A combined combustor and recuperator is formed with the recuperator surrounding the combustor. Cold gas conduits (14, 16, 20) through the recuperator follow along involute paths toward the combustor. Hot has conduits (26) through the recuperator follow counterflow paths along corresponding involute curves outward from the combustor. The openings (18) in the combustion chamber wall through which cold gas enters the combustion chamber may be directed to impart flow direct to the cold gas to support particular desired behaviour of the cold gas in the portions of the combustion chamber concerned, e.g. supporting a stable vortex flame, enhancing mixing, providing a protective barrier layer.