Comparative study on chemical kinetic schemes for dual-fuel combustion of n-dodecane/methane blends

The ignition characteristics of dual-fuel mixtures consisting of high-reactivity n-dodecane and low-reactivity methane are numerically investigated. The performance of five state-of-the-art n-dodecane chemical mechanisms including comprehensive low hydrocarbon kinetics for single-fuel (SF) and dual-fuel (DF) combustion are studied. The sensitivity of the total fuel to air equivalence ratio (ϕ) and n-dodecane to methane mole ratio (α) on the DF combustion process is investigated. We point out how n-dodecane enables faster methane ignition by rapidly formed radicals. Methane is shown to act as a diluent prolonging the ignition delay time (IDT) compared to a SF n-dodecane case by a factor ranging between 1 and 8 at the present conditions. For the first time, (1) DF combustion for n-dodecane is investigated and IDTs are quantified in terms of α and ϕ, (2) DF IDTs are indicated to be bounded by SF methane and n-dodecane IDTs, (3) performance of the state-of-the-art n-dodecane kinetic schemes for SF and DF combustion are pointed out, (4) the laminar flame speeds for n-dodecane and methane combustion are numerically evaluated and shown to be bounded by the SF flame speeds, and (5) examples on the most sensitive reaction steps in DF cases are pointed out for laminar flame speed. Moreover, the results indicate that α is a key control factor dictating the DF IDT. Finally, the mechanisms which could serve as reasonable candidates for future SF and DF combustion are suggested.