Determining combustion zone acoustic admittance of non-metal and metalized energy condensed systems
The work is devoted to the experimental study of combustion zone dynamic characteristics for metallized and non-metallized solid propellants. The goal of the study consists in developing a device to determine acoustic admittance and the pressure-response function of solid propellant combustion zone at various pressure pulsation frequencies and operation pressure. The pulsed T-burner consisting of a classical T-burner and two auxiliary pressure pulsation generation (AG) chambers is proposed. Changing the T-chamber sections number allows varying frequency of created longitudinal vibrations combustion products, making it possible to measure acoustic admittance of the combustion zone in a wide frequency range. Nozzle design envisages the possibility of changing the throat diameter before launching by replacing the molybdenum liner. A pyrotechnic compound placed in the AG free space ensures the tearing up of metal diaphragm, clamped in the channel, connecting AG and T-burner. To determine the solid propellant acoustic admittance a series of firings is being performed. For each firing cylindrical charges with a channel are prepared and glued to T-chamber cover. During the T-chamber firing without AG the installation, the operation time necessary for the right setting of time delay of triggering pyrotechnic compositions in AGs for the next firings is determined. Further firings are performed with AG, in which the decay constants of the two pressure pulses, created at the main operation segment, and at the end after both charges burning out are being fixed. Acoustic admittance of the solid propellant combustion zone and a function of combustion zone pressure-coupled response are calculated according to the obtained coefficients. The acoustic admittances of a non-metallized solid propellant (AP / low-molecular rubber) and metallized propellant (AP / butyl-rubber /Al) were measured at frequencies in the range 150 to 850 Hz. Comparison of the obtained results to the published data indicates the perspective of the proposed installation implementation. A significant relative error of acoustic admittancehav and pressure-coupled response function determination requires more close attention to the technique of pulse pressure forming in the T-chamber. The obtained acoustic admittance values can be used as boundary condition for solid fuel power plants acoustic stability calculation while employing various numeric methods.