Project Details
Projekt
Experimental investigations of cyclic variations in homogeneous premixed SI engines with EGR variations
Applicant
Dr.-Ing. Benjamin Böhm
Subject Area
Energy Process Engineering
Term
since 2019
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 349537577
Exhaust gas recirculation (EGR) also offers great potential for minimizing NOx emissions in hydrogen-fueled engines. The EGR rate can also be used to control power output, which benefits engine efficiency, and can be a means to enable stoichiometric operation without the occurrence of anomalous combustion phenomena. This subproject has the global objective of experimentally investigating cycle-to-cycle fluctuations and their causes in engines with homogeneous fuel-air mixtures and high EGR rates. In funding period 1, the development of the early flame in the turbulent in-cylinder flow under variation of EGR rates was investigated in detail for this purpose. Iso-octane was used as a representative hydrocarbon-based fuel. In funding period 2, these investigations will be extended to the carbon-free fuel hydrogen. In addition to the turbulent flow field, the thermodiffusive and hydrodynamic instabilities typical of hydrogen flames affect the flame wrinkling and the local reaction rate, which directly affects the dynamics of flame propagation. The goal is to better understand the effects of intrinsic instabilities, EGR, and lean mixtures on early flame formation and cycle-to-cycle fluctuations, and to provide data for model development and validation of numerical simulations. For this purpose, flow velocities, flame fronts as well as mixture formation are to be recorded using laser-optical measurement methods. In addition to the quantification of the measured variables, a major challenge is the simultaneous multi-parameter measurement, with which interactions of relevant parameters are to be captured. Whenever possible and reasonable, high-speed measurement techniques will be used to evaluate the data also time-dependently. For the planned investigations, an optically accessible spark ignition engine with port fuel injection will be used, which allows external EGR (without water vapor) via a gas mixing system and internal EGR via a variation of the valve timing. For this purpose, an engine test bench is available at the department, which was set up in particular for model validation and, in addition to reproducible operation, enables defined and extensively characterized boundary conditions. Cause-and-effect chains will be analyzed in order to identify causal relationships between mixture and turbulence structure on the one hand with ignition and on the other hand with the early flame development. In close cooperation with subproject 2, experimental and numerical data will be used for a backward analysis in time to identify flow structures that have an influence on the combustion process and cause cycle-to-cycle fluctuations.
DFG Programme
Research Units
Co-Investigator
Professor Dr. Andreas Dreizler
