Non-renewable fossil fuels have met global energy demands, but their dwindling supply raises environmental concerns, urging shifting to sustainable energy sources. Biodiesel with its renewable, biodegradable, and eco-friendly properties has gained attention as a promising alternative. The present study is an investigation of biodiesel combustion characteristics. An experimental test rig has been constructed, comprising an airline, fuel line, burner head, pressure swirl atomizer and combustor tube. The impact of different operating conditions as air/fuel mass ratio of 20, 30, 40 and 50, thermal load of 35, 45, 55 and 60 kW and diesel/biodiesel blend ratio of 0, 5, 10 and 15 are investigated. The temperature patterns, centerline axial temperature, dimensionless visible flame length, exhaust species concentrations and combustion efficiency are investigated. The obtained results indicated that at air to fuel ratio of 30 and thermal load of 45, with increasing biodiesel blend ratio from 0 to 15%, the flame length decreased by about 42 %, CO and NO decreased by about 15% and 24%, respectively while O2 and CO2 increased by about 22% and 14%, respectively. Combustion efficiency reduced as the biodiesel blend ratio increased. The small biodiesel blend ratios can replace diesel fuel without any modification in combustion systems.