Suppression of instabilities in a premixed methane–air flame in a narrow channel via hydrogen/carbon monoxide addition

Kang, Xin; Gollan, Rowan; Jacobs, Peter A.; Veeraragavan, Ananthanarayanan

doi:10.1016/j.combustflame.2016.07.003

Cited by 84 publications

(21 citation statements)

References 36 publications

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“…The hyperbolic tangent wall temperature ramp is moved to the centre of the channel length, in order to avoid the flame interacting with the inflow boundary. This periodical flame oscillation, is attributed to the competition between the flame propagation speed and the local flow velocity [78]. The flame propagation speed which is larger than the local flow velocity in the flame-upstream-moving phase, however, is weakened due to the large surface heat losses.…”

Section: Reaction Mechanismsmentioning

confidence: 99%

“…Validation work of the model for simulating the flame structure in a 12-mm wide channel was reported in our previous article [78]. A cell-centred, finite volume method is employed for the discretisation of the governing compressible Navier-Stokes equations, which are given in our previous articles [78,82].…”

Section: Numerical Approachmentioning

confidence: 99%

“…Other studies used time-accurate models, e.g. Pizza et al [56], Nair et al [62] and Jiménez et al [74,91] for H 2 /air, Nakamura et al [59], Miyata et al [61] and Kang et al [78] for CH 4 /air, to capture the flame dynamics involving various modes of flame stabilities and instabilities.…”

Section: Introductionmentioning

confidence: 99%

“…Micro/mesoscale combustion which can be viewed as combustion in narrow passages or ducts on the order of the flame thickness (dimension < 1 mm for microscale and > 1 mm for mesoscale), has drawn wide research interest in the past two decades [4,5,46,55,67,78,106,138,159,[164][165][166][167]. Compared to traditional lithium-ion or alkaline batteries, micro/mesoscale combustion using hydrogen or hydrocarbons as energy sources could offer considerably higher (tens of times) energy densities per unit mass and instant rechargeability, thereby leading to fewer logistical issues [1,168].…”

Section: Introductionmentioning

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: Reaction Mechanismsmentioning

confidence: 99%