Teilprojekt A05 Wagner
Measurement of thermochemical parameters of fluid boundary layers and film thicknesses using laser absorption spectroscopy
Physical and chemical processes near the cylinder-wall or in the exhaust treatment system play an important role in the continuing optimization of combustion processes, the reduction of fuel consumption and the primary pollutant formation in the context of internal combustion engines. The interaction between the walls with the injected fuel, the exhaust treatment additive and/or the combustion gases is strongly coupled to the currently not well understood mass and heat transport processes. Therefore the devolvement of new models needs more detailed experimental investigations on generic systems. Within the CRC/Transregio, we focus on the coupling between the wall and fuel film in the ICE cylinder and on exchange processes between additive films and exhaust gases in near-wall exhaust gas conversion processes.
The overall focus of this subproject is the characterization of thermochemical states in multiphase flow systems to investigate dynamics in exhaust gas systems as well as pollutant formation diving flame-wall interactions under generic and practical conditions. For the wide range of operating conditions and the harsh environments, diagnostic methods have to be developed which allow simultaneous measurements of the gas phase (SCR and flames) and the liquid phase (SCR, oil film). The characterization of the boundary layer, both in a combustion environment and in exhaust gas systems, should be enabled by means of the newly developed measurement methods. In addition, for the used spectroscopic methods, fundamental questions regarding the interpretation of the parameter extraction in measurements with complex gas matrices and with rapid changes in the process conditions must be clarified and new models for the description of the measured spectra have to be developed.
The work in this subproject is characterized by a quantitative determination of the thermochemical parameters (gas concentrations, temperatures, pressure, film thickness, film composition) with a high temporal resolution (kHz).
A 2-D TDLAS spectrometer in the mid-infrared spectrum was successfully developed and validated for spatially resolved measurements of gas concentrations over Urea-Water-Solution (UWS) films. Furthermore, a laser based spectrometer for measuring the film thickness of a UWS was developed and validated against a CHR reference sensor. Using a newly developed TDLAS system, which can simultaneously measure the temperature and the water concentration with high temporal resolution, measurements of in-cylinder temperature and water concentration were performed. It could be shown that the temperature falls below 0 °C and thus, as shown in the water concentration in Figure 1, also falls below the dew point of water. This causes a condensation of H2O, and thus a decrease of the concentration in the gas phase. This effect is reversed as soon as the cylinder internal volume returns to the thermal equilibrium with the surrounding walls (Figure 1). In addition, measurements of NOx concentrations in the exhaust gas of the engine have been made. Finally, measurements of combustion relevant line data with significantly reduced uncertainty as well as the majority of spectroscopic parameters were carried out.
For the investigation of the above questions, laser-optical measurement methods, based on absorption spectroscopy, will be used and further enhanced. Absolute mole fractions and temperatures will be measured using direct tunable diode laser absorption spectroscopy (dTDLAS). This method will be extended to film thickness measurements as well as multi-parameter diagnostics based on super-continuum laser absorption spectroscopy (SCLAS).
In contrast to other measurement methods used in this Collaborative Research Centre, laser absorption spectroscopy is able to provide absolute species concentrations without additional in-situ calibration. Especially in the spectral regions of the near-IR and the short mid-IR (NIR, MWIR) it is planned to adapt TDLAS to the conditions during in-cylinder combustion and exhaust gas aftertreatment. Here we aim to preserve the unique combination of selectivity, sensitivity and robustness of this method.
Current objectives include the development and validation of new spectroscopic models, and the implementation of suitable algorithms in the measurement data processing. Furthermore, detailed investigations of the near-wall thermochemical states in the sidewall quenching (SWQ) burner (A04 (Dreizler)) and the optically accessible engine (C01 (Böhm)) will be carried out, which include an extension of the measuring method to high-pressure applications.
In cooperation with the other experimental subprojects in this Collaborative Research Centre, the quantitative determination of relevant process parameters (gas concentrations, temperatures, pressure, film thicknesses, film composition) supports the model development for near-wall multiphase flows in Combustion engines, exhaust gas purification systems and the construction of an experimental reference database for validation purposes.
The further development of film thickness measurement (FMLAS) is carried out in cooperation with A02 (Tropea / Roisman). As in the first funding period, A02 (Tropea / Roisman) provides a film generating unit for water and Urea-Water-Solutions to validate the FMLAS against a commercially available chromatic confocal resonance sensor (CHR). For the implementation of the various experiments and the phenomenological description of the measurement results, close cooperation will be for example made with the subprojects of the hot gas flow channel (A01 Stephan), the Side-Wall-Quenching burner (A04 Dreizler) and the transparent engine (C01 Böhm). In addition, the quantitative results of the various experiments will be exchanged and discussed with their respective experimental subprojects and the modeling subprojects involved (B01 (Gambaryan-Roisman), C03 (Hasse / Sadiki), C05 (Sadiki / Hasse), B05 (Deutschmann)).
- Bürkle, S., Biondo, L., Ding, C.-P., Honza, R., Ebert, V., Böhm, B., Wagner, S.: In-Cylinder Temperature Measurements in a Motored IC Engine using TDLAS. Flow Turb. Combust. 101(1), 139–159 (2018).14
- Schmidt, A., Kühnreich, B., Kittel, H., Tropea, C., Roisman, I.V., Dreizler, A., Wagner, S.: Laser Based Measurement of Water Film Thickness for the Application in Exhaust After-treatment Processes, Int. J. Heat Fluid Flow 71, 288–294 (2018).15
- Diemel, O., Honza, R., Ding, C., Böhm, B., Wagner, S., In situ sensor for cycle-resolved measurement of temperature and mole fractions in IC engine exhaust gases, accepted for the 37th Symposium on Combustion (2018).
- Bürkle, S., Walter, N., and Wagner S., Laser-based measurements of pressure broadening and pres-sure shifts coefficients of combustion relevant absorption lines in the near infrared region, Appl. Phys. B 124:121 (2018).