NOVELTY - The arrangement has a waste heat recovery system (10) comprising a heat storage device (20) arranged outside from a heat exchanger (11), downstream from a pump (14) and upstream from an expander (12). The recovery system comprises a main line (21) in which working fluid e.g. water, is heated in the heat exchanger and expanded in the expander. The heat storage device is made of heat storage material being in thermal contact with the working fluid through a partition wall for storing heat from a heat source and releasing previously stored heat to heat the working fluid.    USE - Internal combustion engine arrangement e.g. diesel engine arrangement and spark ignition engine arrangement, for use in industrial vehicles.    ADVANTAGE - The waste heat recovery system can store the heat from the heat source and release the previously stored heat with respect to heat capacity to heat the working fluid in an effective manner, while protecting the working fluid from overheating to increase service life of the waste heat recovery system and avoiding need to change the working fluid, thus reducing maintenance cost of the arrangement. The arrangement enables more efficient use of thermal energy from the heat source without impairing overall efficiency by avoiding fan activation and without damaging elements of the working fluid in wide range of operating conditions, thus increasing efficiency of waste energy recovery and usage, while providing high thermal efficiency and high heat transfer rate during phase change. The arrangement utilizes heat storage material with high heat storage capacity and longer storage period, thus improving performance of the arrangement in a steady state condition. The arrangement allows phase-change material i.e. heat storage material, to undergo phase change when heat is transferred from the heat source to the heat storage material and when the heat storage material transfers heat to the working fluid so as to ensure that melting or solidifying temperature is reached in working or operative conditions of the arrangement.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of a waste heat recovery system.    Waste heat recovery system (10)    Heat exchanger (11)    Expander (12)    Pump (14)    Heat storage device (20)    Main line (21)