Diesel DeNO(x) experiments have been conducted using the selective noncatalytic 'thermal DeNO(x)' process in a diesel fuelled combustion-driven flow reactor which simulated a single cylinder (966 cm(3)) and head equipped with a water-cooling jacket and an exhaust pipe. NH3 was directly injected into the cylinder to reduce NO, emissions. A wide range of air/fuel ratios (A/F = 20-40) was selected for NOx reduction where an initial NOx of 530 ppm was usually maintained with a molar ratio (beta = NH3/NOx) of 1.5. The results indicate that a 34% NOx reduction can be achieved from the cylinder injection in the temperature range, 1100-1350 K. Most of the NOx reduction occurs within the cylinder and head section (residence time < 40 ms), since temperatures in the exhaust are too low for additional NOx reduction. Under large gas quenching rates, increasing beta values (e.g. 4.0) substantially increase the NOx reduction up to 60%, which is comparable with those achieved under isothermal conditions. Experimental findings are analysed by chemical kinetics using the Miller and Bowman mechanism including both N/H/O species and CO/hydrocarbon reactions to account for CO/UHC oxidation effects, based on practical nonisothermal conditions. Comparisons of the kinetic calculations with the experimental data are given as regards temperature characteristics, residence time and molar ratio. In addition, the effects of CO/UHC and branching ratio (alpha = k(1)/(k(1) + k(2))) for the reaction NH2 + NO = products are discussed in terms of NO reduction features, together with practical implications. (C) 2002 Elsevier Science Ltd. All rights reserved.