Ignition Model Research Articles

Numerical investigation on the effect of ignition timing on a low-temperature hydrogen-fueled Wankel rotary engine with passive pre-chamber ignition

Adopting the low-temperature hydrogen evaporated from the liquid hydrogen is capable of improving volumetric efficiency for the Wankel rotary engine (WRE). Considering the difficulty in ignition and slow flame propagation of low-temperature hydrogen-air mixtures, the passive pre-chamber is used to improve ignition and combustion. A three-dimensional computational fluid dynamics model for a turbulent jet ignition (TJI) WRE fueled by low-temperature hydrogen was established. The effects of low temperature and TJI on the in-cylinder flow field, combustion, emissions and leakage in the TJI-WRE fueled by low-temperature hydrogen were studied under different ignition timings. The results indicated that low-temperature tends to suppress the flame propagation, whereas TJI can accelerate the flame speed and promote flame propagation to the unburned zone in the combustion chamber. Combining low-temperature hydrogen with the passive pre-chamber can achieve high engine thermal efficiency and power while significantly reducing leakage. With the ignition timing set at 18 °CA before the top dead center, the indicated thermal efficiency reached 39.49% and the indicated mean effective pressure peaked at 0.77 MPa. Compared to the original engine, fresh mixture leakage through spark plug cavities and adjacent chambers was reduced by 72.13% and 78.79%, respectively.

Construction of a numerical model for cigarette smoking and combustion and simulation of combustion cone shape

Abstract Understanding the thermal conditions inside a burning cigarette is a top priority for controlling chemical emissions and cigarette design. Since experimental methods are difficult to observe in depth, this paper starts from the perspective of numerical simulation and models the structure of the tobacco distribution of the cigarette, integrating the end surface ignition model, puffing model, chemical reaction model, heat and mass transfer and diffusion model have established a three-dimensional comprehensive model that can represent the changes in combustion cone morphology during cigarette combustion. The model covers chemical reaction and mass transfer as well as generation, flow and reaction mechanism. The simulation results show that the model can better predict the temperature distribution, component distribution and combustion cone morphology changes during cigarette smoking and combustion. It provides an effective means for in-depth research on cigarette combustion.

Theoretical kinetics study of hydrogen abstraction reactions of O2(X3Σg/a1Δg) + CnH2n+2 (n ≤ 4)

The chain-initial reactions of small-molecule alkane (CnH2n+2(n ≤ 4)) oxidation participated by electronically excited oxygen O2(a1Δg) are crucial for understanding the role of O2(a1Δg) in plasma-assisted combustion and fuel reforming. Accordingly, in the present work, the energy barriers for the reactions O2(X3Σg/a1Δg) + alkane (n ≤ 4) → products were investigated by using high-precision quantum calculations. Rate constants for each reaction channel within the temperature range of 300–1500 K were predicted based on transition state theory (TST), supplementing plasma kinetics parameters. The energy barriers and rate constants for methane and ethane oxidation dehydrogenation reactions showed good agreement with literature data, validating the accuracy of the computational method employed in this work. The calculations revealed that the dehydrogenation sites have vital impacts on the reaction system. The energy barriers of the reaction channels involved in O2(a1Δg) were reduced at different dehydrogenation sites. Specifically, the change rate of each reaction energy barrier at primary, secondary and tertiary site was about 40 %, 65 % and 65 %, respectively. The reactions involving O2(a1Δg) significantly increased the reaction rate coefficient, especially for single hydrogen abstraction at the secondary and tertiary sites. The effect of O2(a1Δg) on ignition promotion and its regularity were further studied through kinetic simulations. The results suggested that adding O2(a1Δg) reduces the ignition delay time (IDT) of small molecular alkanes by approximately one order of magnitude, attributed to variations in energy barrier and branching ratios of different reaction channels. Notably, the H-atom abstraction reaction on primary site showed the largest sensitivity in IDT at 800 K, particularly for propane and isobutane, with IDT change rates of 98.0 % and 96.3 %, respectively. This study provided reasonable rate coefficients for kinetic modeling of plasma-assisted alkane ignition.

Experimental and Statistical Analysis of Iron Powder for Green Heat Production

In the current investigation, a novel methodology was employed to assess iron powder as a recyclable and sustainable energy carrier. Concurrently, an examination of the modeling of iron powder ignition and the ensuing heat output from the burner was undertaken. The flame temperature was determined by examining the light intensity emitted by the particles as they melted, which is directly related to the particle’s cross-sectional area. An account of the characterization of the experimental procedure, validation, and calibration is presented. Through measurements, distinct one-to-one correlations have been established between the scales of flame combustion and the temperatures of particles of varying sizes of iron. Additionally, a theoretical model for the combustion of expanding particles, particularly iron, within the diffusion-limited regime has been rigorously developed. This model delves into the spectra acquired from particle flames within the burner, utilizing Partial Least Squares Regression (PLSR) and Principal Component Analysis (PCA). This study investigates the use of optical fiber spectroscopy to predict flame temperature and assess iron powder size. The aim was to investigate how different sizes of iron powder affect flame temperature and to create calibration models for non-destructive prediction. The study shows that smaller particles had an average temperature of 1381 °C while larger particles reach up to 1842 °C, demonstrating the significant impact of particle size on combustion efficiency. The results were confirmed using advanced statistical methods, including PLSR and PCA, with PCA effectively differentiating between particle sizes and PLSR achieving an R2 value of 0.90 for the 30 µm particles.

Assessing the Cascading Post-Earthquake Fire-Risk Scenario in Urban Centres

The frequency of urban fires has grown in recent years everywhere, especially in historic districts, including in Portugal, due to the existence of sensitive igniting materials, the proximity of buildings, the complex urban layout, and the presence of many people. The current study proposes a technique, applied in the Baixa Pombalina (downtown) area in Lisbon, to undertake an appropriate evaluation of the post-earthquake fire cascading effect, which may cause major damage. The earthquake vulnerability and damage scenario were carried out using the Risk-UE method. An empirical fire ignition model was then applied to determine the quantity and location of fire ignitions for different return periods. Furthermore, the simple fire spread Hamada’s model was applied to both the equally spaced grid buildings, as in the original Hamada procedure, and the current study area layout for different time thresholds. Finally, the risk assessment for both models was carried out, allowing for the estimation of earthquake and fire losses, respectively. The results demonstrated that the models are comparable, showing that the Hamada model might be a useful tool for large-scale evaluations aimed at disaster-risk reduction and management since it gives useful information for managing and reducing natural and anthropogenic hazards.

Experiment and Numerical Prediction on Shock Sensitivity of HMX–Based Booster Explosive with Small Scale Gap Test at Low and Elevated Temperatures

In order to analyze the effect of temperature changes on the shock initiation performance of HMX–based booster explosive, which consists of 95% HMX and 5% FPM2602 by weight, a temperature calibration test of acceptor was designed. The temperature changes in the booster at low and elevated temperatures under the constraint of steel sleeve were obtained. Based on the temperature calibration results, polymethyl methacrylate (PMMA) was selected as gap material to conduct a small scale gap test (SSGT) of HMX–based booster under different temperature conditions. The corresponding critical gap thickness was tested. Based on SSGT results at different temperatures, the shock initiation processes were simulated by adjusting parameters of ignition and growth reactive rate model. The critical gap thickness and critical initiation pressure of HMX–based booster at different temperatures were numerically predicted. By combining SSGT experimental data and simulation results, the attenuation law and fitting prediction formula of the critical initiation pressure of HMX–based booster were proposed. The mechanism of temperature effect on the shock sensitivity of HMX–based booster explosive was analyzed. The research results indicate that the critical gap thickness of HMX–based booster gradually increases with the rise in temperature, and the critical initiation pressure gradually decreases during the shock initiation process under the heating temperature conditions. In addition, the simulation results show that the heated HMX–based booster under steel constraints becomes more sensitive at high temperatures (>120 °C), while the cooled booster is more insensitive, but its critical initial pressure does not change significantly between 88 °C and 120 °C. The experimental and numerical prediction results are important for the shock initiation safety and design of an insensitive booster explosive.

FLAIM: A reduced volume ignition model for the compression and thermonuclear burn of spherical fuel capsules

We present the “First Light Advanced Ignition Model” (FLAIM), a reduced model for the implosion, adiabatic compression, volume ignition and thermonuclear burn of a spherical DT fuel capsule utilising a high-Z metal pusher. FLAIM is characterised by a highly modular structure, which makes it an appropriate tool for optimisations, sensitivity analyses and parameter scans. One of the key features of the code is the 1D description of the hydrodynamic operator, which has a minor impact on the computational efficiency, but allows us to gain a major advantage in terms of physical accuracy. We demonstrate that a more accurate treatment of the hydrodynamics plays a primary role in closing most of the gap between a simple model and a general 1D rad-hydro code, and that only a residual part of the discrepancy is attributable to the heat losses. We present a detailed quantitative comparison between FLAIM and 1D rad-hydro simulations, showing good agreement over a large parameter space in terms of temporal profiles of key physical quantities, ignition maps and typical burn metrics.

Numerical analysis of the ignition and gas-phase flame evolution of pulverized coal based on online experimental diagnostics

A transient ignition model employing a reduced chemical mechanism was developed to investigate the ignition characteristics and the gas-phase flame evolution of pulverized coal particles. The chemical percolation devolatilization (CPD) model was chosen to simulate the devolatilization process, and its accuracy was validated using a high-temperature entrained-flow reactor. Additionally, a novel method was introduced to cross-validate the single-particle simulation results with real-time OH-PLIF experimental measurements of particle streams, particularly at a large particle spacing ratio. The ignition mode was determined using the ignition delay time and volatile burnout time. Results show that as the oxygen volume fraction increases from 5% to 50% at a temperature of 1800 K, the ignition mode transitions from homogeneous ignition (GI) to heterogeneous ignition (HI). Notably, the same ignition mode was observed regardless of whether GI was defined using gas-phase temperature or OH levels. In the homo-heterogeneous ignition mode, the gas-phase flame intensity, characterized by OH levels, increases rapidly, then decreases, and re-increases slightly. The sequence of gas-phase reactions initiates with volatile combustion, followed by the co-combustion of residual volatiles and newly generated CO, and culminates in the combustion of CO itself. Online experimental findings confirmed that CO originates from char oxidation. Throughout this process, the gas-phase flame front extends outward until the volatiles are consumed.

Investigation of Al-Li particle ignition dynamics with different Li content

Promoting the ignition of aluminum powder is considered an effective method to inhibit the agglomeration of aluminum powder in propellants and enhance combustion efficiency. This study utilizes laser ignition technology and high-speed photography to investigate the ignition and combustion processes of single aluminum particles and aluminum-lithium alloy particles. The focus is on comparing the effects of the diameter of micron-sized metal particles and the lithium content in aluminum-lithium alloy particles on the ignition and combustion processes of metal particles. The results show that the ignition delay time is directly proportional to the diameter of the metal particles and inversely proportional to the lithium content. For the aluminum-lithium alloy particle with a lithium content of 3.5 %, even if the diameter is close to 300 μm, the ignition delay time is only 125.5 ms, which is much smaller than that of the pure aluminum particle with a diameter of 208 μm. Compared to aluminum particles and aluminum-lithium alloy particles, there is basically no difference between the two during the combustion stage. However, in the ignition stage, aluminum-lithium alloy particles sequentially exhibit a red gas-phase flame corresponding to lithium and a yellow gas-phase flame corresponding to aluminum. This indicates that during the ignition process of aluminum-lithium alloy particles, lithium first reacts with the oxidative atmosphere and releases heat, providing a heat source for the subsequent ignition of aluminum particles. This also explains why the ignition delay time of metal particles is inversely proportional to the lithium content. An ignition model for aluminum particles in a multi-component atmosphere is established, which further considers the chemical reactions between lithium and oxidative gases, making the model applicable to aluminum-lithium alloy particles. This ignition model effectively describes the impact of particle diameter and lithium content on the ignition process of metal particles. The model is further verified, and the results show that the calculated ignition delay is in good agreement with the experimental data. Overall, this study provides deeper experimental and theoretical insights into the ignition and combustion processes of aluminum-lithium alloys, and the findings can guide the application of aluminum-lithium alloys in propellants.

Static analysis-based rapid fire-following earthquake risk assessment method using simple building and GIS information

After the occurrences of large-scale earthquakes, secondary damage (e.g., fire following earthquake) can result in tremendous losses of life, properties, and buildings. To reduce these disaster risks, fire following earthquake assessment methods composed of ignition and fire-burned rate estimation models have been utilized. However, previous methods required for large amounts of building and GIS information, and complex modeling and analysis processes, leading to significant time consumption. This paper proposed a static analysis-based rapid fire following earthquake assessment method using simple information and implemented it in Pohang City, South Korea. Based on previous studies, the best-fit model for the ignition rate estimation was selected, and a cluster-based fire-burned rate estimation model was developed using simple building information (e.g., construction year, building occupancy, story, and total floor area) from the public building database (e.g., building registration data). For the fire-burned rate estimation model, fire-resistant structure types were defined using simple building information, and this was utilized to generate clusters of buildings at a regional level by comparing fire-spread distances for each fire-resistant structure type with adjacent distances among the buildings. This proposed method was applied to Pohang City, South Korea, and validated as follows: (1) the selected ignition rate model predicted similar ignition numbers to the actual reported number (actual number of ignitions = 4 vs. predicted number of ignitions = 3), and (2) the fire-burned rate model estimated fire-burned areas with a marginal difference compared to the fire spread simulation (fire-burned area using the proposed model = 13,703.6 m2 vs. results of fire spread simulation = 16,800.0 m2, with an error of approximately 18%).

Laser ignition on single droplet characteristics of aviation kerosene at different pressures and initial diameters: ignition, combustion and micro-explosion

In this study, an experimental system for single-droplet ignition by laser under different pressures is established, and the laser ignition is used to examine how pressure and initial diameter influence ignition properties of RP-3 aviation kerosene single-droplet. The findings reveal that depending on the extent of the impact of bubble rupture on the droplet's shape, The droplet's morphological alterations can be classified into three types: micro-expansion, puffing, and micro-explosion. The ignition and combustion of droplets is segmented into four distinct phases: heating, ignition, intense combustion, boiling combustion. The flame width diminishes with rising pressure. Single droplet ignition delay time is strongly influenced by the pressure, which is reduced by 92.7 %, 94.1 % and 94.3 % for the three droplets from small to large diameters with the pressure increases from 1 bar to 4 bar. The change trends of droplet diameters are first increasing and then decreasing. The whole burning rate of RP-3 droplets goes up with the rise of pressure. A droplet laser ignition model is proposed, the minimum ignition energy of RP-3 droplets with an initial diameter of 1.42 mm at pressures of 1–4 bar are obtained to be 0.88 J, 0.80 J, 0.68 J, and 0.59 J, respectively.

Simulation and fabrication of reactive metamaterials for controllable energy response

AbstractSimulations and experiments were conducted to control the shock‐to‐detonation transition by energy trapping in localized regions of nitromethane that contained arrays of embedded dense particles (tantalum rods). The localizations were additively manufactured and designed with simulations carried out with ALE3D, that used the ignition and growth reactive flow model for the explosive. Modelling demonstrated enhanced reactivity when the tantalum rods were present, leading to a detonation that otherwise did not occur for the same strength shock without rods. Experiments that confirmed predictions of the simulation were conducted using Fritz plane wave lenses to drive various input shocks into the system. Photon doppler velocimetry was the primary diagnostic used to measure shock input and reaction progression. These results suggest that it is possible design explosives to localize sensitivity to shock loading within an insensitive material increasing the overall safety of fielded energetic materials.

Indirect drive ICF design study for a 3 MJ NIF enhanced yield capability

A proposed upgrade to the National Ignition Facility is under consideration that would ultimately increase the maximum operating envelope for the laser to 3.0 MJ with a peak power of 450 TW. This upgrade would provide opportunities to address an expanded set of data needs for NNSA’s Stockpile Stewardship mission, including the potential to generate fusion yields ≥30 megajoules. A simplified model of ignition and burn is used to scope the theoretical maximum target yield as a function of laser driver energy. We examine two indirect drive ICF target designs that make use of the 3 MJ laser drive using a common model for integrated laser-hohlraum simulations. These two designs compare and contrast the impacts of two different ablator materials, pure carbon and CH. Additionally, the potential for increased backscatter from these larger scale designs is discussed.

Comprehensive modeling of ignition and combustion of multiscale aluminum particles under various pressure conditions

The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time. This study seeks to develop theoretical ignition and combustion models for aluminum particles ranging from 10 nm to 1000 μm under wide pressure ranges of normal to beyond 10 MPa. Firstly, a parametric analysis illustrates that the convective heat transfer and heterogeneous surface reaction are strongly influenced by pressure, which directly affects the ignition process. Accordingly, the ignition delay time can be correlated with pressure through the pb relationship, with b increasing from –1 to –0.1 as the system transitions from the free molecular regime to the continuum regime. Then, the circuit comparison analysis method was used to interpret an empirical formula capable of predicting the ignition delay time of aluminum particles over a wide range of pressures in N2, O2, H2O, and CO2 atmospheres. Secondly, an analysis of experimental data indicates that the exponents of pressure dependence in the combustion time of large micron-sized particles and nanoparticles are –0.15 and –0.65, respectively. Further, the dominant combustion mechanism of multiscale aluminum particles was quantitatively demonstrated through the Damköhler number (Da) concept. Results have shown that aluminum combustion is mainly controlled by diffusion as Da > 10, by chemical kinetics when Da ≤ 0.1, and codetermined by both diffusion and chemical kinetics when 0.1 < Da ≤ 10. Finally, an empirical formula was proposed to predict the combustion time of multiscale aluminum particles under high pressure, which showed good agreement with available experimental data.

Experimental observation of crack formation on surface of charring timber

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

Theoretical study of the second- and third-H-abstraction reactions of monomethylhydrazine and nitrogen dioxide and its application to hypergolic ignition modeling

The chemical kinetics of the second–H-abstraction and the third-H-abstraction reactions of monomethylhydrazine (MMH) and nitrogen dioxide (NO2) and its application to modeling hypergolic ignition of MMH/NO2 were investigated in this work. Potential energy surfaces (PESs) for the key reactions were obtained by employing the CCSD(T)/CBS//M06-2X/6-311++G(d,p) single-reference method and the MRCI(7e,6o)/CBS//M06-2X/6-311++G(d,p) multi-reference method. The RRKM/Master Equation approach was used to calculate the temperature- and pressure-dependent rate constants. For the second-H-abstraction reactions, the trans-CH3NNH and HNO2/HONO are the major products. For the third-H-abstraction reactions, the bimolecular reaction of cis-CH3NNH+NO2→CH3NN+HNO2 is more favorable. The calculated rate constants and thermodynamics data were fitted and incorporated into two existing mechanisms to investigate their influence on modeling MMH/NO2 hypergolic ignition. The modeling results show that the system reactivity of MMH/NO2 is promoted by the second- and third-H-abstraction reactions, as the ignition delay times decrease by a factor of two at 300–800 K. The production rate and sensitivity analyses further validate the significance of the second-H-abstraction reactions at low temperatures. The sensitivity analyses at 1000 K also indicate the necessity of further investigations on CH2O, N2H2/NO2, and CH3NH/NO2 sub-mechanisms for modeling the MMH/NO2 combustion at high temperatures. This work provides not only new kinetic and thermochemical data but also a better understanding of the hypergolic ignition of MMH/NO2.

Research on nonequilibrium plasma-assisted evaporation and ignition of n-decane droplet

To evaluate the nanosecond pulsed discharge plasma-assisted evaporation and ignition attributes of hydrocarbon fuel droplets, numerical models are established. The influences of nonequilibrium plasma on the characteristics of n-decane droplet evaporation and ignition are numerically studied through a loosely coupled method employing a one-dimensional (1D) fully transient model of droplet evaporation and ignition and a model of nanosecond pulse plasma discharge. The results show that the reaction rate of the initial phase of n-decane droplet ignition is increased by nonequilibrium plasma. In addition, both the evaporation and ignition of the droplet are accelerated. Increasing the reduced electric field of the discharge leads to decreases in the droplet ignition delay time, survival time, and shortening amplitude. The evaporative cooling effect, which occurs at the initial phase of droplet ignition and typically decreases the local temperature surrounding a droplet surface, is weakened by the plasma. As the reduced electric field increases, the time to generate a high-temperature zone (&amp;gt;1800 K) decreases, while its duration increases. The initial phase of n-decane droplet ignition, in which the flame temperature increases while the flame radius decreases, is strongly affected by the plasma during the initial ignition phase. However, the plasma has little impact on the peak flame temperature and the flame radius during the stable combustion phase of the droplet. According to reaction kinetics analysis, the plasma directly interferes with the elementary reactions R330 (nC10H22 + O = 3-C10H21 + OH) and R331 (nC10H22 + O = 2-C10H21 + OH) of n-decane/air combustion. Moreover, the dissociation and oxidation processes of intermediate products are accelerated. Then, the important reaction rates, which determine the ignition delay time, increase indirectly. Thus, the overall ignition delay time of the n-decane droplet is shortened.

Extensive validation of a combustion and pollutant emission model of a pre-chamber engine including different pre-chamber geometries

In this work, a 0D/1D model of a single-cylinder pre-chamber spark ignition (PCSI) engine is extensively validated with experimental data in terms of performance, combustion, and emissions by varying the pre-chamber geometry and operating conditions.In the first stage, an experimental study is carried out on the PCSI engine at 1600 rpm and wide-open throttle, exploring different pre-chamber (PC) designs and various relative air/fuel (A/F) ratios, λ, in the main chamber.In the second stage, a phenomenological combustion model for PCSI engines is coupled with additional user-defined sub-models of in-cylinder turbulence, heat transfer, and pollutant emissions. These are integrated into a 1D engine model and used to reproduce a set of 16 measured data for a reference PC geometry. The model adequately describes the performance, pollutant production, and burn rate in both the pre- and main-chamber considering the effects of jet-induced turbulence and distributed multiple flame kernels in the main chamber.The predictive capability of the 1D model is further tested on an extended dataset composed of 163 points, including variations in the PC geometry, proving to satisfactorily reproduce experiments in terms of performance, combustion, and emissions. This last aspect represents the novelty of the present work, demonstrating the reliability of the physical background included within the in-cylinder sub-models.

Dynamic damage and non‐shock ignition behavior of polymer bonded explosive under lower velocity impact

AbstractThe accidental ignition of polymer‐bonded explosives (PBXs) caused by hot spots has been the focus of domestic and international research. Micro‐crack friction plays a crucial role in the formation these hot spots. In this study, confined tests were conducted to investigate the ignition response of PBX under impact loading. The experimental results revealed that the PBX underwent ignition under the given conditions of a pressure load with a pulse width of 50 μs and an amplitude of 638 MPa. The viscoelastic statistical cracking model (Visco‐SCRAM) and hot‐spot ignition model were used to describe the damage behaviors and ignition responses of the PBX. The simulation results revealed that more severe damage occurs at the center of the impact face and its vicinity under confined impact conditions, which is consistent with the observed post‐test samples. Additionally, simulation results also predict a trapezoidal shape for the severely damaged region within the PBX. The findings of this study provide insights for understanding the damage behavior and the critical ignition of PBX under impact loading.

Numerical study on ignition start-up process of an underwater solid rocket motor across a wide depth range

Solid rocket motors have important applications in the propulsion of trans-media vehicles and underwater launched rockets. In this paper, the ignition start-up process of an underwater solid rocket motor across a wide depth range has been numerically studied. A novel multi-domain integrated model has been developed by combining the solid propellant ignition and combustion model with the volume of fluid multiphase model. This integrated model enables the coupled simulation of the propellant combustion and gas flow inside the motor, along with the gas jet evolution in the external water environment. The detailed flow field developments in the combustion chamber, nozzle, and wake field are carefully analyzed. The variation rules of the internal ballistics and thrust performance are also obtained. The effects of environmental medium and operating depth on the ignition start-up process are systematically discussed. The results show that the influence of the operating environment on the internal ballistic characteristics is primarily reflected in the initial period after the nozzle closure opens. The development of the gas jet in water lags significantly compared with that in air. As the water depth increases, the ignition delay time of the motor is shortened, and the morphology evolution of the gas jet is significantly compressed and accelerated. Furthermore, the necking and bulging of the jet boundary near the nozzle outlet and the consequent shock oscillations are intensified, resulting in stronger fluctuations in the wake pressure field and motor thrust.