Defining chemical system#

The chemical system refer to the chemical species that may appear as products. Expanding upon the earlier example, we will now establish the chemical system for the complete combustion of a stoichiometric CH\(_4\)-ideal air mixture, represented by the global reaction

\begin{equation} \underbrace{\text{CH}_4 + 2 (\text{O}_2 + 3.76 \text{N}_2)}_{\rm{reactants\ (initial\ state)}} \rightleftharpoons \underbrace{\text{CO}_2 + 2 \text{H}_2\text{O} + 7.52 \text{N}_2}_{\rm{products\ (final\ state)}}. \end{equation}

Given the above global reaction, the products include CO\(_2\), H\(_2\)O, and N\(_2\), which we can define as follows:

self.S.LS = {'N2', 'CO2', 'H2O'};

and that is all we need to define a chemical system in CT.

Tip

When we have prior knowledge of the chemical species involved in the problem, we can streamline the initialization of CT by directly specifying those species. Consequently, we only need to include these specific chemical species in our problem, writing at the prompt:

self = App({'N2', 'CO2', 'H2O'});

Identifying all possible products#

Combustion problems typically entail numerous chemical species, and occasionally we lack prior knowledge of all relevant species in the system. In such cases, we can recall in find_products.m routine introduced in Accessing the databases. This routine allows us to identify all potential chemical species resulting from a chemical transformation (products), given a set of species (reactants). For this example, we can write at the prompt:

self.S.LS = find_products(self, {'CH4', 'O2', 'N2'})

which will yield a list of +200 chemical species. By default, the find_products.m function scans for species in the NASA database, includes condensed species, and excludes ionized species. To search for species in Burcat’s database and include ionized species, we have to enable the flag_burcat and flag_ion options, setting both to true, as follows:

self.S.LS = find_products(self, {'CH4', 'O2', 'N2'}, 'flag_burcat', true, 'flag_ion', true);

This modification generates a list of +1000 chemical species. Alternatively, we can modify the default flag values in the Species.m file.

Tip

In cases where no chemical system is defined, CT automatically identifies all potential products given a set of reactants, i.e., it uses the find_products.m routine to construct the chemical system, taking into account the default flag values flag_burcat, flag_ion, flag_condensed defined in Species.m.

Using predefined chemical systems#

The Combustion Toolbox incorporates a range of predefined chemical systems, outlined in the list_species.m routine. For example, some of the predefined chemical systems are defined below:

  • Calculations for air.

  • Neglects ionization of chemical species.

self.S.LS = list_species('air');

or equivalently

self = list_species(self, 'air');

Chemical species included:

self.S.LS = {'CO2', 'CO', 'O2', 'N2', 'Ar', 'O', 'O3', ...
             'N', 'NO', 'NO2', 'NO3', 'N2O', 'N2O3', ...
             'N2O4', 'N3', 'C'};

  • Calculations for air.

  • Considers ionization of chemical species.

self.S.LS = list_species('air ions');

or equivalently

self = list_species(self, 'air ions');

Chemical species included:

self.S.LS = {'eminus', 'Ar', 'Arplus', 'C', 'Cplus', 'Cminus', ...
             'CN', 'CNplus', 'CNminus', 'CNN', 'CO', 'COplus', ...
             'CO2', 'CO2plus', 'C2', 'C2plus', 'C2minus', 'CCN', ...
             'CNC', 'OCCN', 'C2N2', 'C2O', 'C3', 'C3O2', 'N', ...
             'Nplus', 'Nminus', 'NCO', 'NO', 'NOplus', 'NO2', ...
             'NO2minus', 'NO3', 'NO3minus', 'N2', 'N2plus', ...
             'N2minus', 'NCN', 'N2O', 'N2Oplus', 'N2O3', 'N2O4', ...
             'N2O5', 'N3', 'O', 'Oplus', 'Ominus', 'O2', 'O2plus', ...
             'O2minus', 'O3'};

  • Calculations for hydrocarbon (HC) combustion in air.

  • Neglects most dissociation chemical species and excludes ions.

self.S.LS = list_species('HC/O2/N2');

or equivalently

self = list_species(self, 'HC/O2/N2');

Chemical species included:

self.S.LS = {'CO2', 'CO', 'H2O', 'H2', 'O2', 'N2', 'Ar'}

  • Calculations for hydrocarbon (HC) combustion in air.

  • Considers soot formation and a small set of minor species.

  • Excludes ionized chemical species.

self.S.LS = list_species('soot formation');

or equivalently

self = list_species(self, 'soot formation');

Chemical species included:

self.S.LS = {'CO2', 'CO', 'H2O', 'H2', 'O2', 'N2', 'Ar', 'Cbgrb', ...
             'C2', 'C2H4', 'CH', 'CH', 'CH3', 'CH4', 'CN', 'H', ...
             'HCN', 'HCO', 'N', 'NH', 'NH2', 'NH3', 'NO', 'O', 'OH'};

  • Calculations for hydrocarbon (HC) combustion in air.

  • Considers soot formation and a large set of minor species.

  • Excludes ionized chemical species.

self.S.LS = list_species('soot formation extended');

or equivalently

self = list_species(self, 'soot formation extended');

Chemical species included:

self.S.LS = {'CO2', 'CO', 'H2O', 'H2', 'O2', 'N2', 'Ar', 'Cbgrb', ...
             'C2', 'C2H', 'C2H2_acetylene', 'C2H2_vinylidene', ...
             'C2H3_vinyl', 'C2H4', 'C2H5', 'C2H5OH', 'C2H6', ...
             'C2N2', 'C2O', 'C3', 'C3H3_1_propynl', ...
             'C3H3_2_propynl', 'C3H4_allene', 'C3H4_propyne', ...
             'C3H5_allyl', 'C3H6O_acetone', 'C3H6_propylene', ...
             'C3H8', 'C4', 'C4H2_butadiyne', 'C5', 'C6H2', 'C6H6', ...
             'C8H18_isooctane', 'CH', 'CH2', 'CH2CO_ketene', ...
             'CH2OH', 'CH3', 'CH3CHO_ethanal', 'CH3CN', ...
             'CH3COOH', 'CH3O', 'CH3OH', 'CH4', 'CN', 'COOH', 'H', ...
             'H2O2', 'HCCO', 'HCHO_formaldehy', 'HCN', 'HCO', ...
             'HCOOH', 'HNC', 'HNCO', 'HNO', 'HO2', 'N', 'N2O', ...
             'NCO', 'NH', 'NH2', 'NH2OH', 'NH3', 'NO', 'NO2', ...
             'O', 'OCCN', 'OH', 'C3O2', 'C4N2', 'CH3CO_acetyl', ...
             'C4H6_butadiene', 'C4H6_1butyne', 'C4H6_2butyne', ...
             'C2H4O_ethylen_o', 'CH3OCH3', 'C4H8_1_butene', ...
             'C4H8_cis2_buten', 'C4H8_isobutene', ...
             'C4H8_tr2_butene', 'C4H9_i_butyl', 'C4H9_n_butyl', ...
             'C4H9_s_butyl', 'C4H9_t_butyl', 'C6H5OH_phenol', ...
             'C6H5O_phenoxy', 'C6H5_phenyl', 'C7H7_benzyl', ...
             'C7H8', 'C8H8_styrene', 'C10H8_naphthale'};

  • Calculations for hydrocarbon (HC) combustion (propellants) in air.

  • Considers soot formation and a large set of minor species.

  • Excludes ionized chemical species.

self.S.LS = list_species('HC/O2/N2 propellants');

or equivalently

self = list_species(self, 'HC/O2/N2 propellants');

Chemical species included:

self.S.LS = {'CO2', 'CO', 'H2O', 'H2', 'O2', 'N2', 'Ar', 'Cbgrb', ...
             'C2', 'C2H', 'C2H2_acetylene', 'C2H2_vinylidene', ...
             'C2H3_vinyl', 'C2H4', 'C2H5', 'C2H5OH', 'C2H6', ...
             'C2N2', 'C2O', 'C3', 'C3H3_1_propynl', ...
             'C3H3_2_propynl', 'C3H4_allene', 'C3H4_propyne', ...
             'C3H5_allyl', 'C3H6O_acetone', 'C3H6_propylene', ...
             'C3H8', 'C4', 'C4H2_butadiyne', 'C5', 'C6H2', 'C6H6', ...
             'C8H18_isooctane', 'CH', 'CH2', 'CH2CO_ketene', ...
             'CH2OH', 'CH3', 'CH3CHO_ethanal', 'CH3CN', ...
             'CH3COOH', 'CH3O', 'CH3OH', 'CH4', 'CN', 'COOH', 'H', ...
             'H2O2', 'HCCO', 'HCHO_formaldehy', 'HCN', 'HCO', ...
             'HCOOH', 'HNC', 'HNCO', 'HNO', 'HO2', 'N', 'N2O', ...
             'NCO', 'NH', 'NH2', 'NH2OH', 'NH3', 'NO', 'NO2', ...
             'O', 'OCCN', 'OH', 'C3O2', 'C4N2', 'RP_1', 'H2bLb', ...
             'O2bLb'};

  • Calculations for Silicon (Si) combustion (propellants) in air.

  • Considers soot formation and a minor set of minor species.

  • Excludes ionized chemical species.

self.S.LS = list_species('Si/HC/O2/N2 propellants');

or equivalently

self = list_species(self, 'Si/HC/O2/N2 propellants');

Chemical species included:

self.S.LS = {'CO2', 'CO', 'H2O', 'H2', 'O2', 'N2', 'Ar', 'Cbgrb', ...
             'C2', 'C2H4', 'CH', 'CH', 'CH3', 'CH4', 'CN', 'H', ...
             'H2O2', 'HCN', 'HCO', 'N', 'NH', 'NH2', 'NH3', 'NO', 'O', 'OH', ...
             'O2bLb', 'Si', 'SiH', 'SiH2', 'SiH3', 'SiH4', 'SiO2', 'SiO', ...
             'SibLb', 'SiO2bLb', 'Si2'};

Summary#

% Initialize CT and define chemical system
self = App({'CO2', 'CO', 'H2O', 'H2', 'O2', 'N2', 'Ar'});

% Initialize CT
self = App();
% Define chemical system
self = list_species(self, {'CO2', 'CO', 'H2O', 'H2', 'O2', 'N2', 'Ar'});

% Initialize CT and define chemical system
self = App('HC/O2/N2');