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Numerical investigation on the start-up of methane-fueled catalytic microreactors

机译：甲烷燃料催化微反应器启动的数值研究

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Transient simulations have been performed in a plane-channel, methane-fueled microreactor made of either cordierite or FeCr alloy walls and coated with a platinum catalyst. A two-dimensional model for the flow domain was used, which included detailed catalytic and gas-phase chemical reaction mechanisms. In the solid wall, axial heat conduction and surface radiation heat transfer were accounted for. Simulations were performed by varying the inlet pressure, the solid wall thermal conductivity and heat capacity, the inlet velocity, and the equivalence ratio at fuel-lean stoichiometries. The effect of solid material properties as well as the impact of gas-phase chemistry and surface radiation on the ignition (t_(ig)) and steady-state (t_(st)) microreactor times has been assessed. An increase in inlet pressure from 1 to 5 bar induced a ～50% reduction in both t_(ig) and t_(st) owing to the enhancement of the catalytic reactivity with rising pressure. A similar behavior was also attested when increasing the equivalence ratio from 0.4 to 0.6. Reactors with low wall thermal conductivity (cordierite material) exhibited shorter ignition times compared to higher thermal conductivity ones (FeCr alloy) due to the creation of spatially localized hot spots that promoted catalytic ignition. At the same time, the ceramic material required shorter times to reach steady-state. Higher inlet velocities reduced the time required for steady-state, however, at the cost of increased cumulative reactor emissions. Surface radiation heat transfer played a key dual role in the start-up process of low thermal conductivity channels. Radiation increased t_(ig) by removing heat away from the initial hot spot, but from the other side it decreased t_(ig) due to a very efficient transfer of heat from the rear to the front of the reactor. Gas-phase chemistry elongated the steady-state times for both ceramic and metallic materials and impacted the emissions of catalytic microreactors.
机译：在由堇青石或FeCr合金壁制成并涂有铂催化剂的甲烷甲烷燃料平面反应器中进行了瞬态模拟。使用了二维的流域模型，其中包括详细的催化和气相化学反应机理。在固体壁中，考虑了轴向热传导和表面辐射热传递。通过改变入口压力，固体壁导热系数和热容量，入口速度以及贫油化学计量比下的当量比来进行模拟。评估了固体材料性能以及气相化学和表面辐射对微反应器点火时间（t_（ig））和稳态时间（t_（st））的影响。入口压力从1 bar增加到5 bar导致t_（ig）和t_（st）都降低了约50％，这是由于随着压力的升高催化活性的增强。当当量比从0.4增加到0.6时，也证明了类似的行为。低壁热导率的反应器（堇青石材料）与高热导率的反应器（FeCr合金）相比，具有较短的着火时间，这是由于在空间上局部产生了促进催化着火的热点。同时，陶瓷材料需要更短的时间才能达到稳态。较高的入口速度减少了稳态所需的时间，但是以增加的反应堆累积排放为代价。在低热导率通道的启动过程中，表面辐射传热起着关键的双重作用。辐射通过将热量从初始热点移走而增加了t_（ig），但另一方面，由于热量从反应器的背面到正面的非常有效的传递，辐射降低了t_（ig）。气相化学反应延长了陶瓷和金属材料的稳态时间，并影响了催化微反应器的排放。

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