Effect of multiple bluff bodies on hydrogen/air combustion characteristics and thermal properties in micro combustor

The bluff body is commonly used to improve micro combustion. The micro combustor with multiple rectangular bluff bodies in a single row was proposed. The effects of bluff bodies on H₂/air combustion characteristics were numerically studied. The temperature distributions, ignition position, combustion efficiency and blow-out limit were investigated via changing the total width and number of bluff bodies. The results show that the combined use of multiple bluff bodies can further expand the blow-out limit of H₂/Air. The effect of high temperature and viscous force on the flow velocity is main factors for the flame morphology. When the total width of bluff bodies is 2 mm, the blow-out limit decreases with the increase of bluff body number. When the total width of bluff bodies is 4 mm and 6 mm, the blow-out limit increases with the increase of the number of bluff bodies. With the increase of inlet velocity, the complete combustion efficiency decreases. The combustion efficiency in the combustor with wider blow-out limit decreases more slowly. It indicates that the combustor with multi-bluff bodies is more suitable for the operation conditions with high flow velocity.     

初始条件对燃气轮机DLE燃烧室性能影响研究

以单头部中心分级旋流干式低排放(Dry Low Emission, DLE)燃烧室为研究对象,以天然气为燃料,针对不同的全局当量比、进口温度、进口压力条件开展试验测试和数值模拟,研究燃烧室的燃烧性能以及污染物排放的变化规律。研究发现：随全局当量比增大,中心回流区长度略有增大、宽度变窄、回流速度增大,燃料量的增加使得高温区面积明显扩大,燃烧室出口温升明显增大,出口温度分布系数变化不大,燃烧室出口CO和NO_x排放摩尔分数明显增大;随进口温度的增大,中心回流区长度先明显增大再减小、宽度变窄、回流速度先增大再减小,进口空气温度的升高使得反应速率加快从而导致燃烧室出口温度升高,但温升、出口温度分布系数变化不大,CO和NO_x排放摩尔分数增大;随进口压力的增大,中心回流区长度、宽度略有增大,回流速度增大,燃烧室内部和燃烧室出口温度无明显变化,出口温度分布系数减小,CO和NO_x排放摩尔分数受影响较小。     

Numerical investigation of combustion characteristics for hydrogen mixed fuel in a can-type model of the gas turbine combustor

Numerical simulations are performed to analyze the combustion characteristics of propane fuel mixed with different amounts of hydrogen in a can-type combustor. The volume fraction of the hydrogen fuel varies from 0% to 100% in the fuel mixture. The results indicate that the hydrogen enrichment of the fuel significantly affects the flow structure, mixture fraction, and combustion characteristics. An increase in the volume fraction of hydrogen significantly affects the mean mixture fraction distribution, promotes combustion, and increases the flame temperature and the width of the flammable range within the combustor. Therefore, the degree of temperature uniformity at the outlet of the combustor increases with hydrogen enrichment, corresponding to an increase of 49.64% in the uniformity factor. The hydrogen enriched fuel can also reduce the emissions of CO and CO₂, owing to the reduced amount of carbonaceous fuel.     

Numerical analysis of the combustion characteristics of graphitic hydrogen-chlorine synthesis combustor with different intake strategies

This study investigates the effect of intake strategies on the combustion and flows characteristics of hydrogen-chlorine synthesis combustors via numerical methods. A crucial issue of hydrogen-chlorine synthesis combustor is to have a sufficiently low flame height and high conversion efficiency. In this study, the combustion performance of combustors equipped with the annular tube, plum nozzle, and porous-bullet nozzle has been thoroughly analyzed. The temperature distribution and gas flow are analyzed using the method of fluid-solid coupling, which indicates that the combustor with porous-bullet nozzle had the best gas distribution, the maximum HCl mole fraction at outlet is 97.24%, and the lowest flame height is 3.4 m, which is 27.15% lower than the combustor with the annular tube. Furthermore, the nozzle structure has a great influence on the fluid velocity in the recirculation zone of the combustor. Finally, the effect of hydrogen/chlorine equivalence ratio (?) and inlet volume flow rate were analyzed, and it can be concluded that with the increase of inlet volume flow, the high-temperature area inside the combustor gradually increases. As the equivalent ratio increases, the combustor outlet's mole fraction changes with a normal distribution trend. It is the most appropriate when the chlorine gas flow rate is 1,100 m³/h and ? = 1.05. The research can be applied to the field of high-purity hydrogen chlorine production, providing researchers with some solutions.     

Numerical investigation on the self-ignition and combustion characteristics of H2/air in catalytic micro channel

The self-ignition of hydrogen/air is an important process in the micro thermophotovoltaic system. The transient numerical models of gas-phase reaction and catalytic reaction in the various catalytic micro combustors were built and verified. The self-ignition process of gas-phase reaction caused by catalytic reaction in the catalytic micro channel with conventional heat dissipation was studied. The self-ignition process could be divided into four stages, fuel diffusion stage - pure catalytic reaction stage - flame front moving stage - stable combustion stage. The ignition time and temperature limit at different inlet temperatures, inlet velocities and channel heights were analyzed. The results showed that the wall quenching effect, thermal effect and flame propagation effect are dominant at low temperature, medium temperature and high temperature respectively. The catalyst length and the mixture internal energy were the main factor at low inlet velocity and high inlet velocity respectively. The steady-state time was also studied in the various operation conditions. Finally, the catalytic combustion characteristics in the stable combustion stage were analyzed. The influence of inert section length, inlet temperature and inlet velocity on the maximum temperature and fuel conversion ratio were investigated.     

Numerical study on premixed hydrogen/air combustion characteristics in micro–combustor with slits on both sides of the bluff body

An approach to improve premixed hydrogen/air combustion in micro combustor is numerically studied in this paper. The micro–combustor with slits on both sides of the bluff body shows better combustion efficiency and uniformity of temperature distribution. The effects of the controllable flow ratio (γ) and the angle of bluff body (θ) on combustion characteristics are investigated by using a two–dimensional model with the H₂/O₂ reaction mechanism. The results show that the increase of controllable flow ratio and angle of bluff body can improve combustion efficiency and decrease velocity extinction limit. However, at higher θ, increasing γ do not play an important role in improving combustion efficiency. In addition, at higher inlet velocity, combustion efficiency do not increase dramatically with the increase of θ. Moreover, at high inlet velocity, a special phenomenon of temperature ‘waist’ is observed in the micro–combustor with slits on both sides of the bluff body, which has a huge impact on combustion characteristics. Therefore, controllable flow ratio and angle of bluff body should be reasonably chosen to improve combustion characteristics.     

Numerical study on combustion characteristics of hydrogen addition into methane–air mixture

Understanding of the chemical kinetics and heat transfer mechanism within micro-combustors is essential for the development of stable-combustion technology. Computational Fluid Dynamics (CFD) based numerical simulation has been proven to be an effective approach to analyze the performance of combustion under various conditions. The objective of this paper is to study hydrogen-assisted catalytic combustion of methane. It is proved that methane conversion rate decreases as the inlet velocity increases. The most suitable inlet velocity was 0.2 m/s, while the inlet temperature was 900 K. The ignition temperature will decrease considerably when hydrogen content of the fuel was increased with a fixed value of equivalent ratio, meanwhile, the moment of the ignition temperature advances and methane conversion rate also rises accordingly. This is useful for optimization micro combustion fuel.     

Counter-rotating dual-stage swirling combustion characteristics of hydrogen and carbon monoxide at constant fuel flow rate

In this paper, experimental and numerical methods were used to study the combustion characteristics of a counter-rotating double-stage swirling syngas combustor at constant fuel flow rate, and the effect on it of hydrogen content of syngas. In the experiment, the speed and temperature in the combustor were respectively obtained with PIV and temperature rake, while Reynolds stress equation model and the detailed chemical reaction mechanism of syngas were adopted in the numerical method. The calculation results were in good agreement with the experimental data. Research results indicated that in the working conditions of different hydrogen contents, the flow field structures in the combustor are almost the same, and the maximum temperatures at the outlet remain almost the same. However, as hydrogen content in the fuel increases, the axial velocity in the central area of flow field is increasing, and the outlet temperature distribution coefficient decreases first and then increases. In addition, it was also found in the study that the distribution structure of temperature on the central section of the combustor is almost impervious to the changes in hydrogen content, but with numerical differences, i.e. the higher hydrogen content in the fuel, the farther the stabilization position of flames in the central area is away from the head. It was also indicated in the study that the conventional combustor is no longer applicable to the combustion of syngas, especially the hydrogen-rich fuel. And the work provided the improvement scheme of hydrogen-containing fuel for gas turbine combustor.     

Numerical study on premixed hydrogen/air combustion characteristics and heat transfer enhancement of micro-combustor embedded with pin fins

Aimed at improving the energy output performance of the Microthermal Photovoltaic (MTPV) system, it is necessary to optimize the structure of the micro combustor. In this paper, micro combustor with in-line pin fins arrays (MCIPF) and micro combustor with both end-line pin fins arrays (MCEPF) were presented to realize the efficient combustion and heat transfer enhancement, and the influence of inlet velocity, equivalent ratio, and materials on thermal performance was investigated. The results showed that pin fins embedding is beneficial to improving combustion, and the combustion efficiency of MCIPF and MCEPF reaches 98.5% and 98.7%, which is significantly higher than that of the conventional cylindrical combustor (MCC). However, with the increase of inlet velocity from 8 m/s to 14 m/s, MCIPF exhibits the highest external wall temperature with a range of (1302–1386 K), while MCEPF maintains the best temperature uniformity. As the inlet velocity increases to 10 m/s, the external wall temperature and temperature uniformity reach the optimum. Besides, under the conditions of different equivalence ratios, both external wall temperature and heat flux increases first and then decreases, meanwhile the temperature uniformity of MCEPF is significantly improved compared with that of MCIPF, they all exhibit the highest external wall temperature with an equivalence ratio of 1.1, and the thermal performance is greatly enhanced. By comparing the heat transfer performance of combustors with different materials based on MCEPF, it is interesting to find that the application of high thermal conductivity materials can not only increase the external wall temperature, but also improve the temperature uniformity. Therefore, materials with high thermal conductivity such as Aluminum, Red Copper and Silicon Carbide should be selected for application in micro combustors and their components. The current work provides a new design method for the enhanced heat transfer of the micro combustor.     

Effect of inserted baffles on hydrogen heterogeneous reaction in planar catalytic micro combustor

Heterogeneous reaction characteristics of premixed H₂/Air mixture are numerically investigated in micro combustor with coating platinum (Pt) catalyst on the inner wall. The well-designed combustor with the inserted baffle is committed to improving the transport of bulk species on the catalytic surface, therefore enhancing the fuel conversion ratio. A two-dimensional numerical model with detailed heterogeneous reaction mechanism is developed and verified. In this work, the numerical results reveal that the heterogeneous reaction rate and fuel conversion ratio are significantly improved in the combustor with inserted baffle. The velocity of gaseous mixture swiftly increases between the baffle and catalytic surface, resulting in the increasing adsorption-desorption of bulk species on the catalytic surface. The main influencing factors of inserted baffle body comprise of slit width between two ribs in the same row (W), rib length (L), distance between adjacent baffles row (D), number of baffle row (n) which are studied to obtain a set of optimized parameters of baffle in the well-designed combustor. The optimized parameters of the baffle are W = 0 mm, L = 0.4 mm, D = 4 mm and n = 4, which are employed in the combustor to obtain a high hydrogen conversion ratio. Moreover, the effect of different inlet velocities and equivalent ratios of the mixture on the heterogeneous reaction characteristics are carried out in the designed combustor. As the designed combustor performs well, and the improvement effect of the optimized baffle gradually increases together with the inlet velocity, particularly for high inlet velocity (7 m/s). The promotion effects of baffle in the designed combustor are presented when the rich and lean fuel are adopted at inlet velocity of 7 m/s. Finally, the relative parameters of this work can serve as a reference and guidance for the design of micro scale combustor.     

Thermal management and catalytic combustion stability characteristics of premixed methane/air in heat recirculation meso‐combustors

In order to illuminate heat recirculation effect on catalytic combustion stability and further improve energy conversion efficiency in meso‐combustor, the catalytic combustion characteristics of the combustor with/without preheating channels are numerically studied at steady conditions. It is found that methane conversion rate and combustion efficiency increases by 2% to 3% and approximately 9% in the heat recirculation meso‐combustor, indicating that heat recirculation effect facilitates more complete combustion of methane and medium components. Preheating channels show positive effects on improving combustion stability in the heat recirculation meso‐combustor. On one hand, preheating channels facilitate heat recirculation effect, and heat recirculation rate exceeds 10% for all cases and reaches 31.8% with an inlet velocity of 0.5 m/s, leading to significant increment of methane‐specific enthalpy at the preheating channel outlet. On the other hand, Rh(s)/O(s) ratios of catalytic surface and catalytic surface temperature in main reaction zone are enlarged by the preheating channels, facilitating methane adsorption at catalytic surface. Specially, most of fuels are consumed in a shorter distance with higher methane conversion speed, which brings benefits to promote combustion efficiency and may be helpful to inhibit the combustion instability in heat recirculation meso‐combustors.     

Effect of micro-pin-fin arrays on the heat transfer and combustion characteristics in the micro-combustor

Micro-combustor is an important component elements of the micro-thermophotovoltaic (MTPV) conversion device. The combustion stability is critical to improve its thermal performance, and thus three kinds of combustors are compared by computational fluid dynamics (CFD), which includes single – channel combustor, alternate permutation combustor and in-line combustor. The influences of micro-pin-fin arrays on the performance of the micro-combustor are discussed. Results indicate that the maximum surface temperature of combustor with fins is about 100 K higher than that without fins and the mean temperature and heat flux of in-line combustor are always higher in magnitude than those of the alternate permutation combustor. Analysis in this paper reveals that comparing with single-channel combustor, the micro-combustor with fins greatly enhances the heat transfer process through the wall. There are low velocity zones in the tail of fins, which can gather the reactants and prolong the residence time which make the combustion more sufficient and improve the effect of stable combustion. Meanwhile, under calculated conditions, the influence of micro-pin-fin arrays on the combustion reaction is stronger as the flow rate increase. The fin array in micro-combustor does not only improve the wall temperature but also minimize the wall temperature difference along the axial direction. Moreover, when the inlet velocity is larger than 4 m/s, the hydrogen conversion ratios of micro-combustors with fins was not strengthened obviously with the further increase of inlet velocity.     

Numerical investigation on combustion characteristics of premixed hydrogen/air in a swirl micro combustor with twisted vanes

The combustion characteristics of the swirl micro combustor with twisted vanes (Swirl-MC-TV) and the conventional micro combustor (Conventional-MC) are investigated and compared under different inlet velocities (8–40 m/s), wall materials (quartz, steel, and SiC), and equivalence ratios (0.6–1.4). The results show that the larger area of recirculation zones and the stronger recirculation intensity are the key factors for Swirl-MC-TV to stable combustion. When the inlet velocity is 40 m/s, compared with the Conventional-MC, the wall heat loss of the Swirl-MC-TV is reduced by 15.9%, and the reaction heat and combustion efficiency of the Swirl-MC-TV are increased by 17.5% and 5.9%, respectively. When the wall materials of steel and SiC, combustors have a better preheating effect and higher combustion intensity. When the equivalence ratio is greater than 0.6, the wall heat loss of Swirl-MC-TV is larger but the combustion efficiency and the reaction intensity are still higher than Conventional-MC.     

Numerical comparison of premixed H2/air combustion characteristic of three types of micro cavity-combustors with guide vanes,bluff body,guide vanes and bluff body respectively

Micro-scale combustion is facing the problems of ignition difficulty, combustion instability, and low combustion efficiency. Therefore, it is necessary to improve the combustion characteristics in micro-combustor to expand the application range of micro-combustor. Focusing on the problem of the weak preheating effect of the micro cavity-combustor, the guide vanes are constructed to enhance the combustion near the cavity, and further combine with the bluff body to enhance combustion. The combustion characteristics of three types of cavity combustors with guide vanes (CCGV), bluff body (CCBB), bluff body, and guide vanes (CCGB) respectively are compared and analyzed under different inlet velocities (8–32 m/s), equivalence ratios (0.6–1.4), and wall materials (quartz glass, steel, and SiC). Results show that the guide vanes can greatly improve the combustion intensity near the cavity and improve the combustion stability of the cavity combustor. The combustion efficiency of CCGV and CCGB are increased by 43.04% and 85.96% respectively than CCBB when the inlet velocity is 32 m/s. The reaction heat of CCGV is 244.5 W when inlet velocity is 32 m/s, which is 0.55 times and 1.57 times that of CCGV and CCBB, respectively. The temperature uniformity and mean temperature of the outer wall of CCGV and CCGB both are better than that of CCGB. The combustion efficiency of CCGB is the highest among three combustors under the same equivalence ratio, especially when the equivalence ratio is less than 1. The reaction intensity in the cavity of the CCGV and CCGB with steel wall material is highest than that of the combustor with the other two wall materials. Wall materials with high thermal conductivity have a better preheating effect. Compared with quartz as the wall material, the mean temperature of the external wall of CCGV and CCGB using steel and silicon carbide as the wall material both increase by more than 130 K, and the wall heat loss both increase by more than 50%.     

Numerical investigation on mixing performance and diffusion combustion characteristics of H2 and air in planar micro-combustor

In the present work, the effects of inlet velocity and channel height (H₀ = 0.6 mm, 1.0 mm and 1.4 mm) on the mixing performance, flame stability limit and combustion efficiency of H₂ and air in a 2D planar micro-combustor with a separating plate were studied numerically. The results demonstrate that improved mixing can be achieved with a decrease in inlet velocity and channel height. Moreover, the flame blow-off limit is the largest for a micro-combustor with H₀ = 0.6 mm; the flame becomes inclined at a high velocity and the direction varies with the inlet velocity. Furthermore, a micro-combustor with a medium height (H₀ = 1.0 mm) can achieve the largest blowout limit among the three cases. Finally, for identical inlet velocities, the combustion efficiency increases with decreasing combustor height. In summary, these findings can provide a guideline for the optimal design of such micro-combustors.     

催化肋片对微燃烧室内燃烧特性的影响

针对带有催化肋片的微燃烧室内部的氢氧预混合燃烧过程,利用CFD计算软件建立数值模型,在实验验证的基础上进行了模拟计算。结果表明:不同流速下,燃烧室内布置催化肋片能提高燃烧室外壁面平均温度以及燃烧效率。在低流速时催化肋片布置越靠近入口,表面催化反应对气相反应的抑制程度越大;肋片位置越靠近出口,燃烧室外壁面平均温度越高。在高流速下,催化肋片位置越靠近出口,表面催化反应对气相反应的促进作用越明显,使得燃烧室外壁面温度分布越均匀、燃烧室出口截面温度越高。     

燃烧边界条件对乙醇均质压燃燃烧的影响

在一台由CA6110柴油机改造而成的单缸发动机上进行了燃烧边界条件对乙醇燃料均质压燃（HCCI）燃烧过程影响的试验研究。结果表明，在转速和进气温度一定时，随着过量空气系数的增加，着火始点推迟，燃烧持续期变长，缸内的最大燃烧压力降低，放热率降低，φ50（50％乙醇燃烧放热量所在的曲轴转角）位置推迟，燃烧效率降低；在发动机转速、进气温度和过量空气系数一定时，随着EGR率的升高，着火始点推迟，燃烧持续期延长，φ50位置推迟，放热速率降低，压力升高率变小，缸内最大燃烧压力减小，燃烧效率降低。在转速和供油量一定时，随着进气温度的升高，着火始点提前，燃烧持续期变短，压力升高率变大，缸内的最大燃烧压力变大。得到了发动机转速、过量空气系数和对应于最大指示热效率点的进气温度间的MAP图。     

贫预混预蒸发燃烧室振荡燃烧特性的实验研究

针对燃用航空煤油的贫预混预蒸发模型燃烧室的振荡燃烧特性开展了实验研究。实验表明:在相同的燃烧室入口空气燃料混合物流速下,随着当量比的增加,燃烧室振荡燃烧的振荡主频从132 Hz增加到144 Hz,但燃烧室的均方根脉动压力幅值却从1 464 Pa下降到342 Pa。在当量比不变情况下,入流空气燃料混合物流速较低时,容易引发振荡燃烧现象,而当入流空气燃料混合物流速较高时,则燃烧会变得稳定。分析了整个燃烧实验装置的前4阶轴向声学模态频率,发现实验中所激励出的振荡燃烧主频和第二阶轴向声学模态频率吻合的很好。     

Numerical investigation on implication of dual cavity on combustion characteristics in strut based scramjet combustor

The present study investigates the implication of a dual cavity on combustion and mixing characteristics of strut based combustor numerically. A scramjet combustor with and without cavity are considered to evaluate the influence of cavity on combustion characteristics. Moreover, the effect of spacing between the cavities on combustion performance is also discussed. A separate study is carried out to understand the interplay of the Mach number and the spacing between the cavities on combustion characteristics. Our study reveals that the introduction of a dual cavity in scramjet combustor enhances the mixing and improves combustion performance. Further, it is found that the mixing length is lesser and the penetration height is more when a dual cavity is employed in a combustor. It can also be observed that the size of the recirculation region is found to be larger for the combustor with dual cavity among all configurations at the spacing S₂ = 12.7 mm. Further, the combustion efficiency and fuel penetration height are found to be maximum at Mach 2.5 with a spacing S₂ = 12.7 mm.     

随机堆积床内过滤燃烧特性的实验研究

本文提出了一种可视化燃烧室,用于对3种尺寸的随机堆积结构开展过滤燃烧实验,该结构分别由直径为5,10,15 mm的氧化铝颗粒堆积而成。通过搭建燃烧平台,研究了不同颗粒直径堆积床中火焰的燃烧波高度、火焰传播速度、火焰温度及排放特性。结果表明：在可燃工况下,颗粒直径5 mm堆积床中火焰最高温度随火焰传播过程减小,火焰传播速度变快;而在颗粒直径10和15 mm堆积床中火焰最高温度随火焰传播过程增大,火焰传播速度变慢。