This study presents a combined experimental and numerical investigation of the combustion characteristics of hydrogen-enriched gasoline blends in an optical constant-volume combustion chamber (CVCC). The analysis focuses on flame propagation speed, ignition delay, mass fraction burned (MFB), combustion duration, peak chamber pressure, pressure rise rate, heat release characteristics, and post-combustion species formation under controlled thermodynamic conditions. Hydrogen energy share (HES), defined as the ratio of hydrogen chemical energy to the total fuel energy supplied, was varied from 0% to 40%. Experiments were conducted at elevated initial temperature and pressure. Flame evolution was visualized using high-speed shadowgraph imaging, while transient chamber pressure was measured using a high-precision pressure transducer. Flame propagation behavior was quantified through post-processing of the captured images using the PIVLab technique. Complementary three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) simulations were performed in double precision using ANSYS Fluent 2024 R2 to replicate the CVCC combustion process. The governing continuity, momentum, energy, and species transport equations were solved using the finite volume method. A coupled pressure-based solver was employed to capture compressibility effects, while turbulence closure was achieved using the realisable k–ε model. Spatial gradients were evaluated using the least-squares cell-based method, and a first-order implicit upwind scheme was applied for temporal discretization. Combustion chemistry for hydrogen–gasoline blends was modeled using a reduced chemical kinetic mechanism, while a single-step global reaction model was employed for pure gasoline cases. Spark ignition and initial conditions were matched to the experimental configuration. Model validation was achieved through comparison of simulated flame propagation and pressure histories with experimental measurements, showing good agreement across all HES conditions. Both experimental and numerical results indicate that increasing HES significantly accelerates combustion. At 40% HES, earlier MFB phasing and shorter combustion duration were observed, along with increases in peak chamber pressure and maximum pressure rise. The peak heat release rate increased by up to 14.6%. Post-combustion species analysis revealed notable reductions in CO₂, CO, and HC with the increasing hydrogen energy share.