Periodic Partial Extinction in Acoustically Coupled Fuel Droplet Combustion.
John W Bennewitz1, Dario Valentini1, Miguel A Plascencia1
1Department of Mechanical and Aerospace Engineering, UCLA Henry Samueli School of Engineering and Applied Science, Los Angeles, CA 90095-1597.
Combustion and Flame
|July 26, 2019
Summary
High-amplitude acoustic waves cause periodic partial extinction and reignition (PPER) in burning liquid fuel droplets. This combustion-acoustic coupling is influenced by fuel properties and acoustic strain rates.
Area of Science:
- Combustion Science
- Acoustics
- Fluid Mechanics
Background:
- Prior studies quantified droplet flame response to moderate acoustic excitation.
- This work investigates higher amplitude acoustic forcing effects on liquid fuel combustion.
Purpose of the Study:
- Explore liquid fuel droplet combustion response to one-dimensional acoustic standing waves.
- Investigate the phenomenon of periodic partial extinction and reignition (PPER).
- Quantify combustion-acoustic coupling using the local Rayleigh index.
Main Methods:
- Experimental study of burning liquid fuel droplets in an atmospheric waveguide.
- Utilized phase-locked OH* chemiluminescence imaging.
- Performed local temporal pressure measurements.
Main Results:
- Identified distinct combustion regimes: sustained oscillatory flames, PPER, and full extinction.
- Observed PPER in ethanol, JP-8, and Fischer-Tropsch synthetic fuel.
- Quantified combustion-acoustic coupling and analyzed strain rates.
Conclusions:
- Acoustic forcing amplitude dictates combustion behavior, leading to PPER or extinction.
- Fuel-specific reaction time scales influence combustion-acoustic interactions.
- Understanding strain rates aids in interpreting PPER mechanisms.
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