An exhaust system for an internal combustion engine, especially in a vehicle, comprising at least one first catalytic converter unit (18) with at least one catalytic converter device (24), through which internal combustion engine exhaust gas can flow and a fuel-operated heater (36). The at least one first catalytic converter unit (18) comprises a heat exchanger volume (50) through which heater exhaust gas leaving the heater (36) can flow.

An internal combustion engine system includes at least one combustor, a compressor arranged to compress air, an air guide arranged to guide compressed air from the compressor to at least one of the at least one combustor, an expander arranged to expand exhaust gases from at least one of the at least one combustor and to extract energy from the expanded exhaust gases, and an exhaust guide arranged to guide exhaust gases from at least one of the at least one combustor to the expander, wherein the exhaust guide is at least partly integrated with the air guide.