Abstract Laminar diffusion flames present an elementary configuration for investigating soot formation and validating kinetic models before these are transferred to turbulent combustors. In the present article, we present a joint experimental and modelling investigation of soot formation in a laminar co-flow burner. The diffusion flames are analysed with the aid of laser diagnostic techniques, including elastic light scattering (ELS), planar laser-induced fluorescence of OH (OH-PLIF) and line-of-sight attenuation (LOSA), to measure the spatial distribution of soot, gas phase species and the line-of-sight integrated soot volume fraction (ISVF), respectively. The experimental dataset is supplemented by location-specific TEM images of thermophoretically sampled soot particles. The simulation of the sooting flames is carried out with a recently developed discretisation method for the population balance equation (Liu and Rigopoulos, 2019, Combust. Flame 205, 506-521) that accomplishes an accurate prediction of the particle size distribution, coupled with an in-house CFD code. By minimising numerical errors, we ensure that the discrepancies on the modelling side are mainly due to kinetics and are able to carry out an investigation of alternative models. We include a complete set of soot kinetics for PAH-based nucleation and condensation, HACA-based surface growth and oxidation as well as size-dependent aggregation, and consider three different gas phase reaction mechanisms (ABF, BBP and KM2). Based on predictions of the gas phase composition and particle size distribution of soot, modelled counterparts of the laser diagnostic signals are computed and compared with the experimental measurements. The approach of directly predicting signals circumvents the difficulties of explicitly representing the OH concentration in terms of the measured OH-PLIF data and avoids using ‘hybrid’ modelled and measured values to approximate the OH concentration. Moreover, the LOSA signal is directly converted to the line-of-sight ISVF instead of a measure of local soot volume fraction to avoid tomographic inversion errors. Lastly, the predicted ELS signal is computed in terms of the particle size distribution resolved by the population balance model, thus circumventing the approximation of an integral soot property using a presumed size distribution. While we cannot obtain quantitative agreement between experiments and simulations, the accuracy of the numerical approach and the direct prediction of experimental signals allow us to conduct sensitivity analyses of key empirical parameters and investigate the importance of the PAH chemistry and its influence on the competition between nucleation, condensation and surface growth.

中文翻译：

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层流乙烯扩散火焰中烟尘粒子演化的种群平衡建模和激光诊断验证

摘要 层流扩散火焰提供了一种基本配置，用于研究烟灰形成和验证动力学模型，然后再将其转移到湍流燃烧室。在本文中，我们对层流共流燃烧器中的烟灰形成进行了联合实验和建模研究。借助激光诊断技术分析扩散火焰，包括弹性光散射 (ELS)、平面激光诱导的 OH (OH-PLIF) 和视线衰减 (LOSA)，以测量分别为烟灰、气相物种和视线积分烟灰体积分数 (ISVF)。实验数据集由热泳采样烟尘颗粒的特定位置 TEM 图像补充。烟尘火焰的模拟是使用最近开发的群体平衡方程离散化方法（Liu and Rigopoulos, 2019, Combust. Flame 205, 506-521）进行的，该方法实现了对粒度分布的准确预测，并结合了内部 CFD 代码。通过最小化数值误差，我们确保建模方面的差异主要是由于动力学引起的，并且能够对替代模型进行调查。我们为基于 PAH 的成核和冷凝、基于 HACA 的表面生长和氧化以及尺寸相关的聚集提供了一套完整的烟尘动力学，并考虑了三种不同的气相反应机制（ABF、BBP 和 KM2）。基于对烟尘气相组成和粒度分布的预测，激光诊断信号的模拟对应物被计算并与实验测量值进行比较。直接预测信号的方法避免了根据测量的 OH-PLIF 数据明确表示 OH 浓度的困难，并避免使用“混合”建模和测量值来近似 OH 浓度。此外，LOSA 信号直接转换为视线 ISVF，而不是局部烟尘体积分数的测量，以避免断层摄影反演错误。最后，根据总体平衡模型解析的粒度分布计算预测的 ELS 信号，从而避免使用假定的粒度分布来近似积分烟尘特性。虽然我们无法在实验和模拟之间获得定量的一致性，