Experimental dataset and processing scripts for ultra-lean methane and biogas combustion in an optically accessible single-cylinder engine

This dataset contains the experimental data and processing scripts supporting the thermo-optical investigation of ultra-lean methane and CO2-diluted methane combustion in an optically accessible AVL 5402 single-cylinder research engine. The experiments were conducted under spark-ignition and ultra-lean conditions (λ ≈ 5.5). The dataset includes crank-angle-resolved in-cylinder pressure data, cylinder volume traces, calculated apparent heat release rate (HRR), mass fraction burned (MFB) metrics (CA10, CA50, CA90), IMEP values, and exhaust gas emissions (dry basis, ppm and vol.%). Python scripts used for signal filtering and combustion analysis are provided to ensure reproducibility. The dataset is made available for peer review and will be publicly accessible upon article acceptance.