Contact IFS:
Chair in Automotive Powertrain Systems
Dipl.-Ing. Wolfgang Gross
Project Partners:
University of Kassel, Institute for Automotive Engineering
Abstract:
Driven by stricter emission and fuel consumption regulations modern DI-Diesel enginies exhibit increasing combustion pressures. High combustion pressure in combination with high pressure gradients act as broadband excitation force, which stimulates natural vibrations of piston, conrod and crankshaft during engine operation. Starting from the combustion chamber the assembly of piston, conrod and crankshaft and the main bearings represent the system of internal vibration transfer which dominates the engine noise, as described in [1] and [2]. Based on the work carried out in the previous project “Piston Conrod Dynamics” this project serves to improve and extend the level of knowledge concerning the acoustic behavior of a modern EU6-Diesel engine with lightweight design components. To achieve this goal experimental and analytical investigations are carried out. First the modal behavior of single components and then the dynamic properties of the entire moving system were examined in detail in simulation and test as a base for the investigations. A successful correlation between experimental modal analysis (EMA) and Finite Element Analysis (FEA) forms the basis of model validation. The experimental investigations under fired conditions were done in an anechoic test bench to generate exact input and validation values for simulation models of structural dynamic and elastohydrodynamic coupled multi body systems. The measured values of combustion pressure, airborne and structure-borne sound allowed to identify the engine´s vibrational behavior in the whole operating range. After definition of a reference operating point various test series were carried out, such as injection timing and temperature variation. To understand the behavior of the conrod as the key component in more detail its elongation at the conrod shank during engine operation was also measured. The usage of semiconductor strain gauges allowed the recording of the natural vibrations of the conrod in a very accurate way up to a frequency about 10 kHz. Furthermore temperature measurements of piston and liner under fired conditions, allowed the determination of their warm contours using inverse methods. Variation of injection timing and conrod stiffness demonstrated main drivers for the dynamic behavior. In a further step measurement of the oil film thickness between the liner and the piston generated an improvement understanding of an unknown quantity in the simulation model. For this purpose the combination of inductive and capacitance measurements were used.
Focus: Calculation and measurement verification of dynamic contact forces between the piston and cylinder, taking into account transient thermal boundary conditions.
Funding: BMWi/AiF - Federal Ministry for Economic Affairs and Energy / German Federation of Industrial Research Associations / Research Association for Combustion Engines eV
For further information on the project, please also contact the Research Association for Combustion Engines (FVV).