, hydrogen (H2) is emerging as a prospective alternative fuel for driving internal combustion engines. Employing lean combustion technology in tandem with turbulent jet ignition (TJI) has the potential to enhance combustion rates while mitigating NOx emissions. Therefore, an experiment was developed to investigate the combustion characteristics of ultra-lean premixed H2/air by TJI. An active pre-chamber (PC) with an additional H2 supply was selected. Moreover, the effect of nozzle structures and equivalence ratio was discussed. The results show that with a nozzle diameter of 3 mm and an elevation of ΦPC to 1.4, the lean flammability limit is extended to an equivalence ratio of 0.13, with a consistently stabilized ignition delay within 4 ms. Increasing the nozzle number also extends the lean flammability limit, but it incurs higher energy losses. Additionally, two ignition mechanisms exist in TJI: flame ignition and combined ignition. The transition from flame ignition to combined ignition commonly occurs when the equivalence ratio of the main chamber drops below 0.3. This transition typically results in higher peak pressures and burnt fuel ratio, lower combustion duration, and longer ignition delay.

Experimental Research on Heat Transfer and Ignition Characteristics of Series Fault Arc Combustion in 220VAC Power System

ABSTRACT This paper studied the heat transfer and ignition characteristics of series fault arcs combustion in the 220VAC power system. Series fault arcs with seven currents (4-30A) were generated to investigate the outward heat transfer characteristics of arc combustion. The distance between the fault arc and the combustibles was changed in experiments to study ignition characteristics. Electrode temperature and arc near-domain temperature, ignition time, and temp-erature of the combustible surface were measured. The results show that the ambient air temperature rise (T-T 0) is inversely proportional to the radial distance from the fault arc (r), and there is a linear relationship between the temperature (T-T 0) and the current divided by the radial distance from the fault arc (I/r). As for the temperature of the electrode, the larger current causes a higher electrode temperature. A semi-infinite solid ignition model is used to deal with the ignition process of the combustibles. Experimental results show that there is a good linear relationship between the current (I 2) and the ignition time ( t ig − 1 / 2 ). This study quantitatively evaluates the hazards of arc combustion and is of great significance for explaining the ignition mechanism of an arc-type electrical fire.

Dynamic compression-shear ignition mechanism of Al/PTFE reactive materials

Ignition of Al/PTFE reactive materials can occur under dynamic loading. The ignition mechanism involves a mechanical-thermal-chemical coupled process, which draws the attention of scientists and engineers. However, it is difficult to understand the mechanism, especially under complex loadings. In this paper, three different shapes of Al/PTFE sample, 0° cylinder, 30° oblique cylinder and 45° oblique cylinder, were designed. The dynamic ignition tests were carried out by Split Hopkinson Pressure Bar (SHPB). The deformation, damage and fracture process were analyzed. The mechanical response depended on the shape of the sample, which determined the dynamic compression-shear states, further it induced different ignition behavior. The energy absorption rate ignition criterion was proposed to take the place of the traditional strain rate ignition criterion. The new criterion could match the testing well. In addition, numerical simulation on SHPB was conducted. It verified that Johnson-Cook model would describe the dynamic behavior of Al/PTFE reactive materials. The damage and the fracture of Al/PTFE under dynamic compression-shear loading was quantified well, and further was related to the ignition behavior observed during the tests. Finally, the dynamic compression-shear ignition mechanism of Al/PTFE reactive materials was revealed.

Ignition mechanism of near α high temperature titanium alloy

The risk of titanium fire increases significantly with the development of future aero-engine, however, the burning mechanisms of titanium alloys remain uncertain. Therefore, the ignition behavior and mechanism of near α high-temperature titanium alloy are studied in this work by an integrated experiment method, including laser-oxygen concentration ignition method, infrared temperature measurement and observation of molten metal by high-speed camera. Based on this, the ignition boundary curve is determined and the ignition temperature of the alloy is found to decrease from 1595 to 1527 ℃ with the laser power increasing from 200 to 325 W and oxygen concentration increasing from 21% to 60%. The ignition microstructure is characterized by FIB and TEM to study the evolution of reaction products. Pores are found to form beneath the TiO<sub>2</sub> surface layer, which can be attributed to the instablity of TiO. The failure mechanism of protective oxide layer is further analyzed according to the thermal stress caused oxide layer damage model. When the temperature approaches the ignition temperature, which is below the melting point, the high vapor pressure of TiO leads to the formation of porous defects beneath the TiO<sub>2</sub> surface, thus accelerating the fracture and failure of the TiO<sub>2</sub> layer under thermal stress. It is revealed that critical conditions of temperature and instantaneous temperature change rate are needed to realize ignition. Based on this, an ignition model is further constructed to discuss the relationship among ignition temperature, laser power and oxgyen concentration. According to the experimental data fitting, the reaction activation energy of TA19 alloy during the ignition stage is calculated to be about 280 kJ/mol, and the function for calculating ignition temperature is given as follows: <inline-formula><tex-math id="M2">\begin{document}$ 1.2 \times {10^{10}}{{\mathrm{e}}^{\frac{{ - 280000}}{{R{T_{{\text{ig}}}}}}}}{c^{\frac{1}{2}}} + $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2.png"/></alternatives></inline-formula><inline-formula><tex-math id="M2-1">\begin{document}$ 0.52{P_{\mathrm{L}}} - 315 = 0 $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2-1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2-1.png"/></alternatives></inline-formula>. This provides a theoretical reference for predicting the ignition temperatures of near α high temperature titanium alloy and other types of titanium alloys under complex airflow conditions in aircraft engines.

Low-temperature ignition and oxidation mechanisms of tetrahydropyran

Cyclic ethers are relevant as next-generation biofuels and are also combustion intermediates that follow directly from unimolecular decomposition of hydroperoxyalkyl radicals. Accordingly, cyclic ether reactions are crucial to understanding low-temperature oxidation for advanced compression-ignition applications in combustion where peroxy radials are central to degenerate chain-branching pathways. Reaction mechanisms relevant to low-temperature ignition of cyclic ethers contain intrinsic complexities due to competing reactions of carbon-centered radicals formed in the initiation step undergoing either ring-opening or reactions with O2. To gain insight into mechanisms describing tetrahydropyran combustion, ignition delay time and speciation measurements were conducted. The present work integrates measurements below 1000 K of ignition delay times and species profiles in rapid compression machine experiments from 5 – 20 bar, spanning several equivalence ratios, with jet-stirred reactor experiments at 1 bar and stoichiometric conditions. The experiments are complemented with the development of the first chemical kinetics mechanism for tetrahydropyran that includes peroxy radical reactions, including O2-addition to tetrahydropyranyl (Ṙ), HOȮ-elimination from tetrahydropyranylperoxy (ROȮ) and hydroperoxytetrahydropyranyl (Q˙OOH), bi-cyclic ether formation, β-scission of Q˙OOH, and ketohydroperoxide formation.Negative-temperature coefficient (NTC) behavior is exhibited in the experiments and is reflected in the model predictions, which were within experimental uncertainty for several conditions. Disparities between the model predictions and experiments were analyzed via sensitivity analysis to identify contributing factors from elementary reactions. The analyses examine the role of ring-opening products of tetrahydropyranyl and hydroperoxytetrahydropyranyl isomers to identify reaction mechanisms that may contribute to model uncertainties. The detection of 66 species in the JSR experiments indicates that tetrahydropyran undergoes complex reaction networks, which includes interconnected reactions of aldehyde radicals and alkyl radicals. Primary radicals pentanal-5-yl and butanal-4-yl are derived from ring-opening reactions of tetrahydropyran-1-yl and undergo subsequent decarbonylation to form alkyl radicals (1-butyl and 1-propyl) that undergo reaction with O2 and may contribute to chain-branching, in addition to pathways involving tetrahydropyran-derived ketohydroperoxides.

The dispersion and ignition behavior of zirconium particles under the effect of a shock wave

Experiments of the interaction process between shock waves and zirconium particles have been carried out using a self-designed shock tube. The interaction process was recorded using a high-speed shadowgraph imaging system, pressure testing system, and infrared thermal imager. The wave-systems structures resulting from the interaction between shock waves and accumulated zirconium powders have been characterized. Generally, the axial distance of the powder cloud reduces with the increase in accumulation thickness, which in turn increases with the addition of shock Mach number. The incident shock wave with an intensity of 1.53 Ma was enough to ignite zirconium powders under these experimental conditions. The ignition delay time for zirconium powders decreases with the addition of shock Mach number, while it decreases for thinner accumulations. Besides, the flame propagation characteristics and the ignition mechanism of zirconium powders are discussed in detail. The results can serve as a supplementary guide for the utilization and safe operation of zirconium powders.