Experimental investigation and kinetic modelling of NO formation at elevated pressures using laser diagnostic in a Rapid Compression Machine

• Applicants: Professor Dr.-Ing. Alexander Heufer; Professor Dr.-Ing. Hans-Jürgen Koß
• Subject Area: Technical Thermodynamics ; Hydraulic and Turbo Engines and Piston Engines
• Term: from 2019 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 418305555

Reducing pollutant emissions in combustion processes is one of the major challenges worldwide. In this context not only the overall greenhouse gas emissions but also the local release of pollutants is of high relevance. For tackling this problem a detailed understanding of the combustion and the pollutant formation kinetics is necessary in order to understand and model its mechanisms. Only by this appropriate counter measures can be developed.As a consequence this proposal aims to investigate the reaction mechanism of nitrous oxide using a combination of theoretical and experimental approach. On the theoretical side kinetic models will be optimized based on literature information and data resulting from this project. A special focus will be on the low temperature reaction scheme since currently available models show a large scatter in the predictions in this temperature regime. On the experimental side investigations of fuel-air mixtures doped with nitrous oxide in a rapid compression machine (RCM) will deliver new information. Besides conventional ignition delay time measurements, one-dimensional quantitative nonintrusive NO concentration and temperature measurements will be conducted in the early-cycle combustion process in the RCM. Spatial resolution of the diagnostic is required because of temperature gradients in the charge. Thus, the proposed diagnostic is based on spontaneous Raman scattering (SRS) and laser-induced fluorescence (LIF). While LIF yields the local NO concentration with high sensitivity, SRS will be applied to measure light attenuation and temperature. These latter quantities are the two most important factors required for quantification of NO-LIF. Calibration of both NO-LIF and SRS will be performed at the end of compression in the RCM. SRS diagnostics are based on nitrogen. The temperature will be inferred from the spectral band shape of Stokes N2-SRS, whereas anti-Stokes N2-SRS will yield attenuation spectrally very close to an attractive NO-LIF emission wavelength (~ 236 nm). This type of combined SRS/LIF diagnostic was recently developed by the applicants at the LTT for automotive combusting fuel jets in a high-pressure vessel. In the currently proposed first half of the project, the most important research question for the LTT will be whether that (slightly modified) diagnostic can be applied to the discussed combustion processes in the RCM and whether the resulting measurement uncertainties are at least as low as in those previous works. The potential and limitations of this diagnostic in the current environment will be investigated. Complete quantification of NO-LIF will be conducted for a few selected operating conditions of the RCM in the first half of the project. The results of that first half will be used for planning the second half, in which a larger number of NO-LIF measurements will be conducted for various operating conditions.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Gerd Grünefeld