Premixed Combustion Flame Instability Characteristics (PREFIC)

由于热扩散不稳定性和流体动力不稳定性，预混火焰的胞状不稳定性和自加速现象在燃料燃烧中普遍存在。池底不稳定性对火焰的结构和速度有很大影响，由此产生的自加速效应在球形火焰研究中已被广泛观察到，对各种燃烧系统的湍流燃烧速度有很大的影响，并造成更大的火灾和爆炸危险。绘制细胞不稳定和自加速区域图有助于改进燃烧系统设计和火灾爆炸危险研究中广泛使用的燃烧模型。该项目分为两个主要工作包，研究从基础数据获取到不稳定的原因，最后是自加速的后果。采用显微摄影和图像处理技术对火焰胞状结构进行数学表征和量化，而不是传统的通过计算火焰尺寸或压力历史来测量燃烧速度。引入胞状因子来表示火焰胞状结构特征，并首次通过测量胞状结构参数来计算和分析火焰前沿胞状结构的变化规律，这些参数是定量确定胞状火焰充分发展的临界点和描述自加速的主要参数。本文将发展一种新的火焰加速燃烧速度模型。提出了改进的关联式，将瞬变效应和多维效应结合在一起，作为有限速率化学，这对预测工程模型的发展至关重要。

Cellular instability and self-acceleration of premixed flames are commonly observed in fuel combustion, due to the thermal-diffusive and hydrodynamic instability. Cellar instability significantly influences the flame structure and speed, and the resultant self-acceleration has been widely observed in spherical flame studies, with high influences on the turbulent burning velocity of various combustion systems and causing higher fire and explosion hazards. Mapping the regimes of cellular instability and self-acceleration could help improve combustion modelling which is widely used in design of combustion systems and investigation of fire and explosion hazards.The project is divided into two main work packages, in which the research is moving from basic dada acquirement to the cause of instability and in the end of the consequence of self-acceleration. The flame cellular structure will be mathematically characterised and quantified by the microscopic photography and image processing technique rather than traditionally by measuring burning velocity through calculation of flame size or pressure history.A newly defined Cellularity Factor is introduced to represent the flame cellular structure characteristics, and the variation regularity of flame front cells is firstly calculated and analysed by measuring the cellular structure parameters, which are the primary parameters to quantitatively determine the critical point of the fully developed cellular flame and to describe the self-acceleration. Present work will develop a new burning velocity model for flame acceleration.Improved correlations are proposed, incorporating transient and multidimensional effects, as finite rate chemistry, which are crucial for the predictive engineering model developments.