Application of Novel Flame Acceleration Enhancing Obstacles to Pulse Detonation Engines

This work aims to explore the effect of novel obstacle geometries on flame acceleration and transition to detonation in pulse detonation engines. To this end, a pulse detonation engine ground test demonstration rig has been developed and tested using stoichiometric propane-air mixtures. Much of this work has been invested into rig and instrumentation development as well as performing and analysing experiments. The rig has been tested using two different combustion chamber diameters, 0.089m and 0.038m, with lengths of 1m and 1.18m respectively. In addition, experiments were carried out with an orifice filled tubular insert which restricted the internal diameter to 0.032m over a distance of 14 tube diameters.

A semi-empirical model has also been developed and validated for use in the prediction of flame acceleration (FA) through circular orifice plates. This was validated for a range of obstacle blockage ratios (BR) and tube lengths. The model was found to perform well, within one order of magnitude in all cases. Where modelling predictions fell beyond one standard deviation of the experimental mean it is thought that the discrepancy is a result of insufficient purging.

Experimental shock speed, pressure and flame speed have been analysed using statistical density functions for a range of orifice fractal dimensions, orifice plate BR and obstacle lengths. Of particular interest are the novel experimental results produced by varying orifice fractal dimension or BR in separate tests along the length of the obstacle. It was found that decreasing the orifice plate BR along the obstacle length increased the exit flame speed by a mean value of 27% over a constant 0.57BR orifice. Experimental results for higher fractal dimension orifice plates produced greater shock speeds than circular orifices with 12D long obstacles. This effect diminished with increased obstacle length.