Numerical investigation of the effect of orifice number and diameter in a turbulent jet ignition system on hydrogen combustion

This paper presents the results of a numerical investigation focused on the influence of pre-chamber geometry, specifically, the number and diameter of orifices, on hydrogen combustion characteristics in a turbulent jet ignition (TJI) system.Computational fluid dynamics (CFD) simulations were conducted using AVL FIRE software in two configurations.In the first case, the number of orifices was varied while maintaining a constant diameter, whereas in the second case, the orifice diameter was adjusted to preserve an equivalent total flow cross-sectional area.The obtained results indicate that both geometrical parameters significantly affect the combustion behaviour, particularly in terms of mixture stratification, pressure distribution within the main combustion chamber, and nitrogen oxide (NO) formation.It was determined that the number of orifices exerts a more pronounced effect on combustion performance than their individual diameter.An increased number of orifices with a diameter of 1.5 mm enhanced system efficiency due to improved flow penetration and jet momentum (the most favourable solution is 5 holes with a diameter of 1.5 mm).Under the condition of a constant total discharge area, the configuration comprising 5 orifices with d = 1.34 mm yielded the most favourable results (combustion efficiency was approximately 1% lower than in the best-performing configuration).This configuration ensured stable combustion operation with respect to the analysed performance and emission parameters.