Study on Particulate Formation in Diffusive Combustion

扩散燃烧中碳质颗粒的形成是一个非常令人关注的问题，因为它不仅消除了不完全燃烧，而且还危害健康。为此，人们一直致力于阐明碳烟的形成机理。本文从理论和实验两个方面研究了燃烧过程中燃料浓度非均相状态下碳烟颗粒的形成和熄灭过程。这项研究的主要观点可以概括如下。(1)。讨论了干煤烟和多环芳烃(PAH)的形成，以便能够预测在火焰中普遍存在的高温下它们的浓度。这是基于多组份热化学平衡的考虑，其中只考虑了煤烟的气态中间物质。这使得可以定性地描述用加热流动反应器测量的颗粒形成，表明碳氢比…燃料量和燃料生成热是控制颗粒物形成的主要因素。在此基础上，提出了基于均相冷凝和团簇形成的碳烟生成局部平衡模型，用于预测随时间变化的碳烟产生量和最终碳烟产生量。(2)。利用高速摄影和缸内气体快速采样技术，在模拟直喷式柴油机上对柴油机燃烧早期的热分解和氧化进行了研究。测量结果显示了点火前燃料喷雾和热裂解的详细行为。此外，还对深碗式燃烧室的局部气体成分进行了研究，以了解碳烟的形成过程。结果表明，在燃料-空气混合允许的时间内，气体从燃烧缸进入间隙，在该空间内的燃烧对碳烟的形成有很大影响。(3)。应用图像处理技术对直喷式柴油机的火焰概念进行了研究，重点研究了对湍流混合和碳烟形成有重要影响的湍流。分析结果表明，整个空间内的湍流流场几乎是均匀各向同性的。此外，还详细讨论了旋涡和燃烧室几何形状对火焰行为的影响。(4)。基于实验结果和化学平衡的考虑，采用湍流混合模型来描述高速直喷式柴油机的燃烧过程。该模型使我们能够预测几个发动机变量对污染物排放的影响。较少

The formation of carbonaceous particulates in the diffusive combustion is a matter of great concern from removing not only imcomplete combustion but also health hazards. For this reason, much efforts have been concentrated to elucidate the mechanism of soot formation. In the present study, the process of the formation and extinction of soot particlates in the heterogeneous states of fuel concentration during combustion was theoretically and experimentally investigated. The main points of the study may be sumarized as follows. (1). The formation of both dry soot and polycyclic aromatic hydrocarbons (PAH) was discussed to enable prediction of their concentrations at elevated temperatures that prevail in flames. This is based on multicomponent thermochemical equilibrium considerations, in which only gaseous intermediate substances of soot are considered. This allows qualitative description of particulate formation measured with a heated flow reactor, suggesting that the carbon-hydrogen ra … More tio of fuel and the fuel formation enthalpy are main factors that govern particulate formation. Furthermore, a partial-equilibrium model for soot formation based on the homogeneous condensation and the cluster formation was proposed for prediction of time-dependent soot yields and final soot yield. (2). Thermal decomposition and oxidations in the earlier stages of diesel combustion were studied with simulated direct-injection diesel engine using high-speed photography and a fast in-cylinder gas-sampling technique. The measured results show the detailed behavior of fuel spray and thermal cracking of the fuel before ignition. Also, the local gas composition in the deep-bowl type combustion chamber were investigated to know how soot formation proceeds. The results show that within time allowable for fuel-air mixing, gas flow from the combustion bowl into the clearance, and combustion in this space greatly affect soot formation. (3). A picture processing technique was applied to study the flame notion in a direct-injection diesel engine, with a special attention to turbulence which significantly affects the turbulent mixing and soot formation. The analysed results showed that the turbulent flow field is almost uniform and isotropic over the space. Furthermore, the effects of the swirl and chamber geometry on the flame behavior were discussed in detail. (4). Based on the experimental findings and chemical-equilibrium considerations, the turbulent mixing model was applied to describe the combustion process in high-speed direct-injection diesel engines. This model enables us to predict the effect of several engine variables on the pollutant emissions. Less