In the present study, direct detonation initiation by a point energy source in a rich H-2-NO2/N2O4-Ar mixture has been investigated using high-resolution one-dimensional numerical simulations performed with detailed chemistry. In particular, the effect of the 2-step energy release profile on the critical initiation energy and the dynamics of the failure process has been studied for the first time. Three reduced reaction models exhibiting a similar first step of energy release but a second step of different strengths have been employed. As the second step of heat release is strengthened, the overall behavior gets closer and closer to a 1-step process. It was found that the critical initiation energy for successful detonation initiation decreases as the second step of heat release is strengthened and the width of the overall heat release pulse is reduced. This feature has been investigated by studying the competition between chemical heat release and unsteadiness along the path of Lagrangian particles. The decrease of the critical initiation energy for stronger second step of heat release seems to be a result of the decrease of the sensitivity of this second step to unsteadiness-induced quenching behind a decaying shock wave. In view of the present results and previous experimental observations on propagating and diffracting detonation in H-2-NO2/N2O4(-Ar) mixtures, it seems that the 2-step energy release presenting the specific characteristics observed in rich H-2-NO2/N2O4(-Ar) mixtures, i.e. a strong and rapid first step and a weak and slow second step, constitutes a feature which is not essential for detonation propagation but makes detonation direct initiation and transmission to open space more difficult. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.