粉末颗粒气力加注特性实验研究

Experiment study of characteristics of powder pneumatic filling

粉末发动机是以粉末颗粒为燃料的新型发动机,具有多次起动和推力调节的功能.粉末加注是粉末发动机实验组织过程中的重要环节.本研究通过搭建粉末供应系统开展粉末气力加注实验,研究对比了集粉箱加注位置、流化气量对粉末气力加注特性的影响.考虑了供粉过程中储箱内粉末堆积密度的动态变化,并建立了相应的计算方法,同时还采用控制系统理论揭示了储箱内粉末堆积密度的变化规律.结果表明:在相同条件下,较大的流化气量有利于加注过程稳定,但集粉箱加注率较低;气力加注方式下集粉箱内的粉末堆积密度大于储箱内初始堆积密度;采用较小的流化气量与集粉箱壁面切向加注方式有利于提高粉末粒径分布均匀性;集粉箱壁面切向加注方式下,流化气量较小时储箱内粉末的堆积密度是先增大后减小,且堆积密度最终值小于初始值,而流化气量较大时,储箱内粉末的堆积密度是先增大后减小再增大后减小,且堆积密度最终值大于初始值;储箱内粉末堆积密度的动态变化过程类似于欠阻尼二阶系统,流化气量较小时系统阻尼系数较小,而流化气量较大时系统阻尼系数较大,且是一个变阻尼过程.

Powder engine is one kind of new concept engines with multiple ignition capability and thrust modulation function.Powder filling is an important process of the powder engine tests.The powder pneumatic filling experiments were carried out to investigate the effects of the filling position of the powder collection box and the mass flow rate of fluidization gas on the stability and performance of powder pneumatic filling.It’s found that large mass flow rate of fluidization gas contributes to stability of powder pneumatic filling,but its volume efficiency of powder filling is the lowest,only 68.1%,but it’s 93.9%when the mass flow rate of fluidization gas is small.Compared with the vertical inlet of end cap,tangential inlet on the cylinder wall makes the powder uniformity better.In the pneumatic filling mode,the powder bulk density in the collection box is greater than the bulk density in the powder tank.In addition,the mass of powder calculated by position displacement is always larger than the mass of powder measured by the electronic balance.It indicates powder bulk density in tank is constantly changing during the powder pneumatic filling experiments.The actual powder bulk density in the powder tank is calculated by a model established in this paper,it’s found that when the mass flow rate of fluidization gas is low,the bulk density of the powder in the tank is increased first and then decreased,and the final bulk density is less than the initial value.While the mass flow rate of fluidization gas is high,powder bulk density in the tank is first increased,then decreased,then increased and then decreased,and the final bulk density is greater than the initial value.The compression mechanism of powder bulk density in the tank is similar to the motion law of the damper spring vibrator when it is forced to vibrate.It can be described by the damped second-order system response function.When the mass flow rate of fluidization gas is small,the damping coefficient of the system is smaller.While the mass flow rate of fluidization gas is large,the damping coefficient is larger and is variable.