Combustion Propagation Research Articles

An evaluation of the combustion temperature profile of Ba(NO3)2-based composition

The study examined both theoretical and experimental combustion temperatures of Ba(NO3)2-based samples of composition with an oxidizer excess coefficient of α~0.72 under various pressures. The results indicate that at low pressures, the combustion temperature of the samples is significantly lower than the calculated value. The temperature profile in the combustion wave at atmospheric pressure was determined, revealing that the samples exhibit a high surface combustion temperature. The majority of the heat required for the propagation of the sample's combustion is released in the condensed phase. These findings underscore the influence of pressure on combustion characteristics and emphasize the importance of considering phase interactions in understanding combustion behaviors.

Including detailed chemistry features in the modeling of emerging low-temperature reactive flows: A review on the application to diluted and MILD combustion systems

Developing and optimizing new reactive systems with carbon-neutral fuels like biofuels, e-fuel, hydrogen, or ammonia is crucial for sustainable energy. This requires advanced technologies capable of fuel flexibility, high efficiency, and minimal pollutant emissions. However, these energy carriers still produce pollutants, especially NOx. To address this, engineers aim to lower combustion process temperatures by adopting different strategies such as burned gas recirculation, staging or increasing the air-to-fuel ratio. Yet, lean flames, though effective at emission reduction, are prone to instability and extinction, posing safety and mechanical risks. Emerging technologies like MILD Combustion, based on burned gas recirculation and reactant dilutions offer interesting solutions. The review article begins by synthesizing experimental studies and numerical simulations of MILD turbulent combustion. It then explores fundamental phenomena specific to diluted combustion (where MILD regimes are included as sub-sets), including autoignition and flame propagation. Using high-fidelity simulations and advanced experiments, it examines flow and mixing roles in reactive zones stabilization. Moving forward, the review paper addresses the inclusion of detailed chemical properties in modeling turbulent combustion systems. Scientific challenges revolve around modeling the intricate interactions between combustion chemistry and flow turbulence while maintaining computational efficiency compatible with industrial constraints. To address this, various simplified chemistry methods – such as reduced, tabulated, or optimized chemistry – have been developed. Additionally, turbulence/chemistry coupling modeling remains unresolved in simulations, with three main routes – geometrical, statistical, or reactor-based approaches – available for turbulent combustion modeling. The state-of-the-art in simplified chemistry and turbulent combustion modeling for low-temperature regimes is then focused on capturing MILD regimes, where there is a crucial impact of dilution by burnt gases, heat transfer, and turbulence mixing on the chemical flame structure. Recent advancements enabled by machine learning and deep learning algorithms are also highlighted. Lastly, the article underscores the critical need for data to validate models, emphasizing the importance of scale-bridging experiments.

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

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

Experimental study on the combustion and flame propagation characteristics of CH4/O2/N2 premixed turbulent jets

The combustion and flame propagation characteristics of CH4/O2/N2 premixed turbulent jets are investigated experimentally in a constant volume chamber (CVC) under different initial temperature (Tini, 300/400/500/600K) and oxygen fractions (γ, 0.4/0.6/0.8/1.0) conditions using High-speed camera and schlieren system. Four types of jet tip velocity were found: primary vortex motion at the jet top (M-type 1), secondary vortex motion (M-type 2), weaker positive and negative feedback between the flame and the flow field (M-type 3), and stronger positive and negative feedback (N-type 4). With the decrease of γ, the jet acceleration and deceleration mechanism is changed from the top vortex motion mechanism in M-type 1 and M-type 2 to the positive and negative feedback mechanism in M-type 3 and N-type 4. The interaction between the pulsating flow field and the heat release from the pre-chamber transitions to the flow field momentum dissipation. For M-type 1 and M-type 2, there is no significant difference in overpressure dynamics. The N-type 4 exhibits lower peak pressure and pressure rise rates. Moreover, the flame mode was predicted under higher Pini (10 bar ≤ Pini) and lower γ (γ ≤ 0.4) based on empirical equations established by the self-similar analytical model.

Effect of H2O on macroscopic flame behaviors and combustion reaction mechanism of 1,1-difluoroethane (R152a)

1,1-difluoroethane (R152a) is one of the most prospective low GWP refrigerants but may trigger fires and explosions once it leaks. Understanding the flame propagation process and combustion mechanisms at different relative humidity conditions is essential to use flammable refrigerants safely. In this study, a high-speed camera has recorded the flame propagation of R152a combustion near the flammability limit. Combining with macroscopic experimental phenomena, we revealed the effect of H2O on the microscopic mechanism of R152a combustion by using reactive force field molecular dynamics simulations with a reliable force field. The promotion effects of H2O on the oxidation of R152a were revealed from an atomistic perspective. The differences of oxidation intermediates and products in different environments were analyzed for the first time. The H2O/O2 environment was the most potent promoter of R152a decomposition, followed by the O2 and the pyrolysis environment. The O2/H2O environment reduced the apparent activation energy of R152a, significantly enhanced the consumption rate of R152a, and enriched the number of species. O2 reacts with H2O or H to form OH to accelerate the reaction process. The H2O could provide more OH active fragments for the reaction. Moreover, it promotes the formation of HF and H2, H2O + F→HF + OH, H2O + H→H2 + HO. This study aims to provide a guiding theory for the safe application and disaster prevention of flammable refrigerants.

Study on the Effect of Two-Stage Injection Strategy for Coal-to-Liquid/Gasoline Reactivity-Controlled Compression Ignition Combustion Mode.

An experimental study was carried out on a modified single-cylinder dual-fuel engine in reactivity-controlled compression ignition (RCCI) mode using pilot fuels with different physicochemical properties, and the effects of the pilot fuels and the two-stage injection strategy on the combustion and emission characteristics of the RCCI mode were explored. The results show that when coal-to-liquid (CTL) is used with a high cetane number as the pilot fuel, the reactivity stratification of the fuel-air mixture is more pronounced. With the advancement of pilot injection timing (SOI1), the heat release rate (HRR) of the CTL/gasoline mode gradually changes from a bimodal pattern to a unimodal pattern. Among them, the bimodal HRR includes CTL premixed combustion and gasoline flame propagation, as well as CTL diffused combustion and gasoline multipoint spontaneous combustion, while the unimodal HRR represents CTL premixed combustion and gasoline multipoint spontaneous combustion. However, the HRR of the fossil diesel/gasoline RCCI combustion mode always exhibits a unimodal form. With the advancement of the main injection timing (SOI2), the gravity center of heat release (CA50) is more advanced when using CTL as the pilot fuel due to the short ignition delay. Overall, compared to fossil diesel, using CTL as the pilot fuel is conducive to controlling the pressure rise rate, which expands the operating range of the RCCI combustion mode. Besides, for both pilot fuels of CTL and fossil diesel, the advancement of SOI1 lowers particle emissions, and the advancement of SOI2 reduces NOx emissions, while the two-stage injection achieves higher indicated thermal efficiency.

Reconstruction method considering the electrostatic signal waveform of velocity distribution in flame based on EST

The velocity distribution of flame is an important combustion dynamic parameter that is used to analyze the stability, heat transfer and propagation of combustion. Digital particle image velocimetry and laser Doppler velocimetry are commonly used to measure the velocity distribution of flame. However, these methods work by adding tracer particles into the flame. A dual-section electrostatic tomography (EST) system is designed to detect the induction signal of the charged particles generated by the ionization process of combustion. The velocity distribution of flame is reconstructed through the electrostatic direct velocity tomography (EDVT) method. However, the different distance between the movement trajectory of the charged particles and a pair of electrodes for the cross-correlation calculation causes the difference in the induced signal waveform. It leads to an error in the cross-correlation velocity calculation. By analyzing the influence of the single charge induction signal waveform on the calculation of cross-correlation velocity, the reason for this error is clarified. Therefore, an electrostatic signal-waveform-based direct velocity tomography (ESDVT) method is proposed. The experimental results from a belt-type electrostatic device show that the average value of the L2-norm error of the ESDVT method is reduced by 40.9% compared with the EDVT method. Finally, using the method proposed in this paper, the velocity distribution at different sections of the Meker flame is reconstructed without adding tracer particles.

Effects of methane concentration on flame propagation mechanisms and dynamic characteristics of methane/coal dust explosions

The study explores the flame propagation and explosion dynamic behavior of gas/powder two-phase compound explosions, taking methane and coal dust mixture as the research object. The influence of different methane concentrations on the compound explosion characteristics was researched. The vertical pipeline, high-speed camera, ion current probe, and pressure sensor be used to test the propagation behaviors, microstructure characteristics, and explosion dynamics of compound explosion flames. The function of methane concentration on the propagation behaviors, combustion reaction zone thickness, flame temperature, propagation velocity, and explosion pressure of compound flame was revealed, and the propagation mechanisms of gas/powder compound explosion flames were explained. The experimental research discovered that the compound flame of methane/coal dust explosion presents a white luminous zone with uniform distribution and appears to have an approximate homogeneous combustion state. The explosion dynamics parameters all showed a trend of first increased and then decreased as the methane concentration increased, but the reaction zone thickness of the combustion first reduced and then increased. In addition, the dominant position of homogeneous or heterogeneous combustion in the combustion reaction zone will also switch with the change in methane concentration. The compound flame is similar to premixed gas combustion under optimal methane concentration, the combustion zone thickness (δ) and preheating zone thickness (β) are the smallest, and the compound explosion shows powerful performance. In addition, the flame propagation mechanisms of methane/coal dust compound explosion were elucidated based on the theory of heat.

In Situ Formation of Titanium Diboride/Magnesium Titanate Composites by Magnesiothermic-Based Combustion Synthesis

In situ formation of TiB2–Mg2TiO4 composites was investigated by combustion synthesis involving the solid-state reaction of Ti with boron and magnesiothermic reduction of B2O3. Certain amounts of MgO and TiO2 were added to the reactant mixtures of Ti/B/Mg/B2O3 to act as the moderator of highly exothermic combustion and a portion of the precursors to form Mg2TiO4. Two combustion systems were designed to ensure that synthesis reactions were sufficiently energetic to carry on self-sustainably, that is, in the mode of self-propagating high-temperature synthesis (SHS). Consistent with thermodynamic analyses, experimental results indicated that the increase in pre-added MgO and TiO2 decreased the combustion temperature and propagation velocity of the flame front. MgO was shown to have a stronger dilution effect on combustion exothermicity than TiO2, because the extent of magnesiothermic reduction of B2O3 was reduced in the MgO-added samples. In situ formation of the TiB2–Mg2TiO4 composite was achieved from both types of samples. It is believed that, in the course of the SHS progression, Mg2TiO4 was produced through a combination reaction between MgO and TiO2, both of which were entirely or partially generated from the metallothermic reduction of B2O3. The microstructure of the products exhibited fine TiB2 crystals in the shape of short rods and thin platelets that existed within the gaps of Mg2AlO4 grains. Both constituent phases were well distributed. A novel and efficient synthesis route, which is energy- and time-saving, for producing Mg2TiO4-containing composites was demonstrated.

Reverse combustion propagation in an oxygen-limited and -enriched N2/O2 flow for a bed packed with rice husk

Propagation characteristics of reverse combustion significantly impact the conversion of solid fuels in packed beds, especially under variable reaction atmosphere conditions. In this study, the propagation of reverse combustion was experimentally studied in an oxygen-limited and -enriched O2/N2 flow with an oxygen concentration range of 21–100 % for a bed packed with rice husk. The temperature profile measured by thermocouples along the bed height was processed to appreciate the driving mechanism of combustion front, as well as the reaction structure inside the bed. Besides, the contribution of volatiles gas-phase oxidation and char surface oxidation to reverse combustion was also evaluated. Results show that compared to the air case, an oxygen-enriched condition broadens the operating range of oxygen flow rate for the oxygen-limited reverse combustion. Under high oxygen concentration conditions, the low-temperature oxidation of rice husk inside the reaction front becomes enhanced. Such chemical reaction effect widens the whole reaction front thickness and thereby reduces the oxidation intensity in local regions, resulting in a faster ignition rate and a lower temperature for combustion front. It is found that this process is dominated by the gas-phase oxidation of volatiles, of which oxygen consumed is above 60 % of the supplied. As oxygen concentration increases, the gas-phase oxidation of volatiles becomes further enhanced. Correspondingly, the oxidation ratio of char is gradually approaching a limit, about 12 %, especially at the oxygen concentration above 50 %. These findings will facilitate a better fundamental understanding of driving mechanism of this special combustion process and thereby provide an important theoretical basis for efficient thermal conversion of solid fuels.

Propagation of Combustion Over Composites Based on Porous Silicon and Sodium-Perchlorate Monohydrate

Propagation of Combustion Over Composites Based on Porous Silicon and Sodium-Perchlorate Monohydrate

The effect of particle size on physicochemical and thermal analysis of rice husk for explosion studies

The effect of rice husk particle size on physicochemical and thermal behaviour was studied for identify whether it has the potential to explode. The thermal degradation of the lignocellulosic constituent in rice husk was evaluated via thermogravimetric analysis (TGA). Rice husk morphology and elemental composition were evaluated via scanning electron microscopy with energy dispersive X-ray (SEM-EDX). Results showed that the rice husk samples were richer in cellulose than in lignin in terms of weight percent, indicating that they were combustible. Uncontrolled combustion propagation can lead to an explosion. However, the presence of ±5 wt% silicon in rice husk may reduce the explosion severity due to its low thermal conductivity. Furthermore, the smallest particle size, 71 µm recorded faster thermal degradation and more explosive as compared to 106, 160 and 250 µm. This preliminary data is very useful to improve the safety technique specifically for rice husk dust explosion protection, prevention, and mitigation.

On the Mechanism of Combustion Propagation in Porous Nanothermites

On the Mechanism of Combustion Propagation in Porous Nanothermites

Numerical investigation on explosion hazards of lithium-ion battery vented gases and deflagration venting design in containerized energy storage system

Large-scale Energy Storage Systems (ESS) based on lithium-ion batteries (LIBs) are expanding rapidly across various regions worldwide. The accumulation of vented gases during LIBs thermal runaway in the confined space of ESS container can potentially lead to gas explosions, ignited by various electrical faults. However, a systematic simulation and assessment of the battery vented gases explosion under deflagration venting design still lack. In this work, a three-dimensional combustion model was developed within the frame of open source computational fluid dynamics code OpenFOAM based on a full-scale container, and the LIBs vented gases in realistic proportion were selected as the combustion gas. Coupled boundary conditions were introduced to enable the response of explosion vent doors and top deflagration vent panels on pressure. The internal and external overpressure, flame temperature, and wind velocity fields were employed to assess the gas explosion hazards to ESS container structure and surroundings. The results demonstrate that altering the vent door pressure, without the top vent panel, still leads to serious explosion accidents. There will be unacceptable overpressure for the container structure, as well as serious visible flames and high-speed airflow invading the external environment. Lower vented gas concentrations can reduce explosion hazards, and introducing the vent panel design aids to promote such reduction. The overpressure within the container is significantly decreased by guiding the top external secondary combustion through the vent panel, and the influence range for the environments is also significantly reduced on X-axis. The ignition location can affect the propagation of gas combustion within the container, and the proposed complete vent panel design minimizes the impact on the container structure and surroundings. The findings of this work can offer new references for the safety design of the LIBs ESS.

Burning rate catalysts action on the trinitroresorcinol combustion wave parameters

AbstractThe effect of burning rate catalyst—3% nickel salicylate (NS) with 1% carbon nanotubes (CNT)—on the combustion wave parameters of trinitroresorcinol (TNR) at 2 MPa as well as on the structure and elemental composition of the carbon frame on the surface of quenched TNR samples at 2 and 15 MPa were studied. The catalyst itself increases the burning rate by ∼4.3 times. It is shown that for the sample with NS and CNT, the accumulation of nickel particles formed during the decomposition of the catalyst occurred (∼110 times) at 2 MPa on the carbon frame. The degree of catalyst particles accumulation at 15 MPa is ∼60 times lower than at 2 MPa, so the burning rate increases by only 1.3 times. At 2 MPa the catalyst significantly (by ∼68 K) increases the combustion surface temperature, by ∼2.7 times increases the temperature gradient in the carbon frame zone, and reduces the length of the primary (fizz zone) and secondary flames. As a result, the heat release rate on the frame is 13.5 times higher than on the carbon frame of the sample without a catalyst. For TNR samples the thermal conductivity coefficient, based on the characteristics of the framework obtained, was calculated, and it was shown that the thermal conductivity coefficient of the carbon frame for a sample with NS and CNT is significantly (∼8 times) higher than for a sample without a catalyst. From the calculation of the heat balance of the c‐phase at 2 MPa it follows that the combustion leading zone of the sample with a catalyst is the carbon frame, from which ∼98% of the necessary for combustion propagation heat enters the c‐phase; for a sample without a catalyst, the heat gain from the gas zone is ∼20%; the leading zone is the reaction layer of the condensed phase. Thus, the mechanism of combustion catalysis of aromatic nitro compounds is the same as for double‐base propellants. Two conditions are necessary for combustion catalysis: the formation of a carbon frame on the combustion surface, on which catalyst particles accumulate, and the carbon frame thermal conductivity coefficient must be significantly higher than that of the gas zone above combustion surface of the sample without a catalyst.

Preparation of Si@PVDF composite microspheres by electrostatic spraying for enhanced energetic characteristics

In this study, Si@PVDF composite microspheres are prepared by the electrostatic spraying method. The spheres are with average diameter of around 2 μm (when at ideal stoichiometry), within which Si nanopowder is uniformly distributed. The exothermic properties of samples are studied through simultaneous thermogravimetry and differential scanning calorimetry. Benefiting from the improved interfacial contact quality, Si@PVDF shows increased chemical reactivity in terms of reduced reaction onset temperature, peak temperature and apparent activation energy than those of physically mixed Si/PVDF counterpart. Si/PVDF cannot be ignited through Joule heating, either in the powder of pellet form, while self-sustained combustion propagation is observed for Si@PVDF pellets. The combustion behaviors of Si@PVDF pellets are systematically studied in open-air (where light signal is analyzed) and constant-volume (where pressure signal is analyzed) conditions. The results show that the combustion process is influenced by the equivalence ratio, porosity of the pellet and the accessibility of O2 gas in the environment. Overall, the encapsulation of Si nanopowder into PVDF microspheres using electrostatic spraying shortens the mass and heat transfer distance and thus realizes enhanced energetic characteristics.

An experimental study of the combustion characteristics of novel Al/MOX/PVDF metastable intermixed composites

The combustion of metastable intermixed composites (MICs) containing fluoropolymers is yet still not well understood. In this study, five new Al/MOX/PVDF nanocomposites (MOX: WO2, WO3, CuO, Fe2O3, Bi2O3) are prepared using a high-energy ball milling method. The thermal decomposition behaviors, combustion characteristics, and combustion products of the MICs are compared using TG-DSC, laser ignition test, and a multifunctional combustion diagnostic system. It is proved that PVDF efficiently promotes the energy release of conventional thermites. All five composites show a higher heat of reaction than Al/MOX in an argon environment by over 30%. Al/WO3/PVDF has the fastest combustion propagation speed in the confined combustor (72.5 mm⋅s−1). Due to the low boiling temperature and low thermal conductivity of the product, Al/Bi2O3/PVDF exhibits the lowest ignition delay (62 ms), the best pressure output performance (27.5 MPa⋅s−1), and the least product agglomeration (D43 = 15.2 μm). Due to the highest heat of reaction (3829 J⋅g−1), Al/CuO/PVDF has the highest flame temperature (2544 °C). The combustion flame temperature of Al/MOX/PVDF nanocomposites is suggested to be controlled by the heat of reaction, the ignition delay is mainly controlled by the thermal conductivity of the material, and the main factor affecting the high pressure output is the boiling point of the combustion products. This study can provide a theoretical basis for the development and application of MICs.

Программный робот-проектировщик для выбора автоматических установок пожаротушения

Автоматические установки пожаротушения (АУП) широко применяются для защиты пожароопасных объектов, при этом выпускается большое количество АУП разных типов. Актуальная задача для проектировщиков – выбор АУП, обеспечивающих эффективную защиту объекта. Для выбора оптимального варианта важно провести сравнительную оценку возможных типов АУП. Для решения этой задачи предлагается использовать программный робот-проектировщик RPA. Разработана автоматизированная программа выбора АУП, которая выполняет функции робота-проектировщика, а пользователь ведет с ним диалог по исходным данным, оценке и выбору предлагаемых вариантов. Automatic fire extinguishing systems (AFESs) are the basis for the protection of fire-hazardous facilities. Currently, a large number of AFESs of various types are produced. The issue of selecting AFES is of significant importance because it influences both the cost of the technical means used and the efficiency of the facility protection. Recommendations for the choice of automatic fire extinguishing system are given in the VNIIPO paper “Selecting the type of automatic fire extinguishing systems”. The calculation of technical means and efficiency indicators is carried out for each type of AFES for the comparative evaluation in accordance with these recommendations. The calculations are entered manually and require considerable time with the assistance of specialists. The estimated figures used are difficult to compare and are very approximate for the comparative analysis, because they are based on average data. The human factor has a significant impact on the objectivity of the evaluation. Automation of calculations, according to the established methods of calculation, would greatly simplify the selection of the AFES and make the choice objective. The use of estimated figures based on actual data increases the reliability of the evaluation significantly, including the starting of fire extinguishing response time and the response time of fire extinguishing process, being the most optimal criteria for evaluating the efficiency. The possibility of using AFES, accepted in SP 485.1311500.2020, should also be taken into account, including the rate of combustion propagation of combustible materials used. During the evaluation it is reasonable to take into account the damage from a fire, determined, for example, by the area exposed to fire. Reliability is the most important indicator of the AFES efficiency. Nowadays, program-controlled RPA robots are widely used to perform the control functions of typical processes in a dialogue with a human. The challenge was set to create a program-controlled robot for selecting the AFES, according to the initial data of the protected facility, being the same for all used AFESs. The robot performs an independent automatic evaluation of technical means and selection of the optimal AFES according to comparable estimated figures, based on actual data for all AFESs simultaneously. An automated program for selecting AFES was developed to accomplish this task. The program performs the functions of a program-controlled robot (Certificate of state registration No. 2022664536), and is presented in the Internet web application available at: https://firerobots.ru/calculate. A unified approach based on the general requirements of the code of practice SP 485.1311500.2020 makes it possible to compare different fire extinguishing systems. The initial data of the protected facilities entered into the program, and the system makes calculations of technical means, and determines the estimated figures for effective fire extinguishing. The proposed technical solutions make it possible to create an AFES selection system using a service program that performs the functions of a design robot, including: interactive input of information, automated calculations in accordance with regulatory requirements and calculation formulas, receiving the necessary objective evaluation data on efficiency and pricing, selection of the optimal AFES from a number of AFESs used for the protection of facilities

Laser and pre-chamber ignition, combustion and flame propagation characteristics of CH4/air mixtures in a constant volume combustion chamber

The most important stages determining the qualitative and quantitative characteristics of a combustion process are mixture preparation, ignition, combustion itself and pollutant emissions. Among these, the ignition phenomenon stands out in terms of ensuring a reliable operation under every working condition (which also affects subsequent stages). In this study, the influence of the properties and the type of the ignition source on combustion and flame propagation characteristics of methane/air mixtures were investigated by using a passively Q-switched Nd:YAG crystal laser and a pre-chamber ignitor in a constant volume combustion chamber. The number of consecutive pulses and the air-fuel-equivalence ratio are studied parameters. With the laser ignition system, it was possible to ignite fuel-air mixtures at very lean conditions. However, as flow conditions in the combustion chamber varied due to the protruding part of the pre-chamber ignitor, ignition possibility decreased and combustion metrics worsened. The number of pulses affected combustion parameters such as the ignition delay time, the combustion duration, the rate of pressure rise etc. in a non-monotonic manner. Deteriorations and improvements on such parameters were detected depending on the air–fuel-equivalence ratio λ.

A quasi-implicit and coupled multiscale scheme for simulating combustion of pellets of core-shell structured intermetallic particles

A comprehensive theoretical and computational framework is developed to simulate combustion and flame propagation in a packed pellet of core-shell structured intermetallic energetic particles. A coupled multiscale approach is adopted, in which the atomic diffusion process in micron-scale particles is strongly linked to the macro-scale energy transport in the pellet. Species transport equations are solved for the core-shell structured particle, with the diffusivity treated as a temperature-dependent parameter. The energy equation is solved for the pellet, with the source term governed by the evolution of species concentrations in the core-shell structured particle. A quasi-implicit numerical scheme is developed to ensure stability and a generalized Crank-Nicholson scheme is adopted to tune the degree of implicitness and control the order of temporal accuracy. Further, the temperature dependence of properties and phase change of materials are considered. The theoretical and computational framework is applied to simulate combustion of pellets with Ni/Al core-shell particles of diameters in the range of 10–100 µm. An attempt is made to simulate experiments as closely as possible and the predictions are compared with the available experimental data. Suitable diffusivity model parameters that best describes the experimental data are identified. Parametric studies are conducted to study the effects of particle size, interstitial gas, and pressure on the combustion velocity. Results provide novel insights on the combustion process and directions for future studies.