A heat exchanger comprises a casing, within which there is present a first pipe wound in a spiral, in which a first fluid flows, the casing being designed to receive a second fluid that is in heat-exchange relationship with the first fluid. During regeneration on demand, the ratio of air to fuel for the corresponding operating point of the diesel engine is adjusted so as to achieve the substantially highest possible exhaust-gas temperature. The transmitter side transfer controller also provides a receiver side transfer controller information indicating which piece is uploaded to which relay server using a secure communication protocol.