Rußnukleation in Hochdruckflammen mit geringer Rußbildung: Experiment und Modellierung
Zusammenfassung der Projektergebnisse
Even though research on soot formation in hydrocarbon-fuelled combustion has been ongoing for decades there still is a knowledge gap on the species structure and composition responsible for the important step from reactive molecular species to the first appeareance of larger clusters forming nucleation centres for incipient soot. These so-called ‘nucleation flames’ up to now have been mostly investigated at sub-atmospheric (around 30 mbar) and atmospheric pressure. In the present research project, we have extended measurements into the elevated pressure regime between 1 and 10 bar applying spatially resolved optical diagnostics, fine-wire thermocouple temperature measurements and soot sampling with TEM analysis in premixed ethene/air flames. The expected low soot concentrations (ppb levels) and small particle sizes (2 – 10 nm) necessitated the development, installation and testing of sensitive diagnostic techniques such as multi-pass laser extinction, cavity ringdown extinction (CRDE) and time-resolved laser-induced incandescence (TiRe-LII). Two optically accessible premixed flame burners (denoted “burner 1&2”) were utilized in the labs of the proposers, while a twin-version of burner #2 was donated to one of our collaboration partners in the US. In flames stabilized in burner #1 (consisting of a central flame shielded by a non-sooting coannular flame) the soot volume fraction, fv, scales with pressure in a power-law function with the exponent n between 1.4 and 1.9 for flames with equivalence ratio φ = 2.1. Soot nucleation and growth causes fv to increase with height above burner (HAB), and the measured soot particle diameter increases with pressure, equivalence ratio and HAB. The influence of the burner geometry and shielding of the sooting ethene/air flames by a nitrogen coflow or by a surrounding non-sooting fuel-rich methane/air flame was investigated at atmospheric pressure by 2D CFD simulations as well as by CRDE measurements of fV., the latter under guidance of our French collaboration partners from Lille University. The combined influence of species diffusion and heat transfer on the axial temperature and species concentration profiles is significant at atmospheric pressure and becomes less at 10 bar. The measured soot volume fraction profiles of different ethene/air φ = 2.1 flames with diameters of 20 and 60 mm and air or inert (N2) shielding co-flows showed almost no difference at low heights above the burner (i.e., ≤ 14 mm) but become significant at larger heights, especially for the low diameter (20 mm) flame with nitrogen as shielding coflow. In an effort to enable sensitive measurements of soot volume fraction in flames at elevated pressures, the CRD-mirrors were mounted in chambers attached instead of the windows to the main burner vessel of burner #2 continuously purged by dry nitrogen. This, for the first time, allowed fV -measurements of slightly sooting premixed ethene/air flat flames up to 5 bar for different equivalence ratios, pressures and HAB positions. Laser-induced fluorescence (LIF) imaging experiments of OH and flame temperatures in burner #2 were compared with CFD modeling (both done by the collaboration partners at TAM university, USA) and with rapid-insertion TC measurements in our lab. A major intention envisioned in this project, the collaboration between our department and three external groups from France (Lille University, P. Desgroux group), USA (Texas A&M University, W. Kulatilaka group) and Italy (Politecnico di Milano, CRECK modeling group of T. Faravelli) was partially successful, despite the severe restrictions in traveling and personal lab visits due to the Corona pandemic.
Projektbezogene Publikationen (Auswahl)
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Near-threshold soot formation in premixed flames at elevated pressure. Carbon, 181, 143-154.
Mi, Xiaotong; Saylam, Ahmad; Endres, Torsten; Schulz, Christof & Dreier, Thomas
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Soot formation at near-threshold sooting premixed C2H4/air flames at elevated pressure, Poster presentation at the 4th International Sooting Flame Workshop (ISF-4), Univ. of Adelaide, ZOOM-Meeting, January 20th 2021
X. Mi; A. Saylam; T. Endres; C. Schulz & T. Dreier
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TiRe-LII particle sizing in low-sooting ethylene/air premixed flames at 1–5 bar using two different model functions and fitting codes, 9th International Workshop on Laser-Induced Incandescence, Univ. of Strathclyde, Glasgow, 12th – 15th June 2022
A. Saylam; R. Senge; T. Dreier; T. Endres & C. Schulz
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Behavior of Premixed Sooting Flame in a High-Pressure Burner. Reactions, 4(1), 155-170.
Saylam, Ahmad
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Characterization of a high-pressure flame facility using high-speed chemiluminescence and OH LIF imaging. Experiments in Fluids, 64(4).
Swain, Will; Wang, Yejun; Parajuli, Pradeep; Hay, Matthew; Saylam, Ahmad; Dreier, Thomas; Schulz, Christof & Kulatilaka, Waruna
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Influence of lateral species diffusion and heat transfer on the evaluation of near-threshold sooting flames. Combustion and Flame, 253, 112775.
Saylam, Ahmad; Endres, Torsten & Schulz, Christof
