Link to the talk (pdf)
Rationale: 90% of the World energy comes from combustion
Challenges of combustion:
Pollution (NOx and C02)
NOx: produces acid rain
CO2: greenhouse gas
Efficiency:
Safety: Combustion of hydrogen. Hydrogen's energy density is not high, one has to compress hydrogen quite a lot for combustion. Highly compressed hydrogen is quite dangerous.
Challenges:
Rapid mixing of air and fuel
Mixing quality -> emissions
Air at high p and T=> auto-ignition
High flame speed -> flashback
Fuel and operational flexibility
Needs:
Better fundamental understanding of physics/kinetics at relevant conditions
Experimental data at the parameter range
Simulated models to predict outcomes.
Hydrogen is a hard fuel to handle (high flame speed, very inflamable, etc)
Mixing in turbulent reactions takes place at the smaller scales of turbulence
How to resolve them in numerical simulations?
And how to couple with the combustion reactions?
Need to resolve smaller than the Kolmogorov length scale.
Reations: example -> hydrogen and oxygen making steam (simplest reaction)
19 subreactions have to happen to produce steam
Methane + plus takes 500 rections with more than 50 different species. Burning longer hydrocarbons takes even more reactions and catalysts.
Two basic geometries:
jet in co-flow (mixed, pre-mixed0
Anchored channel flow
premixed
Solid walls produce turbulence, so high resolution is needed near walls if one wants to have them. Avoiadable.
Boundaries:
Inner: turbulent non-reflecting inlet (NSCBC)
Outer: non-reflective outlet conditions (NSCBC)
Navier-Stokes Characteristic Boundary COnditions (NSCBS), Poinsot & Lele (1992)
Set the time derivative at the boundary (required a hook in pde)
The subroutine rewrites the boundary condition before the runge-kutta adds to the f-array
Timestep controlled by the fastest reaction.
Sample: H2 combustion with Lithium mechanism (PhD thesis of Andera Gruber)
resolution: 630x200x280
Box size: 2cm! Not applicable to industrial scales yet.
250 k CPU hours.
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