Ignition Performance Research Articles

Effect of Initial Crack Position on Low‐intensity Impact Ignition Performance of Solid Propellant

ABSTRACTThe micro‐crack defects produced in the process of storage and use of solid propellants have an important influence on the safety of solid propellants. In this study, the low‐intensity impact ignition performance of crack‐containing hydroxyl‐terminated polybutadiene (HTPB) propellant was studied. According to the typical HTPB solid propellant formula, the mesoscopic models of defect‐free HTPB propellant and HTPB propellant with different crack positions were established. The Cohesive element was inserted globally. The friction heat generation inside the material and microcracks, the deformation heat generation of ammonium perchlorate (AP) particles and the exothermic reaction of AP particles were considered. The drop hammer impact process of HTPB propellant with crack defects was simulated, and the influence of initial crack position on the low‐intensity impact ignition response time of solid propellant was studied. The results show that the ignition response time of the defect‐free HTPB propellant is 0.38 ms, and the ignition temperature is 621 K; the ignition time of HTPB propellant with crack defects in AP particles, interface, and matrix is 0.33, 0.34, and 0.36 ms, respectively. The ignition temperature is 578, 584, and 597 K.

Encapsulated Water Imparts Unprecedented Flame Retardancy to Cross-Linked Polystyrene Foams.

Water is an optimal flame retardant owing to high vaporization and specific heat, greenness and low-cost. The challenge, however, lies in how to integrate water into the matrix materials, and how to ensure its retention. To address the challenge, we developed cross-linked polystyrene foams (cPSs) that contain water within closed pores. These composite cPSs achieved a flame retardancy rating above V-0 in the UL-94 test when the water volume fraction in the ablation layer exceeded 33%. Notably, a representative composite, cPSs-M2, demonstrated significant improvements: the peak heat release rate (PHRR) and total heat release (THR) were reduced by 55.4 and 31.1%, respectively. Additionally, the time to ignition (TTI) and flame performance index (FPI) increased by over 10 and 25 times, respectively. Water evaporation is further and significantly delayed by flame-retardant coating and salts incorporation. The estimated service life of the surface-coated composite cPSs is projected to exceed eight years.

A Review of Ignition Characteristics and Prediction Model of Combustor Under High-Altitude Conditions

High-altitude relight is a critical challenge for aero-engines, directly impacting the safety and emergency response capabilities of aircraft. This paper systematically reviews the physical mechanisms, key factors, and relevant prediction models of high-altitude relight, highlighting the detrimental effects of extreme conditions such as low pressure and temperature on fuel evaporation rates, flame propagation speeds, and turbulent combustion processes. A comprehensive overview of the current state of high-altitude relight research is presented, alongside recommendations for enhancing the ignition performance of aero-engines under extreme conditions. This paper focuses on the development of ignition prediction models, including early empirical and semi-empirical models, as well as physics-based models for turbulent flame propagation and flame kernel tracking, assessing their applicability in high-altitude relight scenarios. Although flame kernel tracking has shown satisfactory performance in predicting ignition probability, it still overly relies on manually set parameters and lacks precise descriptions of the physical processes of flame kernel generation. Future studies on some topics, including refining flame kernel modeling, strengthening the integration of experimental data and numerical simulations, and exploring the incorporation of new ignition technologies, are needed, to further improve model reliability and predictive capability.

One-Step Realization of Skeleton Editing, gem-Dinitromethyl Functionalization, and Zwitterionization in a Laser-Sensitive 1,3,4-Oxadiazole Energetic Molecule.

The single-atom skeletal editing technology is an efficient method for constructing molecular skeletons, which has broad coverage in synthetic chemistry. However, its potential in the preparation of energetic heterocyclic molecules is grossly underexplored. In this work, an unexpected one-step reaction for the synthesis of novel energetic molecules was discovered which combines single-atom skeletal editing, gem-dinitromethyl functionalization, and zwitterionization in one step. The reaction demonstrates high efficiency while maintaining the characteristics of being mild and facile. The reaction mechanism was verified by experimental evidence and theoretical calculations. This reaction produces a novel energetic molecule (NPX-04) with good laser ignition performance, indicating its promise as a laser-sensitive energetic material.

The Effects of Pilot Structure on the Lean Ignition Characteristics of the Internally Staged Combustor

In order to explore the influence of pilot structure on the lean ignition characteristics in a certain type of internally staged combustor, the current study was conducted on the effects of the auxiliary fuel nozzle diameter, the rotating direction of the pilot swirler, and the swirl number on the lean ignition fuel–gas ratio limit, combining numerical simulation and experimental validation. The optimization potential of the mixing structure of this type of internally staged combustor was further explored. It indicated that the lean ignition fuel–gas ratio limit was significantly influenced by the diameter of the auxiliary fuel nozzles the swirl number of the pilot swirler and the combination of the same rotating direction for both pilot swirlers, while the mass flow rate of air was constant. Increasing the diameter of the auxiliary fuel path nozzles (0.4~0.6 mm) and having excessively higher or lower swirl numbers of the pilot module primary swirlers are not conducive to broadening the lean ignition boundary. Compared with the two-stage pilot swirler with the same rotation combination, the fuel–gas ignition performance of the two-stage pilot swirler with the opposite rotation combination is better. Under the typical working conditions (the air mass flow rate is 46.7 g/s and the ignition energy is 4 J), for a pilot swirler with a rotating direction opposite to the main swirler, the diameter of the auxiliary fuel nozzles is 0.2 mm, the swirl number of first-stage of pilot swirler is 1.4, and the lean ignition fuel–air ratio was reduced to 0.0121, which is 32.78% lower than the baseline scheme, which further broadens the lean ignition boundary of the centrally staged combustion chamber.

Experimental study on ignition characteristic and performance of a two-stroke engine fueled with aviation kerosene

Two-stroke spark ignition engines are widely used in Unmanned Aerial Vehicles. Aviation kerosene offers advantages over aviation gasoline due to its higher flash point and lower volatility, making it likely to be adopted more widely in the future. However, the poor evaporation and atomization characteristics of aviation kerosene result in suboptimal ignition performance, especially in the engine start-up phase. To explore the fitting mixture concentration and temperature conditions for achieving better ignition performance of aviation kerosene, A series of experimental studies are conducted on a two-stroke engine. The intrinsic factors affecting engine performance are analyzed. The experimental results indicate that optimal ignition characteristics, maximum power output, and a reduced misfire rate can be achieved at mixture concentration of 0.6 and mixture temperature of 80?C. Furthermore, the misfire rate is most sensitive to the combustion duration, while the cyclic variations show significant sensitivity to ignition delay. The results provide guidance for optimizing ignition performance during the start-up phase of two-stroke engines fueled with aviation kerosene.

Composite Structure MgB2@KNO3 With Multi-Effect Synergies to Improve Combustion Performance and Energy Release of B

ABSTRACT With the deepening of research, boron compounds have gradually gained favor among researchers due to their high calorific value and excellent ignition and combustion performance. In this paper, MgB2@KNO3, which exhibits excellent ignition and combustion properties, was synthesized using ultrasonic dispersion and magnetic stirring. The improved ignition mechanism and energy release characteristics of MgB2@KNO3 were elucidated using DSC/TG, SEM, EDS, XRD, and optical characterization, in conjunction with computational results from NASA-CEA. The surface activation energy and ignition energy of MgB2@KNO3 are 35.7% and 25%, respectively, lower than those of conventional B/KNO3 mixtures. Compared to the mixed sample of B/KNO3, the heat release of MgB2@KNO3 increased by 72.4%. The synergistic and effective interactions between oxygen, magnesium vapor, and boron in MgB2@KNO3 systems result in efficient energy release performance, making MgB2@KNO3 a promising material for use as a high-energy fuel in propellants, explosives, and pyrotechnic products.

Hydrogen driven HCCI engine combustion and performance indices: a numerical investigation

ABSTRACT Interest in hydrogen-powered engines is growing due to their potential to reduce greenhouse gas emissions and decrease reliance on fossil fuels. This research examines how the start of combustion (SOC) impacts the performance of homogeneous charge compression ignition (HCCI) engines using hydrogen exclusively. Using numerical simulations with a 0D multi-zone HCCI model, the study investigates parameters such as compression ratio (CR), equivalence ratio (ER), and intake charge temperature (ICT) to assess their influence on engine performance. The results uncover hydrogen’s unique combustion behaviour, characterised by its physiochemical properties and low-temperature combustion. The study identifies an optimal ER range of 0.1 to 0.3, with various ICTs and it is playing a pivotal role in promoting auto-ignition and accelerating combustion. However, an ER of 0.4 and ICT of 393 K produces relatively higher indicated thermal efficiency, which is affected by knocking due to a higher rate of pressure rise, constraining the ER range. Additionally, the research explores the potential of charge dilution to expand the ER range in HCCI mode. These insights provide valuable guidance for enhancing the operation of hydrogen-fuelled HCCI engines, facilitating the transition to cleaner and more efficient propulsion systems in transportation.

Advanced Al Hydrogel Propellants: Preparation, Thermal Stability, and Self-Sustainable Combustion Characteristics.

A new group of Al-based hydrogel propellants has been prepared and evaluated, aiming to replace currently used Al-ice propellants. The theoretical specific impulse (Isp) of these formulations is around 235 s. To enhance the ignition and combustion performances of these propellants, a 2% metastable intermixed composite Al@PVDF-CuO and minor ammonium perchlorate (AP) were introduced. The measured maximum ignition temperature of these hydrogel propellants was 2277 °C, higher than that of the Al-ice propellant (1700 °C). This increase in the ignition temperature could be attributed to the enhanced reactivity and energy release provided by the additives. Additionally, the initial mass loss temperature for this kind of hydrogel propellant, ranging from 211 to 235 °C, indicates higher thermal stability compared to the evaporation temperature of moisture water, indicating the strong water-locking capability of the gelling agent triaminoguanidine-glyoxal polymer (TAGP). The two main reaction steps involved in the combustion process are the oxidation of Al by H2O with H2 release, which coincides with the decomposition of TAGP at 246 °C, and a subsequent oxidation step with remaining H2O and TAGP residues peaking at 320 °C. The burn rate of these propellants is stable and controllable, ranging from 2.5 to 5.9 mm·s-1, which is crucial for maintaining a consistent thrust during propulsion. The combustion condensed products are predominantly α-Al2O3, which could influence the overall combustion efficiency and thermodynamic properties of the system. The effect of AP on the Al-water reaction has been further studied using reactive force field (ReaxFF) molecular dynamic simulations. It has been shown that the presence of AP may lead to a slight decrease in H2 production, which was attributed to the increase in the H2O concentration as the major decomposition product of AP.

Effect of SnO2 Nanoparticles Content on Ignition and Combustion Performance of Boron Particles

Abstract Boron is a potential metallic fuel substitute for solid propellant, however, its application has been limited by the surface oxide layer. Metal oxide are proposed to improve its oxidation performance. In the paper, boron particles were coated with SnO2 nanoparticles (n-SnO2) by a hydrothermal method. The B@SnO2 particles were characterized by SEM, TEM, and XRD. The results show that the boron particles were uniformly coated with n-SnO2 with range from 5 nm to 20 nm. The thermal oxidation, ignition and combustion performances were characterized by using TG-DSC, oxygen bomb calorimeter and laser ignition testing system. The relationship between the content of SnO2 and the performance of ignition and combustion were established. Significant reduction of oxidation temperature of boron particles was observed after coating with n-SnO2. The effect was more obvious with increasing SnO2 content. Furthermore, with the increase of SnO2 content, the ignition delay time of B@SnO2 particles decrease, its heat of combustion and combustion efficiency first increase then decreases gradually. Compared with boron particles, the maximum combustion efficiency of B@SnO2 particles reaches to 86.03%, increased by 57.19%, and the minimum ignition delay time reaches to 8 ms, decreased by 46.7%. Therefore, the coating significantly reduced ignition temperature and increased heat, and the particles has profound application potential as the solid fuel.

Ignition characteristics of AlNi films with different modulation periods on TaN exchangers

Abstract In order to reduce the ignition sensitivity of Al/Ni energy-bearing thin films, five kinds of Al/Ni energy-bearing thin films with different modulation periods were prepared by magnetron sputtering technology, and the transducer was prepared by integrating Al/Ni and TaN together by means of micro-electro-mechanical system technology. The surface topography and cross-section topography of Al/Ni energy-bearing thin films were characterized by scanning electron microscopy. The thermal reaction performance of Al/Ni energy-bearing thin films was detected and analyzed by differential scanning calorimetry. The ignition performance of Al/Ni@TaN was tested by capacitive ignition. The results showed that the Al/Ni energy-bearing thin films prepared by magnetron sputtering were tightly bonded. The temperature corresponding to the first exothermic peak of Al/Ni energy-bearing thin films showed increasing trend with the increase of modulation period. When the modulation period was 400nm, the minimum ignition voltage of Al/Ni@TaN transducer was 11V. When the modulation period was 800nm, the flame height of Al/Ni@TaN transducer was the highest under the condition of 25V and 33μf.

On the importance of species immiscibility in mixing-layer dynamics at supercritical pressures

The mixing dynamics of injected propellants is a key factor in determining the ignition performance and combustion-instability response of rocket engines, internal combustion engines, and gas turbines. A key source of uncertainty in the prediction of phase-exchange dynamics is the immiscibility of the injected propellants at supercritical pressure conditions, which induces liquid/vapor phase separation and surface-tension dynamics. While experimental observations indicate the presence of liquid/vapor interfacial structures, this interfacial dynamics is typically neglected in numerical analyses. To address this issue, the objective of the present study is to systematically evaluate the importance of species immiscibility on the phase-exchange dynamics of cryogenic LOX/GH2 mixing layers at typical rocket engine injection conditions. This is accomplished by comparing simulations of (i) a recently developed interface-capturing Regularized-Interface Method (RIM) formulation, and (ii) the commonly employed Diffuse-Interface Method (DIM) formulation. Analysis shows that the interfacial dynamics significantly impact the atomization and mixing of the propellants in the near-injector region, which is not captured by the DIM formulation. The findings of this study extend to other immiscible injection systems, such as LOX/kerosene and hydrocarbon-fuel/air, thereby highlighting the importance of resolving species immiscibility in simulating high-pressure combustion engines.

A preliminary investigation on a novel vortex-controlled flameholder for aircraft engine combustor

This study proposes a novel vortex-controlled flameholder (VCF) to enhance the combustion performance, particularly the lean ignition and blowout characteristics of afterburners in advanced aircraft engines across a wide range of operating conditions. Additionally, both experimental and numerical investigations were conducted to explore the effects of the cavity structure on the flow field, lean ignition, lean blowout, flame propagation characteristics, and outlet temperature rise distribution of the flameholder. Two distinct cavity structures designated closed-cavity (case-1) and open-cavity (case-2) were examined, the findings indicating that both case-1 and case-2 can generate large-scale vortex flow structures within the cavity, contributing to achieving excellent combustion stability. Case-2 demonstrated better lean ignition and blowout performance compared to case-1. Furthermore, both case-1 and case-2 exhibited the same ignition process, which comprised four distinct phases: Phase 1 involved the formation of an effective flame kernel; Phase 2 pertained to the ignition of the entire cavity by the flame kernel; Phase 3 represented the full development of the flame downstream of the cavity; Phase 4 described the formation of a fire tornado that anchors the flame front. Interestingly, the outlet temperature rise in case-1 is lower than that in case-2 at low fuel-to-air ratio (FAR) conditions. As the FAR increases, the difference in the outlet temperature rises between the two cases gradually narrows.

The Electrochemical and Combustion Properties of HAN‐ECSP Using Cu2O/Cu Electrode

AbstractElectrically controlled solid propellant based on hydroxyammonium nitrate (HAN‐ECSP) cause extensive research by scientists. Nevertheless, research on the performance of ECSP is currently focused on the formulation of propellants, and few studies have been published on the design of electrodes and the influence of electrochemical properties on the combustion performance of propellant. Metal have been reported as one of potential electrodes in HAN‐ECSP, but it has many drawbacks, such as being prone to corrosion during electrochemical and ignition combustion testing. Hence, modifying metal electrodes is one of the best ways to improve their adaptability in the HAN‐ECSP system. In this work, Cu2O/Cu and Cu2O/CF electrodes were prepared by oxidation methods and subsequent calcination with tube furnace. It can be seen from the experimental results that the Cu2O/Cu and Cu2O/CF have positive effect on the overpotential and corrosion resistance. Furthermore, the ignition delay time at 210 V of the propellant decreases from 3.28 s (Cu) to 2.05 s (Cu2O/Cu), 3.89 s (CF) to 1.85 (Cu2O/CF), respectively. Thus, Cu2O/Cu electrode is more suitable in the HAN‐ECSP system, and the electrochemical performance of HAN‐ECSP is an important factor that evaluate its ignition performance. Lower overpotential and higher current retention rate in the system will improve the ignition and combustion performance of the propellant. In general, this work reveals the influence of the electrochemical performance of propellants on their combustion performance, and provides data support and advices for improving the combustion performance of HAN‐ECSP.

Ignition and Combustion Performance of B@HMX Composite Microunit Prepared by Recrystallization of Solvent Evaporation.

Fuel boron (B) has the advantage of a high calorific value. However, a coating of boron oxide (B2O3) is present on the outermost layer of the B particles, which will greatly hinder the oxidation of B. In this study, the high-energy 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) is used to increase the activity of B powder, so as to enhance the ignition and combustion performance of B. Samples with various HMX contents are successfully prepared by recrystallization of the solvent evaporation method. The study of morphology and composition reveals that HMX is coated on the surface of B particles to form composite microunits. Interestingly, the heat and gas released during the decomposition of HMX facilitated the evaporation and destruction of the oxide film. Consequently, this promotes the oxidation reaction of B and results in a reduction in its initial oxidation temperature to 762.45 °C. The results of ignition and combustion tests show that the shortest ignition delay time of the sample with the mass ratio of B to HMX of 1:5 is 1.11 s, which is 0.38 s earlier than that of the physical mixed sample. In addition, the maximum height and width of the combustion flame are the largest. These results show that B@HMX composite microunits with a high energy activation effect provide an effective strategy for better application of B powder.

Ignition mechanism of a dual trigger electrode hollow cathode

Abstract Hollow cathodes serve as the electron source for thrusters and are critical elements of the electric propulsion system. To overcome the limitations of the small orifice blockage in the discharge path of the conventional hollow cathode on the ignition performance, a dual trigger electrode heater-based cathode with a sub-millimeter columnar bias electrode inserted into the emitter cavity is proposed. Both experiments and simulations indicate that the dual trigger electrode cathode provides faster ignition time and self-healing ability from poisoning. A coupled plasma-thermal model reveals the ignition mechanism from the discharge process, power deposition, and ion sputtering. The electric field penetration induced by the inner electrode enhances the energy injection of emitted electrons and internal ohmic heating to establish an efficient discharge from upstream to downstream. Primary ignition of the inner electrode enhances the power deposition on the emitter with ion bombardment dominated, raising the emitter temperature rapidly by 150 K from 1173 K in the preheating phase to accelerate the electrode switching. Energetic ions during the primary ignition perform explosive scanning sputtering of the emitter, uniformly cleaning the tungstate layer from the emitter surface and allowing the cathode to self-heal from poisoning, as verified by destructive environmental tests.

Performance analysis of dual-fuel engines using acetylene and microalgae biodiesel: The role of fuel injection timing

This study evaluates the impact of varying fuel injection timing (FIT) and dual-fuel modes on the performance and emissions of a compression ignition (CI) engine under different load conditions. The biodiesel used was derived from Chlorella protothecoides microalgae through a two-step transesterification process, and its elemental composition was characterized using gas chromatography-mass spectrometry (GC-MS). Acetylene gas was introduced into the engine intake manifold at a rate of 3 L per minute (LPM), while a blend of 20 % methyl ester from Chlorella protothecoides (B20 MEOA) served as the primary injected fuel. To predict engine performance and emission characteristics, advanced machine learning models were employed and evaluated using four statistical criteria, including R-squared, mean absolute error (MAE), and mean squared error (MSE). Experimental results indicated that the optimal configuration involved a dual-fuel mode combining B20 MEOA with acetylene gas and an advanced FIT of 25° before top dead center (bTDC). Performance analysis revealed that under all load conditions, the specific fuel consumption (SFC) decreased by 7.3 %, while brake thermal efficiency (BTE) increased by 1.6 % compared to conventional diesel. Emission testing showed a 7.6 % rise in nitrogen oxide emissions, alongside significant reductions in unburned hydrocarbons (12.5 %), carbon monoxide (25.6 %), and smoke intensity (7.5 %) relative to standard diesel operation. Optimization of the engine parameters ensured that key metrics, such as brake power (BP) and brake-specific fuel consumption (BSFC), remained within acceptable limits. The random forest model outperformed other machine learning models, demonstrating superior accuracy in predicting performance and emissions across all statistical measures. This study underscores the potential of combining advanced biodiesel blends with optimized FIT strategies to improve engine efficiency and emissions control, offering a promising approach for sustainable dual-fuel engine operations.

In situ iron coating of amorphous boron and characterization of its energy release behavior

Boron was widely employed as metal fuel in solid propellants for its higher gravimetric and volumetric combustion enthalpies. However, the low melting point and high boiling point of B2O3 on the surface of boron particles significantly hinder its ignition and combustion performance, seriously preventing the full realization of its thermodynamic potential. To address this issue, B@Fe composite fuels with different iron contents from 1.59 % to 7.09 % were prepared via liquid phase reduction in this paper and the quasi-static high temperature oxidation, ignition and combustion reaction characteristics and corresponding mechanism were studied, in order to provide effective modification techniques in supporting the large-scale engineering application of boron as metal fuel. The study results show that B@Fe can effectively reduce the ignition temperature and maximum heat flow temperature of amorphous boron, and increase the maximum mass gain rate. The ignition temperature and maximum heat flow temperature have an exponential function with the iron coating content. Iron coated amorphous boron can effectively shorten the laser ignition delay time by more than 50 %, and significantly change the flame structure, flame evolution process and combustion duration. Both amorphous boron and iron-coated amorphous boron flame showed a multi-layer structure, including the outer green flame, the middle yellow flame and the central incandescent flame. However, with the increase of the iron coating content, the flame height increased from 5.5 cm to 6.3 cm, the flame structure changed from mushroom type to triangle type, and the central incandescent flame area increased significantly. The equivalent combustion duration increased from 975 ms to 1997 ms, and the flame temperature increased from 1288 to 1505 °C. The emission spectra of BO2 and BO lines are captured during combustion. B@Fe with the increase of iron content, a large number of small diameter micropores appear in the condensed combustion products(CCPs) of composite fuels, and a grid-like structure was formed. With the increase of iron coating content, the boron content of condensed combustion products decreases, and the oxygen content increases. The main components of CCP include B, B2O3, B6O, FeB, Fe2B and Fe3B. Based on the ignition combustion experiment of B@Fe composite fuel, ignition combustion analysis model of B@Fe composite fuel was established.

Influence of steam induction on the performance and hydrogen knock limit of a hydrogen-gasoline spark ignition engine

This study examines the effect of steam induction on the performance and hydrogen knock limit of a hydrogen-gasoline dual-fuel Spark Ignition (SI) engine. The experimental setup includes gasoline direct injection, along with steam and hydrogen port induction. Steam-to-fuel ratios of 7.5 %, 15 %, and 22.5 % were used, and hydrogen was introduced in step sizes of 2 LPM until knock onset. The extension of the hydrogen knock limit was achieved through steam induction and retarding spark timing. Under the default configuration, the maximum achievable hydrogen flow rate was 8 LPM, which increased to 20 LPM with retarded spark timing and 22.5 % steam proportion. Steam induction initially increased and then decreased brake thermal efficiency, brake mean effective pressure, in-cylinder pressure, and heat release rate. In contrast, advancing spark timing and hydrogen enrichment consistently improved performance and combustion characteristics. Cyclic variation showed a decreasing trend with the introduction of steam and hydrogen. Unlike hydrogen enrichment, steam addition reduced CO and NOX emissions.

Experimental study of fuel distribution and combustion characteristics under subatmospheric pressure in an afterburner

The fuel distribution and ignition characteristics of an afterburner with typical components under subatmospheric inlet conditions are important references for improving the performance of the afterburner at high flight altitudes. In this work, lean ignition limits, outlet temperature distributions, fuel droplet size distributions and flame propagation processes in the afterburner were obtained experimentally. The results show that with increasing fuel injection angle, the fuel atomization characteristics improve, but the flame intensity fluctuation increases, and the ignition performance deteriorates; thus, a proper ratio of liquid-phase fuel to vapor-phase fuel is one of the key elements for successful ignition. On the one hand, the increased stabilizer blockage ratio results in a localized flow velocity increase near the trailing edge of the stabilizer, which effectively promotes fuel atomization in the shear layer, resulting in a fuel droplet size reduction of 25–30 μm. On the other hand, the extent of the recirculation zone increases, and a large low-pressure and low-turbulence recirculation zone is not conducive to fuel atomization in the flow direction. During the ignition process in an afterburner with all the typical components, the flame kernel first propagates along the flow direction for a certain distance and then propagates and anchors toward the shear layer. At subatmospheric pressures, the decrease in the intensity of the combustion reaction causes a reduction in the heat released by combustion, and the fuel droplet size increases by 10–25 μm, which requires more heat for evaporation. Therefore, the flame propagates an increased distance along the flow as the pressure decreases. Furthermore, the difficulty of ignition increases, and the ignition equivalence ratio increases by 0.1–0.15.