Biogas, an alternative fuel, has potential to be applied in diesel engines. To employ biogas in diesel engine of dual fuel type, air-biogas mixer is required. In an earlier design of the mixer, venturi mixer with two biogas inlets was hardly giving homogeneous mixture. In this work, venturi mixer is redesigned taking into account the gaps of the existing literatures, for different gas substitutions and engine loads. In this work, the air-biogas venturi mixer is studied with computational fluid dynamics. The mixer has three biogas inlets each of 7.2 mm diameter and placed 120 degrees apart from each other at the throat. At various biogas substitutions, engine load conditions and at consequent variations of air supply, the amount of biogas and diesel are needed to be varied. Hence, there is a need to investigate the mixer for various biogas substitutions and load variations. The substitution levels analyzed are 80%, 60%, 40% and 20%. The same mixer is also analyzed for different engine loads. The results show that, the distribution of biogas in the divergent portion of the mixer is quite uniform for different substitution levels and engine load variations. Thus mixer is observed to meet the functional requirements in aforementioned cases. (C) 2018 Elsevier Ltd. All rights reserved.