This archive contains data files from spark-ignited homogenous combustion internal combustion engine experiments. Included are two-dimensional two-component velocity fields acquired in a small, high-resolution field of view near the spark plug, and images of hydroxyl radical chemiluminescence recording the early flame-kernel growth. Included are in-cylinder pressure measurements, external pressure and temperature data, as well as details on the geometry of the optical engine to enable setups of simulation configurations. Included are tables of one-per-cycle parameters for each test with methane or propane at stoichiometric, dilute limit, lean limit, and rich limit, operation conducted at 40kPa and 1300 RPM.