Close-coupled, thermoelectric exhaust-gas energy recovery in a gasoline engine with exhaust-gas turbocharger and asynchronously variable exhaust valve control is possible without any serious adverse effects on the engine's performance. Both reduction of the load on the generator, at a corresponding TEM efficiency and reduced air-fuel mixture enrichment thanks to an improved thermal protection of the components, allow considerable savings in consumption. The investigated prototype's only shortcomings compared to the production engine are in transient-state operation (acceleration of the vehicle) and cold start (light-off time). Implementation in the vehicle, however, requires a lot of work in terms of control technology and design. For example, the exhaust valve lift sequence on the heat exchanger side has to be able to be changed from the standard profile (synchronous opening) to a combination of 'late exhaust valve closing' (VEC ECEV,HE = 390 °CAaTDc) and 'late exhaust valve opening' (LEO EP(EV,HE) = 60 °CA) depending on the engine's operation conditions. This switch-over can, for example, be implemented in the design by a two-stage sliding-cam system. The additional asynchronously 'variable exhaust valve closing' (VEC ECEV,HE = 340...420 °CAaTDc) option provides significant benefits and substantially more degrees of freedom for engine operation and thermal management. One conceivable design would be to combine an asynchronously rotating exhaust camshaft with a possibility of switching over between the standard profile and 'late exhaust valve opening' (LEO EPEV,HE = 60 °CA) valve lift curve.
Close-coupled exhaust gas energy recovery in a turbocharged direct-injection gasoline engine
2013
12 Seiten, 9 Bilder, 1 Tabelle, 1 Quelle
Conference paper
English
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