Entwicklung eines Systems zur variablen Verdichtung für Viertakt-Dual-Fuel-Großmotoren

• Development of a variable compression ratio system for large four-stroke dual-fuel engines

Marten, Christopher Samy; Pischinger, Stefan (Thesis advisor); Schmitz, Katharina (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

Variable compression offers significant ecological and economic advantages in the field of large dual-fuel engines. By reducing NOx, SOx and CO2 emissions using alternative fuels, such a system enables fuel consumption costs to be reduced by increasing the efficiency of the internal combustion engine.As part of this thesis, a two-stage VCR connecting rod was developed under the boundary conditions of a new DF engine. The connecting rod has an eccentric piston pin bushing, which allows the effective connecting rod length to be varied using the gas and inertia forces during engine operation and thus to adjust the piston position at top dead center. The connecting rod uses a newly developed eccentric bushing system with locking devices to fix the eccentric bushing in its end positions. In addition, a hydraulic circuit with the functions of a hydraulic freewheel, decoupled locking device units and piston cooling was developed. The main components have been designed as modular units. In addition, a mechanical actuation was developed to initiate the switching process, and the influence of the VCR system on base engine components such as piston and crankshaft was determined. The functionality of the system was virtually validated with the help of structural analysis using FEA, multi-body simulation, 1D stress calculation and 1D hydraulics. Using 1D gas exchange simulations, a fuel cost analysis was carried out in which the load profile of a modern cruise ship application was used. A reduction in fuel costs of ∆KGVCR = 4,2 % and ∆KGVCR&VVT = 4,7 % could be quantified. Finally, the hydraulic subsystems "hydraulic module" and "locking device" were examined for functionality on two new developed component test benches. Low leakage rates, high flow rates and one hundred percent switching reliability of the hydraulic module could be detected for all operating points. The locking device showed the expected system behavior, but with a sensitivity in regard to friction, which is caused by the used hydraulic sealings. Finally, countermeasures were shown to improve the switching capability and further investigations were suggested.

Institutions

• Chair of Themordynamics of Mobile Energy Conversion [412310]