Development of a skeletal combustion mechanism for natural gas engine using n-butanol-diesel blend as pilot fuel

Experiments have shown that as a pilot fuel, n-butanol-diesel blend can further ameliorate the performance and emissions of natural gas (NG) dual-fuel engine. A skeletal n-heptane-toluene-n-butanol-methane-ethane-propane (HTBMEP) mechanism including 513 reactions and 117 species was constructed in this study using the decoupling method for the future numerical simulation of n-butanol-diesel-NG combustion in engine. The detailed NG mechanism was first reduced, and the reduced mechanism containing H2/CO/C1 and C2-C3 sub-mechanism as the basis was then coupled with the fuel-related sub-mechanisms of n-heptane, toluene and n-butanol, the supplementary C2-C4 reactions, and PAHs (A1-A7) and NOx formation models. The HTBMEP mechanism was finally established by optimizing the coupled mechanism. Through the extensive validation of zero-dimensional ignition delay, laminar flame speed and premixed flame species profile and three-dimensional in-cylinder pressure and heat release rate, the mechanism is proved to be reliable in engine combustion simulation. The further numerical study shows that when the NG substitution rate and n-butanol blend ratio increase, the ignition delay is prolonged, while the combustion duration increases and decreases, respectively. At 70% NG substitution rate, the addition of n-butanol reduces NOx and soot emissions simultaneously.

Automated summary

Experimental results demonstrate that n-butanol-diesel blend as a pilot fuel can improve the performance and emissions of natural gas (NG) dual-fuel engine. A simplified HTBMEP mechanism was constructed with 513 reactions and 117 species for numerical simulation of n-butanol-diesel-NG combustion in engine, showing reliability through extensive validation. Further numerical study indicates that increasing NG substitution rate and n-butanol blend ratio affect combustion processes and emissions.