Oscillatory motor

The Weissenbetg Rheogoniometer is well suited to research on homogeneous viscoelastic fluids and elastic melts. For oscillatory shear a second motor-drive mechanism is added. This allows the use of 60 frequencies in the range of 7.6 x 10 to 40 Hz at ampHtudes between 2 x 10 and 3 X 10 rad. An electronic circuit improves the precision of oscillatory measurements, particularly at frequencies neat the natural resonance frequency of the instmment itself (298). 

When an energetic material burns in a combustion chamber fitted with an exhaust nozzle for the combustion gas, oscillatory combustion occurs. The observed frequency of this oscillation varies widely from low frequencies below 10 Hz to high frequencies above 10 kHz. The frequency is dependent not only on the physical and chemical properties of the energetic material, but also on its size and shape. There have been numerous theoretical and experimental studies on the combustion instability of rocket motors. Experimental methods for measuring the nature of combustion instability have been developed and verified. However, the nature of combustion instability has not yet been fully understood because of the complex interactions between the combustion wave of propellant burning and the mode of acoustic waves. 

Combustion of a propellant in a rocket motor accompanied by high-frequency pressure oscillation is one of the most harmful phenomena in rocket motor operation. There have been numerous theoretical and experimental studies on the acoustic mode of oscillation, concerning both the medium-frequency range of 100 Hz-1 kHz and the high-frequency range of 1 kHz-30 kHz. The nature of oscillatory combustion instability is dependent on various physicochemical parameters, such... 

Fig. 13.21 shows another example of oscillatory burning of an RDX-AP composite propellant containing 0.40% A1 particles. The combustion pressure chosen for the burning was 4.5 MPa. The DC component trace indicates that the onset of the instability is 0.31 s after ignition, and that the instability lasts for 0.67 s. The pressure instability then suddenly ceases and the pressure returns to the designed pressure of 4.5 MPa. Close examination of the anomalous bandpass-filtered pressure traces reveals that the excited frequencies in the circular port are between 10 kHz and 30 kHz. The AC components below 10 kHz and above 30 kHz are not excited, as shown in Fig. 13.21. The frequency spectrum of the observed combustion instability is shown in Fig. 13.22. Here, the calculated frequency of the standing waves in the rocket motor is shown as a function of the inner diameter of the port and frequency. The sonic speed is assumed to be 1000 m s and I = 0.25 m. The most excited frequency is 25 kHz, followed by 18 kHz and 32 kHz. When the observed frequencies are compared with the calculated acoustic frequencies shown in Fig. 13.23, the dominant frequency is seen to be that of the first radial mode, with possible inclusion of the second and third tangential modes. The increased DC pressure between 0.31 s and 0.67 s is considered to be caused by a velocity-coupled oscillatory combustion. Such a velocity-coupled oscillation tends to induce erosive burning along the port surface. The maximum amplitude of the AC component pressure is 3.67 MPa between 20 kHz and 30 kHz. - ...

To obtain measurements during oscillatory shear, the drive motor causes the fixture to oscillate from high to low shear rates deforming the sample. The transducer detects the periodic stress which is generated by the deformation. The magnitude of the stress is converted into dynamic shear moduli. 

In the Initiation of steady shear flow and the steady shear flow experiments, the shaft angle encorder was attached to a timing motor and data acquisition proceeds In the same way as In the oscillatory experiments. These tests were performed at shear rates between 5xl0 2 sec and 2000 sec . ... 

Damping by wall friction may be addressed on the basis of the theory of oscillatory boundary layers [35], [36]. Under conditions in real motors, the oscillatory boundary layer at the wall is much thinner than the mean-flow boundary layer [37], and the tangential acoustic velocities just outside the oscillatory boundary layer are (TJT ) times those outside the mean-flow boundary layer, where is the wall temperature and the gas temperature in the chamber. Dissipation in the oscillatory boundary layer may be analyzed by considering a flat element of the surface exposed to the complex amplitude V(T JT,) of velocity oscillation parallel to the surface, where equation (24) has been employed for the acoustic field in the chamber, with the coordinate system locally aligned in the direction of velocity oscillation. Neglecting locally the effects of density changes and the spatial variations of acoustic amplitudes, we write the combination of equations (1-2) and (1-5) for the velocity v parallel to the wall as... 

OSCILLATORY BURNING IN LIQUID-PROPELLANT ROCKET MOTORS... 

Oscillatory Burning in Liquid-Propellant Rocket Motors... 

One of these examples is again the technically important catalytic converter. If sulfur is present in the engine exhaust gas because of impurities in the gasoline and the motor oil, all the SO2 formed during combustion is converted to SO3 over the catalyst—potentially leading to health hazards in urban areas. Olsson and Schoeoen (27) found that SO3 formation on Pt and Rh monoliths was largely suppressed when the CO/SO2 oxidation was carried out under conditions in which autonomous oscillations occur. In this case, oscillatory operation has a positive effect on the selectivity of the catalyst. 

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