Homogeneous charge compression ignition (HCCI) engine technology promises to reduce NOx and soot emissions while achieving high thermal efficiency, Temperature and mixture stratification are regarded as effective means of controlling the start of combustion and reducing the abrupt pressure rise at high loads. Probability density function methods are currently being pursued as a viable approach to modeling the effects of turbulent mixing and mixture stratification on HCCI ignition. In this paper we present ail assessment of the merits of three widely used mixing models in reproducing the moments of reactive scalars during the ignition of a lean hydrogen/air mixture (phi = 0.1, p = 41 atm, and T = 1070 K) under increasing temperature stratification and subject to decaying turbulence. The results front the solution Of the evolution equation for a spatially homogeneous joint PDF of the reactive scalars are compared with available direct numerical simulation (DNS) data [E.R. Hawkes, R. Sankaran, P.P. Pebay, J.H. Chen, Combust. Flame 145 (1-2) (2006) 145-159]. The mixing models are found able to quantitatively reproduce the time history of the heat release rate, first and second moments of temperature, and hydroxyl radical mass fraction from the DNS results. Most importantly, the dependence of the heat release I-ate oil the extent of the initial temperature stratification in the charge is also well captured. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved.