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首页> 外文期刊>Combustion and Flame >A numerical study of the pyrolysis effect on autoignited laminar lifted dimethyl ether jet flames in heated coflow air
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A numerical study of the pyrolysis effect on autoignited laminar lifted dimethyl ether jet flames in heated coflow air

机译：气流加热下自燃层流提升的二甲醚喷射火焰热解效应的数值研究

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摘要

The liftoff, autoignition, and stabilization characteristics of autoignited laminar lifted dimethyl ether (DME) jet flames in heated coflow air are numerically investigated by varying the fuel jet velocity, U-0. The detailed numerical simulations are performed using the laminarSMOKE code with a 55-species detailed kinetic mechanism of DME oxidation. An unusual U-shaped liftoff height, H-L, behavior under MILD combustion condition is observed from the simulations, which is qualitatively consistent with previous experimental results. From additional numerical simulations with modified mass diffusivity of hydrogen, it is verified that the decreasing HL trend of the lifted flames under relatively-low U-0 conditions is mainly attributed to the fast diffusion of hydrogen generated from the DME pyrolysis. The species transport and displacement speed analyses verify that the differential diffusion effect renders the lifted flames to be leaner at the center of the jet, ultimately leading to the change of their stabilization mechanism from the autoignition to the autoignition-assisted flame propagation mode with increasing U-0. The chemical explosive mode analysis (CEMA) identifies important variables and reactions contributing to the autoignition of the DME jet flames, through which the fast diffusion rates of small species are found to cause the deviation of 2-D autoignition characteristics from that of 0-D homogeneous ignition. The effects of DME pyrolysis on the characteristics of the autoignited laminar DME jet flames are further investigated by varying the fuel tube length, L-res. H-L shows a non-monotonic behavior with increasing L-res because the flame structure changes from a MILD combustion to a tribrachial edge flame and to an attached flame while the stabilization mechanism also changes from the autoignition to the autoignition-assisted flame propagation mode as the degree of the DME pyrolysis increases. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
机译：通过改变燃料喷射速度U-0，对在加热的同流空气中自燃的层流提升的二甲醚（DME）喷射火焰的升起，自燃和稳定特性进行了数值研究。使用具有55种DME氧化详细动力学机制的laminarSMOKE代码执行详细的数值模拟。从模拟中观察到在MILD燃烧条件下异常的U形升空高度H-L行为，在质量上与先前的实验结果一致。通过对氢气质量扩散率进行修正的其他数值模拟，可以证明，在相对较低的U-0条件下，上升火焰的HL趋势下降，主要归因于DME热解产生的氢气的快速扩散。物质传输和位移速度分析证明，微分扩散效应使举升的火焰在射流中心更稀，最终导致其稳定机制从自燃转变为自燃辅助火焰传播模式，U值增加-0。化学爆炸模式分析（CEMA）识别了导致DME喷射火焰自燃的重要变量和反应，通过这些变量和反应，发现小分子物质的快速扩散速率导致了2-D自燃特性与0-D的偏离。均匀点火。通过改变燃料管的长度L-res，进一步研究了DME热解对自燃层状DME喷射火焰特性的影响。 HL显示L-res增加的非单调行为，因为火焰结构从MILD燃烧转变为三臂边缘火焰和附着火焰，而稳定机制也从自燃转变为自燃辅助火焰传播模式。 DME热解度增加。 （C）2019燃烧研究所。由Elsevier Inc.出版。保留所有权利。

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