Experimental study of pulse detonation engine with liquid ethanol and oxygen mixtures

Pulse detonation engine burns fuel and oxidizer using detonation waves. As in other volume-limited propulsion devices, the use of liquid fuel in a pulse detonation engine is preferred. An experimental study of a pulse detonation engine with liquid ethanol fuel and oxygen mixture was carried out. The research of detonation in ethanol was limited to gaseous mixtures only, and to the best of our knowledge, this is the first published data on detonation in a heterogeneous liquid ethanol and oxygen mixture. Single-cycle tests were made with several engine lengths (45-75 cm) and diameters (6-15 mm), a variety of equivalence ratios, and different deflagration-to-detonation (DDT) enhancement methods. A two-fluid atomizer was used for ethanol injection, and the droplet size distribution was measured. The heterogeneous stoichiometric mixture had a Sauter mean diameter of 30 mu m at the exit of the atomizer, and the droplet size distribution shifted toward a larger diameter for higher equivalence ratios and downstream along the tube. A fully developed detonation was observed at and above 60-cm-long smooth tube. A maximum velocity deficit of 400 m/s relative to the theoretical Chapman-Jouguet detonation velocity for the gaseous ethanol-oxygen mixture was measured. A weak ignition source of 1.1 mJ and DDT enhancement methods were demonstrated. Shchelkin spirals and grooved insert, with blockage ratio of 53% and 51%, respectively, were tested. A 15-cm grooved insert enabled a decrease in the required detonation tube length from 60 cm to 45 cm, whereas the Shchelkin spiral showed a significantly lower effect.