Homogenous gas-phase reactions in exhaust-gas tail pipes of internal combustion engines
Final Report Abstract
The project, performed in close interaction with the partners at KIT, Germany, and Shanghai Jiao Tong University (SJTU), China, has investigated interactions of the fuel-specific oxidation chemistry for selected hydrocarbon (methane, ethane, propene, butenes) and oxymethylene ether (OMEn) fuels with that of typical exhaust gas components such as NOx. The investigations have been designed to provide detailed information, suitable for the development and critical examination of reaction kinetic models, under conditions relevant for exhaust gas aftertreatment. A plug-flow reactor (PFR) equipped with mass spectrometric detection at Bielefeld University (UBi) was used to measure multiple species– temperature profiles in the range of 700-1200 K and at atmospheric pressure, chosen to represent gas engine pre-catalyst exhaust gases. In the system NO/NO2/NH3/O2/CO/CH4/C2H4, species profiles were quantified for several gas mixtures of increasing complexity under highly diluted conditions. The reactivity of the different mixtures could be satisfactorily represented by several established literature models. Because of the delicate balance required for NO and NH3 to avoid emissions of either component, a more detailed inspection of the kinetics with the project partners was warranted to address several discrepancies in the mechanisms. Interactions of medium-sized alkenes, namely of propene and two butene isomers, again representative components in exhaust gases, with NO were then investigated experimentally in collaborative experiments of all partners at the National Synchrotron Laboratory (NSRL) in Hefei, China, using tunable vacuum ultraviolet radiation for photoionization and mass spectrometric detection of a significant number of reaction intermediates and products. A temperature range of 725 - 1250 K at atmospheric pressure was studied in a flow reactor for fuel-lean (propene) and fuel-rich (propene, butenes) conditions. Significantly different behavior depending on the fuel structure was observed between the oxidation reactions with and without NO, leading both to inhibiting and promoting effects on the system’s reactivity, and multiple indications for a rich interaction chemistry between the fuel reactions and NO were seen. The experiments were followed by in-depth systematic kinetic model development by the project partners, leading to appreciable agreement with the experimental results, and identifying remaining open questions for further investigations. As representatives of potentially sustainably produced alternative fuels in the oxymethylene ether (OMEn) fuel family, dimethyl ether (DME) and dimethoxymethane (DMM) were chosen as further targets to study their interaction with different amounts of NO in the UBi PFR in a temperature range of 400 -1000 K at atmospheric pressure. Again, intriguing changes in the overall reactivity as well as species indicating strong fuel–NOx interaction were found. Literature models which were just emerging failed in to represent the observed interaction behavior. The experimental data can thus be seen as an important basis for further model development. Exploratory investigations, although initially not planned, were performed with and without a vanadiabased catalyst in the CH4 oxidation in presence of NO in the UBi PFR. The observed influences of the catalyst on the detected species profiles can serve as a first indication for further, more detailed investigations of the heterogeneous influences in the planned project work at SJTU, including detection of species at NSRL, and according model development by the KIT and SJTU partners.
Publications
- Kinetische Analyse homogener Gasphasenreaktionen in Abgasnachbehandlungssystemen von Verbrennungsmotoren, 29. Deutscher Flammentag, Sept. 17–18, 2019, Bochum, Germany
S. Schwarz, W.H. Yuan, L. Ruwe, S. Schmitt, J. Horstmann, H. Zhang, H. Gossler, L. Maier, F. Qi, K. Kohse-Höinghaus, O. Deutschmann
- Experimental study on the heterogeneous conversion of NOx and NH3 catalyzed by a vanadia-based SCR catalyst at highly diluted conditions, 30. Deutscher Flammentag, Sept. 28–29, 2021, Hannover, Germany
S. Schmitt, S. Goßler, L. Maier, O. Deutschmann, K. Kohse-Höinghaus
- Exploring the interaction kinetics of butene isomers with NOx at low temperatures and diluted conditions, Combust. Flame 233 (2021) 111557
S. Gossler, L. Ruwe, W. Yuan, J. Yang, X. Chen, S. Schmitt, L. Maier, K. Kohse-Höinghaus, F. Qi, O. Deutschmann
(See online at https://doi.org/10.1016/j.combustflame.2021.111557) - Homogeneous conversion of NOx and NH3 with CH4, CO, and C2H4 at the diluted conditions of exhaust-gases of lean operated natural gas engines. Int. J. Chem. Kinet. 53, 2021, 213–229
S. Schmitt, S. Schwarz, L. Ruwe, J. Horstmann, F. Sabath, L. Maier, O. Deutschmann, and K. Kohse- Höinghaus
(See online at https://doi.org/10.1002/kin.21435) - Inhibiting and promoting effects of NO on dimethyl ether and dimethoxymethane oxidation in a plug-flow reactor. Combust. Flame 224, 2021, 94–107
H. Zhang, S. Schmitt, L. Ruwe, and K. Kohse-Höinghaus
(See online at https://doi.org/10.1016/j.combustflame.2020.08.027) - Insights into the interaction kinetics between propene and NOx at moderate temperatures with experimental and modeling methods. Proc. Combust. Inst. 38 (2021) 795–803
W. Yuan, L. Ruwe, S. Schwarz, C. Cao, J. Yang, O. Deutschmann, K. Kohse-Höinghaus, F. Qi
(See online at https://doi.org/10.1016/j.proci.2020.07.041)
