A numerical study on combustion and emission characteristics of premixed hydrogen air flames

Çam, Ömer; Yılmaz, Harun; Tangöz, Selim; Yılmaz, İlker

doi:10.1016/j.ijhydene.2017.07.017

Cited by 22 publications

(3 citation statements)

References 55 publications

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“…However, the fuel-air mixture flow pattern, including any recirculation, is critical to achieving flame stability. Improvements in flame stability would be desirable and may be especially advantageous in applications in which reduced emissions are needed (Cam et al, 2017;Pashchenko, 2020). Various attempts have been made to achieve such improvements.…”

Section: Introductionmentioning

confidence: 99%

Combustion Characteristics of Methane-Air Mixtures in Millimeter-Scale Systems With a Cavity Structure: An Experimental and Numerical Study

Chen

2022

Front. Energy Res.

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The management of internal features of a cavity structure for channels offers the possibility of inherently effective operation within the flammable limits of a combustible fluid stream while preserving high stability for the flame. However, the precise mechanism by which the cavity method generally provides increased flame stability for millimeter-scale systems remains unclear. The combustion characteristics of methane-air mixtures in millimeter-scale systems with a cavity structure were investigated experimentally and numerically to gain a greater understanding of the mechanisms of flame stabilization and to gain new insights into the characteristics of combustion within spaces with extremely small dimensions. The quenching distance was determined both experimentally and numerically. Stable temperature profiles were obtained from thermographic measurements using infrared radiation. The measurements were compared with the model predictions. Subsequent model calculations demonstrate the effects of variations in wall thermal conductivity, heat losses, flow velocity, equivalence ratio, and channel dimensions. Design recommendations were made. The experimental and numerical results indicated that the quenching distance is slightly larger than commonly believed. The cavity structure has little effect on the quenching distance, but can improve the efficiency and performance of the systems considerably. The cavity structure can effectively extend flammability limits, with an increase of about 18% in the operating range defined by the equivalence ratio of the mixture. The length scale of the systems plays a vital role in stabilizing the flame. The thermal conductivity of the solid material is vital in determining the efficiency and performance of the systems. The design with anisotropic thermal conductivity has significant performance advantages. The flow velocity of the fluid and the equivalence ratio of the mixture are important factors affecting the efficiency and performance of the systems.

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Section: Introductionmentioning

confidence: 99%

Combustion Characteristics of Methane-Air Mixtures in Millimeter-Scale Systems With a Cavity Structure: An Experimental and Numerical Study

Chen

2022

Front. Energy Res.

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“…Combustion of porous media [10,11], combustion of bluffbody [12-14], method of external heating [15], besides the field being electrical [16]. As a consequence, the associated study findings revealed that these techniques significantly increase the limit of blow-off [17,18], thermal function [19,20], and emissions combustion [21,22]. However, a typical micro TPV system is shown in Figure 1 involves 3 prime components: An emitter, a fuel source, and a TPV cell array.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of an Improved Non-Circular MC Fuelled with H/Air for Thermo-Photovoltaic (TPV) Applications

Ayad¹,

Khdher²,

Albazzaz³

et al. 2022

MMEP

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In recent years, researchers have paid special attention to wall uniformity temperature and improvement in a micro-combustor (MC) for applications as thermos-photovoltaic (TPV) since they have a direct influence on feasibility and efficiency of the required conversion of energy. Numerous experimentation and numerical studies in the field of micro-combustion have been carried out and published in this respect. This study focuses on the flame and flow behaviour in an improved MC. Utilizing the famous approach of fluid dynamics being computational (CFD), the impact of geometrical flow parameters behaviour and temperature of wall is explored and measured. The generated model is being used to evaluate the effects of Hydrogen (H) mass flow rate (MFR) and H/air equivalency ratios on the flame pattern and outer temperature of wall of conventional and enhanced MCs. Moreover, the influence of various MC cross sections (CS), such as square, circular, and flat, on temperature of wall is examined. The findings reveal that when the MFR rises, the wall outside temperature rises as well. The MC with flat cross-sections (CSs) is found to be more effective in terms of power of emitter and efficiency of emitter.

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“…They reported that maximum radiation efficiency of the micro combustors achieves at equivalence ratio of 0.8 regardless micro combustor dimensions. In addition, Cam et al 13 and Faramarzpour et al 14 reported that the maximum radiation efficiency occurs for equivalence ratio between 0.8 and 1 during their numerical studies on the stepped micro combustors. Akhtar et al 15 numerically studied effect of cross-section shapes of the stepped micro combustors.…”

Section: Introductionmentioning

confidence: 99%

Combustion characteristics of hydrogen‐air mixture in a radial micro combustor for using in thermophotovoltaic devices

2021

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Requirement of a fast rechargeable and powerful energy source for micro scale devices leads to increase attentions to various micro combustors for usage as heat source in micro thermophotovoltaic devices. Meanwhile, extracting as much thermal energy as possible from chemical energy of fuel by testing a variety of shapes of micro combustion chambers is at the heart of micro combustion subject. Present research has been purposed to find out performance and feasibility of a radial micro combustion chamber by numerical study of combustion characteristics of H 2 -air pre-mixture and calculation of emitter and total efficiency of the system. Governing equations are considered three-dimensional, incompressible, and steady state for turbulent combustion. In addition, detailed kinetics of H 2 -air combustion is chosen for the combustion mechanism. Inlet velocity, equivalence ratio, and wall material properties consisting of emissivity and thermal conductivity with external thermal convection coefficient are parameters, which have been chosen for investigations. Results indicated drastic effect of inlet velocity on the location of combustion zone. In fact, increasement of the inlet velocity causes to transfer combustion zone to the wall, which leads to increase wall temperature and consequently, emitter and total efficiency of the system. Equivalence ratio has more impact on the combustion temperature. While wall thermal conductivity and wall radiation emissivity play a decisive role in the total efficiency of the system. It was founded as the wall radiation emissivity decreases, heat recirculation increases. It causes to expand high temperature zone through the fluid and wall so that the total efficiency increases.By considering the present radial micro combustion chamber as a heat source for a micro thermophotovoltaic device, it was founded that maximum total efficiency of 3.14% is accessible for the condition in which the outer wall surface has maximum average temperature. Highlights• The inlet velocity has drastic impact on the radiation heat transfer rate.• Existence of the vortexes is suitable for intensifying the reactions.• Wall thermal conductivity has maximum effect on the emitter and total efficiency.

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A numerical study on combustion and emission characteristics of premixed hydrogen air flames

Cited by 22 publications

References 55 publications

Combustion Characteristics of Methane-Air Mixtures in Millimeter-Scale Systems With a Cavity Structure: An Experimental and Numerical Study

Combustion Characteristics of Methane-Air Mixtures in Millimeter-Scale Systems With a Cavity Structure: An Experimental and Numerical Study

Numerical Study of an Improved Non-Circular MC Fuelled with H/Air for Thermo-Photovoltaic (TPV) Applications

Combustion characteristics of hydrogen‐air mixture in a radial micro combustor for using in thermophotovoltaic devices

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