In one embodiment, a fuel reformer can comprise: a mixing zone capable of
mixing a fuel and an oxidant to form a fuel mixture and a reforming zone
disposed downstream of the mixing zone. The reforming zone comprises a
primary substrate and a secondary substrate. The primary substrate is
disposed upstream of the secondary substrate and has a primary thermal
mass that is greater than a secondary thermal mass of the secondary
substrate. One embodiment of a method for operating a fuel reformer can
comprise: mixing an oxidant and a fuel to form a fuel mixture, combusting
the fuel mixture, heating the secondary substrate above its light-off
temperature, changing an air to fuel ratio of the fuel mixture to a
reforming mixture, producing an exotherm and a reformate at the secondary
substrate, heating a primary substrate with the exotherm to above its
light-off temperature, and producing a reformate.