OpenFOAM 2.0.0: Chemistry

Pyrolysis modelling

As part of OpenFOAM’s continual development for fire safety simulation, we have introduced modelling of pyrolysis. Pyrolysis is the decomposition of organic material at elevated temperatures, and is usually the primary chemical reaction that occurs in the burning of solid matter, such as wood. The process produces gases which can result in visible flames and leaves behind a solid residue that is rich in carbon, known as char, which often undergoes combustion. Unlike combustion, pyrolysis does not involve reactions with oxygen.

Simulations involving pyrolysis are undertaken in OpenFOAM by creating an extruded surface mesh for the solid, as in surface film simulations. The solid region is described by one or more solid species which react to release gas into the bulk mesh. The modelling accounts for energy exchange in the solid phase due to conduction, mass transfer, radiation and chemical reactions, but assumes the gas and solid to be at the same temperature at the solid/gas interface.

The images below show coupling of pyrolysis and combustion in which the blue surface, in the background, undergoes pyrolysis in conjunction with combustion in the foreground. Viewed from left to right, the images show the spread of combustion at times of 15, 30 and 45 seconds.

Source code

• fireFoam solver
  $FOAM_SOLVERS/combustion/fireFoam
• pyrolysisModels
  library $FOAM_SRC/regionModels/pyrolysisModels

Example

• Burning panels example
  $FOAM_TUTORIALS/combustion/fireFoam/les/oppositeBurningPanels

Chemistry Validation Solver

A new solver called chemFoam has been created to perform chemistry calculations simulations on a single-cell geometry, mainly for validation purposes. The mesh is created by the solver; fields are also created from initial values specified by the user in an initialProperties file.

The code includes 4 example cases to validate the stiff chemistry solver, including hydrogen combustion, that includes 10 species and 27 reactions, through methane combustion, n-Heptane combusion, and finally to iso-Octane, that includes 874 species and 3796 reactions. Results of the 4 tests (left to right: h2, gri, nc7h16, ic8h18) are plotted as temperature vs time and show excellent agreement with results from Chemkin II (Senkin).

Source code

• chemFoam solver
  $FOAM_SOLVERS/combustion/chemFoam

Examples

• Hydrogen combustion
  $FOAM_TUTORIALS/combustion/chemFoam/h2
• Methane combustion
  $FOAM_TUTORIALS/combustion/chemFoam/gri
• n-Heptane combustion
  $FOAM_TUTORIALS/combustion/chemFoam/nc7h16
• iso-Octane combustion
  $FOAM_TUTORIALS/combustion/chemFoam/ic8h18