In this paper, ignition characteristics of syngas (H-2/CO) under homogeneous charge compression ignition environment have been studied using direct numerical simulation (DNS) and detailed reaction mechanism with temperature stratification. 2D DNS are performed by varying several parameters such as fuel composition, temperature fluctuation (T') and with different temperature and composition correlations. Results show that high H2 content syngas mixture exhibits increase in peak mean heat release rate (HRR) and decrease in spreading of mean HRR. Also, for large T', deflagration mode of ignition becomes dominant source of HRR and reduces the effects of fuel composition on peak mean HRR. On the contrary, spontaneous mode of ignition becomes dominant source of HRR and occurs more homogenously for small T', and this phenomenon becomes significant for low H2 content syngas mixture. The effect of different correlations between temperature and composition on ignition in syngas illustrate that HRR occurs from mixed mode of deflagration and spontaneous ignition for uncorrelated cases, whereas spontaneous mode of ignition occurring homogeneously is the major source of HRR for negatively correlated cases. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.