Numerical Investigations Of Flame Propagating In Micro Pipes

The development of Micro-Chemical energy generators makes it necessary to study the flame propagating in micro-thin pipes and tunnels. In this paper, we apply several models to laminar flame propagating in micro-thin pipes, and experiments approached. Four major aspects are contained, the numerical investigation of thermal-fraction models and theory analysis about flame propagating in micro-thin pipes, the numerical investigation with semi-stable models including N-S equations for that kind of flame, discussion about Lewis number in the propagation, experiments about flame in thin round quartz-class pipes.Theory analysis shows the temperature field, fraction field and declares the relations of burning rate and quenching limit. When burning rate reaches 60% or that with adiabatic wall, the flame is quasi-quenching. Studying the flame in micro-thin pipes with thermal-fraction models proves theory analysis results and the relations of burning rates, flame propagating speed, heat losses at wall and initial gas flow speed are obtained. Thus micro-scale thermal effects are revealed.Based on the quasi-steady model, we can reduce computing time and speculate what conditions make flame quench. Introduce N-S equations into this model to get exact flame figures, which makes the results capable of forecasting experiments. Flame figure, burning rate and flame propagating speed are iterated out with temperature and fraction fields. It is proved that heat losses at wall seriously affect the flame figure but composed gas flow speed doesn't. Equivalence ratios change with flame figure, and flame's incline angle to the wall reaches the maximum when equivalence ratio Φ≈1. But the accurate equivalence radio is only available for accurate Lewis numbers.Lewis numbers of free radical is obviously unequal to 1, which makes the Le = 1 assumption unreasonable. Free radical diffuses and distorts the flame figure. H radicals diffuse much faster than thermal conduction, which accelerates the flame propagating speed. OH radicals play an important role of flame quenching duing to its sensitivity to temperature. In addition, H radicals have very small radial grads while OH radicals have much larger ones. Real Lewis numbers consummate this quasi-stable model, and accurate flame propagating speed is calculated.An industrial camera with a macroshot, which is linked to a computer, gives a perfect observation system for our flame in micro-thin pipes. Experiments confirm the outcome about the figure of semi-quenching flames, but encounter the premix problem for some mixture, which is also a kind of micro-scale effect.