Effects Of Equivalence Ratio Research Articles

Hydrogen generation from gasification of woody biomass upon acid mine drainage sludge as a novel catalyst under an air medium

In this study, the feasibility of employing acid mine drainage sludge (AMDS), mainly consisting of iron oxide (Fe2O3), as a novel catalyst for the air gasification of woody sawdust to produce H2-rich gas was evaluated for the first time. The effects of temperature, equivalence ratio (ER), and contact mode of the feedstock and catalyst on gas yield and H2 selectivity were investigated. Using the AMDS catalyst, a comparably higher gas yield (56.79 wt%) and higher content of H2 (18.31 vol%) and CO2 (36.45 vol%) were obtained compared to those obtained in the non-catalytic case owing to stimulated water–gas shift and steam–methane reforming reactions caused by the redox cycle of Fe2O3 within the gasification process. Gas yield and H2 concentration were enhanced by increasing the temperature from 750 to 850 ℃ (up to 65.11 wt% and 21.73 vol%, respectively) due to promoted endothermic reactions. Although increasing the ER from 0.1 to 0.3 dramatically increased the gas yield, it was not conducive to the promotion of H2 production, primarily because of the stimulated hydrogen oxidation reaction. The ex situ contact mode, where feedstock and catalyst were placed in the reactor and catalyst bed, respectively, resulted in a higher gas yield and H2 selectivity compared to those achieved by the in situ case, in which a mixture of feedstock and catalysts was located in the same reactor. Overall, the gasification of woody sawdust over an AMDS catalyst in an air medium has the potential to mitigate the challenges of AMDS treatment along with the production of valuable H2-rich gas.

Effect of Equivalence Ratio on Acoustic Characteristics in Pre-cooled Turbojet Engine Afterburner

Effect of Equivalence Ratio on Acoustic Characteristics in Pre-cooled Turbojet Engine Afterburner

Generalized description and extrapolation of extinction stretch rates from spherically expanding flames

The extinction stretch/strain rate is an important global parameter for validating kinetics and modeling laminar and turbulent flame extinctions. Here, we propose a generalized approach to extrapolate the extinction stretch rate from spherically expanding flames, based on the nonlinear relation between the flame speed and the stretch rate applicable to general Lewis numbers (Le’s). Results show that the extinction events for Le<1, lean hydrogen/air flames can only be obtained by considering finite flame thickness, indicating the importance of finite, incomplete reaction in the extinction of such flames. On the other hand, both the previous nonlinear formulation with complete reaction and the present finite flame thickness descriptions can predict extinction for the Le>1, rich hydrogen/air flames, for which the extinction mechanism is that of preferential diffusion. The effects of equivalence ratio and pressure have also been examined and explained, which highlight the essential role of proper definitions in explaining the extinction stretch rate responses. The present generalized description is particularly useful for the investigations of flame extinction and chemistry at elevated pressures within internal combustion engines.

An experimental and modeling study on autoignition of 2-phenylethanol and its blends with n-heptane

2-Phenylethanol (2-PE) is an aromatic alcohol with high research octane number, high octane sensitivity, and a potential to be produced using biomass. Considering that 2-PE can be used as a fuel additive for boosting the anti-knocking quality of gasoline in spark-ignition engines and as the low reactivity fuel or fuel component in dual-fuel reactivity controlled compression ignition (RCCI) engines, it is of fundamental and practical interest to understand the autoignition chemistry of 2-PE, especially at low-to-intermediate temperatures (<1000 K). Based upon the experimental ignition delay time (IDT) results of neat 2-PE obtained from our previous rapid compression machine (RCM) investigation and the literature shock tube study, a detailed chemical kinetic model of 2-PE is developed herein, covering low-to-high temperature regimes. Besides, RCM experiments using binary fuel blends of 2-PE and n-heptane (nC7) are conducted in this work to investigate the nC7/2-PE blending effects, as they represent a dual-fuel system for RCCI operations. Furthermore, the newly developed 2-PE model is merged with a well-validated nC7 kinetic model to generate the current nC7/2-PE binary blend model. Overall, the consolidated model reasonably predicts the experimental IDT data of neat 2-PE and nC7/2-PE blends, as well as captures the experimental effects of pressure, equivalence ratio, and blending ratio on autoignition. Finally, model-based chemical kinetic analyses are carried out to understand and identify the controlling chemistry accounting for the observed blending effects in RCM experiments. The analyses reveal that nC7 enhances 2-PE autoignition via providing extra ȮH radicals to the shared radical pool, while the diminished nC7 promoting effect on 2-PE autoignition with increasing temperature is due to the negative temperature coefficient characteristics of nC7.

Autoignition of iso-octane at ultra-lean and lean conditions

Ignition delay times (IDTs) of iso-octane/air mixture were measured in a high-pressure shock tube and a rapid compression machine at ultra-lean (Φ = 0.2) to lean (Φ = 0.4 – 0.6) equivalence ratios, pressures of 20 – 40 bar, and temperatures of 630 – 1250 K. Measured IDTs were longer at lower equivalence ratio, and the equivalence ratio effect was most prominent in the intermediate temperature range. IDTs were shorter at higher pressures and, likewise, the dependence on pressure was maximum at intermediate temperatures. Predictions of existing chemical kinetic models were compared with the experimental data. Notable differences were observed between the model predictions and the newly obtained IDT data at fuel-lean conditions. Sensitivity analyses were performed to identify key reactions affecting fuel reactivity at various temperature regimes. Rate coefficients of two sensitive reactions, IC4H8+IC4H9↔AC8H17 and AC8H17O2↔AC8H16OOH-C, were modified to improve model performance at intermediate and low temperatures for fuel-lean conditions.

Investigation of pressure gain characteristics for kerosene-hot air RDE

Total pressure gain is one of the most significant performance metrics for rotating detonation engines. In this study, total pressure gains of kerosene-hot air(523K∼553 K) RDE for different combinations of A8/A3.2 and A3.1/A3.2 are measured by EAP(Equivalent Available Pressure).It is found that total pressure gain tends to increase with the decrease of A8/A3.1.The highest total pressure gain of -15% occurs at A8/A3.1 = 0.87.And the highest total pressure gain of each configuration approximately increases linearly with the decrease of A8/A3.1 with the maximum deviation of 3.3% for the same A8/A3.1 under different combustor widths. The total pressure gain climbs with the decrease of Pt2/P3.2. And there appears a clear demarcation point at Pt2/P3.2 of 1.89 for the effects of Pt2/P3.2 on total pressure gain because of different total pressure loss mechanisms. The equation of total pressure gain is rewritten to separate inlet losses from other losses. Positive total pressure gain is obtained when inlet losses are excluded for some cases. In order to take the effects of equivalence ratios, types of fuel, combustion efficiency and widths of combustion chamber on total pressure gains into account, Qv is introduced which is defined as the actual heat released by the combustion of fuel entering the combustion chamber for 1 hour in unit pressure and unit combustion chamber volume. There appears to be an approximately linear trend in pressure gain as a function of Qv for each A8/A3.1 A simple pressure gain model is developed to describe the variation of total pressure gain with A8/A3.1 and Qv. Higher Qv and lower A8/A3.1 are required to achieve positive total pressure gain which is not easy to be realized at the same time. As an important parameter for calculation of Qv, the average pressure of combustion chamber is approximately equal to the product of velocity of detonation waves and mass flux of nozzle outlet. A comparison is made among total pressure gain measured by EAP, (Mach-Corrected Static Pressure)and MFF(Mass Flow Function). They are basically linear with relative errors falling within +/-10%.

Performance Analysis of a Novel Water/Electricity Cogeneration System Based on Plasma Waste Gasification and a Small Modular Reactor

A hybrid system consisting of plasma gasification, multistage flash (MSF) desalination, and a small modular reactor (SMR) power plant is proposed for power and water cogeneration. In the novel configuration, the syngas from the plasma gasifier is burned to drive the gas turbine to generate electricity. The exhaust from the gas turbine is used to heat the steam of the SMR power plant and the seawater. The new design is thoroughly evaluated from a thermodynamic and economic point of view. In the hybrid system, 36.12 MW of electricity is generated from medical waste, and 23.75 MW of heat that can be utilized by MSF desalination is also generated from medical waste, with waste‐to‐electricity efficiency and energy efficiency of medical waste being 40.39% and 52.88%, respectively. The exergy efficiency of medical waste is 37.99%. In addition, the new design has a short dynamic payback period of 3.7 years, and the project's net present value can reach 430036.07 k$ over a 20 year lifetime; internal rate of return can reach 54%. Meanwhile, the effects of equivalence ratio and plasma temperature on the performance of the hybrid system are discussed. These results confirm the feasibility of the new design.

Study on pressure wave response and overpressure attenuation law of explosion-proof doors

In order to evaluate the pressure relief characteristics of the explosion-proof door, experiments were conducted in a self-built small size explosion-proof door experimental platform. The details of pressure changes in the pipeline were monitored in detail through four monitoring points set on the right end of the pipe, horizontal pipe, the main ventilation fan tunnel and below the explosion-proof door. The overpressure attenuation law at different positions and the effect of equivalent ratio on overpressure attenuation were studied when the explosion-proof door was normally opened for pressure relief and failed to open for pressure relief. The results showed that when the explosion-proof door cannot be opened for pressure relief, the overpressure of the main ventilation fan tunnel and the explosion-proof door will increase dramatically. Compared with the normal pressure relief by opening the explosion-proof door, it increased by 130.69 % and 100.36 % respectively. Through the explosion-proof door pressure relief, the overpressure attenuation at the main ventilation fan tunnel and the explosion-proof door exhibited a linear. However, the overpressure attenuation at the main ventilation fan tunnel was the most obvious when the ϕ = 0.94, and the overpressure attenuation at the position of the explosion-proof door was the most obvious when the ϕ = 1. With the increase of ϕ, the time interval between two overpressure peaks at each monitoring point showed a downward trend, and the decreasing trend was more obvious at the main ventilation fan tunnel compared to other monitoring points. It was also noted that the trend of the time interval between the two overpressure peaks at the four monitoring points will gradually stabilize with the increase of the equivalence ratio. Additionally, the peak overpressure decline rate at the explosion-proof door position was always greater than that in the main ventilation fan tunnel. This indicates that the overpressure attenuation effect at the explosion-proof door is stronger than that at the main ventilation fan tunnel.

The Effect of Air Equivalent Ratio on Combustion and Gasification Process Characteristics of Oil Palm Biomass in Fluidized Bed Reactor

This study investigated the effect of air equivalent ratios (ERs) (0.1-5) on the temperature distribution in the fluidized bed reactor during gasification and combustion process. The cylindrical reactor with the diameter of 20 cm and height of 150 cm was used in this study. The conical shape connector was installed at the bottom of the reactor for different air supplying patterns, including tangential flow and up-flow. The mixed oil palm cake was used as a feedstock. The temperature distribution in the reactor during combustion and gasification process was observed by applying the numerical calculation using ANSYS software (Ver.19.0, Fluent) with 3D model. The effect of air supplying patterns and air equivalent ratios were then investigated. The results showed that the temperature distribution obtained from simulation was not consistent with the experiment results for an up-flow air supplying method. In the case of tangential air inlet, the results from simulation were similar to the experimental results. Consequently, these results will be the guideline for further studies of biomass gasification and combustion using fluidized bed gasifier with different inlet air patterns and ERs.

Minimum tube diameters for detonation propagation in CH[formula omitted]/H[formula omitted]-air mixtures: Implications for natural gas cooktop burners

The minimum detonation diameter for methane (CH4)/hydrogen (H2)-air mixtures is numerically evaluated to assess detonation risks in cooktops designed to work with natural gas. A one-dimensional mathematical model that considers heat and friction losses for detonations propagating in pipes is used for that purpose. The initial conditions are selected to emulate the operation of a commercial cooktop working with different CH4/H2 blends. Results show that for H2 content in the blend higher than 45%, a conventional cooktop air–fuel mixer may pose a detonation hazard since the minimum detonation diameters predicted by the model are smaller than the diameter of the mixing tube (i.e., dmin<dmixer). Additionally, the individual effect of equivalence ratio, Φ, and hydrogen content, % H2, in the fuel blend are evaluated separately. An increased risk of detonation is present for (i) CH4/H2-air mixtures with Φ→1, and (ii) higher % H2 content. Finally, the effect of the natural gas composition was evaluated, showing that 100% CH4 is not a good surrogate for this fuel since there is a considerable decrease in dmin and in the admissible H2 content in the blend when the real composition is considered.

Relevance of soot formation characteristics to equivalence ratio and CO2 addition of acetylene flame

Soot is a common byproduct of fuel combustion that not only blocks machine operation but damages the environment and human health. A premixed acetylene flame was used to investigate the effects of equivalence ratio (2.30–2.66) and CO 2 addition (10% ∼ 50%) on soot formation characteristics evaluated by TG, SEM, TEM, Raman, FT-IR, and XPS. In the flame at φ = 2.47, the produced soot exhibits a higher activation energy with a larger particle size, less disordered structure, lower level of aliphatic carbon and higher degree of graphitization. The addition of 25% CO 2 results in the formation of soot with low activation energy, large particles, more disordered carbons, low sp 2 /sp 3 ratio and low surface oxygen content. Furthermore, it is found that the soot oxidation reactivity is correlated to the disorder structure, graphitized degree and oxygen-containing groups. Rate of production (ROP) analysis was conducted by kinetic simulation to better understand the characteristics of acetylene soot formation. • Characteristics of acetylene soot at various equivalent ratios and CO 2 are studied. • Natures of soot show volcano curves with flame equivalence ratio and CO 2 addition. • Soot reactivity is related to disorder carbon, graphitization and oxygen content. • Effects of equivalent ratio and CO 2 on rate of production of benzene are exhibited.

Stratified Flames in Dual Annular Counter-Rotating Swirl Burner for Wider Operability Gas Turbines

Abstract This study investigates numerically the effects of equivalence ratio (Φ) on flow/flame interactions and emissions of stratified oxy-methane (CH4/O2/CO2) flames in a dual annular counter-rotating swirl (DACRS) burner for wider operability and environmental-friendly gas turbines. The flow mixture entering the combustor is split into two coaxial streams of different equivalence ratios. The central stream is characterized by higher Φ to continuously ignite the flame for enhanced flame stability, whereas the annular stream is a highly lean mixture to sustain the environmental performance of the combustor. The partially premixed combustion model is adopted in the ansys-fluent 2021-r1 software to model the reaction kinetics of the generated stratified flames in the two-dimensional axisymmetric domain. Nine cases of the same inlet velocity ratio (primary stream to secondary stream) of 3.0 are examined at a fixed oxygen fraction (OF: volumetric percentage of oxygen in the O2/CO2 mixture) of both streams of 30%. Flame stratification is achieved by varying the equivalence ratios of the primary (Φp = 0.9, 0.8, and 0.7) and secondary (Φs = 0.7, 0.55, and 0.4) streams. The results indicate effective flame/flow interactions, complete combustion, and reduced emissions for the DACRS stratified flames.

Ignition limit and shock-to-detonation transition mode of n-heptane/air mixture in high-speed wedge flows

In this work, oblique detonation of n-heptane/air mixture in high-speed wedge flows is simulated by solving the reactive Euler equations with a two-dimensional (2D) configuration. This is a first attempt to model complicated hydrocarbon fuel oblique detonation waves (ODWs) with a detailed chemistry (44 species and 112 reactions). Effects of freestream equivalence ratios and velocities are considered, and the abrupt and smooth transition from oblique shock to detonation are predicted. Ignition limit, ODW characteristics, and predictability of the transition mode are discussed. Firstly, homogeneous constant-volume ignition calculations are performed for both fuel-lean and stoichiometric mixtures. The results show that the ignition delay generally increases with the wedge angle. However, a negative wedge angle dependence is observed, due to the negative temperature coefficient effects. The wedge angle range for successful ignition of n-heptane/air mixtures decreases when the wedge length is reduced. From two-dimensional simulations of stationary ODWs, the initiation length generally decreases with the freestream equivalence ratio, but the transition length exhibits weakly non-monotonic dependence. Smooth ODW typically occurs for lean conditions (equivalence ratio < 0.4). The interactions between shock/compression waves and chemical reaction inside the induction zone are also studied with the chemical explosive mode analysis. Moreover, the predictability of the shock-to-detonation transition mode is explored through quantifying the relation between ignition delay and chemical excitation time. It is demonstrated that the ignition delay (the elapsed time of the heat release rate, HRR, reaches the maximum) increases, but the excitation time (the time duration from the instant of 5% maximum HRR to that of the maximum) decreases with the freestream equivalence ratio for the three studied oncoming flow velocities. Smaller excitation time corresponds to stronger pressure waves from the ignition location behind the oblique shock. When the ratio of excitation time to ignition delay is high (e.g., > 0.5 for n-C7H16, > 0.3 for C2H2 and > 0.2 for H2, based on the existing data compilation in this work), smooth transition is more likely to occur.

Preliminary Experimental Results and Modelling Study of Olive Kernel Gasification in a 2 MWth BFB Gasifier

Gasification is a promising and attractive thermochemical method for biomass-to-energy conversion, with fluidized bed reactors being one of the best options for large-scale operations. Olive residues in particular are potentially excellent candidate biomass fuels in the Mediterranean area, due to the region’s increased capacity in olive oil production. Herein, the gasification experiments of olive kernels in a 2 MWth air-blown, bubbling fluidized bed reactor located at CENER’s facilities (BIO2C) in Navarra, Spain are presented. Even though technical issues were demonstrated due to the operation of the plant with a high-density biomass fuel and given the scale of the process, a quasi-steady-state and isothermal 12 h operation at an equivalence ratio of 0.25 ± 0.03 was attained. Given the satisfactory experimental results, an Aspen Plus simulation model of the process was also attempted. Notably, the proposed methodology agrees well with the experimental results and can be regarded as a starting point in future studies examining the gasification of relevant biomass in a MW-scale unit. Next, the effect of equivalence ratio and residual biomass moisture content were also evaluated, with the scope of designing future experiments that require minor modifications in the already existing apparatus. Finally, a syngas utilization route through the provision of energy for district heating purposes in the nearby village of Aoiz was proposed.

Flame acceleration and deflagration-to-detonation transition in a channel with continuous triangular obstacles: Effect of equivalence ratio

Aiming to gain sufficient data to develop methods capable of predicting and evaluating the danger of potential explosion or even detonation hazards associated with industrial process piping systems, this paper experimentally studied the effect of equivalence ratio on flame acceleration and deflagration-to-detonation transition (DDT) of hydrogen-oxygen mixture in a channel equipped with continuous triangular obstacles. This obstruction can simulate the effect of continuous blockage or rough walls in process pipelines. High-speed schlieren photography and OH* chemiluminescence recording were used for visualization. Results show that significant vortex motion accelerates the delayed combustion between obstacles and generates strong jet flow to promote flame acceleration. DDT occurs when the equivalence ratio (Φ) is from 0.25 to 2.5. Minimum detonation initiation time and distance are obtained at Φ = 1.0 and 1.1. The equivalence ratio significantly influences DDT by affecting deflagration speed and shock strength. DDT mechanism for equivalence ratios closer to 1.0 is the survival of local detonation generated by intricate flame-shock interactions. While for equivalence ratios far from 1.0, i.e., extremely lean or rich fuel (Φ = 0.25, 2.0 and 2.5), DDT can be formed due to a combined effect of viscous heating at the boundary layer and preheat caused by shock compression.

Experimental study on the flame stabilization mode in the rear-wall-expansion cavity

The present study experimentally investigates the transition of flame stabilization mode at Ma = 2.92 using a model scramjet combustor. The combustion mode is analyzed by pressure measurement and quasi-one-dimensional analysis. The effects of both equivalence ratio and aft wall offset on flame behaviors are further characterized by CH* chemiluminescence. The results show that the transition from cavity stabilized combustion mode to jet-wake stabilized combustion mode is realized by increasing the equivalence ratio. And the quasi-one-dimensional analysis reveals that all cases work in the Early Scram mode and approach thermal chocking after increasing equivalence ratio. As the equivalence ratio increases, the amplitudes of the flamebase and heat release gradually increase, and their distributions gradually migrate downstream. The amplitude of flamebase and heat transfer remains prominent with the consistent rise in equivalence ratio. At the same time, the spatial distribution of heat release tends to spread out upstream and occasionally appear upstream of the leading edge of the cavity, indicating that the flame stabilization mode transforms from cavity stabilized combustion mode to jet-wake stabilized combustion mode. The spatial variation of local heat release rate is responsible for the transition of flame stabilization mode. A slight aft wall offset promotes the transition from cavity stabilized combustion mode to jet-wake stabilized combustion mode at a higher equivalence ratio.

Flame Structure of Ammonia/Hydrogen/Oxygen/Argon Mixtures at High Pressure

The search of alternative fuels is one of the most important issues. Hydrogen is the most attractive one since its combustion products include only water. However, due to its specific properties wide implementation of hydrogen is not possible. There is an idea to use chemical carriers of hydrogen, for example, ammonia. The addition of hydrogen, which is the product of ammonia cracking, can improve the combustion characteristics of ammonia. The work presents experimental data on the structure of NH3/H2/O2/Ar flames at 4 atm. Equivalence ratio values were 0.8, 1.0 and 1.2, NH3/H2ratio – 1/1. Flame structure was measured with molecular beam mass spectrometry with soft electron impact ionization. In the experiments, flames were stabilized on the flat burner. Temperature profiles were measured with thin S-type thermocouples. Numerical simulations were performed with PREMIX code from CHEMKIN package. The comparison of the experimental and numerical data enabled to reveal the mechanism of NH3/H2oxidation showing the best predictive capability. Experimental and numerical data showed that the nitrogen-containing species which are present in the post-flame zone are N2and NO whereas concentration of N2O and NO2is negligible. It was revealed that in terms of NO reduction slightly rich conditions are more effective. In addition, the effect of equivalence ratio on the peak concentration of NO, N2O and NO2was analyzed. Rich conditions appeared to be more effective to reduce peak concentrations of NO, N2O and NO2.

Ethylene combustion performance with varying the N2 content in a porous burner

Direct emissions of volatile organic compounds (VOCs) not only pollute the environment, but also waste a lot of resources. To overcome above problem, this paper creatively proposed the solution by porous media combustion technology. In this study, ethylene with different N2 content levels of 10%, 30%, and 50% (used to simulate VOCs) was experimentally burned in a self-designed porous medium burner stacked with 9 mm alumina balls. The effects of equivalence ratio, premixed gas flow velocity and dilution ratio on flammable region, maximum combustion temperature, combustion wave velocity, pollutant emissions and combustion treatment efficiency were investigated. The maximum combustion temperature increased with the equivalence ratio and the premixed gas flow velocity. Consequently, the corresponding combustion treatment efficiency increased and CO emissions decreased. With increasing the dilution ratio, the flammable region, maximum combustion temperature, and combustion treatment efficiency became smaller but CO emissions and the combustion wave velocity became larger, except the case with 10% N2 content in which combustion was better than that with pure ethylene. In general, with relatively higher φ (φ ≥ 0.50), medium Vfv (Vfv ≥ 0.50), and appropriate α (α = 10%), the premixed gas could burn well with high combustion treatment efficiency.

Experimental and numerical investigations on NOx formation and reduction mechanisms of pulverized-coal stereo-staged combustion

With the gradual increase of intermittent renewable energy, the coal-fired power generating units must provide flexible peak shaving capabilities. However, the new requirement comes with increasing challenges for the pulverized coal utility boilers, as it tends to have lower combustion efficiency and higher NOx emission at extremely low loads. Accordingly, this work aims at coupling the NOx formation and reduction mechanisms with computational fluid dynamic simulation to thoroughly explore the technology for NOx abatement. The effect of the different primary air equivalence ratios on the Whitehaven bituminous combustion was experimentally and numerically studied. The combustion experiments were performed in a down-fired facility. Moreover, the numerical model validated well with the experimental results. The results reveal that, by reducing the primary air equivalence ratio, the combustion efficiency of pulverized coal stereo-staged combustion increased. Furthermore, the formation and reduction rate of fuel-NOx by HCN decreased but those by NH3 slightly increased. In addition, the fuel-NOx reaction rates from char-nitrogen decreased. The NH3 was oxidized to NOx, while HCN mainly played the role of reducing NOx. The primary air equivalence ratio of 0.24–0.28 was found to be the optimal range for the pulverized coal stereo-staged combustion technology.

Experimental investigation on the flame stabilization modes of liquid kerosene in a cavity-based scramjet combustor

The flame stabilization modes of liquid kerosene is investigated in a model scramjet combustor with flight condition of Ma 6. The effects of equivalence ratio and cavity configuration schemes on the flame stabilization modes are studied. Flame propagations and the evolution of the flow field from the ignition to the establishment of stable flame in the supersonic flow are acquired through high-speed photography and schlieren photography. Only cavity-recirculation-region stabilized combustion can be obtained in the single-cavity scramjet combustor. The intensity of combustion is weak and is termed as local ignition with low combustion efficiency. In the tandem-cavity scramjet combustor, the flame stabilization mode is largely determined by the total equivalence ratio. The flame could spread into the mainstream and even propagate against the supersonic flow as the equivalence ratio increases. The positive feedback mechanism between combustion and precombustion shock train is responsible for the evolutions of the flame stabilization modes, where the interactions between shock waves and turbulent boundary layer play a key role in the flame propagation process. The large-scale eddies in the shear layer of the upstream cavity shed at the cavity aft wall and could enhance the turbulent levels of the incoming flow of the downstream cavity. Consequently, an intense kerosene flame can be ignited in the tandem-cavity combustor. The flame could not spread to the mainstream in the single-cavity combustor due to the lower turbulence level weakening the interaction of combustion products in the recirculation zone with unburned reactants in the supersonic flow.