In the present study, hydrogen enrichment for biodiesel-diesel blends was evaluated to investigate the performance and emission characteristics of a compression ignition engine. Biodiesel was obtained from waste oil and blended to pure diesel fuel by volume fraction of 0%, 10% and 20%. After that, pure hydrogen was introduced through the intake air at different flow rates. Effects of pure hydrogen on performance and emission characteristics were investigated by evaluating power, torque, specific fuel consumption, CO, CO2 and NOx emissions. Experimental study revealed that waste oil biodiesel usage deteriorated performance and emission parameters except CO emissions. However, the enrichment test fuels with hydrogen fuel can improve performance characteristics and emission parameters, whereas it increased NOx emissions. Brake thermal efficiency and specific fuel consumption were improved when the test fuels enriched with hydrogen gas. Because of absence of carbon atoms in the chemical structure of the hydrogen fuel, hydrogen addition dropped CO and CO2 emissions but increment in cylinder temperature caused rising in NOx emissions. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.