Including olfactory cues in virtual reality (VR) would enhance user immersion in the virtual environment, and precise control of smell would facilitate a more realistic experience for users. In this paper, we present aBio, an active bi-olfactory display system that delivers scents precisely to specific locations rather than diffusing scented air into the atmosphere. aBio provides users with a natural olfactory experience in free air by colliding two vortex rings launched from dual speaker-based vortex generators, which also has the effect of cushioning the force of air impact. According to the various requests of different applications, the collision point of the vortex rings can be positioned anywhere in front of the user's nose. To verify the effectiveness of our device and understand user sensations when using different parameters in our system, we conduct a series of experiments and user studies. The results show that the proposed system is effective in the sense that users perceive smell without sensible haptic disturbance while the system consumes only a very small amount of fragrant essential oil. We believe that aBio has great potential for increasing the level of presence in VR by delivering smells with high efficiency.