Theory

The exhaust composition is that of complete combustion of CH $_y$ with dry air at the excess-air ratio $\lambda$ (Excess-air ratio), equation (1). The dry air brings 3.7279 mol N₂, 0.04459 mol Ar and 0.00172 mol CO₂ per mole of O₂ (the ratios of the air mole fractions). The mole fractions of the products, divided by their total, give the mixture's molar mass and heat capacity (see Fluid).

The presets: diesel $y = 1.8$ , gasoline $y = 1.87$ , natural gas $y = 4$ (methane). A fuel with more hydrogen gives more water vapour, a lower molar mass and a higher heat capacity.

Equations

\mathrm{CH}_y + a\,(\mathrm{O_2} + 3.7279\,\mathrm{N_2} + 0.04459\,\mathrm{Ar} + 0.00172\,\mathrm{CO_2}) \rightarrow (1 + 0.00172\,a)\,\mathrm{CO_2} + \tfrac{y}{2}\,\mathrm{H_2O} + (\lambda - 1)\left(1 + \tfrac{y}{4}\right)\mathrm{O_2} + 3.7279\,a\,\mathrm{N_2} + 0.04459\,a\,\mathrm{Ar}

(1)

a = \lambda\left(1 + \frac{y}{4}\right)

(2)

where	meaning	unit
$y$	H/C atom ratio of the fuel	-
$\lambda$	Excess-air ratio	-
$a$	Moles of O₂ supplied per mole of carbon	mol/mol

Default and rule

Default: diesel
Rule: Diesel (CH $_{1.8}$ ).
Source: Stoichiometry of complete combustion, equation (1). The surrogate H/C ratios are the program's presets; they are not taken from a cited source.

Valid range diesel (CH1.8), gasoline (CH1.87), natural gas (CH4), custom

Choices

Diesel, gasoline, natural gas, custom (H/C typed in H/C atom ratio). Used only when the fluid is exhaust gas and the heat-capacity model is temperature dependent.

Complete combustion

Lean or stoichiometric only ( $\lambda \ge 1$ ); rich mixtures form CO and H₂, which are not modelled.

Theory

Equations

Default and rule

Valid range diesel (CH1.8), gasoline (CH1.87), natural gas (CH4), custom

Related 4