Optical Study and Numerical Simulation of the Effect of <i>n</i>‐butanol Mass on the Combustion Process of a <i>n</i>‐butanol/Diesel Dual‐Fuel Engine

ABSTRACT n ‐butanol, with its higher calorific value compared to methanol and ethanol, is well‐suited for diesel engine combustion. This study investigates the impact of n ‐butanol addition on the combustion process in a n ‐butanol/diesel dual‐fuel engine using both experimental and numerical approaches. Experiments were conducted on a modified optical engine equipped with two injectors: one for n ‐butanol injection in the intake and another for two‐stage diesel injection directly into the cylinder. The study varied the n ‐butanol mass (5, 10, 15, and 20 mg) while maintaining a constant diesel mass. High‐speed photography combined with a two‐color method was employed to capture flame propagation and carbon smoke generation. Numerical simulations using three‐dimensional software further analyzed the effects of n ‐butanol mass on injection, combustion, and emission characteristics, including cylinder pressure, temperature, heat release rate (HRR), and emissions (NO X , CO, and HCHC). The results revealed that flame clusters formed in the cylinder center and along the cylinder wall. Increasing n ‐butanol mass significantly extended ignition delay and reduced combustion duration. The high latent heat of vaporization (LHV) and low cetane number of n ‐butanol suppressed the initial exothermic rate, while diesel auto‐ignition triggered high‐temperature reactions in the pre‐mixed n ‐butanol, enhancing dual‐fuel combustion exothermicity. This led to gradual increases in cylinder pressure and HRR. Emission analysis showed that n ‐butanol introduction increased OH and HO 2 radical concentrations, alongside elevated NO X and CO levels. These findings provide insights into optimizing n ‐butanol/diesel dual‐fuel combustion for improved performance and emissions control.