Optical Study and Numerical Simulation of the Effect of n-butanol Mass on the Combustion Process of a n-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 HO₂ 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.