Gas turbine combustion chambers

Claim 1

A combustion chamber comprising: a. a stepped flame tube placed in an air stream and comprising: 1. an upstream section bounding a first combustion zone extending parallel to the air stream, 2. a downstream section wider than the upstream section and bounding a second combustion zone extending parallel to the air stream, said downstream section having an upstream portion which extends over a major length thereof and has imperforate generally annular walls and passages therebetween for the entry of cooling air flowing film-like along said imperforate walls, and 3. shoulder means extending outwardly of the first combustion zone and generally transversely of the air stream direction, to form a step between said upstream and downstream tube sections, said step having a multiplicity of air intake apertures therethrough to admit into said second combustion zone a flow of air taken from said air stream and flowing substantially parallel thereto, and solid portions between said intake apertures to produce wakes in said flow of air, b. fuel injection means in the first combustion zone for emitting jets of fuel towards the upstream end of said first combustion zone, c. means for supplying the injection means with fuel at an idling flow rate, d. air inlet means for feeding the first combustion zone with combustion air, said air inlet means comprising means for directing air from the air stream substantially parallel thereto along said upstream tube section, and a plurality of openings through said flame tube, adjacent the downstream end of said upstream section, for introducing air from the air stream substantially radially into the first combustion zone, whereby the combustion air is entrained by said jets of fuel and recirculated in said first combustion zone, said air inlet means being so dimensioned that the combustion air forms a substantially stoichiometric mixture with the fuel at said idling flow rate, the first combustion zone having such a volume that combustion of the stoichiometric mixture takes place within the first combustion zone, and e. means for injecting a supplementary flow of fuel in said flame tube upstream of said second combustion zone to cause combustion of said supplementary flow of fuel in said wakes behind the said portions of said shoulder means, the volume of said second combustion zone being such that the combustion chamber has an overall volume sufficient to ensure re-ignition in flight.