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Study on Relative Scales between Fuel Clouds and Turbulence in a Transient High-Speed Combustion

瞬态高速燃烧中燃料云与湍流的相对尺度研究

基本信息

批准号：
12650188
负责人：
CHIKAHISA Takemi
金额：
$ 2.62万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-12650188/
关键词：
Diffusion Turbulence Combustion Scale Spray Entropy Mixing Air Entrainment

项目摘要

Rapid mixing of fuel and air is essential to improve combustion in diffusion flames, and an understanding of the microscopic structure in the diffiision process is important. However, the relationship between the structure of the heterogeneous distribution of fuel clouds and the local turbulence structure is not well understood. Additionally there is no appropriate index for the analysis of degree and scale of the heterogeneity. This research investigates a method for identifying the homogeneity degree and the scale of clouds : in this study large-scale cluster of fluids, for example fuel vapor (or air), is termed "cloud". The method is based on the entropy concept of statistical dynamics, and it identifies the homogeneity degree of the fuel concentration. Entropy values increase with the progress of uniformity in diffusion processes, and by analyzing entropy values it is possible to identify the scale of the heterogeneity.The microscopic structure of turbulent jets and diesel spray flames were investigated using entropy analysis. The results show that the diffusion intensity is highest at the vicinity of the nozzle exit, and that the heterogeneity scale increases downstream along the spray axis, with smaller size scales remaining inside larger clouds. Downstream, small-scale structures diffuse while large-scale structures remain clear. The analysis was applied to a spray flame with jet impingement. The jet impingement clearly enhanced the combustion, and the entropy analysis indicated that the impingement broke fuel clouds into a number of clearly distinguishable clouds and this resulted in faster diffusion and faster completion of combustion. The research demonstrates the possibility of the entropy method.

燃料和空气的快速混合对于改善扩散火焰中的燃烧是至关重要的，而了解扩散过程中的微观结构是重要的。然而，燃料云的非均匀分布结构与局地湍流结构之间的关系还不是很清楚。此外，还没有合适的指标来分析异质性的程度和规模。本研究探讨了一种识别云的均匀程度和尺度的方法：在本研究中，大尺度的流体簇，例如燃料蒸汽(或空气)，被称为云。该方法基于统计动力学中的熵概念，识别燃料浓度的均匀程度。在扩散过程中，随着均匀程度的提高，熵值也随之增大，通过对不均匀程度的分析，可以确定扩散过程的非均匀程度。结果表明，喷嘴出口附近的扩散强度最大，非均匀尺度沿喷雾轴向向下游增大，较小的尺度分布在较大的云团内部。在下游，小尺度结构扩散，而大尺度结构保持清晰。将该分析应用于具有射流冲击的喷雾火焰。喷流撞击明显地增强了燃烧，熵分析表明，撞击将燃料云分解成多个明显可区分的云团，从而导致更快的扩散和更快的燃烧完成。本研究论证了熵值法的可行性。