A Study of Pressure Transient Propagation in Fuel-Gas Mixtures

This research covers the various stages of an investigation involving the measurement of transient propagation velocities in a pipeline carrying aviation kerosene of specification 2494, with and without the inclusion of free nitrogen gas. The numerical method of characteristics was used to solve the quasi-linear hyperbolic partial differential equations governing the propagation of pressure transients and gave good agreement with measured values, provided the effects of column separations were taken into account. It is further shown that if column separation was unrecognised the errors encountered in the measurements of wave velocity were considerable. In order to assess the influence of entrained gas on pressure transient propagation nitrogen was injected into the pipe carrying kerosene. The tests undertaken showed that by introducing free nitrogen gas a reduction of up to 70% in the wave velocity and hence the surge pressure at the valve was achieved when the gas/fuel ratio was as low as 1% by volume at NTP.
The final stages of this research involved the description of mathematical models and experiments involving the measurements of wave velocity through gas bubble/liquid kerosene mixtures being transported in horizontal and vertical pipelines. A theoretical analysis is presented which takes into account the size of the gas bubble when calculating the celerity through gas/liquid mixtures. It was found experimentally that the size of the gas bubbles introduced into the liquid kerosene had a significant influence on the wave velocity. Results showed that, in a horizontal pipeline, for a large number of small sized gas bubbles present in the pipeline a higher celerity was obtained than with a small number of large sized gas bubbles for a constant mixture quality.