Grupo de Investigación "Mecánica de Fluidos"
http://hdl.handle.net/10016/9434
2016-06-28T05:59:53ZEffect of the equivalence ratio, Damköhler number, Lewis number and heat release on the stability of laminar premixed flames in microchannels
http://hdl.handle.net/10016/21569
Effect of the equivalence ratio, Damköhler number, Lewis number and heat release on the stability of laminar premixed flames in microchannels
Sánchez-Sanz, Mario; Fernández-Galisteo, Daniel; Kurdyumov, Vadim N.
The effect of the equivalence ratio on the stability and dynamics of a premixed flame in a planar micro-channel with a step-wise wall temperature profile is numerically investigated using the thermo-diffusive approximation. To characterize the stability behavior of the flame, we construct the stability maps delineating the regions with different flame dynamics-in the inlet mass flow rate m vs. the equivalence ratio phi parametric space. The flame stability is analyzed for fuels with different diffusivity by changing the Lewis numbers in the range 0.3 1. As the fuel Lewis number approaches unity, the stability behavior of the flame for lean and rich mixtures becomes more similar to give, in the equidiffusional case Le(F) = 1, a symmetric stability map around the stoichiometric mixture phi = 1. In all cases considered, the most stable flames are always found around the stoichiometric mixtures phi = 1, when the flame instabilities are completely suppressed for very diffusive fuels Le(F) < 1, or are reduced to a narrow range of inflow velocities for fuel Lewis numbers equal or greater than unity. The ratio between the size of the channel and the flame thickness d turns out to be Of great importance in the stability behavior of the flame. Keeping the rest of parameters constant, an increase in d for lean flames makes the flame considerably more unstable, confirming the findings of previous works. Nevertheless, as the stoichiometric ratio approaches phi = 1, that trend is reversed to give flames that become more stable as the size of the channel is increased.
2014-05-01T00:00:00ZThe differential diffusion effect of the intermediate species on the stability of premixed flames propagating in microchannels
http://hdl.handle.net/10016/21551
The differential diffusion effect of the intermediate species on the stability of premixed flames propagating in microchannels
Fernández-Galisteo, Daniel; Jiménez, Carmen; Sánchez-Sanz, Mario; Kurdyumov, Vadim N.
The propagation of premixed flames in adiabatic and non-catalytic planar microchannels subject to an assisted or opposed Poiseuille flow is considered. The diffusive-thermal model and the well-known two-step chain-branching kinetics are used in order to investigate the role of the differential diffusion of the intermediate species on the spatial and temporal flame stability. This numerical study successfully compares steady-state and time-dependent computations to the linear stability analysis of the problem. Results show that for fuel Lewis numbers less than unity, LeF 1, flames propagating in adiabatic channels suffer from oscillatory instabilities. The Poiseuille flow stabilises the flame and the effect of LeZ is opposite to that found for LeF < 1. Small values of LeZ further destabilise the flame to oscillating or pulsating instabilities.
2014-08-26T00:00:00ZAn experimental and numerical study of flames in narrow channels with electric fields
http://hdl.handle.net/10016/21539
An experimental and numerical study of flames in narrow channels with electric fields
Murphy, Daniel C.; Sánchez-Sanz, Mario; Fernández Pello, Carlos
The advancement of microscale combustion has been limited by quenching effects as flames cease to be much smaller than combustors. The long studied sensitivity of flames to electrical effects may provide means to overcome this issue. Here we experimentally and numerically investigate the potential of electric field effects to enhance combustion. The results demonstrate that, under specific conditions, externally electric fields will sustain combustion in structures smaller than the quenching distance. The analysis proposes a reduced mechanism to model this result and provides a study of the governing parameters. We find good qualitative agreement between the model and experiments. Specifically, the model is found to successfully capture the capacity to increase and decrease flame speed according to electric field magnitude and direction. Further, in both experiments and computations the sensitivity to electrical enhancement increases for more energetic mixtures. We do find that the model underpredicts the maximum achievable speed enhancement observed, suggesting that additional phenomena should be included to expand the range of conditions that can be studied.
The proceeding at: 14th International Conference on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2014). Took at 2014, November, 18-21, in Awaji Island, Hyogo Japan. The event Web site in: http://powermems2014.org/
2014-11-18T00:00:00ZCritical radius for hot-jet ignition of hydrogen-air mixtures
http://hdl.handle.net/10016/18522
Critical radius for hot-jet ignition of hydrogen-air mixtures
Carpio, Jaime; Iglesias, Immaculada; Vera, Marcos; Sánchez, Antonio L.; Liñán, Amable
This study addresses deflagration initiation of lean and stoichiometric hydrogen–air mixtures by the sudden discharge of a hot jet of their adiabatic combustion products. The objective is to compute the minimum jet radius required for ignition, a relevant quantity of interest for safety and technological applications. For sufficiently small discharge velocities, the numerical solution of the problem requires integration of the axisymmetric Navier–Stokes equations for chemically reacting ideal-gas mixtures, supplemented by standard descriptions of the molecular transport terms and a suitably reduced chemical-kinetic mechanism for the chemistry description. The computations provide the variation of the critical radius for hot-jet ignition with both the jet velocity and the equivalence ratio of the mixture, giving values that vary between a few tens microns to a few hundred microns in the range of conditions explored. For a given equivalence ratio, the critical radius is found to increase with increasing injection velocities, although the increase is only moderately large. On the other hand, for a given injection velocity, the smallest critical radius is found at stoichiometric conditions.
2013-03-07T00:00:00Z