Autoignition of hydrogen, leading to flame development under turbulent flow conditions is numerically investigated including a detailed chemical mechanism. The chosen configuration consists of a turbulent jet of hydrogen diluted with nitrogen which is issued into a coflow of heated air. Numerical simulations are performed with the Conditional Moment Closure model, to capture the transient evolution of the flow. Turbulence closure is achieved using the kappa-epsilon model. Simulations revealed that the injected hydrogen mixes with coflowing air autoignites and a stable diffusion flame is established Sometimes flashback,., of the ignited mixture is observed, whereby the flame travels upstream and stabilizes. It is found that the constants assumed in various modeling terms can severely influence the degree of mixing. Hence, certain modifications to these constants are suggested, and improved predictions are obtained. The sensitivity of autoignition length to the coflow temperature is investigated. The predicted autoignition lengths show a reasonable agreement with the experimental data and LES results. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.