Shorter Ignition Delay Times Research Articles

The prospects of burning coal and oil processing waste in slurry, gel, and solid state

This paper presents the experimental investigation results of ignition and combustion characteristics of fuels based on typical coal flotation waste which is formed and accumulated around the world in large volumes (about 200–300 million tons per year). We focus on the comparison of these characteristics for waste-derived fuels in different states: slurry, gel, and solid. We analyze the ignition delay times, minimum (threshold) ignition temperatures, combustion heat, concentrations of anthropogenic emissions, and the relative efficiency of fuels. We have determined that minimum ignition temperatures and shorter ignition delay times are achieved in the solid state (50–80% lower than in the slurry and gel state). The lowest concentrations of the most hazardous emissions are present in the liquid (slurry) state (NOx and SOx are 18–75% lower than from the combustion of coal in the solid state). The conditions were identified for the efficient use of coal and oil processing waste as part of composite fuels. The relative fuel effective utilization factor of waste-derived fuel mixtures in different states ranged from 0.11 to 45.5. It is maximal for fuels in the slurry state. The obtained data has been compared with the results of other studies.

Influencing Factors of High-Pressure Discharge Nanothermite Composites Based on Al/Bi2O3

To optimize the reactant synthesis and improve the pressure property of Al/Bi2O3, the influencing factors in the dynamic pressure discharge of nanothermite reactions are investigated, including the oxide type, Bi2O3 particle size, and fuel-to-oxidant mole ratio. All samples are prepared by the ultrasonic mixing method. The synthesized Al/Bi2O3 composites are characterized by X-ray diffraction analysis and scanning electron microscopy. By using a closed bomb, the pressure discharge characteristics, including the peak pressure, ignition delay time, and pressurization rate, are obtained. Among the as-prepared nanothermites Al/CuO, Al/Fe2O3, and Al/Bi2O3, the latter shows the best pressure discharge performance. For the Al (100 nm)/Bi2O3 (47 nm) composite with an optimal stoichiometric ratio, the maximum peak pressure, the pressurization rate, and the shortest ignition delay time are 4559 kPa, 11.398 GPa/s, and 27.20 ms respectively. The results indicate that the nano-Bi2O3 particle size also produces a significant effect on the pressure output.

On the influence of initial conditions and facility effects on rapid compression machine data

The influence of rapid compression machine (RCM) facility-effects on ignition delay time is investigated using multi-zone model simulations that consider the role of crevice volume and compression time. Four virtual machines are defined, each with a unique combination of crevice volume (∼5 to 7 mL) and compression time (25–50 ms). These machines are used to simulate autoignition of four fuels (iso-octane, n-heptane, PRF50, and ethanol) from low to high temperatures at equivalence ratios of ϕ = 0.5, 1.0, 2.0 and compressed pressures of pc = 10, 20 and 40 bar. This range of simulation conditions provides a diverse array of autoignition responses, including single-stage and two-stage autoignition. Furthermore, the simulation conditions are obtained for each machine by using various combinations of compression ratio, initial temperature, and argon:nitrogen fraction in the diluent gas. The results show that for a given machine, the test method used to obtain the compressed condition can strongly influence the ignition delay time, particularly under two-stage ignition conditions. The disparity between the test methods grows with the duration of the second stage of ignition, thus the test method dependence is most pronounced for iso-octane (i.e., PRF100). Comparison of the virtual machines shows that increased crevice volume (at roughly constant surface-area-to-volume ratio) leads to enhanced heat loss and therefore longer ignition delay times. For short ignition delay times (<10 ms), lengthening the compression time from 25 to 50 ms initiates reactivity prior to the end of the stroke, thus leading to a reduction in the ignition delay time. However, the simulations reveal that even for long ignition delay times, in excess of 100 ms, the ignition delay times are still sensitive to the compression time due to crevice heat loss dynamics that occur in the first ∼20 ms after the end of compression. A comprehensive comparison of the data suggest that variability among unique machines may be minimized by making measurements at low-to-moderate compression ratios and avoiding RCM designs with small crevice volumes.

Immobilized oleaginous microalgae as effective two-phase purify unit for biogas and anaerobic digester effluent coupling with lipid production

Oleaginous microalga Scenedesmus sp. was immobilized in alginate-gel beads and applied as two-phase purify unit for biogas and anaerobic digester effluent from palm oil mill. Optimal microalgal cell concentration and bead volume ratio were 106 cells mL−1 and 25% v/v, respectively. The use of 20% effluent and light intensity at 128 µmol·proton·m−2 s−1 most promoted CO2 removal by immobilized microalgae and achieved the maximum CO2 removal rate of 4.63 kg-CO2 day−1 m−3. This process upgraded methane content in biogas (>95%) and completely remove nitrogen and phosphorus in the effluent. After process operation, 2.98 g L−1 microalgal biomass with 35.92% lipid content were recovered by simple sieving method. Microalgal lipids are composed of C16-C18 (>98%) with prospect high cetane number and short ignition delay time. This study has shown the promising biorefinery concept which is effective not only in CO2 fixation, biogas upgrading and pollutant removal but also cost-effective production of microalgae-based biofuel.

Numerical simulation of the effects of evaporation on the n-heptane/air auto-ignition process under different initial air temperatures

Numerical simulations are carried out to study the effects of fuel evaporation and mixing on autoignition process of n-heptane/air with complex chemistry. By assuming that n-heptane spray evaporation and mixing are infinitely fast under initial air temperature Tair of 740–1200 K and pressure of 1–24 atm, homogeneous gaseous mixture of n-heptane/air with different equivalence ratio can be obtained. Three types of the most reactive mixture fraction ηMR are identified in mixture fraction space: ηMR,LTand ηMR,ig are associated with the shortest first-stage ignition by low temperature chemistry (LTC) and the total two-stage ignition delay time respectively, while ηMR,HT corresponds to the shortest single-stage ignition delay time by the high temperature chemistry (HTC). With the increasing initial air temperature Tair, ηMR,ig and ηMR,LT will increase, but the corresponding ignition delay times decrease. When Tair is high enough to make the temperature of gaseous mixture higher than the upper turnover temperature of NTC region in very lean mixture, ηMR,HT will appear with shortest ignition delay time. Moreover, the ignition delay time at ηMR,HT could be less than that at ηMR,LT in the spray autoignition process under high initial air temperature Tair=1200K and low initial pressure, 1 atm and 6 atm. This finding suggests that in spray autoignition process, due to the cooling effect of evaporation, LTC reaction and HTC reaction may coexist if the interval between the ignition delay times of ηMR,HT and ηMR,LT is quite small, and also that the high temperature ignition may precede the low temperature ignition. In addition, sensitivity and reaction pathway analysis are performed to disclose the controlling chemical kinetics at the three types of the most reactive mixture fraction ηMR of the case with high initial air temperature 1200 K and pressure 6 atm.

Oxidation of a Levitated 1-Butyl-3-methylimidazolium Dicyanoborate Droplet by Nitrogen Dioxide.

To develop the next generation of hypergolic, ionic-liquid-based fuels, it is important to understand the fundamental reaction mechanisms for the oxidation of ionic liquids (ILs). We consequently studied the oxidation of a levitated 1-butyl-3-methylimidazolium dicyanoborate ([BMIM][DCBH]) droplet by nitrogen dioxide (NO2). The properties of [BMIM][DCBH], including short ignition-delay times, low viscosities, and a wide liquid temperature range, make the ionic liquid especially suitable as a component of a hypergolic fuel. The chemical modifications were monitored with Fourier-transform infrared (FTIR), Raman, and ultraviolet-visible spectroscopies. To identify changes induced by the oxidation, it was first necessary to assign vibrational modes to the FTIR and Raman spectra of unreacted [BMIM][DCBH]. The new features in the oxidized FTIR and Raman spectra could then be identified and assigned on the basis of the possible functional groups likely to form through addition with a nitrogen and an oxygen atom of nitrogen dioxide creating a new bond with the ionic liquid. The assignments suggest that organic nitro-compounds and boron-nitrogen and boron-oxygen containing compounds were produced. A large decrease in the intensity of some [DCBH]- fundamental modes suggests the nitrogen dioxide molecule prefers to react with the anion over the cation.

Low temperature ignition delay times measurements of 1,3,5-trimethylbenzene by rapid compression machine

Due to the increased interest on understanding the combustion chemistry of the larger alkyl aromatic as jet fuel surrogate component, we provide new ignition delay time data of 1,3,5-trimethylbenzene/O2/Ar mixtures, for the temperature range between 880 and 1090 K, at the pressure of 20.0 and 30.0 bar and for different mixture equivalence ratio and fuel concentration, by using a well validated rapid compression machine with heating system. Measurements show that no negative temperature coefficient behavior was observed for this fuel. Subsequently, these low temperature ignition delay time data were used to validate several kinetic mechanisms including those of Gudiyella and Brezinsky (Combust Flame 2012), Diévart et al. (Fuel 2013), and Wang et al. (Combust Flame 2018), all of which significantly overestimate the reactivity of 1,3,5-trimethylbenzene in this temperature range. Sensitivity analysis at typical condition and comparisons of the rate constants of the ignition dominant reactions in different models indicate that a more complete reaction scheme for 1,3,5-trimethylbenzene (T135MB) and more accurate rate constant should be further pursued, especially for the reactions of H abstraction from T135MB and fuel radical consumption reactions. Finally, ignition delay times of toluene is lower than T135MB and n-propylbenzene at the same condition, which indicate that the larger number of side chain and the longer side chain length enhances the low temperature reactivity. In addition, for the same fuel isomer, the effect of the side chain length is stronger than the number of side methyl in accelerating ignition since n-propylbenzene presents an even shorter ignition delay times than T135MB. We believe the present work will be of merit for future jet fuel surrogate model development.

Heterogeneous decomposition and oxidation during combustion of magnesium diboride particles

Magnesium diboride (MgB2) is a potential substitute of amorphous boron (B) as high energy density fuel. The heterogeneous decomposition and oxidation mechanisms during combustion of MgB2 were studied using a laser ignition testing system, an X-ray diffractometer, and a thermogravimetric differential scanning calorimetry combined thermal analysis system. B and magnesium (Mg) were also tested in the laser ignition experiments as control groups. The combustion process of MgB2 contained two stages: an explosion stage and a stable combustion stage. During the explosion stage, a great number of sparks were created and burst out from the sample stack. The color of combustion flame was white at first, and then turned into yellow before the stable combustion stage started. Compare with B and Mg, MgB2 had shorter ignition delay time (8 ms) and longer stable combustion stage time (891 ms), which indicated its outstanding energy release properties. Characteristic emission spectra of MgB2 showed MgO, BO2, and gaseous Mg were the major gaseous intermediate products during combustion. Moreover, decomposition and oxidation products of MgB2 were both found in the condensed combustion products. The thermal oxidation process of MgB2 contains three exothermic peaks: melt and oxidation of Mg impurity (∼650 °C), start of MgB2 decomposition (∼850 °C), and oxidation of Mg-B compounds (∼900 °C).

Experimental study on the discharge ignition in a capillary discharge based pulsed plasma thruster

Low power capillary discharge based pulsed plasma thrusters (CDPPTs) are electrothermally dominated thrusters and they have aroused renewed interest in the investigation and enhancement of the basic performance for the application of micro/nano satellites recently. Research on the ignition mechanism of a CDPPT has been conducted to provide insight into the optimization of the structure design and promotion of the lifetime performance. It has been found that the electrical parameters, the geometry parameters, and the cumulative effect of discharge jointly determine the discharge ignition characteristics. A single ignition process is divided into the breakdown of igniter and the development of the main discharge, while the results show that the jitter of the ignition delay time is mainly introduced from the former. Shorter ignition delay time and lower jitter can be obtained with a higher ignition energy and main charging voltage or a shorter and narrower cavity, which is positively correlated to the electric field distribution along the propellant surface. Moreover, with long duration experiments, it reveals that the surface deposits and morphology of propellant and igniter are the dominant factors that cause the dispersity of the ignition effect and main discharge characteristics.

Influence of biodiesel carbon chain length on in-cylinder soot processes in a small bore optical diesel engine

This study examines the effects of biodiesel carbon chain length on the development of high-temperature flame and soot in single-cylinder, light-duty, optical diesel engine. Planar laser-induced fluorescence of OH (OH-PLIF) and laser-induced incandescence (soot-PLII) are performed separately using petroleum diesel and two biodiesel surrogate fuels. The selected surrogate fuels have a saponification number (SN) of 330 and 233 for shorter and longer carbon chain length, respectively, while the iodine value (IV) characterising the degree of unsaturation is kept similar. The laser-based images are shown together with the chemiluminescence images of naturally occurring cool-flame signals and electronically excited OH (OH∗). The start of high-temperature reaction timing was matched for the tested fuels by adjusting the injection timing so that the in-cylinder ambient conditions at the start of combustion were consistent. The results show that the longer carbon chain biodiesel has shorter ignition delay time, which makes a significant impact on the spatial and temporal development of high-temperature reaction zones. The OH signals for the longer carbon chain length biodiesel are observed close to the piston-bowl wall whereas they appear later in the penetrating front of the wall-interacting jet for the shorter carbon chain length biodiesel. Both fuels show soot formation occurring in the wall-jet head region while the longer carbon chain length biodiesel has higher soot concentration and larger area than that of the shorter carbon chain biodiesel. This is due to lower pre-combustion mixing, reduced fuel oxygen content, and possibly less significant OH-induced soot oxidation.

Ignition kinetics of a homogeneous hydrogen/air mixture using a transient hot jet

The ignition characteristics of a homogenous hydrogen/air mixture using a hot transient jet generated by the combustion of syngas (H2/CO) with varying CO concentrations from 33% to 95% in a pre-chamber is numerically investigated with particular attention to the chemical kinetics. Detailed reaction mechanism for hydrogen and syngas mixture oxidation with 15 species and 41 reactions is employed. The hot jet ignition delay time is determined by the onset of OH∗ radicals and found to increase with increasing CO molar fractions in the pre-chamber fuel, and this increase is more profound for high CO content. The radicals that formed in the main chamber are examined separately from the radicals within the hot jet. Their temporal evolutions reveal that O and OH radicals in the jet play a crucial role in abstraction of H atoms form H2/air mixture in the main chamber, which initiates ignition. Further analysis of the H2O2 rate of change identifies two ignition regimes. For high temperature (T > 1000 K) hot jets, ignition is caused by the chain branching reaction H+O2↔O+OH directly, resulting in short ignition delay times (0.14, 0.19, 0.26 ms). For low temperature (T < 1000 K) hot jets, ignition is dominated by the accumulation and decomposition of H2O2, resulting in long ignition delay times (0.4, 0.67, 1.26 ms). By separating the thermal and chemical effects of the hot jet, it is found that the thermal effects are dominant but composition of the hot jet has little effect on the ignition characteristics.

Fast Flame Annealed Porous CuFe2O4 for Photoelectrochemical Hydrogen Production

Photoelectrochemical (PEC) water splitting is one of the promising renewable energy techniques that can store solar energy into one of the clean and renewable energy resources, hydrogen (H2). However, facilitating the renewable PEC water splitting system on a global scale is still challenging. Especially, finding suitable p-type photocathodes is critical which have a narrow bandgap, a great solar to hydrogen (STH) efficiency and economical fabrication processes with earth abundant elements. Metal oxides have shown remarkable advantages that satisfy the important requirements to be an excellent photocathode among the suggested candidates. Copper ferrite (CuFe2O4) is a promising but rarely studied p-type photocathode based on the relatively narrow bandgap (~1.7eV) which can utilize a great portion of solar light to realize the maximum STH efficiency of ~30% and photocurrent of ~25mA/cm2 theoretically. In addition, CuFe2O4 has positive flat band and photocurrent onset potentials (~1.0 VRHE) that are critical to achieve high operating photocurrent with n-type photoanode for an ideally unbiased entire solar water splitting system. Moreover, it consists of earth abundant elements. However, there are still limiting features for the use of CuFe2O4 photocathode since it has shown a relatively poor photocurrent and the synthesis process inevitably requires long time annealing at high temperature to produce less defective and better crystalline material for a high charge transport property. Here, we employed the rapid and high temperature (>980°C) flame as an annealing process for CuFe2O4 photocathode synthesis, demonstrating the significantly enhanced photocurrent (-1.82 mA/cm2 at 0.4VRHE in Ar purged 1M NaOH) as a single material photocathode whose photoactivity is greater than that of most studied photocathodes. There are several unique advantages of the flame annealing compared with other conventional annealing methods for the synthesis. For example, the flame does have negligible ramping time to reach high temperature above 980°C due to its short ignition delay time that finally makes the high crystalline CuFe2O4 in only 16 minutes. Moreover, the flame is operated in the open atmospheric environment and the amount of oxygen can be easily controlled by adjusting the fuel to oxygen equivalence ratio as a combustion parameter. Oxygen rich environment was employed for CuFe2O4 annealing to provide fully oxidized condition for an amorphous Cu and Fe mixture prepared by sol-gel method. Finally, the porosity of CuFe2O4 was highly increased by flame annealing, and the physical structural change positively affects the enhancement of the light absorption property and the specific surface area increase.

A Mathematical Model for Processes in Coal–Water Slurries Containing Petrochemicals under Heating

One of the promising directions for improving the environmental, technical, and economic efficiency of coal-fired thermal power plants is the use of the multicomponent fuels based on coal and combustible liquids. Such fuels, as a rule, are called coal–water slurries containing petrochemicals (CWSPs). The typical wastes of coal enrichment, low-grade coals, oil production, and oil refining wastes as well as used flammable liquids, for example oils, can be included in the fuel composition. To date, mathematical models have not been developed for predicting the effective conditions for the ignition of promising CWSPs at minimum ambient temperatures and with short ignition delay times. This problem was solved in the present work. On the basis of the experimental results, three modes of physical and chemical transformations were established when heating single particles of the composite fuel. The first one is the intensive thermal decomposition of the coal component after evaporation of the liquid components of...

Ignition and combustion of a single aluminum particle in hot gas flow

For simulating the aggregated aluminum bulks on the burning surface of solid propellants, large aluminum particles (40–160 µm) are used in this work. The isolated aluminum particles are ignited in hot oxidizing gas. Based on the bright-spot diameter profiles and the known respective reaction mechanisms, the total ignition and combustion process of aluminum particle can be divided into three stages, namely, pre-heating, ignition and combustion. The initial and bright-spot diameters of the aluminum particle are measured directly from the images by using the in-house automated data processing routines. Ignition delay time, ti, and combustion time, tc, are also obtained by post-processing the sequential images and can be associated with the particle diameters, D, in the form of ti = aD + b and tc = αD, respectively. The changing trends of ignition delay time and combustion time with the effective oxidizer mole fraction in the range of 22.8%–49.1% are distinctly different. The oxidizing environments with a high effective oxidizer mole fraction can result in short combustion time but long ignition delay time. For small particles (40–110 µm), the environmental effective oxidizer mole fraction exerts a limited effect on the sum of ignition delay time and combustion time, which indicates total time. By considering the effects of particle sizes and effective oxidizer mole fractions of environments, the percentages of ignition delay time in the total time are analyzed. These results suggest that with the goal of decreasing the total time, suitable methods can be employed for different conditions. Furthermore, we observe and discuss the phenomenon of aluminum particle microexplosion in an environment with high effective oxidizer mole fraction, which decreases particle combustion time by a large margin.

Rational Design and Facile Synthesis of Boranophosphate Ionic Liquids as Hypergolic Rocket Fuels.

The design and synthesis of new hypergolic ionic liquids (HILs) as replacements for toxic hydrazine derivatives have been the focus of current academic research in the field of liquid bipropellant fuels. In most cases, however, the requirements of excellent ignition performances, good hydrolytic stabilities, and low synthetic costs are often contradictory, which makes the development of high-performance HILs an enormous challenge. Here, we show how a fuel-rich boranophosphate ion was rationally designed and used to synthesize a series of high-performance HILs with excellent comprehensive properties. In the design strategy, we introduced the {BH3 } moiety into the boranophosphate ion for improving the self-ignition property, whereas the complexation of boron and phosphite was used to improve the hydrolytic activity of the borohydride species. As a result, these boranophosphate HILs exhibited wide liquid operating ranges (>220 °C), high densities (1.00-1.10 g cm-3 ), good hydrolytic stabilities, and short ignition delay times (2.3-9.7 milliseconds) with white fuming nitric acid (WFNA) as the oxidizer. More importantly, these boranophosphate HILs could be readily prepared in high yields from commercial phosphite esters, avoiding complex and time-consuming synthetic routes. This work offers an effective strategy of designing boranophosphate HILs towards safer and greener hypergolic fuels for liquid bipropellant applications.

Ignition delay time and sooting propensity of a kerosene aviation jet fuel and its derivative blended with a bio-jet fuel

Ignition delay time and sooting index of kerosene blended with a bio-jet fuel is measured for a comparative study with general aviation fuels. The new blended fuel is similar to a kerosene jet fuel (Jet A-1 or Korean domestic jet fuel) in terms of properties, H/C ratio, density, and heat of combustion. But, its ignition characteristics and sooting propensity are different from those of Jet A-1. Ignition delay time is measured by a shock tube and it is found that the blended fuel of kerosene and a bio-jet fuel has NTC (negative temperature coefficient) behavior. Ignition delay times of the blended fuel are compared with those of jet fuels (Jet A-1 and Jet A) over a wide range of temperature from 700 K to 1200 K at 20 atm. The blended fuel has shorter ignition delay time at low temperature below 900 K. It can be explained by short ignition delay of components in a bio-jet fuel at low temperature. In terms of sooting propensity, blending with a bio-jet fuel reduces the propensity remarkably to a half.

Small Skeletal Kinetic Reaction Mechanism for Ethylene–Air Combustion

Ethylene is a fuel considered for high speed ram- and scramjet combustion applications, mainly because of the short ignition delay time resulting from its high reactivity. Further research and development on these combustion systems would benefit from simulations of Large Eddy (LES) type, which allow some chemical detail to accurately predict combustion characteristics and pollutant formation. In the present work a chemical kinetic mechanism suitable for LES is presented, consisting of 66 irreversible reactions between 232 species. The mechanism is extensively validated for combustion characteristics related to ignition and flame propagation, over a wide range of pressure, temperature and equivalence ratios that previously published mechanism of this size have not covered. Agreement with a detailed reference mechanism is good for ignition delay, flame temperature and laminar burning velocities. In addition, overall concentration profiles of major stable products are in overall good agreement with referenc...

Exploring BH2CN-based hydrophobic hypergolic fuels and effective fuel “additives”: Imidazolylidene cyanoborane complexes

Two hydrophobic imidazolylidene-cyanoborane complexes were prepared by the introduction of {BH2CN} into the molecular formula via treatment of imidazolium iodide and NaBH3CN avoiding literature's tedious and hazardous procedures. These two complexes were fully characterized using IR spectroscopy, 1H NMR and 13C NMR spectroscopy and high-resolution mass spectrometer. The X-Ray structure of NHC-1 has been determined. NHC-2 was proved to be hypergolic with WFNA and displayed the attractive properties such as water immiscibility, wide liquid range (Tg=−22°C), short ignition delay time (13ms), high density (0.98g/cm3), good density impulse (ρIsp, 347sgcm−3), showing the promising application potential as a fuel and an efficient fuel additive.

Hypergolic Ignition of Hydrogen Peroxide/Gel Fuel Impinging Jets

Impinging jet experiments were conducted using doublet, triplet, and quintuplet injector configurations to measure ignition delay of hydrogen peroxide with gel hydrocarbon fuel containing sodium borohydride () particles. Rheological characterization and surface tension measurements of gel fuel mixtures were obtained to demonstrate their non-Newtonian shear thinning behavior and determine the influence of addition. Cold-flow experiments were conducted to elucidate system startup transients. First light times decreased with increasing reactant flow velocity, whereas ignition delay decreased until a plateau was achieved beyond . Variation of reactant flow and global equivalence ratios exhibited a relative independence of such conditions on ignition delay. Doublet and triplet injector configurations produced comparable first light and ignition onset times, whereas the average ignition time for the quintuplet injector configuration was nearly doubled. Transition of flow conditions (from fans to a more conical flow structure) downstream of impingement may have detrimentally influenced ignition for the quintuplet configuration by affecting the overall reactive surface area and volume in which the reactants are distributed. These results indicate that more complex multi-injector geometries are not necessary to achieve short ignition delay times for this system, and reactant flows may be varied to optimize for performance without adversely affecting ignition delay.

Two-stage autoignition and edge flames in a high pressure turbulent jet

A three-dimensional direct numerical simulation is conducted for a temporally evolving planar jet of n-heptane at a pressure of 40 atmospheres and in a coflow of air at 1100 K. At these conditions, n-heptane exhibits a two-stage ignition due to low- and high-temperature chemistry, which is reproduced by the global chemical model used in this study. The results show that ignition occurs in several overlapping stages and multiple modes of combustion are present. Low-temperature chemistry precedes the formation of multiple spatially localised high-temperature chemistry autoignition events, referred to as ‘kernels’. These kernels form within the shear layer and core of the jet at compositions with short homogeneous ignition delay times and in locations experiencing low scalar dissipation rates. An analysis of the kernel histories shows that the ignition delay time is correlated with the mixing rate history and that the ignition kernels tend to form in vortically dominated regions of the domain, as corroborated by an analysis of the topology of the velocity gradient tensor. Once ignited, the kernels grow rapidly and establish edge flames where they envelop the stoichiometric isosurface. A combination of kernel formation (autoignition) and the growth of existing burning surface (via edge-flame propagation) contributes to the overall ignition process. An analysis of propagation speeds evaluated on the burning surface suggests that although the edge-flame speed is promoted by the autoignitive conditions due to an increase in the local laminar flame speed, edge-flame propagation of existing burning surfaces (triggered initially by isolated autoignition kernels) is the dominant ignition mode in the present configuration.