Hochschule für Technik und Umwelt FHNW

Dauerhafte URI für den Bereichhttps://irf.fhnw.ch/handle/11654/35

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A specifically designed injector for controlled lube oil addition in view of investigation of pre-ignition phenomena in dual–fuel/gas engines
(Frontiers Research Foundation, 11.05.2021) Süess, Pascal; Schneider, Bruno; Wüthrich, Dario; Wüthrich, Silas; Herrmann, Kai
Internal combustion engines will continue to play a role during a transitional phase, especially in heavy-duty or marine applications. In this context, lean-burn gas/dual-fuel combustion is an attractive concept to reduce CO2, combined with considerably lower particulate and NOX pollution, and with efficiencies comparable to diesel combustion. However, ignition processes still pose considerable challenges, with pre-ignition in particular being a major issue. The underlying mechanisms are probably based on self-ignition of lube oil in hot zones. In order to investigate fundamentals of such phenomena in optically accessible test rigs, a novel injector was specifically developed to induce pre-ignitions artificially. The so-called “PieZo-Droplet-Injector” (PZDI) enables dosing of minor amounts of lubricating oil or even the injection of single droplets with diameters in the range of 100–200 µm. The working principle relies on a needle actuated with a piezo stack, which pushes a certain amount of lube oil in a bore so that (even single) droplets can be ejected through an adjustable nozzle. To confirm the PZDI functionality and to investigate droplet characteristics based on adjustable operating parameters, tests were performed under ambient conditions as well as in a constant volume combustion chamber under reasonable pressure and temperature conditions. Overall, the PZDI showed an excellent behavior in terms of capabilities to inject small amounts or even single droplets of lube oil. At last, this specially developed injector allows selective lube oil addition in an optically accessible engine test facility for upcoming examination of pre-ignition phenomena under real operating conditions.
01A - Beitrag in wissenschaftlicher Zeitschrift
Flow field investigation of a single engine valve using PIV, POD, and LES
(MDPI, 2023) Hoffmann, Jana; Mirsch, Niklas; Vera Tudela, Walter; Wüthrich, Dario; Rosenberg, Jorim; Günther, Marco; Pischinger, Stefan; Weiss, Daniel; Herrmann, Kai
Due to stringent emission regulations, it is of practical significance to understand cycle-to-cycle variations in the combustion of fossil or renewable fuels to reach future emission regulations. The present study aims to conduct a parametric investigation to analyse the influence of the valve lift and different mass flows of an inlet valve of the test engine “Flex-OeCoS” on the flow structures. To gain a deeper understanding of the flow behaviour, an optical test bench for 2D Particle Image Velocimetry (PIV) and a Large Eddy Simulation (LES) are used. Turbulence phenomena are investigated using Proper Orthogonal Decomposition (POD) with a quadruple decomposition and the Reynolds stress transport equation. The results show good agreement between the PIV and LES. Moreover, the main flow structures are primarily affected by valve lift while being unaffected by mass flow variation. The turbulent kinetic energy within the flow field increases quadratically to the mass flow and to the decreasing valve lift, where large high-energetic flow structures are observed in the vicinity of the jet and small low-energetic structures are homogeneously distributed within the flow field. Furthermore, the convective flux, the turbulent diffusive flux, the rate of change, and the production of specific Reynolds stress are the dominant terms within the specific Reynolds stress transport equation.
01A - Beitrag in wissenschaftlicher Zeitschrift
Investigation of flow fields emanating from two parallel inlet valves using LES, PIV, and POD
(MDPI, 2023) Hoffmann, Jana; Vera Tudela, Walter; Mirsch, Niklas; Wüthrich, Dario; Schneider, Bruno; Günther, Marco; Pischinger, Stefan; Weiss, Daniel; Herrmann, Kai
Understanding cycle-to-cycle variations (CCV) is of practical importance for the combustion of fossil and renewable fuels, as increasingly stringent emission regulations require reductions in the negative effects of such variations. The subject of this study is the flow around inlet valves, since oscillations of such inlet flows affect the flow structure in the cylinder and are thus one of the causes of CCV. To this end, a parametric analysis of the influences of the mass flow rate and valve lift of two parallel engine intake valves on the flow structures is performed. This follows on from an earlier similar study where the flow around a single intake valve was investigated. To analyse the flow behaviour and, in particular, the interactions of the flow leaving these two valves, an optical test rig for 2D particle image velocimetry (PIV) and a large eddy simulation (LES) are used. Proper orthogonal decomposition (POD), together with a quadruple decomposition and the Reynolds stress transport equations, are used to study the turbulence phenomena. The PIV and LES results are in good agreement with each other. The detailed LES analysis of the flow structures shows that, for small valve lifts, the flow separates along the whole perimeter of the intake valve, and for larger valve lifts, the flow escapes only to one side. This is, for combustion engines with the tumble concept, the stage at which the tumble movement develops. Moreover, the flow structures are strongly influenced by the valve lift, while they are unaffected by the variation in the mass flow. The turbulent kinetic energy in the flow field increases quadratically with a decreasing valve lift and increasing mass flow. The large, high-energetic flow structures are particularly dominant near the jet, and the small, low-energetic structures are homogeneously distributed within the flow field. The specific Reynolds stress transport equation shows the limitations of two-dimensionality and large timesteps in the PIV results and the limitations of the LES model.
01A - Beitrag in wissenschaftlicher Zeitschrift
Multiscale characterisation of staple carbon fibre-reinforced polymers
(MDPI, 06.11.2023) Zweifel, Lucian; Kupski, Julian; Dransfeld, Clemens; Caglar, Baris; Baz, Stephan; Cessario, Damian; Gresser, Götz T.; Brauner, Christian
The aim of this study was to characterise the microstructural organisation of staple carbon fibre-reinforced polymer composites and to investigate their mechanical properties. Conventionally, fibre-reinforced materials are manufactured using continuous fibres. However, discontinuous fibres are crucial for developing sustainable structural second-life applications. Specifically, aligning staple fibres into yarn or tape-like structures enables similar usage to continuous fibre-based products. Understanding the effects of fibre orientation, fibre length, and compaction on mechanical performance can facilitate the fibres’ use as standard engineering materials. This study employed methods ranging from microscale to macroscale, such as image analysis, X-ray computed tomography, and mechanical testing, to quantify the microstructural organisations resulting from different alignment processing methods. These results were compared with the results of mechanical tests to validate and comprehend the relationship between fibre alignment and strength. The results show a significant influence of alignment on fibre orientation distribution, fibre volume fraction, tortuosity, and mechanical properties. Furthermore, different characteristics of the staple fibre tapes were identified and attributed to kinematic effects during movement of the sliver alignment unit, resulting in varying tape thicknesses and fuzzy surfaces.
01A - Beitrag in wissenschaftlicher Zeitschrift
Tailored flexibility in inherently brittle epoxy-based composites through gradient interphase formation with bio-based thermoplastic elastomer grades
(Elsevier, 05.07.2023) Zweifel, Lucian; Kupski, Julian; Brauner, Christian
This study focuses on tailoring elastic behaviour in an inherently brittle epoxy-based fibre-reinforced composite material formed through a gradient interphase with a bio-based thermoplastic elastomer. The fast-curing epoxy Araldite LY3585/Aradur 3475 was tested with two bio-based Pebax block copolymer grades. First, the interphase was characterised via optical hot-stage microscopy and Raman spectroscopy. The analysis unveiled pronounced diffusion followed by a reaction-induced phase separation, which led to the formation of an interphase with a thickness exceeding 200 μm at the temperatures associated with the curing process. Second, composite laminates were fabricated through a combined process of fused filament fabrication and vacuum infusion, incorporating a flexible domain with variable stiffness properties. The material architecture exhibited brittle-to-ductile behaviour at the micrometre scale, with tailored flexible response under bending and stiff behaviour in tension. Consequently, the study anticipates using multi-scale toughened material structures for more efficient generative design concepts.
01A - Beitrag in wissenschaftlicher Zeitschrift
Tätigkeitsbericht 2022
(Institut für Automation, Hochschule für Technik FHNW, 04/2023) Isler, Rolf; Gabrys, Jadwiga
Tätigkeitsberichte über aktuelle Forschungsobjekte, die im Institut im Jahr 2022 bearbeitet wurden
05 - Forschungs- oder Arbeitsbericht
Tätigkeitsbericht 2023
(Institut für Automation, Hochschule für Technik FHNW, 04.04.2024) Isler, Rolf; Gabrys, Jadwiga
Tätigkeitsberichte über aktuelle Forschungsprojekte, die im Institut im Jahr 2023 bearbeitet wurden.
05 - Forschungs- oder Arbeitsbericht