A systematic experimental and numerical investigation on the effects of chamber geometry and fuel–air mixture conditions on flame propagation and subsequent turbulent jet formation in a pre-chamber ignition system is conducted. Investigation of initial pre-chamber pressure showed that higher pre-chamber pressure led to slower flame propagation, resulting in slower combustion, longer jet formation delays and increased discharge of unburnt mixture losses. Though the percentage of mixture lost remained similar between 10 and 15 bar cases, the actual standard volume of ejected mixture was substantially higher at 15 bar. Experiments in an optically accessible quartz pre-chamber combustor were performed using propane-air mixtures with high speed imaging and Schlieren to characterize the flame growth and jet behaviour across different aspect ratio of the pre-chamber (L/D ratio: 4:1. 1:1 and 1:4) and orifice diameters (2 – 6 mm), while maintaining constant pre-chamber volume. Stoichiometric mixtures provided the fastest combustion, while ϕ = 0.6 and ϕ = 1.4 led to lower flame speeds, reduced pressures, and higher unburnt gas loss. Analysis of burning velocity showed that it was more strongly influenced by the bulk velocity of the mixture—driven by pressure and temperature rise—than by the laminar flame speed alone. The study also examined the coupled effects of L/D ratio and orifice size, showing that a larger orifice negatively impacted chamber consumption in short chambers (L/D = 0.7) due to reduced radial flame development, but improved it in longer chambers (L/D = 1.5) by enhancing flame-wall interaction. The most effective configuration was L/D = 0.7 with a 3 mm orifice, which achieved the highest-pressure peak, fastest chamber consumption rate, and lowest fuel loss. This baseline case was further optimized by testing conical and capsule-shaped pre-chamber geometries while preserving the same volume. Both modifications reduced flame quenching at wall corners and improved overall combustion performance, with the conical design yielding the shortest flame travel time and lowest unburnt fuel loss.