NOVELTY - The device has a feed pump (6), a heat exchanger (8), an expansion machine (10) e.g. turbine and piston engine, and a condenser (12) arranged in a pipeline circuit (4), where working medium i.e. water, is circulated in the pipeline circuit. A vapor storage unit (40) is arranged in a pipeline (26) of the pipeline circuit between the heat exchanger and the expansion machine for storing the vaporous working medium circulating in the pipeline circuit. The vapor storage unit is directly connected with the heat exchanger and the expansion machine over a branch pipeline.    USE - Device for utilization of waste heat of exhaust gas of a combustion engine i.e. air-compressing, self-activating or mixture-consolidating, spark-ignition combustion engine, of a motor car.    ADVANTAGE - The vapor storage unit is arranged in the pipeline of the pipeline circuit between the heat exchanger and the expansion machine for storing the vaporous working medium circulating in the pipeline circuit, so that the heat energy in the vaporous working medium is stored in the vapor storage unit and can be used based on a short term load request, and the heat loss caused by the prolonged distances of the heat exchanger and the expansion machine is reduced. The vapor storage unit is directly connected with the heat exchanger and the expansion machine over the branch pipeline, so that vapor is immediately available for operation of the expansion machine during a short term load request without any time delay caused by the prolonged distances. The device is provided with a controllable valve for controlling the flow of vapor, so that pressure fluctuations in the heat exchanger and the subsequent pipelines can be reduced.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for utilization of waste heat of a combustion engine.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic circuit diagram of a waste heat utilization device.    Pipeline circuit (4)    Feed pump (6)    Heat exchanger (8)    Expansion machine (10)    Condenser (12)    Pipeline (26)    Vapor storage unit (40)