Investigation of the Roles of NCN and HNO Reactions on NOx Formation in Combustion Processes

• Applicant: Professor Dr. Gernot Friedrichs
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2009 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 134123282

NCN radicals and HNO play important roles as intermediates in the formation of nitrogen oxides (NOx) in combustion processes. The detailed and complex reaction mechanisms used to develop and optimize pollutant reduction strategies rely on accurate rate constant parametrizations for many elementary gas phase reactions. Although much work has been done to develop NOx formation submechanisms, in recent years it has become clear that the NCN radical pathway to prompt-NO formation is not properly implemented in the models.During the first funding period of this project, direct rate constant measurements of some of the most important NCN reactions could be performed for the first time. Similar shock tube investigations of selected bimolecular NCN reactions will be continued in order to assemble a complete NCN high temperature mechanism. Using laser absorption techniques, including a newly developed mid-IR detection system, concentration-time profiles of many species (NCN, OH, CN, HCN, CH, N) will be measured. Moreover, additional experiments will be performed to clarify the somewhat disputed values of the enthalpy of formation and the high temperature absorption cross section of NCN. The combination of all data result in a purely experimentally based NCN submechanism that will be validated against experiments of more complex reaction systems and implemented into modern flame mechanisms. Flame simulations will show if the overarching research goal, i.e. a reliable modeling of NOx formation in flames, will be met. In terms of HNO, during the first funding period this difficult to measure species could be detected behind shock waves for the first time. Further optimization of the frequency modulation detection system will enable rate constant measurements of selected HNO reactions including HNO + O2, H and OH. So far, high temperature data on HNO kinetics are rare and largely scattered; hence these measurements provide the basis for an improved HNO flame model for both prompt-NO formation and fuel-N-conversion.

• DFG Programme: Research Grants