A Bayesian approach to estimate flame spread model parameters over the cylindrical PMMA samples under various gravity conditions

IF 5.8 2区工程技术 Q2 ENERGY & FUELS

Combustion and Flame Pub Date : 2024-11-14 DOI:10.1016/j.combustflame.2024.113828

Shinji Nakaya , Taro Takemata , Yuxuan Ma , Fangsi Ren , Mitsuhiro Tsue

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引用次数: 0

Abstract

The flammability limit of cylindrical polymethyl-methacrylate (PMMA) samples in an opposed-flow was observed experimentally under various gravity levels at 1

G

or more utilizing a centrifuge. Flame spread on the sample was observed, and the limiting oxygen concentration (LOC) was measured in various opposed-flow velocities ranging from 5 to 30 cm/s. Two rotating radii of the centrifuge were tested to assess the effects of Coriolis force on the LOC. A scale analysis model, based on an energy balance equation, was evaluated for thermally thick cylindrical samples. The buoyancy-induced flow was modeled in the analytical model. Model parameters were evaluated with a Bayesian approach: The Metropolis Hasting (a Markov Chain Monte Carlo) method. The results indicated that flames were tilted by the Coriolis force when the oxygen concentration was sufficiently rich from the LOC in 4

G

. However, the effects were negligible under the oxygen concentration conditions near LOC. No significant difference in the LOC was also observed even when the rotating radius of the centrifuge changed. At 1

G

or higher, the LOC approached to a certain value asymptotically with decreasing the opposed-flow velocity. The LOC also increased with increasing the gravity level and sample diameter. The measured LOCs were used to sample model parameters using MCMC methods. Consequently, a suitable fitting curve of the model to the experimental LOC was obtained. Using the predicted model parameters, the LOC under microgravity, Moon, and Mars conditions were predicted as a function of the opposed-flow velocity. In microgravity, the LOC increased greatly with decreasing the forced flow velocity (the radiative extinction regime), and the minimum LOC (MLOC) was recognized. On Moon, the credible interval of LOC was rather large in the low-velocity region, and the MLOC was also recognized. Moreover, it was possible that the cylindrical PMMA sample exhibited the highest flammability not under microgravity but a partial gravity condition.

Novelty and Significance

From observing the limiting oxygen concentration of the flammability limit for cylindrical polymethyl-methacrylate (PMMA) samples in opposed-flows under various gravity conditions, we developed a model of limiting oxygen concentration (LOC) for thick cylindrical samples with the buoyancy induced flow was developed, and we estimated difficult-to-predict parameters using Bayesian statistical methods. Using this model, we can estimate the flammability limits under various gravity conditions of manned space exploration, including Moon and Mars. In addition, the present study shows that the minimum limiting oxygen concentration (MLOC) is the lowest in partial gravity. These results open a new research field for partial gravity combustions, apart from the normal gravity and microgravity and contribute to the understanding on the fire safety on manned space explorations to Moon and Mars.

查看原文本刊更多论文

用贝叶斯方法估算各种重力条件下圆柱形 PMMA 样品上的火焰蔓延模型参数

利用离心机在 1G 或更高的重力水平下，对圆柱形聚甲基丙烯酸甲酯（PMMA）样品在对流下的可燃性极限进行了实验观察。观察了样品上的火焰蔓延情况，并测量了在 5 至 30 厘米/秒的不同对流速度下的极限氧浓度（LOC）。测试了离心机的两个旋转半径，以评估科里奥利力对 LOC 的影响。根据能量平衡方程，对热厚圆柱形样品的比例分析模型进行了评估。在分析模型中对浮力引起的流动进行了建模。模型参数采用贝叶斯方法进行评估：Metropolis Hasting（一种马尔可夫链蒙特卡罗）方法。结果表明，当氧气浓度与 4G 中的 LOC 相比足够丰富时，火焰会因科里奥利力而倾斜。然而，在氧气浓度接近 LOC 的条件下，这种影响可以忽略不计。即使离心机的旋转半径发生变化，LOC 也没有明显差异。在 1G 或更高的重力条件下，随着对流速度的降低，LOC 逐渐接近某一值。LOC 也随着重力水平和样品直径的增加而增加。测量的 LOC 被用于使用 MCMC 方法对模型参数进行采样。因此，得到了模型与实验 LOC 的合适拟合曲线。利用预测的模型参数，预测了微重力、月球和火星条件下的 LOC 与对流速度的函数关系。在微重力条件下，随着强制流速的降低（辐射消光机制），LOC 大大增加，并确认了最小 LOC（MLOC）。在月球上，低流速区域的 LOC 可信区间相当大，也确认了 MLOC。新颖性和意义通过观察圆柱形聚甲基丙烯酸甲酯（PMMA）样品在不同重力条件下对向流动的可燃性极限氧浓度，我们建立了浮力诱导流动下厚圆柱形样品的极限氧浓度（LOC）模型，并使用贝叶斯统计方法估算了难以预测的参数。利用该模型，我们可以估算载人太空探索（包括月球和火星）各种重力条件下的可燃性极限。此外，本研究还表明，在部分重力条件下，最低极限氧浓度（MLOC）是最低的。这些结果为除正常重力和微重力之外的部分重力燃烧开辟了一个新的研究领域，有助于人们了解月球和火星载人太空探索的消防安全。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Combustion and Flame 工程技术-工程：化工

CiteScore

9.50

自引率

20.50%

发文量

631

审稿时长

3.8 months

期刊介绍： The mission of the journal is to publish high quality work from experimental, theoretical, and computational investigations on the fundamentals of combustion phenomena and closely allied matters. While submissions in all pertinent areas are welcomed, past and recent focus of the journal has been on: Development and validation of reaction kinetics, reduction of reaction mechanisms and modeling of combustion systems, including: Conventional, alternative and surrogate fuels; Pollutants; Particulate and aerosol formation and abatement; Heterogeneous processes. Experimental, theoretical, and computational studies of laminar and turbulent combustion phenomena, including: Premixed and non-premixed flames; Ignition and extinction phenomena; Flame propagation; Flame structure; Instabilities and swirl; Flame spread; Multi-phase reactants. Advances in diagnostic and computational methods in combustion, including: Measurement and simulation of scalar and vector properties; Novel techniques; State-of-the art applications. Fundamental investigations of combustion technologies and systems, including: Internal combustion engines; Gas turbines; Small- and large-scale stationary combustion and power generation; Catalytic combustion; Combustion synthesis; Combustion under extreme conditions; New concepts.