Abstract: 1. Combustion apparatus comprising a duct for containing a flow of air and including an air-fuel mixing device comprising an assembly of transversely spaced longeron members which extend along the duct and are inclined to the general direction of flow through the duct and to the walls of the duct so that a major portion of the flow through the duct will pass through the spaces between the longeron members, each longeron member having longitudinal edges adapted in operation to shed continuous vortices and a baffle extending across the upstream end of the longeron members and forming behind it a sheltered pilot combustion zone, and means adapted to generate pilot vortices of combustible mixture in the pilot zone, to cause each pilot vortex to divide, and to direct the divided portion of each pilot vortex to pass downstream along adjacent parts respectively of adjacent longeron members.