We describe using detailed numerical simulations, the properties of detonation waves occurring in single-phase rotating detonation engines and the evolution of a shock-driven liquid fuel droplet. The studies span vastly different scales from the microscale at which the behavior of an isolated liquid fuel droplet has been investigated to device-scale simulations of a gas-phase rotating detonation engine.
Rotating Detonation Engines (RDEs) represent a relatively new concept in pressure gain combustion, where a detonation wave (DW) formed from injected mixture, travels circumferentially within an annular channel. The DW compresses the fuel to much higher pressures, resulting in the extraction of additional work and efficiencies not accessible through the conventional Brayton cycle. Mode transition in RDEs refers to an abrupt change in the number of detonation waves due to a change in inlet conditions such as the injected fuel reactivity and total pressure, and can affect engine performance. Through detailed numerical simulations in a 2D unrolled RDE geometry, an alternate mechanism for mode transition is proposed, along with a corresponding quantitative criterion that is validated using simulation data. A simple model to predict the number of DWs following mode transition is proposed and verified using simulation data.
In the second part of this thesis, we describe detailed numerical simulations of a liquid fuel droplet impacted by a Mach 5 shock wave, considering the effects of chemical reactions and phase change due to evaporation. The fuel droplet undergoes significant deformation and morphological changes following shock impingement, as the droplet surface becomes unstable to the Kelvin-Helmholtz instability. The production of fuel vapors by the droplet impairs the growth of such surface instabilities, leading to reduced growth of the droplet surface area when compared with a non-evaporating droplet. As the fuel vapors react, a diffusion flame is formed on the droplet-windward side, leading to intense droplet heating and enhanced vapor production in this region. Our results show significant spatial inhomogeneities are present in the droplet flowfield in all the cases investigated, which must be considered in the development of reduced order point-particle models for system-level simulations of detonation engines.