Combustion Wave Propagation Research Articles

Numerical analysis of detonation combustion wave in pulse detonation combustor with modified ejector with gaseous and liquid fuel mixture

The detonation combustion phenomenon is supersonic combustion process and follows on thermal explosion in combustor. Deflagration to detonation transition occurs in detonation tube due to pressure oscillation in PDE combustor, which is driven by acoustic combustion phenomena in detonation tube. As this combustion process has great significance role for future propulsion system, the present objective is to investigate the effect of modify ejector having half angles of α = (− 4°, 0°, + 4°) on detonation combustion wave propagation regime. Further the propulsion thrust of liquid kerosene and gaseous hydrogen–air mixture are also analyzed. This numerical simulation has been analyzed by LES turbulence model for DDT and shock wave pressure oscillation in pulse detonation combustor at Fluent based CFD plat form. The one-step irreversible chemical kinetics model analyzes the details exothermic chemical reaction mechanism inside the combustor. However, the shrouded ejector with taper angle of α = +4° performed the strong starting vortex generation and shortest possible time of 0.032 s for fully developed detonation wave. The simulation results also shows that thrust force augmentation of hydrogen–air mixture is greater compared to combustion process of liquid kerosene–air mixture with significant magnitude of 38 N. Although kerosene–air mixture produces less pollutant number but the propagation flame velocity is 2550 m s−1 for hydrogen/air mixture, which is near about C–J velocity and comparatively higher than kerosene/air combustion process.

Experimental Study on Combustion Characteristics of Lean Methane-air Mixture in a Combustor Filled with Staggered Alumina Cylinders

ABSTRACT The premixed combustion of lean methane-air mixture in a structured porous combustor filled with alumina cylinders was experimentally studied. The alumina cylinders with a diameter of 6.5 mm and a height of 19.5 mm were regularly staggered placed in the combustor and the average porosity of the packed bed was approximately 0.43. The characteristics of interest were the temperature distribution, the peak combustion temperature, and the combustion wave propagation velocity. The parameters investigated that affect these characteristics included gas inlet velocity and equivalence ratio. Results indicated that the combustion wave propagation was stable and super-adiabatic combustion phenomena were observed under the test conditions of the equivalence ratios in the range of 0.162–0.324 and inlet velocities in the range of 0.43–0.86 m/s. The lean flammability limit was extended to an equivalence ratio of 0.162 at the inlet velocity of 0.43 m/s. The larger equivalence ratio and inlet velocity can supply more fuel to be sufficient combustion, resulting in the higher peak combustion temperature. The combustion wave propagation velocity was inversely correlated with the equivalence ratio. With increasing inlet velocity, the combustion wave velocity increased. The order of magnitude of the combustion wave velocity was 0.1 mm/s. The pressure drop across the structured porous packed bed was remarkably smaller than that of the random one.

Formation of combustion wave in lean propane-air mixture with a non-uniform chemical reactivity initiated by nanosecond streamer discharges in the HCCI engine

The propagation of combustion wave, which is formed as a result of impact of a filamentary pulsed periodic non-equilibrium discharge on a mixture that is not ignited by only compression in the HCCI engine, has been simulated. The discharge for a short time locally activated the mixture in the engine cylinder at a certain crankshaft rotation angle at the compression stage. The approach to evaluation of the temperature and composition in the region activated by high-frequency corona discharge has been proposed. Multi-pulse and multi-channel nature of discharge was accounted for in our model. The densities of chemically active species produced during streamer propagation were found using two-dimensional axially symmetric fluid model. The obtained composition and temperature in the activated zone were the initial conditions for modeling the propagation of combustion wave along the cylinder radius in 1D approximation. Special terms were included in equations responsible for the compression along the axis of cylinder to mimic the real change in pressure in cylinder. The calculations were performed for a lean C3H8-air mixture, which is characterized by the presence of low-temperature heat release (LTHR) stage, and intermediate and high temperatures heat release (ITHR and HTHR) stages. It was shown that the ignition timing in activated zone depends on the specific energy input into the streamer channel, the radius of activated region coupled with the volume fraction of activated region treated by discharge, and the moment of discharge initiation relative to the top dead center (TDC). The speed of combustion wave, the occurrence of auto-ignition in the end gas and transition to combustion, accompanied by “knocking” or strong pressure fluctuations are largely determined by the moment of discharge initiation and the specific energy input. The significant effect of discharge is explained by the stimulation of oxidation kinetic mechanisms at LTHR and ITHR stages.

Geometric influence on the propagation of the quasi-detonations in a stoichiometric H2-O2 mixture

Combustion wave propagation was studied experimentally in an obstructed narrow channel filled with stoichiometric H2-O2 mixtures using a simultaneous schlieren and soot foil technique. The propagation modes uncovered were classified as fast-flames, discontinuous detonation, and continuous detonation. In this study blockage ratio (BR) was found to have a strong effect on the detonation limit. For BRs of 33% and 66%, the ratio of the obstacle opening and detonation cell size (d/λ) at the detonation limit was found to be 0.6 and 6.0, respectively. This order of magnitude change in the detonation limit was found to be governed by a change in propagation mechanism associated with the discontinuous detonation mode. For all BRs the discontinuous mode is characterized by detonation failure, as it diffracts through the obstacle opening, and then re-initiation. For the low BR obstacles detonation re-initiation is driven by the generation of a detonation Mach stem that propagates along the top and bottom walls following oblique reflection of the decoupled detonation leading shock wave. For the high BR obstacles shock reflection off the top and bottom walls does not produce a detonation wave, instead a detonation is initiated at the proceeding obstacle face following a roughly normal reflection of the leading shock. These propagation mechanisms are not governed by obstacle BR, but rather the obstacle height and spacing is the key parameter as they control the strength of the shock at the point of reflection.

Combustion Hotspots of Energetic Condensed Systems

The conditions of occurrence, nature, size, and shape of combustion hotspots of energetic condensed systems and the spatial dynamics of the hotspot combustion wave are discussed. A model for the propagation of hotspot combustion waves in condensed systems is briefly described based on the cellular automata method. A possible explanation for the occurrence of unsteady effects in the combustion of solid rocket propellants is proposed.

Preface

Dear reader, we provide you with the Proceedings of the XVI All-Russian Seminar with international participation “Dynamics of Multiphase Media” (XVI DMM) held in Novosibirsk, Russia, on September 30 - October 5, 2019. The Seminar was organized by the Khristianovich Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences and Novosibirsk State University of Architecture and Civil Engineering (Sibstrin) under the auspice of the Russian National Committee for Theoretical and Applied Mechanics.The main topics of the seminar were as follows:• Problems of constructing physical and mathematical models of mechanics of reacting/inert heterogeneous media and their application to the flows of liquids and gases in porous media, wave and detonation processes in gases;• Physical, chemical and mathematical problems of ignition and combustion of mixtures of gases and solid particles;• Laboratory and full-scale experimental studies of the processes of filtration of liquids and gases in porous media;• Computational and analytical methods for solving the problems of mechanics of heterogeneous media and its applications to ecology, gas/oil recovery, drying, heat and mass transfer in apparatuses of chemical technologies, etc.The problems under consideration are characterized by a close interconnection of fundamental and applied research as well as development of new technologies. In this regard, at the seminar, special attention was paid to the practical application of promising methods to solve all of the above problems by introducing them into the design and construction of oil and gas production facilities, their explosion and fire safety.Invited lectures by leading experts and oral presentations by participants were presented at the sessions. In conjunction with the seminar, a scientific school for young participants was organized by Novosibirsk State University of Architecture and Civil Engineering (Sibstrin) which included lectures and master classes with the demonstration of the capabilities of modern software for solving multiphase problems.More than 150 papers were presented at the seminar sessions, and many of the authors offered their works for publishing in these Proceedings. The present volume provides comprehensive state-of-the art knowledge in the field of multiphase flows and related problem of combustion and detonation, experimental and numerical studies of homogeneous and heterogeneous flows. Taking into account the wide range of problems considered, we divided all the papers into 4 chapters.Chapter 1 contains articles on various topics of multiphase flows, including the classical problems of the dynamics of particles and droplets in gas flows, as well as filtration flows in porous media. The works on the construction of mathematical models of mechanics of reacting / inert heterogeneous media and their application to the processes of movement of liquids and gases are presented. Various problems associated with phase transitions are also considered. Multiphase flows have wide industrial applications, and in this chapter the reader will find various examples, including cold gas-dynamic spraying, medical applications, river hydraulics, and much more.Chapter 2 discusses issues related to the construction of new models of heterogeneous media mechanics in terms of the propagation of detonation and combustion waves in porous bodies, in rarefied and dense suspensions of reacting metal and organic particles, and in drops of various hydrocarbon fuels. The kinetic mechanisms of the combustion of hydrocarbon fuels in the capillaries and pores of the substance are considered and the effects associated with these physical processes are examined. Significant attention was paid to the issues of explosion and fire safety in industrial processes involving reactive aerosols and pyrophoric gases used in the electronic and aerospace industries.List of XVI DMM Chair, Volume Editors, images are available in the pdf.

Pore scale numerical simulation of heat transfer in propagating thermal wave during filtration combustion of rich and lean methane-air mixtures

The porous media combustion phenomenon was numerically studied with focus on the heat transfer effect in propagating combustion wave for lean and ultra-rich mixture compositions using the approach when the three-dimensional porous structure and interstitial flow are simulated directly at pore scale with explicit consideration of the thermal interaction between fluid and solid phases including the detailed chemical kinetics model and solid-to-solid radiation. The results demonstrate that irregularity of the porous structure leads to a large spatial variation of the process parameters and the flow inhomogeneity. The most intensive heat sources placed within the cavities where the flow is developed. During the process, the interface heat transfer and radiation contribute to heat recuperation mechanism that leads to thermal non-equilibrium in the combustion wave. The heat is transferred through the bed via radiation layer-by-layer due to restricted visibility of the particles. The numerical data about a local variation of the process parameters were presented. The data of this type can be used for modification of the volume-averaged models within the context of spatial variation consideration. It was shown that there is a correlation between the heat release rate, the interface heat flux, the radiative heat flux, and its root mean square values.

On numerical modelling of gas flows through axisymmetric porous object with heterogeneous combustion sources under forced filtration

The time-dependent gas flows through axisymmetric porous objects with heterogeneous combustion sources are considered. The mathematical model, which describes the process, and the numerical method are proposed. The regimes of heterogeneous combustion wave propagation in axisymmetric porous object with various location of ignition zones under forced filtration are investigated. It is shown that the gas tends to bend around the heated zone and flows through colder regions as in the case of two-dimensional plane flows.

Combustion of Gasless Systems: Thermocapillary Convection of Metal Melt

The role of thermocapillary convection in combustion of gasless binary mixtures containing a low-melting reagent was explored by numerical modeling. Variation in relative amounts of reagents and starting sample porosity was found to change a mode of combustion wave propagation over the binary systems under consideration.

Three-dimensional pore-scale numerical simulation of methane-air combustion in inert porous media under the conditions of upstream and downstream combustion wave propagation through the media

Abstracts Porous media combustion of lean and ultra-rich methane-air mixtures was numerically studied using the approach when the process is simulated at the pore scale with explicit consideration of the three-dimensional porous structure and interstitial flow with thermal interaction between fluid and solid phases including the detailed chemical kinetics model and solid-to-solid radiation. The geometrical model of the packed bed was generated synthetically by simulation of particles falling under gravity force. A novel workflow for a randomly packed bed meshing at the pore scale was used to avoid the point contact problem. The results demonstrate that the model predicts a thermal nonequilibrium and heat recuperation mechanism in the combustion wave in the low-velocity regime correctly. The inhomogeneous structure of the porous media leads to large spatial variation of the process parameters such as velocity and temperature. It was shown that radiation makes a significant contribution to heat transfer in the region of a large temperature gradient. Radiative heat flux is transferred through the bed via radiation layer-by-layer due to restricted mutual visibility of the opaque particles. The mixture composition has a significant impact on the heat release rate and wave velocity and direction as well as thermal flame thickness and exhaust gas composition. At the macro scale, the mode of combustion wave propagation is quasi-steady whereas at the pore scale with little time steps the unsteady effects can be observed. Different subregions of the flame front propagate with not equal velocity, stand or accelerate depending on the local flow and porous matrix inhomogeneity. For the lean mixture the oscillatory regime of propagation was detected and analyzed.

Effect of large-scale perturbation on the critical condition of detonation formation in stoichiometric CH4-2O2 mixtures

The effects of large-scale perturbation induced by orifice plate on the critical condition of detonation formation are investigated systematically in a circular tube with an inner diameter of 90mm and 6m long. The orifice plates with the blockage ratio (BR) of 0.5, 0.7, 0.93 and 0.96 are employed. Four pressure transducers (PCB102B06) are used to determine the average velocity while the smoked foils are employed to record the detonation cellular patterns. The experimental results indicate that a detonation can propagate at a steady velocity with small deficit when the initial pressure (P0) is greater than the critical value (Pc). The velocity deficit is enhanced sharply as the critical condition is approached by gradually decreasing the initial pressure. At P0 below the critical pressure, the detonation failure can be observed. In the smooth tube without obstacles, the critical pressure is 2.5kPa and the corresponding velocity deficit is 25% approximately. After the orifice plates are introduced into the tube, the critical pressure and the velocity deficit both are increased significantly. The critical pressure are 7.5, 11, 15 and 16kPa, respectively. The maximum velocity deficit is about 30%. By measuring the average velocity immediately after the combustion wave propagation through the orifice plates, it can be found that only when the average speed is greater than 85% times the products speed of sound, can the detonation be produced at the end of the tube. Finally, the critical condition of detonation propagation are analyzed in detail. In the cases of smaller BRs (0.5 and 0.7), the critical conditions are consistent with the criterions of d/λ>1 and L/λ>7. However, these two criterions both are invalid for BR=0.93 and 0.96 cases.

Analysis of two-dimensional combustion waves arising in the presence of a competitive endothermic reaction

We consider a system of reaction-diffusion equations describing combustion dynamics. The reaction is assumed to undergo two competitive reactions, one which is exothermic and one which is endothermic. The one-dimensional model has been shown to exhibit complex behaviour, from propagating combustion waves with a constant speed to period doubling cascades and the possibility of chaotic wave speeds. In this study, we extend the combustion model from one to two dimensions by exploring a model of an insulated strip with no heat loss and axially symmetric spread. In particular, we compare and contrast the behaviour of the systems in one and two dimensions. 
 
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Combustion Wave Propagation of a Modular Porous Burner with Annular Heat Recirculation

A numerical investigation of the different arrangements of porous media in a combustor with annular heat recirculation is conducted. The effect of annular heat recirculation and porous block arrangement on the characteristics of combustion wave propagation is numerically studied. Results show that power input, heat capacity of porous matrix, arrangement of porous blocks, and annular heat recirculation are major factors that influence the propagation of combustion wave. The overall temperature of ceramic porous burner is higher than that of ceramic-metal type burner due to the lower heat storage capacity of the former, especially for the temperature downstream. The flame temperature is higher upstream and lower downstream with metal foams in the annulus than that without metal foams. The flame temperature of uniformity type burner is more uniform than that of gradually-varied and modular type burners. The flame front moves more slowly with metal foams in the annulus than that without metal foams due to the better preheating effect of metal foams. The flame position moves downstream, and the flame temperature gradually decreases and is eventually extinguished due to the low preheating temperature.

Effect of disorderness in two-dimensional discrete adiabatic combustion waves in a heterogeneous solid medium under stable regime.

The effect of disorderness for the propagation of stable combustion waves in a two-dimensional discrete adiabatic system are studied by considering two systems, namely, (i) periodic and (ii) disorder. The discrete periodic system is modeled by regular arrangement of burnt and unburnt point heat sources. In contrast, the discrete disordered system is modeled by the concatenation of regular burnt and randomly distributed unburnt heat sources. Four different kinds of discrete disordered systems (S1, S2, S3, and S4) are modeled by varying the joint frequency count of unburnt heat sources without changing the domain size of the system. Results show that the disordered structure of the discrete system plays a crucial role in the combustion dynamics, shape of the combustion wave, and it affects the propagation of stable combustion waves with the manifestation of sparse and chaotic finger patterns. Quantitative analysis performed for the width and roughness of combustion front show that the disordered structure and ignition temperature (ε) of the discrete system plays a crucial role. The burn rates of discrete system are sensitive to change in structure of the system and ε. It is observed that the burn rates obtained for the discrete disordered system is always less than that of burn rates of the discrete periodic system. The burn rates calculated for the present model are compared with the available experimental data on combustion of thermite systems.

Numerical Simulation of Two-Phase System of “Combustible Liquid – Solid Fuel” Combustion in a Fixed Bed

Investigation of combustion of complex heterogeneous systems and particularly of twophase “combustible liquid – solid fuel” systems is topical because of the need to improve combustion of multicomponent and non-standard fuels as well as for resolution of specific ecological problems. The qualitative and quantitative peculiarities of combustion of two model combustible systems, notionally corresponding to the “sawdust – oil” and “wood chips – oil” mixtures are investigated numerically. The main peculiarity of the systems is volatility of the fluid component, being gaseous-flow driven inside porous media. A one-dimensional plain problem of combustion of compact layer with the ignition from the bottom and from the upper side is considered. It is demonstrated that due to low gas permeability of the fine-dispersed solid matrix (sawdust), air flow velocity is relatively low which results in slow formation of the combustion front (the characteristic time is tens of minutes). In case of coarse solid phase (wood chips), airflow rate is higher and corresponding time of temperature fronts formation is smaller (a few minutes). Both for the cases of fine-dispersed and coarse particles solid matrix phase, when set on fire from below, the fluid component is evacuated from the hot zone before the combustion front is formed. Since that, the main characteristics of the temperature front dynamics correspond to “dry” fuel system. In case of upper side ignition the combustion wave is formed at the time of the order of 100 s (when the used magnitudes of parameters are being used again), then it spreads downstream of the layer, accompanied by incomplete oxidation of solid fuel and complete combustion of oxygen. The effect of incomplete solid fuel combustion was noted earlier in the investigations of combustion of lean coal layer and some other systems. The velocity of the combustion wave propagation does not differ much for the cases of upper side and bottom side ignition. But the time of establishing the quasi-stationary velocity of the front to the steady-state value at the initial stage is much less in case of bottom side ignition. The results obtained by the authors can be utilized for optimization of multi-phase fuels combustion in compact layer, the regime parameters of in-situ combustion method of oil recovery increase as well as for improvement of some specific chemical processes.

Numerical Investigation of Combustion Wave Propagation in Obstructed Channel of Pulse Detonation Engine using Kerosene and Butane Fuels

Numerical Investigation of Combustion Wave Propagation in Obstructed Channel of Pulse Detonation Engine using Kerosene and Butane Fuels

Theoretical and Experimental Method for Calculating the Conditions of the Convective Mode of Combustion

A theoretical and experimental method has been proposed for calculating the dependence of the combustion rate of granulated Ti + xC mixtures (0.5 ≤ x ≤ 1) in a convective mode on the key parameters. The dependence of the combustion rate on the nitrogen flow in the convective mode was shown to be quadratic and fundamentally different from the linear dependence according to the filtration combustion theory. The regions in which the conductive and convective modes exist when the volume of the concurrent nitrogen flow changes were determined. The volume of the gas flow corresponding to the transition of combustion wave propagation from conductive to convective mode was shown to increase with the combustion rate of the mixtures in the absence of a nitrogen flow, i.e., with the soot content in the mixture.

Combustion of Activated Carbon Particles Part.1: Experimental Investigation of the Two Distinctive Burning Modes in A Packed Bed

Features of one-dimensional combustion-wave propagation of activated carbon particles (~ 1mm) packed in a quartz tube was examined experimentally. Rich oxygen was introduced into the tube to promote the surface oxidation of the activated carbon particles. An oxidizing mixture flows through a vertically placed quartz tube (from bottom to the top). Followed by the ignition at the top, hot reactive zone propagates downwardly with negligible regression of the specimen, so called “flame spread” mode. Finally reactive zone reaches to the bottom of the reactor, then stays there to consume the activated carbon, so called “regression” mode. A distinctive two-mode burning feature are constantly identified even CO2-diluted oxidizer was employed. Based on the temperature measurement, temperature profile during the burning event is estimated and heat transfer analysis was additionally made in order to understand the combustion mechanism depending on the fuel properties.

Combustion Synthesis of Chromium Nitrides

This paper explores different modes of synthesis by combustion of chromium-nitrogen and ferrochromium-nitrogen alloys. The SH-synthesis of chromium nitrides and ferrochromium nitrides was performed. Regular patterns in layer-by-layer and surface modes of Cr combustion in nitrogen were investigated. The mechanism of non-stationary combustion during the synthesis of chromium was investigated. Regular patterns of chromium and ferrochromium combustion in the cocurrent filtration mode were analyzed, and the possibility to intensify the SHS process using the pressure filtration principle was assessed. The process of chromium powder combustion in the cocurrent flow of nitrogen-containing gas in the range of specific flow rates from 20 cm3/s·cm2 was investigated. Pressure filtration intensifies the process of combustion wave propagation in the Cr–N2 system. Here, the combustion rate increases while the degree of nitridation decreases. We discovered superadiabatic heating modes when the reaction zone was blown with pure nitrogen and a nitrogen-argon mixture. The tempering mode that was realized during pressure filtration allows for the uptake of high-temperature single-phase non-stoichiometric phases of Cr2N.

On the Mechanism of Combustion of Thin Nanostructurized Silicon Plates in Oxygen at an Elevated Pressure

The physical mechanism of combustion of thin nanostructurized silicon plates in oxygen at an elevated pressure is considered. Based on the analysis of experimental data, it has been established that in combustion wave propagation over a nanostructurized silicon film, the liquid silicon droplets resulting from thermochemical destruction of etched silicon undergo combustion, and that the dominant process is the process of heterogeneous combustion of a gas suspension of silicon particles in oxygen. A physicochemical model is presented that describes the speed of combustion wave front propagation in a gas suspension of silicon particles in a liquid phase depending of the oxygen pressure and silicon particle diameter. Dependences of the combustion front speed and of the time of particle combustion on oxygen pressure and size of particles in a gas suspension have been calculated. It has been established that combustion of silicon particles follows the kinetic mechanism with inverse dependence of combustion time on pressure and its proportional dependence on the particle diameter. The dependence of the degree of fragmentation of particles in the combustion wave front on the structure of a nanostructurized sample and oxygen pressure has been calculated. Practically important recommendations for obtaining higher rates of combustion of nanostructurized silicon films at a lower oxygen pressure have been formulated.