Modeling and Numerical Simulation on Ignition and Transition to Flame Spread under a Microgravity Environment

微重力环境下点火和火焰传播过渡的建模和数值模拟

基本信息

批准号：
07650255
负责人：
NAKABE Kazuyoshi
金额：
$ 1.28万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07650255/
关键词：
Microgravity Ignition Flame propagation Numerical Simulation Equations of reaction rate 火炎伝ぱ

项目摘要

A theoretical model describing ignition and transition to flame spread over an inflammable solid material in a microgravity environment with and/or without a slow ventilation wind is developed for application to fire safety in a spacecraft. This study treats a thermally thin cellulosic paper accompanied with both solid and gas phase reactions. A process of ignition and subsequent flame spread on the solid material is complicated by strong coupling between chemical reactions and transport processes not only in the gas phase but also in the solid phase. The objectives of this study are to be able to obtain a more definitive understanding of the ignition and flame propagation mechanisms under a microgravity environment, and also to develop fire safety applications in a spacecraft. In fire safety applications, the transition from ignition to flame spread is crucial to determine whether a fire will be limited to a localized, temporary burn or will transit into a growth mode with a potential … More to become a large fire.Axisymmetric heat and mass transport processes near the heated solid surface accompanied with solid and gaseous reactions were numerically calculated in a quiescent microgravity environment. 3-dimensional unsteady numerical computation was also performed in order to investigate the effects of the ambient wind and oxygen concentration on phenomena of ignition and subsequent flame spread over the surface, since even a slow ambient flow along the sample surface similar to a ventilation flow in a spacecraft has significant effects on flame propagation velocity, and might affect the mechanisms of smoldering and also gaseous combustion. A one-step global gas phase oxidation reaction and three global degradation reactions for the solid phase are used in the present model. The equations for temperature and concentrations are solved using an operator-splitting technique to prevent the solutions from diverging.A higher oxygen concentration increases the gaseous temperature due to an increase in gas phase reaction rate and thus increases the energy feedback rate to the sample material, which increases the supply rate of combustible gaseous degradation products. The transition from autoignition to the flame spread is controlled by the energy feedback rate. Shortly after the ignition, the flame has an umbrella-like shape. The center portion of the flame becomes weaker with time and eventually disappears. Then, a ring-shape flame propagates radially outward. The flame near the propagation front is considered to be a premixed flame followed by a diffusion flame at its tail. Less

一个理论模型描述了在微重力环境中使用和/或没有缓慢通风的微重力环境中易燃的固体物质上的点火和过渡，以便在航天器中使用防火安全性。这项研究处理了用固体和气相反应进行的热薄纤维素纸。通过化学反应和运输过程不仅在气相，而且在固相之间的交通工具之间，而且在固相之间，点火和随后的火焰的散布在固体材料上的过程是通过强耦合来汇总的。这项研究的目的是能够对微重力环境下的点火和火焰传播机制有更确定的了解，并在航天器中开发消防安全应用。在火灾安全应用中，从点火到火焰传播的过渡对于确定火灾是否仅限于局部燃烧，或将其转变为具有潜力的生长模式……更多地成为大火。轴对称热量和质量传输过程在固体和固体反应中实现的加热固体表面附近，在Quiescent Microgravity环境中实质上是在实质上计算的。还进行了三维不稳定的数值计算，以研究环境风能和氧气浓度对点火现象的影响以及随后在表面上散布的火焰现象，因为即使沿着样品表面的缓慢环境流相似，类似于航天器中通风流的缓慢环境流动也对火焰传播的速度也有重大影响，并可能影响smold smold smoldsimiss and Smordersismiss和Smoldersismiss和Smoldsimiss。本模型中使用了固相的一步全球气相氧化反应和三个全局降解反应。使用操作员分解技术来求解温度和浓度的方程，以防止溶液发散。较高的氧气浓度增加了由于气相反应速率的增加而增加气体温度，从而增加了样品材料的能量反馈速率，从而增加了混合脱位产物的供应速率。从自动登记到火焰差的过渡受到能量反馈率的控制。点火开关后不久，火焰具有雨伞状的形状。火焰的中心部分随着时间而变弱，最终消失了。然后，环形火焰从根本上向外传播。繁殖前端附近的火焰被认为是预混合的火焰，然后是尾部的扩散火焰。较少的