Transcript Combustion front instabilities in radical

COMBUSTION FRONT INSTABILITIES IN
RADICAL-DRIVEN PEROXIDE DECOMPOSITION
DAN ILYIN
PH 70
2016/11/15
TALK OUTLINE
• Introduction – project goal, motivation, current objective
• Molecular dynamics simulation setup
• Simulation results
• Discussion
• Near future work and conclusion
PROJECT DESCRIPTION
• Goal:
• Theoretically and computationally examine combustion interface instabilities
• Motivation:
• Long standing problem (over 70 years)
• Still no definite answer – what causes flame to be stable or unstable
• Interesting application of existing theories and numerical methods
• Objectives:
• Create a system that reliably exhibits chemically-driven instabilities
• Relate the simulation results to the theory
REACTION:
H2O2 → O2 + H2O
• Simple and “clean”
• Uses existing force fields
• Initiation with ·OH or HO2·
HO2· + H2O2 → O2 + H2O + ·OH
·OH + H2O2→ HO2· + H2O
MOLECULAR DYNAMICS SIMULATION SETUP
105 HO2
+
1952 H2O2
100518 H2O2
2 nm
98 nm
102575 species; 410195 atoms
20 nm
2 nm
MOLECULAR DYNAMICS SIMULATION SETUP
• Simulation package:
• LAMMPS
• REAX reactive force field
• Simulation procedure:
• Timestep: 0.125 fs
• optimize geometry
• generate Gaussian velocities at 10 K
• 1 ps heat to 300 K
• 10 ps heat to 1000 K
• 50 ps trajectory at NVE
• Output:
• positions, velocities, bonding
(every 50 fs)
• Analysis
• Positions and momenta of species
(bond order > 0.5)
• Reaction dynamics
• Computational resources:
• 112 cores
• 168 hours (7 days)
• 50 GB / file
MOLECULAR DYNAMICS SIMULATION SETUP
105 HO2
+
1952 H2O2
100518 H2O2
2 nm
98 nm
102575 species; 410195 atoms
20 nm
2 nm
ZOOM INTO THIS REGION (7.95 PS)
105 HO2
+
1952 H2O2
10 nm
100518 H2O2
20 nm
10 nm
2 nm
98 nm
102575 species; 410195 atoms
2 nm
7.95 PS: RADICAL MOMENTA, SPECIES POSITION
7.95 PS: RADICAL MOMENTA, SPECIES POSITION
8.00 PS: RADICAL MOMENTA, SPECIES POSITION
DISCUSSION
• Local reaction front shape indeed
correlates with radical motion
• Evidence of chemically-driven surface
instability
• No real “preferred” direction
• No formation of “vortexes” or “plumes”
THEORETICAL VELOCITY FIELD
Light fluid
Heavy fluid
FUTURE WORK
• Near future work:
• Look at spatial distribution of
temperature, pressure
• Change fraction of radicals (50-100%)
• Change shape of radical region
• Minimize simulation noise
• Future work:
• Extract reaction constants
• “Scale up” via hydrodynamic simulations