Deflagration-to-detonation transition in propane-butane-oxygen mixtures, in an open channel with a circular cross section with a diameter of 3 mm, was investigated experimentally. Detonation initiation was carried out by burning the mixture in the prechamber connected to the channel. To measure the velocity of a flame front, photodiodes installed along the axis of the channel were used. To determine the boundary conditions at the entrance to the channel, a piezoelectric pressure transducer was used. The influence of the dimensions of the prechamber and equivalence ratio on the pressure profile, and evolution of the flame front along the axis of the channel are presented. Effect of the prechamber detonation initiation in the channel has been analyzed. It was shown that the dynamics of the flame front and shock waves in the channel can occur in different scenarios depending on the geometry of the prechamber and equivalence ratio. The pre-detonation distances were determined.