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Because of increasing stresses in combustion engines and critical comfort requirements of engine warm-up behavior, FEV has placed a special emphasis on solving cooling system problems. In addition to 3D-CFD calculations and special FEV measurement techniques - such as fiber optical cavitation detection, instationary heat balance measurements during warm-up, etc. - FEV has developed a 1D computer code, known as ‘COOL’, to optimize cooling systems already during the engine design phase or to analyse and eliminate weaknesses in the coolant circuit of existing engines. Beside the algorithm and structure of COOL the paper mainly presents the analysis capabilities of the code. In this connection the emphasis is placed on examples to the current OEMs problem: transient warm-up of DI-diesel engines. The COOL-code is so far a unique CAE tool which exclusively has been applied to projects conducted by FEV. Because of the increasing demand it is planned to commercialize the code in 1998.

The fuel consumption and the emissions of modern passenger cars are highly affected by the fluid and material temperatures of the engine. Unfortunately, the high thermal efficiencies of Direct Injection (DI) Diesel and Spark Ignition (SI) engines cause in many driving situations low heat transfer to the engine components and especially to the oil and the coolant. In these conditions the normal operating temperatures are not achieved. Especially at low ambient temperatures and low engine loads the requirement of a comfortable cabin heating and a fast warm-up of engine oil and coolant cannot be satisfied simultaneously. To reach the required warm-up performance, an Exhaust Heat Recovery System (EHRS) will be demonstrated. Further design and optimization processes for modern cooling systems in fuel-efficient engines require numerical and experimental investigations of supplemental heater systems to meet all requirements under all circumstances.