Numerical investigation on the lean-burn methanol in the main chamber with different active pre-chamber geometries and initial temperature

Methanol, a promising alternative fuel, has garnered extensive attention within the international internal combustion engine community. Nevertheless, its application in such engines faces challenges, including difficulties with cold starting under light load conditions, combustion instability, and elevated unconventional emissions. The pre-chamber jet ignition technology, which enhances ignition energy and accelerates flame propagation, emerges as an efficacious solution to these issues. Accordingly, the research presented in this paper focuses on analyzing the effects of the active pre-chamber’s structural design and initial temperature on ignition jet behavior. Furthermore, it explores the dilution limit of jet-ignited methanol. Findings reveal that the concentration stratification and flame propagation process are substantially affected by the length-to-diameter ratio of the pre-chamber, with those having a smaller aspect ratio exhibiting higher combustion efficiency, jet flow rate, and turbulence intensity. An increase in the initial temperature markedly enhances the jet’s flow velocity and reactivity intensity. The combustion speed and heat release rate are observed to rise with the augmentation of the main chamber mixture’s equivalence ratio. Specifically, a pre-chamber with an aspect ratio (L/D) of 1 achieved a 17% higher combustion efficiency compared to L/D = 3, while the jet velocity peaked at 510 m/s for L/D = 1, compared to 440 m/s for L/D = 2 and 470 m/s for L/D = 3. An increase in the initial temperature from 600 K to 800 K markedly increased the OH radical mass fraction by 35%. The combustion speed and heat release rate were observed to rise with the augmentation of the main chamber mixture’s equivalence ratio. However, when the equivalence ratio falls below 0.3, the ignition delay period of the main chamber lengthens, giving rise to issues such as misfires and diminished combustion stability.