Utilization of hydrogen in a compression ignition (CI) engine (7.4 kW rated power) under dual-fuel mode could reduce all carbon based emissions however it emits high NOx (oxides of nitrogen) emission due to high localized in-cylinder temperature during combustion. The present study is aimed at analysis of effect of localized (burned zone) in-cylinder temperature on formation of NO emission using theoretical (two zone model) and Computational Fluid Dynamics (CFD) simulations. Localized in-cylinder peak temperature (in burned zone) increased from 2278.2 K with base diesel mode to 2402.7 K with dual-fuel mode (16.7% hydrogen energy share). Nitric oxide (NO) emission formed mainly during premixed combustion phase about 363 degrees to 376 degrees crank angle. The NO emission at 16.7% hydrogen energy share with experimental test, two zone model, and CFD simulation are 914 ppm, 1208 ppm, and 1382 ppm. The simulation results are inline with the experimental results with the error band of 15%-23%. It is well established through this study that formation of NO emission at source level is strong function of localized in-cylinder temperature and its distribution pattern in the combustion chamber. (C) 2016 Elsevier Ltd. All rights reserved.