An Approach for Modeling the Effects of Valve Lift Characteristics on Partial Load Operation in Diesel Engines

A manipulation of the charge exchange allows to control 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 aftertreatment system operating
temperature faster. In addition, the warm residual gas increases the combustion chamber
temperature, which reduces the HC and CO emissions. But in exchange 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.
With the aim to determine efficient heating measures for passenger car diesel engines by a
valve train manipulation, simulative and experimental investigations are carried out as part of a
research project at the Institute of Internal Combustion Engines of the Karlsruhe Institute of
Technology.
This work deals with the introduction of an approach to investigate the influences of variable
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valve train timings in diesel engines. The approach combines 1-D simulations and statistical
experimental design (DoE), so that all valve lift characteristics can be used sustainably for
modeling and explaining their influences on the engine operation. That methodology allows to
numerically investigate promising configurations which may also include a second opening of an
exhaust or intake valve (2nd event).
Using this methodology the potential of residual gas retention by favorable configurations with an
2nd event already revealed in various publications could be confirmed with respect to exhaust
gas temperature increase and engine efficiency. This method allows an accurate prediction of
important exhaust thermal management parameters by a wide variation range of valve lift curves
in order to identify significant impacts on the exhaust gas temperature during partial load
operation. Finally, the validation of the DoE model with simulation data and experimental results
show that this approach is well suited for the design of valve lift curves.