Schematic of the reaction mechanisms providing HT NOx reduction by operating an NTC under relatively high frequency air : fuel ratio oscillations. Reprinted from A Study of the NOx Reduction Mechanism for Improving the Performance of Di-Air, K. Yoshida, Y. Bisaiji, N. Takagi, M. Inoue, K. Umemoto and T. Fukuma, 4th IAV MinNOx Conference, 12–13 June 2012, Berlin.