This paper reports on the theoretical and experimental studies of combustion in a bidirectional swirling flow to develop its criterion base. Based on considering known aero-thermochemical similarity criteria, turbulent combustion numbers were calculated for the bidirectional vortex combustor for the first time. Theoretical assessment and experimental studies of the probability of the known combustion mechanisms' implementation in a limited bidirectional swirling flow, containing the secondary flows and separation phenomena, were performed. This gave us a possibility to provide the new correlation of combustion mechanisms with emission dependencies. A joint review of these data allowed us to establish that the greatest environmental efficiency is observed in the range of the air-fuel equivalence ratio of 1.5 < lambda < 1.9. At the same time, it was defined that stable combustion of liquid fuel in the bidirectional swirling flow is available up to the value lambda = 22. Moreover, criterion equations for lean and rich limits of stable combustion were obtained.