### 6.3.6. Hydrocarbon Fuel Analysis Model

The ‘Hydrocarbon Fuel Analysis’ model enables you to define all the properties of a solid or liquid hydrocarbon fuel in a user-friendly way. The solver uses the provided information to derive the parameters of related objects, such as the initial particle mass fractions, material properties of the volatiles released, and stoichiometric or mass coefficients of reactions.

The primary input data corresponds 1-to-1 to what, typically, is available from standard analysis of the solid or liquid fuel:

- Heating value (higher or lower heating value)

- Proximate analysis (mass fractions of ash, moisture, fixed carbon, and volatiles)

  - As Received: 1 = ash + moisture + fixed carbon + volatiles

  - Dry Ash Free: 1 = fixed carbon + volatiles

- Ultimate analysis (mass fractions of carbon, hydrogen, oxygen, nitrogen, sulfur, and chlorine)

  - As Received: 1 = ash + moisture + carbon + hydrogen + oxygen + nitrogen + sulfur + chlorine

  - Dry Ash Free: 1 = carbon + hydrogen + oxygen + nitrogen + sulfur + chlorine.

Some additional input data is required by the solver, for which the default values should be appropriate in many cases:

- Volatiles yield enhancement: Ratio of actual yield under rapid heating to that determined at a slow heating rate in the proximate analysis.

- Average molar mass of volatiles released. Three options are available:

  - `Automatic`: Computes average molar mass from volatiles elementary composition, assuming a mixture of CH4, CO, H2, and H2O

  - `Value`: Use value specified in fuel analysis

  - `Use Material Definition`: Use value defined in volatiles fuel material.

- Reference conditions for heating value (temperature and pressure)

- Moisture latent heat in case of higher heating value specified:

  - `Automatic`: Standard value (2.4423 [MJ/kg])

  - `Value`: User value for given temperature and pressure.

The above data are used to derive the following quantities:

- Initial mass fractions for particle (ash, char and raw combustible).

  Note that initial char mass fraction will typically be zero, as char is produced from raw combustible during pyrolysis.

- Fuel volatiles material properties:

  - Average molar mass

  - Specific reference enthalpy (heating value)

  - Carbon, hydrogen and oxygen content.

- Stoichiometric coefficients for gas phase reactions:

  - Fuel volatiles oxidation

  - NO reburn by fuel.

- Mass coefficients for multiphase reactions:

  - Devolatilization (decomposition of raw combustible into char and volatiles)

  - Char oxidation.

These calculations are performed using a model fuel determined by the fuel analysis data. The model fuel has all chlorine removed but accounts for the oxygen needed to oxidize sulfur to SO2. Nitrogen is included into the model fuel if the multiphase reactions are setup to release HCN to the gas phase, otherwise, the fuel nitrogen is removed.

The total amount of material released to the gas phase during devolatilization is the actual volatiles yield plus the moisture. Carbon, hydrogen and oxygen content of the volatiles are computed from ultimate analysis, which in turn defines the stoichiometric coefficients in the gas phase reactions involving the volatiles material. When the fuel nitrogen model is selected, corrections are made in order to account for the carbon and hydrogen released as HCN.

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