A comparative study of H<sub>2</sub>-air premixed flame in micro combustors with different physical and boundary conditions

Li, J.; Chou, S.K.; Li, Z. W.; Yang, Wenming

doi:10.1080/13647830701642227

Cited by 37 publications

(43 citation statements)

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“…Therefore, the mesh size of 17 µm (mesh-2, 354×36 cells) is determined to be the maximum-sized mesh that can provide grid-independent solutions. This value is found to be slightly lower than many of the mesh densities used in the literature [48,56,62,68,71,75,80] (ranging from 19 to values larger than 50 µm). Since only a few of the past studies used the GCI method, visual observations of the solutions might have a less strict requirement on grid refinement.…”

Section: Grid Resolutionmentioning

confidence: 51%

“…When a particular species data was not available, Sutherland's three coefficient law (based on kinetic theory) [84] was used to calculate transport properties. It should be noted that other studies [56,61,62,68,71,80] have incorporated the CHEMKIN code [85] to evaluate the thermodynamic and transport properties for each species. CHEMKIN used essentially the same thermodynamic database and only a slightly different fitting procedure from the CEA code by Gordon and McBride [83].…”

Section: Numerical Solvermentioning

confidence: 99%

“…This is because the large disparity in acoustic wave speeds and small-magnitude flow velocities renders the system considerably stiff. A large portion of studies in literature [48,62,68,69,71,80] used the SIMPLE (Semi-implicit pressure linked equations) scheme (a pressure-based method originally developed for incompressible flows) [95] to avoid density-based compressible flow issues. Other studies [56] performed modifications to their compressible solvers downward to low Mach numbers through decomposing the pressure into two terms -thermodynamic pressure and hydrodynamic pressure.…”

Section: Numerical Solvermentioning

confidence: 99%

“…At the outlet, the conditions are set to be atmospheric using a very well-established fixed pressure outflow BC (which was adopted in many past studies [48,56,59,62,68,71,72,[75][76][77]80]). The pressure is set at 1.01325×10…”

Section: Considerations On Boundary Conditionsmentioning

confidence: 99%

“…On the other hand, numerical models do not make such assumptions and are capable of quantitatively revealing detailed physical features and can therefore be used as a reliable tool that develops the understanding of current configurations and supports the design of future systems. Some past numerical simulations using a steady-state [48,[68][69][70][71][72][73] or transient [56,61,62,[74][75][76][77][78] model were conducted, with a focus on the flame stabilities and flame dynamics.…”

Section: Introductionmentioning

confidence: 99%

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Micro/mesoscale combustion based portable power generating system

Kang¹

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Micro/mesoscale combustion-driven power generation is a promising alternative to replace traditional batteries for powering small scale electronics owing to its much higher energy densities. However, the considerable heat losses from the combustor walls due to the dramatically increased surface-tovolume ratio, as well as the short flow residence time at small scales pose a technical challenge in stabilising the flame inside the micro/mesoscale combustor. On the other hand, the significantly enhanced flame-wall thermal coupling at small scales can also lead to some unique flame characteristics.Recently, solid state power conversion of the heat released in the micro/mesoscale combustor such as thermoelectric (TE) and thermophotovoltaic (TPV) has been favoured over traditional power conversion methods such as micro-turbines. This is due to the excessive mechanical and viscous losses that rotating machinery suffers from upon miniaturisation.One of the main aims of this thesis is to perform numerical simulations to investigate the fundamental aspects of micro/mesoscale combustion, such as micro-flame behaviours of propagation and stabilisation, the conditions under which flame dynamics occur and the choices that suppress them. A set of modelling techniques that gives guidelines and practices for performing the time-accurate micro/mesoscale combustion simulations has been developed through investigation. Knowledge on standard and well-accepted numerical methods in literature are collected in a cohesive document. The less well-established modelling choices have been thoroughly evaluated and discussed.Using the developed numerical models, the effects of hydrogen and carbon monoxide addition on premixed methane/air flame dynamics is investigated. Results show that the flame instabilities which exist in pure methane/air flames could be effectively suppressed via a small amount of additives. Deep understanding of the underlying physics and chemistry has been gained. The effects of wall temperature profiles on the simulated micro-flame behaviours are also studied. The role of the combustion heat release and the gas-solid heat transfer in determining the micro-flame propagation speed is identified.Experimental works are also carried out, towards a full system demonstration for micro-power generation. The focus is placed on the "wall thermal engineering" on the improvement of the combustor performance and power output. The thermally-orthotropic pyrolytic graphite for the combustor wall material is explored. Compared to an isotropic material of stainless steel, a widened flame stability limit with pyrolytic graphite is demonstrated. Moreover, a uniform and moderate temperature distribution over the combustor surface is achieved, which is favourable for thermoelectric power conversion applications. Meanwhile, a novel, compact mesoscale thermophotovoltaic power generating system using a combination of porous media combustion and a simple band-pass filtering method is developed. The use of the porous media effectively enh...

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Section: Grid Resolutionmentioning

confidence: 51%

Section: Numerical Solvermentioning

confidence: 99%

Section: Numerical Solvermentioning

confidence: 99%

Section: Considerations On Boundary Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Micro/mesoscale combustion based portable power generating system

Kang¹

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Performance Evaluation of H₂/Air Premixed Combustion in a Suddenly Expanded Microcombustor with Wall Fin

2021

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Herein, a 2D, axisymmetric microcombustor with a backward‐facing step and triangular wall fin is considered for enhancement of combustor performance. The outer wall temperature, combustor efficiency, and pressure characteristics of the microcombustor are numerically investigated with a detailed chemical kinetic mechanism and conjugate heat transfer. The proposed microcombustors with variable blockage ratios, wall fin shapes, and locations are analyzed with respect to flow and combustion interaction, along with heat flux exchange between the flame and combustor wall. Combustion performance is also evaluated by means of the amount of heat transferred through the combustor wall, conversion ratio of input chemical energy to exploitable heat, and OH mass fraction distributions. Standard k–ε turbulence along with 9 species and the 19‐step combustion reaction scheme is implemented using the eddy dissipation concept (EDC) model in the numerical study. The results indicate that the wall fin blockage ratio alters the reaction zone and improves combustor performance significantly at lower inlet velocities (4–20 m s−1). The fin location and shape are observed to influence the temperature distribution. However, the higher blockage ratio adversely impacts the combustion characteristics at the higher inlet velocity, that is, 48 m s−1.

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Effect of Obstruction Aspect Ratio in a Suddenly Expanded Micro-combustor

Qamareen

Alam

Ansari

2021

Lecture Notes in Mechanical Engineering

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A comparative study of H₂-air premixed flame in micro combustors with different physical and boundary conditions

Cited by 37 publications

References 25 publications

Micro/mesoscale combustion based portable power generating system

Micro/mesoscale combustion based portable power generating system

Performance Evaluation of H₂/Air Premixed Combustion in a Suddenly Expanded Microcombustor with Wall Fin

Effect of Obstruction Aspect Ratio in a Suddenly Expanded Micro-combustor

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A comparative study of H2-air premixed flame in micro combustors with different physical and boundary conditions

Cited by 37 publications

References 25 publications

Micro/mesoscale combustion based portable power generating system

Micro/mesoscale combustion based portable power generating system

Performance Evaluation of H2/Air Premixed Combustion in a Suddenly Expanded Microcombustor with Wall Fin

Effect of Obstruction Aspect Ratio in a Suddenly Expanded Micro-combustor

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A comparative study of H₂-air premixed flame in micro combustors with different physical and boundary conditions

Performance Evaluation of H₂/Air Premixed Combustion in a Suddenly Expanded Microcombustor with Wall Fin