Flame Holder Research Articles

IDDES simulation of hydrogen-fueled supersonic combustion based on dynamic zone flamelet model

Based on the dynamic zone flamelet model (DZFM), the turbulent combustion of the DLR supersonic combustor with a wedge-shaped flame holder is numerically studied by IDDES. The mixing-relevant flow structures, combustion characteristics, and reaction paths were analyzed. The significant variation of flame modes, turbulence-chemistry interaction modes, and correlations between species (YOH) and mixture fraction suggests that applying a single flamelet for the whole physical space may introduce remarkable errors in describing the reacting states. Dynamically partitioning the flow field based on multiple zone division indices can effectively reduce conditional fluctuations and make the first-order closure assumption more valid. The results also demonstrate the necessity of a low-Re modification to DZFM, even for supersonic combustion.

Experimental investigation on a diffusion jet flame performance using a developed flame holder supplied with air from a concentric pipe

In this study, a diffusion jet flame consisting of a newly developed flame holder with three coaxial pipes to transfer air and fuel to the combustion zone, is investigated experimentally to simulate the ramjet effect. The flame holder is a double cone with three fuel ports on the top cone to improve the mixing of fuel and air. The inner pipe transfer fuel and is connected to the flame holder (which serves as a fuel injection point) and the middle pipe transfer primary air and the outer pipe transfer secondary air to the combustion zone (to investigate the impact of removing still air from around the flame as in ramjet applications). The flame holder and the primary air exit were at fixed positions (Datum Z4= 0) while the secondary air exit position changed many times below and above the datum line. The results showed that the secondary air exit location had an effect on the flame temperature distribution, flame shape, flame length, and flame width. The optimum position of the secondary air pipe was found above the datum line at Z5 = 7.5 mm, where the flame temperature and length are considered relatively high compared to other secondary air pipe positions.

Double coaxial pipe jet control using DBD-PA and bluff body

In this study, a double-tube burner nozzle with a DBD-PA (dielectric barrier discharge plasma actuator) and flame holder was employed to regulate the lifted flame. The flame holder held the lifted flame and the DBD-PA regulated the lifted flame to suppress the lifted flame’s vertical oscillation. To form a lifted flame, pseudo-biogas, a mixture of CH4 and CO2 in the ratio of 6:4, was jetted out through an inner nozzle and air through an annular nozzle. To control the air jet and prevent the lifted flame’s vertical oscillation, the DBD-PA was installed inside an annular nozzle. The DBD-PA was driven intermittently at regular intervals to produce a tangential flow in the same direction as the jetting gas, and the flame holder was placed above the nozzle outlet on the nozzle center axis. The finding indicated that by driving the DBD-PA at the slightly lower frequency than the frequency of the naturally shedding vortices in the free jet, the lifted flame’s vertical oscillation can be reduced by collapsing the jet’s vortex ring at a steady position and with a steady cycle. By impeding the lifted flame’s vertical oscillation, it is forecasted to reduce the blowout of the lifted flame and combustion noise.

The Effects of High Centrifugal Acceleration on Bluff-Body Stabilized Premixed Flames

Abstract An experimental study is conducted on bluff-body stabilized premixed flames in a curved, square cross section duct. High flow velocities coupled with a small radius of curvature of the duct induce high centrifugal acceleration normal to the flame sheet. A cylindrical flame holder spans the width of the square cross section and is positioned at the channel midheight. Flame shear layers are stabilized on the radially inward (upper) and outward (lower) edges of the flame holder. Side-view high-speed Schlieren images and high-speed pressure measurements are captured. Static stability, overall pressure loss, and statistics and velocimetry results from the Schlieren images are reported, and results are compared to a straight configuration with no centrifugal acceleration. Two bluff-body diameters are studied to show the effect of flame holder diameter on static stability. For the curved configuration, blowout velocities are higher for the smaller bluff-body diameter, likely due to flow acceleration effects. Blowout velocities are lower for the curved configuration compared to the straight configuration which may be due to the destabilizing Rayleigh–Taylor (RT) effect on the upper flame layer. Overall pressure loss is slightly higher for the curved configuration than the straight configuration. High-speed Schlieren results show centrifugal acceleration causes significant structural and velocimetric asymmetry in the bluff-body wake. In the curved configuration, the upper flame layer displays destabilizing RT instabilities, and the lower flame layer displays stabilizing RT effects. The upper flame shows vigorous RT instabilities which broaden the flame brush and sustain a flame leading edge independent of inlet Reynolds number or velocity. Conversely, the lower flame exhibits suppression of Kelvin–Helmholtz and flame-generated instabilities in the wake, which confines the flame brush and significantly reduces transverse flame velocities. The lower flame edge profile moves toward the channel centerline with increasing inlet Reynolds number. The upper flame in the curved configuration shows higher flame edge velocities than the straight configuration while the lower flame shows velocities closer to zero. The empirical constant to the power law relation for upper flame edge velocities agrees with RT-dominated flame growth theory for this experimental scale and agrees with other RT-dominated flame studies.

Pressure gradient tailoring effects on vorticity dynamics in the near-wake of bluff-body premixed flames

We investigate the role of mean streamwise pressure gradients in the development of a bluff-body-stabilized premixed flame in the near-wake of the bluff body. To this end, a triangular prism flame holder is situated in three different channel geometries: a nominal case with straight walls, a nozzle with a stronger mean pressure gradient, and a diffuser with a comparatively weaker mean pressure gradient. All geometries are implemented using embedded boundaries, and adaptive mesh refinement is used to locally resolve all relevant thermal (i.e., flame) and fluid-mechanical (i.e., vorticity) scales. A premixed propane flame, modeled using a 66-step skeletal mechanism, interacts with vorticity in the boundary layer of the triangular bluff body in the presence of each mean pressure gradient. Analysis of flame-related enstrophy budget terms reveals key differences in the behavior of baroclinic torque between cases, the specifics of which are tied to larger variations in the mean flow structure, recirculation zone structure, and confinement effects. Our results show that the baroclinic torque changes significantly among the configurations, with the nozzle exhibiting the largest baroclinic torque production. However, these differences are shown to be only a secondary consequence of the background pressure gradient, with the primary consequence being the change in the recirculation zone length resulting from the different channel configurations. These results are relevant for flame stabilization with bluff bodies, where clear understanding of the sensitivities to global mean pressure gradient is important to engineering design.

Impact of passive fuel injections techniques in the flow field of the scramjet combustor

• The introduction of passive injection techniques in a parallel cavities scramjet combustor influences the internal flow filed charateristics. • The effect of fuel injection location on the internal flow field charaterictics is also investigated. • Out of all the configuration , the scrmajet combustor showef optimum performance when the fuel is injected through the wall only. The development of scramjet technology has paved the path of possibilities for researchers to develop light-weighted space missions in the years to come. Many countries around the globe have already tested successful scramjet engines. The researchers are making continuous efforts to improve the combustor design by improvising turbulence inserts and flame holders in the combustor. One such improvisation is the introduction of strut into the parallel-cavities combustor. The research paper uses computational fluid dynamics to investigate the effect of internal flow field variables on a strut and cavity-based scramjet combustor. The current work presents a comparative study by analyzing two different scramjet combustor configurations namely case A and Case B to understand the effect of presence of strut in the cavity combustor. The velocity and static pressure profiles are analyzed at different streamwise locations. At x = 70 mm, the velocity values are reduced to lower magnitude for case B as compared to case A and the static pressure values towards downstream detoriates with reduction in intensity of shock waves. It is seen that the magnitude of velocity values and pressure values increases with increase is Mach number. The high-pressure values are observed for M-2.75. A performance assessment of the combustor is carried out for both the configurations, maximum combustion and mixing performance is obtained for M-2.52 for case B as compared to Case A. The paper further analyses three different fuel injection locations namely fuel injection strut only, fuel injection through the wall only and fuel injection through both strut+wall recognized as the case I, II, and III respectively. From various flow-field parameters analysis, it is seen that the production of eddies and vortices in the combustor region indicates proper mixing which is observed for case I. On studying the mass fraction concentration of H 2 0 species for all the cases it is observed that the H 2 0 species is increasing in the lateral direction which indicates that the combustion efficiency is incrementing in the same direction. The maximum combustion and mixing efficiency is observed for case I than the other two cases.

Ultra-lean dynamics of holder-stabilized hydrogen-enriched flames in a preheated mesoscale combustor near the laminar critical limit

This work experimentally investigates the ultra-lean dynamics of a 40% H2–60% CH4 flame near the laminar critical limit in a preheated mesoscale combustor with a flame holder. These experiments are conducted to verify a conjecture we proposed in a previous publication and reveal the ultra-lean flame dynamics under the synergistic effects of heat and flow recirculation. Notably, not only is our conjecture confirmed, but also some novel flame behaviors are found. As the equivalence ratio ϕ is decreased from 0.500 to 0.320, the conventional stable flame, stable residual flame, periodic residual flame with repetitive local extinction and re-ignition (periodic RFRER), and periodic oscillating residual flame are observed in sequence. For the stable residual flame (0.370 ≥ ϕ ≥ 0.355), the left and right flame roots reside directly behind the flame holder, and the flame tip stays near the combustor exit. For the periodic RFRER (0.350 ≥ ϕ ≥ 0.340), observed experimentally for the first time, the flame roots reside at almost the same location, but the flame tip oscillates up and down over time with pinch-off events. For the periodic oscillating residual flame (0.335 ≥ ϕ ≥ 0.320), found for the first time, the stable flame roots also reside at almost the same location, but the residual flame tip oscillates up and down over time without a pinch-off event. When ϕ decreases to 0.315, the oscillating residual flame extinguishes, and its blow-off dynamics are revealed in detail.

Improving Detonability in a Small-Scale Rotating Detonation Engine Using Partial Premixing

Small-scale rotating detonation engines (RDEs) with low mass flows and high frequency have potential as small thrusters, robust flame holders, and research tools that can be quickly and cheaply modified. However, the necessarily small channel geometry and low mass flow force the detonation wave to propagate near the limits of detonability. Previous success in a small-scale, 28-mm-diameter micro-RDE, operating on nitrous oxide () and ethylene (), exhibited unstable wave behavior with propagation velocities between 47 and 56% the Chapman–Jouguet speed. These results were observed at mass flows from 25 to using an in-chamber jets-in-crossflow (JIC) injection scheme with spark plug initiation. Building upon this work, the current investigation looked to improve the detonation behavior in the micro-RDE without changing the channel geometry or resultant operability and better understand the nature of mechanisms governing the design limitations in RDEs. To improve the wave behavior, a new partially premixed JIC injection scheme was used along with a predetonator ignition device. With these changes, tighter windows of operable mass flows () and equivalence ratios () were observed, between 35 and and 0.6 and 1.3, respectively. Maps of versus before and after detonation showed that the space of conditions conducive to ignition was not isomorphic with the space of conditions that sustained operation. Increases to the injection pressure to chamber pressure ratios improved the probability of detonation but resulted in greater pressure losses than were seen in the original JIC injection scheme. Single wave detonation was achieved for the first time in this RDE and had a peak frequency of 16.6 kHz, or 66% Chapman–Jouguet speed. Increases in fill height drove increases in wave frequency. Decreased fill height estimates compared to the previous design showed that partial premixing decreased the required fill time. These results support that the limits of detonability in small RDEs can be expanded without significantly compromising the characteristic low-mass-flow and high-frequency operation inherent to their geometry.

Experimental Investigation on Flow Characteristics and Ignition Performance of Plasma-Actuated Flame Holder

Improving the performance of flame holders has been a key focus of research on ramjet combustors. The plasma actuator has the potential to improve the ignition performance by manipulating the flow field of the flame holder. In this study, a plasma-actuated flame holder was designed. The aim of this study is to improve the performance of ramjet combustor by applying plasma discharge to the flame holder. The aerodynamic effects and ignition performance of the flame holder were investigated. The results demonstrated that the induced jet direction of the surface arc discharge was perpendicular to the actuator. The induced jet dissipated faster at lower pressures. The aerodynamic actuation intensity and jet area increased with the number of channels of surface arc discharges. Increasing discharge frequencies can increase the discharge times and jet height. The aerodynamic effects under a microsecond pulse duration were better than those under a nanosecond pulse duration. Actuators installed on the inside surface showed better performance than those installed outside. Under different total flow temperature conditions, the plasma-actuated flame holder significantly extended the ignition pressure limit and increased the combustion efficiency by 9.12% and 4.3% on average, respectively.

A Comprehensive Study of Ceramic Matrix Composites for Space Applications

Ceramic matrix composites (CMCs) have grown in popularity as a material for a range of high as well as protection components, increasing the need to better understand the impacts of multiple machining methods. It is primarily composed of ceramic fibers embedded in the matrix. Ceramic materials, especially carbon fibers and carbon were used to create the matrix and fibers. These ceramics include a huge variety of non-metallic inorganic materials that are regularly utilized under high temperatures. The aircraft industry became revolutionized by this unique combination of materials, which made parts better resistant under extreme conditions as well as lighter than the earlier technology. The development, properties, and production of ceramic matrix composites, as well as space applications, are discussed in this article. Ceramic materials have an interesting set of properties, including great strength and stiffness under extremely high temperatures, chemical inertness, low density, etc. In CMC, ceramics are used in the matrix as well as reinforcement. The matrix material keeps things running smoothly while the reinforcement delivers unique special properties. Ceramic matrix composites are developed for applications that required high thermal and mechanical characteristics, which include nuclear power plants, aircraft, chemical plants, space structures, and transportation services. Even though advanced aircraft relies on high-performance propulsion systems, improving the total impulses over the total mass ratio for rocket engines becomes essential for improving their performance that demands reduced engine structural weight as well as higher component heat resistance. The evolution of new ultra-high-temperature composites having high-temperature resistance as well as low density that a substitute super alloy and refractory metal material has become so essential and laid the foundation for high-performance engine design. The benefits of continuous fiber- reinforced CMC with high-temperature engine designs have long been recognized as a better measure of a country’s ability to design and produce spacecraft, modern aircraft, and weapons. Ceramic matrix composites materials are used in various aircraft type engines, aircraft brake disks, high-temperature gas turbines components, slide bearing components, hot gas duct, flame holders and components for burners are made by using oxide CMCs.

Fuel interchangeability investigation of new Russian PNG for conventional gas appliances

Because of Korea's planned import of low-heating-value fuel from Russia, its applicability to household, power generation, and industry needs to be evaluated. In this study, the compatibility of imported fuels from Russia to household gas appliances was studied. The combustion characteristics of three types of piped natural gas (PNG1, PNG2, and PNG3) were investigated by using a simulation model. PNG2, which had the highest nitrogen content of 7%, had the lowest adiabatic flame temperature and smallest bond dissociation energy, so large amounts of CH and OH were generated upstream of the flame. Experiments were conducted with a Bunsen burner to analyze the effect of the fuel composition on a single flame. At the maximum content of 9% for inert components (e.g., nitrogen and carbon dioxide), a high-hydrocarbon content of 6.28% or more was required to keep the flame stable. A fuel interchangeability test was conducted on actual gas stoves; all fuels could be used stably because of the effect of the flame holder and the thermal boundary formed by the clustered flames.

Active Flow Control of a Flame-Holder Wake Using Nanosecond-Pulsed Surface-Dielectric-Barrier Discharge in a Low-Pressure Environment

Flame holders are widely used in ramjet combustors. We propose using surface nanosecond-pulsed surface-dielectric-barrier-discharge (NS-DBD) to manipulate the flame-holder flow field experimentally. The electrical characteristics, induced flow performance, and temperature distribution of NS-DBD were investigated via the electrical and optical measurement system. In the filamentary discharge mode, the discharge energy rose with decrease of the ambient pressure. The discharge pattern of NS-DBD changed from filamentous to uniform around 5 kPa. Starting-vortex intensity and jet-flow angle relative to the wall increased at low pressure. The recirculation zone was asymmetrical at pressures above 60 kPa. The recirculation zone’s area and length were smaller at lower pressures, but when the actuator was operating, the recirculation zone was nearly 11.8% longer. The vorticity increased with pressure. When the pulse width was 300 ns, the actuator had the greatest effect, and the low velocity region (LVR) area and the fuel–air-mixture residence time (FMRT) could be increased by 31.8% and 20.5%, respectively. The actuator had a smaller widening effect on the LVR area at lower pressure. Rising-edge time should increase with pressure to optimize LVR increase; it should be above 300 ns to optimize FMRT increase. We conclude that NS-DBD is a viable method of controlling flame-holder airflow at low pressure.

Effect of inclined fuel injection in the strut wake region for a hydrogen fueled scramjet combustor

The supersonic airflow and injected fuel stream mixing process is complicated for a scramjet combustor because of little supersonic air resident time and high airflow stream momentum. The direction of fuel injection into a supersonic airflow stream plays a significant role in mixing enhancement with turbulence generation. This study investigates the effect of strut-based parallel (primary) and inclined fuel injection in the strut flame holder wake region. The primary strut with parallel injection is derived from the open literature. The base model strut consists of parallel injection, whereas in the new models, the fuel is injected at an angle of θ for both the upward and downward directions. By computing the Reynolds averaged Navier-Stokes equations, finite-rate eddy dissipation turbulence chemistry, and SST k-ω turbulence models, the mixing and combustion behavior for various fuel injections were investigated. The impact of different fuel injections on the downstream wake region is assessed by evaluating the distribution of H2 and H2O species in the radial and axial directions. The turbulence intensity and turbulent kinetic energy are also considered to evaluate the cross-impact of the air stream and fuel stream for inclined fuel injection. Numerical results found that inclined injection significantly impacts the mixing phenomenon with the development of enriched re-circulation zones in the vicinity of the flame keeper. The mixing and combustion efficiencies performance parameters are evaluated for different fuel injection schemes and found the average increased mixing efficiency of 13% and combustion efficiency of 12%, respectively, for inclined fuel injection. From the analysis of mixing efficiency, it is observed that complete mixing has been found after 235 mm, whereas for inclined injection, the complete mixing happened within a 175 mm distance. The maximum of 75% and 62% combustion efficiency has been observed at a 225 mm and 285 mm distance for inclined and parallel fuel injection, respectively.

Mixing and Evolution of Laterally Injected Liquid Fuel in Mach 2 Air Channel with Cavity

ABSTRACT The present study deals with the flow structure and mixing characteristics of liquid fuel injected laterally into a supersonic crossflow. The geometry, with a cavity downstream of the injector, mimics a supersonic combustor with a cavity flame holder. A variety of injection schemes and cavity configurations were investigated by means of high-speed schlieren photography. A reflected shock tunnel was employed to generate a Mach 2 air flow and to simulate the high-temperature environment in the combustor. JP-4 liquid fuel was injected at different jet-to-crossflow momentum flux ratios upstream of and from the front wall of the cavity. Results showed that in direct injection into the cavity adjusting the injection angle has significant effect on the local fuel-air ratio. Upstream injection far from the leading edge of the cavity yielded more effective fuel mixing and shorter dissipation length (Ld) than closer injection, due to the development of a vortex on the lee side of the jet core. These results suggest that a combination of upstream injection far from the leading edge of the cavity and inclined direct injection into the cavity may be beneficial for effective mixing in a supersonic combustor cavity flame holder.

Ignition Characteristics of Scramjet Combustor with Laser Ablation and Laser-Induced Breakdown

The ignition characteristics of an ethylene-fueled scramjet combustor with a cavity flame holder were experimentally investigated in a Mach 2.92 inflow using laser ablation (LA) and laser-induced breakdown (LIB). For the LA method, a 532 nm Nd:YAG laser was focused directly on the cavity floor composed of stainless steel. Meanwhile, for the LIB method, the laser was focused at 2 mm above the cavity floor to ignite the combustor. Optical techniques, including optical emission spectroscopy, x-ray diffraction, and schlieren imaging, were utilized to analyze the characteristics of the two different laser-induced plasmas. High-speed chemiluminescence imaging was employed to visualize the ignition process by the LA and LIB methods. The LA plasma could successfully ignite the flame at more positions than the LIB plasma with the same laser energy, showing an improved ignition capability due to the higher energy utilization, longer lifetime, and more components with a longer existence time than that of the LIB plasma. The initial flame kernel ignited by the LIB plasma could propagate faster than the LA plasma once the flame is successfully ignited, possibly due to the direct heat convection in the airflow.

Appraisal Burning Characteristic and Analysis Effect of Cavity in Scramjet Combustion Chamber

The combustion chamber clearly plays an critical role in generating thrust force so the aircraft can move forward. A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. Researchers are constantly working to improve the efficiency of ultrasonic combustion furnaces by various methods such as: optimize fuel injectors, optimize combustion chamber geometry design, create hole cavity. In this research, the characteristic of supersonic airflow were investigated, and a comparison between the standard chamber and advanced chamber was made to determine the effects of a circular hole (cavity) on pressure and velocity of the fuel mixture through the scramjet. Two dimensional Reynolds-Averaged Navier-Stokes governing(RANS) equations with k− turbulence model and finite rate/eddy dissipation chemistry model have been considered for modelling chemical reacting flows. From the comparison of numerical results, it is found that the development of recirculation regions and additional shock waves from the edge of cavity flame holder is increased and achieved stabilized combustion. From this research analysis, the performance of the scramjet engine with cavity is significantly improved as compared to the design without cavity

Entrainment effects on combustion characteristics of various syngases using a perforated burner

This study concentrates on entrainment effects to achieve distributed regime for different syngas compositions (coke oven gas, biogas, and blast-furnace gas). For this purpose, numerical modeling has been performed through a computational fluid dynamics commercial code. In the modeling, The PDF/Mixture Fraction combustion model, standard k-ℇ turbulence model, and P-1 radiation model have been selected to be used. Entrainment without decreasing oxygen concentration in air was provided from the flame holder wall of the newly generated burner at 10%, 20%, and 30% entrainment rates. For only coke oven gas, oxygen concentration was reduced to 15% O2 with the entrainment in order to achieve ultra-low pollutant emissions level. The results showed that the temperature distributions were achieved more uniform for all cases. The flame zones became more thinner for all cases studied. This provided more invisible or colorless flame appearance, and as a result of this, more uniform thermal field was achieved without substantial decrease in combustion performance. Namely, the temperature values between the outlet temperatures for all entrainments have been close to each other (about 1200–1300 K). In terms of evaluation of distributed regime achievement on NOX and CO pollutant emission levels, one can say that ultra-low emission levels (less than 1 ppm) were achieved with entrainment effects without decrease in oxygen concenration in air excluding coke oven gas. Distributed regime could be achieved at lower oxygen concentration with entrainment for coke oven gas combustion.

NUMERICAL INVESTIGATION ON FLOW ACROSS STRUT-BASED FLAME HOLDER WITH CONVERGING GROOVES

The flow across a modified strut-based flame holder is numerically analyzed using the two-equation Menter SST k-ω turbulence model. The modified strut geometry contains alternative converging cavities and ramps on the top side. This design superimposes the advantages of cavity flame holders into strut-based flame holders. The effect of Mach number, the variation in geometrical parameters such as the length of the ramp, depth of the cavity and convergence angle of the cavities are extensively studied. The numerical simulations were conducted using a commercial software ANSYS FLUENT. The validation of the code is accomplished using an available experimental data for a simple strut configuration with fuel injection. The numerical predictions bear a close resemblance with the experimental data. As the Mach number of the flow is varied, the flow structures obtained is consistent with the flow physics. Different ramp lengths and cavity depths were analyzed to determine the behaviour of the flow. The shorter ramp length seems to carry a higher turbulence rate downstream of the flame-holder. Moreover, by increasing the depth of the cavity larger rate of production of turbulent kinetic energy is achieved in the cavity. The variation in convergence angle of the cavity also helps to impart velocity reduction downstream of the strut. The velocity reduction without shock losses is desirable for a supersonic combustor. The present study reveals that the same can be achieved by increasing the convergence angle of the cavity

Numerical modeling of hydrogen catalytic reactions over a circular bluff body

This paper was intended to delineate numerical research for hydrogen catalytic combustion over a circular cylinder. The wire/rod-type catalytic reactor is a simple geometry reactor with an economical design with less pressure loss. For the single rod in the reaction channel, the flow characteristic and the difference of conversion efficiency between non-gas-phase reaction and gas-phase reaction have been delineated in the present study. The flow field and the chemical reactions were numerically modeled using 2D Large Eddy Simulation combined with the gas-phase and surface reaction mechanisms. The results show that the current numerical simulation has been validated to precisely predict the vortex shedding and its frequency in the cold flows. Despite the variation trends being dominated by the upstream flow, the vortex shedding phenomena were affected by the flue gas generated from the rod surface. It can be seen from the linear relationship between the vortex shedding frequency of reacting flow and Reynolds Number. It is noted that the vortex shedding vanished if the gas-phase reaction was ignited in the reaction channel. In addition, the geometric modified conversion efficiency was proposed to delineate an indicator that could be potential for the optimization of rod-type catalytic reactor. In summary, the fundamental study of a rod in a 2D flow channel can provide information for optimizing the catalytic design or the rod array arrangement in the reactor. Moreover, the rod can also be a partial catalytic flame holder to ignite and stabilize the gas-phase reaction. The obtained results could be the potential for practical applications of rod-type catalytic combustion, catalytic gas turbine, hydrogen generation, partially catalytic reaction flame holder, and other catalytic reactions that can be appreciated.

Influence of CH4/air injection location on non-premixed flame blow-off limits in a novel micro-combustor

Stable flame is still one of the challenging issues in the micro-combustors. Besides, the premixed flame may flash back under the large equivalence ratio, and the non-premixed combustion is an effective way to avoid the flame flash-back issue. In this work, a novel non-premixed CH4/air micro-combustor with the flame holder, the backward-facing steps and the separated preheating channels is developed to avoid the flame flash-back issue and extend the flame blow-off limits. This paper investigates the influence of two different CH4/air injection locations on the flame blow-off limits numerically and profoundly reveals the mechanisms in this micro-combustor. Results show that this novel configuration can considerably anchor the flame without the flame flash-back issue and significantly extend flammability owning to the flow & heat recirculations. Compared with the “Air(out)/CH4(in)” injection location, the “Air(in)/CH4(out)” injection location exhibits a comparatively larger size of recirculation, causing a more vital anchorage ability. In addition, after the preheating in the preheating channels, the CH4/air mixture of the “Air(in)/CH4(out)” injection location presents a higher temperature level than that of the “Air(out)/CH4(in)” injection location. Consequently, compared to the “Air(out)/CH4(in)” injection location, the larger blow-off limits are attained for the “Air(in)/CH4(out)” injection location. These results provide new insights into the stable non-premixed flame and give valuable guidance for designing the similar non-premixed micro-combustor.