Droplet Breakup and Vaporization Effects in High-Speed Liquid-Fueled Combustion
Abstract
For decades, naval aircraft propulsion has been largely limited to the use of Brayton cycles. The next generation of high-performance propulsion devices, such as scramjets, pulse detonation engines (PDE), and rotating detonation engines (RDE), require high-speed, shock-driven combustion, as found in detonation waves. To be practical for aircraft propulsion, these engines will need to be powered by high density liquid fuels. The required high-speed multiphase combustion process is complicated by multiphase effects, such as droplet breakup and vaporization, and strong spatial heterogeneities created by liquid fuel injection. Unlike gas phase high-speed combustion, liquid fuel droplets are unable to react quickly to changes in the gas (e.g. shock acceleration), and lag behind the gas flow (in velocity, temperature, and phase equilibrium), delaying combustion. Larger droplets are slower to equilibrate, but may breakup, accelerating their evaporation and net reaction rate. Liquid fuel injection also creates strong non-uniformities in particle (fuel) concentrations that perturb combustion propagation (e.g. detonation wave), making it unstable and less efficient. The goal of this project is to understand how droplet sizes (driving breakup and evaporation) and heterogeneous spatial distributions (created by fuel injection sprays) effect the propagation of multiphase detonation waves. The specific objective of this project is to test the hypothesis that droplet breakup and vaporization enhances the resilience of a detonation wave to spatial perturbations of droplet concentration (fuel-air ratio). This project will use a combined experimental and simulation approach to test this hypothesis. To determine the mechanisms of droplet breakup and evaporation, shock tube experiments will be conducted with detonation relevant non-dimensional parameters, isolating mixing from reactions, and allowing for high spatial and temporal resolution measurements. The results of these experiments will be used to validate a new simulation model for simultaneous breakup and evaporation of fuel droplets. The effect of high-speed reactions on droplet vaporization rates will then be tested using quasi-1D multiphase detonation experiments. The simulation model will be extended to capture the simultaneous breakup, vaporization, and reaction of droplets and validated against experimental data. Lastly, the effect of spatially heterogeneous distributions of droplets will be determined in detonation tube experiments using prescribed 2D perturbations of droplet distribution to simulate fuel injector patterns. The simulation methods will then be validated under these perturbed conditions. The project will deliver a high-speed multiphase combustion model (validated by experiments), that can be readily implemented in Navy simulation codes. The model will make it possible to perform system-level simulations of detonation engine designs that are under development by the Navy. Additionally, this project will train students in areas vital to national security, enhancing the future naval research workforce.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 31, 2020
- Source ID
- N000142012796
Entities
People
- Jacob McFarland
Organizations
- Office of Naval Research
- Texas Engineering Experiment Station
- United States Navy