Micro/mesoscale combustion based portable power generating system

Kang, Xin (2017). Micro/mesoscale combustion based portable power generating system PhD Thesis, School of Mechanical and Mining Engineering, The University of Queensland. doi:10.14264/uql.2017.378

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Author Kang, Xin
Thesis Title Micro/mesoscale combustion based portable power generating system
School, Centre or Institute School of Mechanical and Mining Engineering
Institution The University of Queensland
DOI 10.14264/uql.2017.378
Publication date 2017-02-28
Thesis type PhD Thesis
Supervisor Ananthanarayanan Veeraragavan
Rowan. J. Gollan
Total pages 281
Language eng
Subjects 0913 Mechanical Engineering
Formatted abstract
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-to-volume 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 enhances the combustion, increases the combustor surface temperature and extends the operational limits. Quartz wafers serving as a simple band-pass filter is used to recycle a large portion of sub-bandgap photons back into the combustor to reduce the system heat losses and improve the TPV system performance.
Keyword Micro/mesoscale combustion
Numerical modelling
Flame stability/instabilities
Combustor wall thermal engineering
Portable power

Document type: Thesis
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Created: Tue, 21 Feb 2017, 18:20:35 EST by Xin Kang on behalf of Learning and Research Services (UQ Library)