BACKGROUND Nowadays with the demanding regulation of exhaust gas emissions comes a requirement on the operation of SI-combustion engine entirely with the stoichiometric fuel-air mixture (λ=1). Since the enriched mixture has been used mainly for preventing the overheating of catalytic convertor, it’s necessary to avoid the overheating with other technical solution. PRINCIPLE The close-coupled converter is together with the cooled exhaust manifold the State-of-the-art design for the most of the current engines. However only the part of the exhaust manifold integrated in cylinder head contains liquid cooling. This design seems to be sufficient (for λ=1 operation) for turbocharged engine (turbine consumes the entalphy of hot gases and thereby reduces their temperature before reaching the converter). Our goal was to develop the new concept for naturally aspirated engines, in which the current design is unable to fulfill the requirements. In our new patented design there is a liquid-cooled area extended beyond the cylinder head flange cooling the entire manifold up to the convertor. The most important is the design of water-jacket which is tied up to cylinder head’s, making single functional unit, reducing cost and technological complexity. DESCRIPTION From technological point of view was created a new part, which is quite uncommon for today’s engine production. It is basically aluminium component containing exhaust and coolant channels which are cast hollow using sand cores installed in the holder mould (the same technology as by cylinder head). The part is mounted to the cylinder head flange using 5 bolts, on the other side with V-clamp to the catalytic convertor. CHALLENGES The component has to withstand high thermal load, especially the V-clamp connection, which is located between two components with highly different temperatures. High temperatures represent the risk of coolant degradation after engine shutdown. The component has an impact on the whole engine, exhaust and also brings considerable changes to the software application. RESULTS New design containing the „Additional cooling of engine exhaust gas“, enables the stoichiometric operation of naturally aspirated SI-engine under all engine operating conditions. This solution has been successfully tested, met all required targets, qualified the concept for use into the serial production.
Ing. Jan Hradiský, ŠKODA AUTO a. s., CZECH REPUBLIC