A model-based and experimental approach for the determination of suitable variable valve timings for cold start in partial load operation of a passenger car single-cylinder diesel engine

Abstract

A manipulation of the charge exchange allows controlling the amount of residual gas during engine warm-up. The residual gas during the warm-up phase leads to an increase of the exhaust gas temperature and supports to reach the exhaust after-treatment system operating temperature faster. In addition, the warm residual gas increases the combustion chamber temperature, which reduces the HC and CO emissions. However, fuel consumption increases. For that reason, such heating measures should be the best compromise of both, exhaust gas temperature increase and engine efficiency, in order to provide efficient heating strategies for passenger car diesel engines. Therefore, simulative and experimental investigations are carried out at the Institute of Internal Combustion Engines of the Karlsruhe Institute of Technology to establish a reliable cam design methodology. For the experimental investigations, a modern research single-cylinder diesel engine was set up on a test bench. In addition, a one-dimensional simulation model of the experimental setup was created in order to simulate characteristics of valve lift curves and to investigate their effects on the exhaust gas temperature and the exhaust gas enthalpy flow. These simulations were based on design of experiments (DoE), so that all characteristics can be used sustainably for modeling and explaining their influences on the engine operation. This methodology allows numerically investigating promising configurations and deriving cam contours which are manufactured for testing. To assess the potential of these individual configurations, the results obtained were compared with each other as well as with the series configuration. Results show that the combination of DoE and one-dimensional simulation for the design of camshaft contours is well suited which was also validated with experimental results. Furthermore, the potential of residual gas retention by favorable configurations with a second event already revealed in various publications could be confirmed with respect to exhaust gas temperature increase and engine efficiency.