Long straight-chain alkanes are the main components of hydrotreated biofuels which are the intermediate products in manufacture of biomass aviation fuels. From economic considerations, it is desirable to apply hydrotreated biofuel in engines and investigate its performance. This work investigated the influence of linear alkanes C17 and C18 on the spray characteristics of conventional jet fuel China RP-3 using a hollow cone pressure swirl nozzle. Detailed flow structures and microscopic spray parameters of the spray cone were measured at injection pressures of 3, 5, 7, 9, and 11 bar using phase Doppler anemometry. Detailed information gained from the present work quantifies the changes of spray characteristics caused by additional linear alkanes C17 or C18. Besides a narrowed spray cone angle and decreased Sauter mean diameter, it also suggested that air entrainment toward the spray cone center will be enhanced by additional linear alkanes C17 and C18. This work will be helpful for designing a swirl nozzle for the application of hydrotreated bio fuels.