Wave Structure of Heterogeneous Detonations at High Operating Pressures

ABSTRACT

An analytical model has been constructed to evaluate the behavior of a single droplet in a heterogeneous detonation flowfield. In this study, mass shed off the droplet is estimated based on viscous boundary layer instabilities at the free surface of the gas/liquid interface at high operating pressures. The trajectory of the droplet is computed by assuming that it travels through a gas medium that matches a Zel’dovich-Von Neumann-Döring (ZND) profile, i.e., gas/liquid momentum exchange is ignored. With application to rocket combustors, three different mixtures are considered: liquid oxygen droplets with both methane and hydrogen gas, as well as kerosene droplets in gaseous oxygen. It is identified that the initial droplet diameter and the dynamic pressure behind the leading shock front are the two most important factors influencing the droplet breakup process. It is found that smaller droplet diameters, higher base pressures, and reactants with lower sound speeds are desired for close coupling of the leading shock front to the heat-release zone. With the droplet atomization model employed, it is concluded that increasing the operating pressure may increase the minimum droplet size that will permit coupling of the heat release with the detonation front. This is due to the increased dynamic pressure behind the wavefront when the operating pressure is increased. Finally, it is noted that the sound speed in the compressed reactant mixture is also of prime importance as induction zone lengths scale with this parameter. As a result the liquid kerosene/gaseous oxygen system provided the smallest induction zone length of the three systems studied.

KEYWORDS:

• Heterogeneous detonations
• rotating detonation engines
• droplet shedding
• shock-droplet interaction
• high pressure

Acknowledgments

The authors would like to acknowledge AFOSR Program officers Dr. Chiping Li and Mr. Eric Paulson in this study. Additionally the authors would like to thank Dr. Swanand Sardeshmukh and Dr. Jenna Humble for their expertise.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the AFOSR under Grant FA9300-20-C-2001