Device and method for providing ignition to a post-combustor for bypass gas turbine

The method involves guiding a fraction of primary flow (10) in an ignition zone (34) of an afterburner in order to maintain the temperature in the zone at a value greater than value of secondary flow (20) in a manner to favor ignition of the afterburner. The primary flow is hot and the secondary flow is cool, where the fraction of primary flow is injected in an upstream part of the zone. An independent claim is also included for an afterburner device for a turbofan engine.