Table I. Key properties [1].

Table II. Fuel composition [1].

For modeling purpose, Shell A is represented as a “binary” mixture of ethanol and the hydrocarbon (HC) component given as C_mH_n, where m and n are taken to be integers. The determination of m and n are based on considerations of the H/C ratio and the average molecular weight of the HC component. The formula of the real and modeled HC component is shown in Table III along with their respective molecular weights.

Table III. Real and modeled properties of the hydrocarbon (HC) component [1].

The use of integer molecular formula introduces some difficulties in describing the fuel combustion chemistry. In general, it is not possible to match both the equivalence ratio and mass fraction of the fuel at the same time because of small difference of the actual C/H/O ratio and the modeled C/H/O ratio. As mentioned in Ref. [1], we take the middle ground. Specifically, using Shell A-air mixture as the example, the actual complete-combustion reaction is written as

     C_6.97H_14.36O_0.15 + 10.49 O₂ + 10.49 × (79/21) N₂ => 6.97 CO₂ + 7.18 H₂O + 10.49 × (79/21) N₂.

Decomposing the fuel into the HC component and ethanol using their respective mole fractions in the fuel (see, Table III), i.e., 0.855 C_7.82H_15.79 + 0.145 C₂H₅OH, the above formula is still exact. Replacing C_7.82H_15.79 by the integer formula (C₈H₁₆), we have instead 0.837 C₈H₁₆ + 0.145 C₂H₅OH as the fuel mixture, where the value 0.837 comes from 0.855 × MW(C_7.82H_15.79)/ MW(C₈H₁₆). The approach taken here is equivalent to matching the mass fraction of the fuel between experiment and simulation. Re-normalization of the mole fractions of the “binary” fuel components yields 0.852 C₈H₁₆ + 0.148 C₂H₅OH, and these mole fraction values are given in Table III.