Characterization of initiator dynamics in a rotating detonation combustor

• Initiation of an RDC with an initiator tube is characterized.
• The blast wave produced by the initiator tube is used to calculate the energy.
• Energy is maximized for rich H2–O2 initiator mixtures and is on the order of 10 J.
• Subcritical initiation and DDT is observed for stoichiometric H2–air mixtures.

The performance of a tangentially-injecting initiator tube of a rotating detonation combustor (RDC) is assessed for a range of initiator conditions. Two initiator fuels are evaluated for a range of RDC channel pressures, and channel widths to determine the effect on the blast wave generated by the initiator tube. Blast wave trajectories exhibit asymmetric bias in the initiator injection (forward) direction. The energy content is estimated by fitting the blast wave trajectory to a theoretical model for blast propagation. Maximum energy deposition is achieved for a rich H2–O2 initiator mixture (ϕ > 2), which provides twice the energy deposition of the highest performing C2H4–O2 mixture. The highest recorded initiator energy deposition is an order of magnitude smaller than the critical value to directly initiate detonation in a stoichiometric H2–air mixture, precluding direct initiation for this configuration. RDC initiation behavior is assessed for a near-stoichiometric H2–air mixture using the highest-performing initiator tube setting, and verifies the absence of direct initiation. A complex, transitory period follows the subcritical initiation event and culminates in stable detonation rotation within several milliseconds.