of the engine for example at relatively low power operating conditions a very high proportion of the combustion e g in the vicinity of 95 will occur in the rich primary and quench zones with a significant portion upstream of the dividing area 510 at a higher power condition this amount may be less approximately evenly split between rich and lean zones by way of example an annular boundary 520 slightly upstream of the dividing area 510 shows the approximate boundary between rich and transition regions with the exemplary process dilution air being introduced through a circular array of relatively large coaligned apertures in the heat shield panels and shells near the upstream leading edges of the downstream heat shield panels a downstream boundary 522 similarly separates the transition and lean zones the locations of the boundaries 520 and 522 will depend upon the location and dimensions of the apertures and upon operating conditions fig2 shows an alternate combustor 120 which differs from the combustor 20 principally in that the walls and their associated panels are dimensioned so that the transition between upstream and downstream chamber portions 154 and 156 is located further upstream the different arrangement may be dictated by the different envelope offered by the associated engine including one or more factors of diffuser geometry relative position of compressor outlet exit and turbine inlet igniter position orientation and the like thus any particular embodiment may have a somewhat differing arrangement of primary quench and lean zone volumes and characteristics fig3 shows the fore and aft panels 174 and 176 of the inboard wall 132 each aft panel 176 is shown as having a circumferential array of alternating large and small apertures 190 and 192 positioned relatively forward along such panel these apertures provide for introduction of the.