Study of crankshaft torsional deformation under steady-state and transient operation of turbocharged diesel engines

The modelling of transient operation of turbocharged diesel engines appeared in the early 1970s, and continues to be in the focal point of research due to the importance of transient response in the everyday operating conditions of engines. The majority of studies have focused so far on thermodynamics, as this directly affects heat release predictions and consequently performance and pollutants emissions. On the other hand, issues concerning the dynamics of engine operation are often disregarded or over-simplified. In the present work, an experimentally validated diesel engine simulation code is used to study and evaluate the importance of a notable engine dynamic issue, i.e. the crankshaft torsional (angular) deformations during turbocharged diesel engine operation owing to the difference between instantaneous engine and load (resistance) torques. The analysis aims ultimately in studying the phenomena under the very demanding, and often critical, transient operating conditions. Detailed crankshaft angular momentum equilibrium is formulated that takes into account instantaneous gas, inertia, friction, load as well as stiffness, and damping torque contributions. Details are provided concerning the underlying mechanism of the crankshaft torsional deformations during steady-state and transient operation. This deformation can assume significant values depending on the engine-load configuration (load change, crankshaft stiffness, kind of aspiration of the engine), and as such it is of great importance for safe engine operation.