基于数字同轴全息的铝颗粒燃烧粒度分布研究

Particle Size Distribution of Aluminized Propellant Combustion Based on Digital In-Line Holography

关键词:  固体推进剂  铝团聚  燃烧诊断  数字同轴全息  粒度分布

Key words:  Solid propellant  Aluminium aggregation  Combustion diagnosis  Digital in-line holography  Particle size distribution

摘要:

铝颗粒的团聚效应会对固体推进剂燃烧造成不良影响，产生积渣、两相流损失等问题。为掌握铝颗粒的团聚机理，了解初始铝颗粒尺寸以及压强对铝团聚的影响，以优化推进剂配方及粒度级配，有必要对三维空间内铝颗粒的粒度分布进行研究。为解决传统检测方法的景深问题，采用了数字同轴全息（DIH）技术，并用普通镜头搭配4f透镜组取代长焦显微镜头构建了成像系统。实验一方面对两种具有不同初始粒径的推进剂A和B进行燃烧测量，另一方面对推进剂B分别在0.1，0.2，0.3MPa三种不同压强下的燃烧进行了测量，然后通过全息重建以及图像处理技术得到了燃烧铝颗粒的粒径信息，相对测量误差在9%以内，最后采用Normal和Log-Normal多峰拟合获取了粒度分布的详细参数。对比实验结果发现，常压下铝团聚体的尺寸随着初始铝粉粒径减小而减小；随着压强增大，铝团聚物的尺寸逐渐变小，体积概率密度逐步由双峰分布变为单峰分布，说明压强升高对于铝团聚有抑制作用。

Abstract:

The agglomeration of aluminium particles will adversely affect the combustion of solid propellant， resulting in problems such as slag accumulation， two-phase flow loss. It is of great importance to study the particle size distribution of aluminium agglomeration in three-dimensional space in order to understand the effects of initial particle size and pressure on aluminium agglomeration， as well as explore the aluminium agglomeration mechanism and optimize the propellant formulation and particle size grading. In this experiment， digital in-line holography（DIH） was used to address the depth-of-field problem in traditional measuring method and the imaging system was composed of an ordinary lens and a 4f lens group instead of telescopic microscope lens. On the one hand， combustion of the two propellants A and B with different initial aluminium particle size were measured. On the other hand， propellant B was measured under three different pressures（0.1，0.2，0.3MPa）， the relative measurement error is within 9%. Finally the particle size information was extracted from the reconstructed image of hologram and the detailed parameters of particle size distribution were obtained by Normal and Log-Normal multi-peak fitting. The comparison results show that the size of aluminium aggregates become smaller as the initial aluminium particle size decreases under atmospheric pressure. Besides， with the increase of combustion pressure， the size of aluminium aggregates tends to be smaller and the probability density function of volume changed from bimodal distribution to unimodal distribution， suggesting that the increasing pressure has an inhibitory effect on aluminum agglomeration.