Teilprojekt A04 Dreizler
Detailed experimental investigation of thermo-kinetic and fluid mechanical properties of flame-wall interactions
In many modern, technical combustion systems, such as piston engines or gas turbines, flame-wall interaction and flame quenching are highly important processes. Quenching on solid surfaces results in wall heat losses, soot deposits and increased emissions of carbon monoxide or unburned hydrocarbons, especially under cold starting conditions. This lowers the efficiency and downgrades the environmental compatibility of the combustion process. The recent trend of downsizing technical combustion devices further increases the relevance of flame-wall interaction, as the surface-to-volume ratio rises. As the underlying phenomena and interdependencies are not yet fully understood, fundamental research on near-wall combustion is considered highly relevant to aid the development of future combustion concepts.
Scope of the subproject A04 is on experimental studies of flame-wall interaction in generic test cases. Focus in the second funding period is put on the so-called sidewall quenching process (Fig. 1), where the flame propagates parallel to the solid surface of the wall. The experiments are designed to access near-wall fluid mechanics and thermochemical states (i.e. chemical reaction progress) as well as their coupling. The main objectives are to generate a better phenomenological and process understanding of flame-wall interaction and to generate validation data to aid the development of modelling in numerical combustion simulations. The first funding period was focused on studies of generic, atmospheric combustion systems at simplified experimental conditions. In the second funding period, the research is evolving towards close to reality conditions, like a pressurized environment, higher turbulence levels or sustainable fuels. Furthermore, the impact of mixture inhomogeneitie close to the wall will be included and evaluated.
Highly resolved, advanced laser diagnostics have been applied to quantitatively access process relevant parameters close to the wall simultaneously. Wall heat fluxes were derived from wall and gas phase temperatures (Fig. 2). Within the quenching region, the peak wall heat flux was observed to be higher for elevated wall temperatures. This finding appeared counter intuitive, as a rising wall temperature first suggests an overall reduced temperature difference between wall and gas phase. However, for elevated wall temperatures, flames are quenched closer to the wall, resulting in steeper wall-normal temperature gradients finally increasing the heat flux. This pointed out that the wall temperature is a crucial parameter to impact wall heat fluxes during quenching.
Gas phase temperatures and carbon monoxide (CO) concentration measurements were used to analyze the reaction progress in terms of thermochemical states (Fig. 3). These experiments revealed that the presence of the wall, i.e. the wall heat loss, impacts both the formation and oxidation of CO significantly and underlined that adiabatic, numerical flamelet calculations are not capable to capture this trend correctly. In a related time scale analysis, it figured out that especially the CO oxidation is dominated by heat transfer processes.
The fundamental flame-wall interaction experiments are performed within the generic, atmospheric sidewall quenching burner outlined in Fig. 1 (left). The quenching wall features a slight curvature to enable optical accessibility of the laser beams below 100 microns close to the surface. Main boundary conditions of the setting can be varied, like laminar/turbulent inflow conditions, wall temperatures or fuel type. The experimental conditions are well controlled and monitored by a series of thermocouples and mass flow controllers. This guarantees for reproducible operation. In the second funding period, the sidewall quenching setup will be adapted for pressurized conditions.
Measurements are conducted using advanced laser diagnostics to simultaneously measure multiple parameters. Gas phase temperatures are measured at both high precision and accuracy using coherent anti-Stokes Raman spectroscopy (CARS). Laser induced fluorescence (LIF) is applied to quantitatively measure concentrations (CO) or to assess spatial species distributions (hydroxyl radical, formaldehyde). Particle image velocimetry provides spatial flow field information. Thermographic phosphor thermometry serves to estimate wall temperatures. The second funding period aims at further refining the applied diagnostics. Beside CO, a second species will be measured quantitatively. Furthermore, an approach to visualize mixture fraction, i.e. mixture inhomogeneity, will be applied.
Present objectives involve the adaption of the current sidewall quenching burner to a pressurized confined configuration. The influence of varying turbulence level, pressure, fuel type and mixture inhomogeneity will be in the focus of the process-related investigation. Besides, laser diagnostics for measuring a second quantitative combustion relevant species are employed for near-wall environments as well as a laser optical technique for mixture inhomogeneity analysis.
For an optimized adaption of the sidewall quenching setting to a pressurized condition, the intense cooperation with subprojects C03 and A05 is pursued. The phenomenological understanding and the experimental data will be used to aid the numerical simulations and modelling (C03, B04, B06). For the adaption and implementation of laser based diagnostics, an intense cooperation with C01 and A05 as well as A06N and C02 is aimed for.
- Jainski, C., Rißmann, M., Jakirlic, S., Böhm, B., Dreizler, A.: Quenching of premixed flames at cold walls. Effects on the local flow field. Flow Turb. Combust. 100(1), 177–196 (2018).
- Kosaka, H., Zentgraf, F., Scholtissek, A., Bischoff, L., Häber, T., Suntz, R., Albert, B., Hasse, C., Dreizler, A.: Wall heat fluxes and CO formation/oxidation during laminar and turbulent side-wall quenching of methane and DME flames. Int. J. Heat Fluid Flow 70, 181–192 (2018).
- Jainski, C., Rißmann, M., Böhm, B., Janicka, J., Dreizler, A.: Sidewall quenching of atmospheric laminar premixed flames studied by laser-based diagnostics. Combust. Flame 183, 271–282 (2017).
- Rißmann, M., Jainski, C., Mann, M., Dreizler, A.: Flame-flow interaction in premixed turbulent flames during transient head-on quenching. Flow Turb. Combust. 98(4), 1025–1038 (2017).
- Jainski, C., Rißmann, M., Böhm, B., Dreizler, A.: Experimental investigation of flame surface density and mean reaction rate during flame–wall interaction. Proc. Combust. Inst. 36, 1827–1834 (2017).
- Bohlin, A., Jainski, C., Patterson, B.D., Dreizler, A., Kliewer, C.J.: Multiparameter spatio-thermochemical probing of flame–wall interactions advanced with coherent Raman imaging. Proc. Combust. Inst. 36, 4557–4564 (2017).
- Ma, P.C., Ewan, T., Jainski, C., Lu, L., Dreizler, A., Sick, V., Ihme, M.: Development and analysis of wall models for internal combustion engine simulations using high-speed micro-PIV measurements. Flow Turb. Combust. 98, 283–309 (2017).
- Ganter, S., Heinrich, A., Meier, T., Kuenne, G., Jainski, C., Rißmann, M., Dreizler, A., Janicka, J.: Numerical analysis of laminar methane-air side-wall-quenching. Combust. Flame 186, 299–310 (2017).