A combustion system includes an annular tube disposed between an inner wall and an outer wall, the annular tube extending from an inlet end to an outlet end; at least one fluid inlet disposed in the annular tube proximate the inlet end, the fluid inlet providing a conduit through which fluid flows into the annular tube; at least one outlet disposed in the annular tube proximate the outlet end; and at least one cooling feature disposed at an underside of the inner wall or the outer wall. The cooling feature maintains a temperature of the inner wall or the outer wall within a predetermined range.