The effects of bluff-body lip thickness on the several physical parameters like flame length, radiant fraction, gas temperature and NO. emissions in liquefied petroleum gas (LPG)-H-2 jet diffusion flame are investigated experimentally. Results indicate that the flame length reduces with the addition of hydrogen in the bluff-body stabilized flame, which can be attributed to the enhanced reactivity and residence time of the mixture gases. Moreover, with increasing lip thickness of the bluff body, the flame length also gets reduced. The soot free length fraction (SFLF) is observed to be enhanced with H-2 addition to the fuel stream. In contrast, the SFLF gets reduced with increasing lip thickness repetition, which is due to the reduced induction period of soot formation. The emission index of NOx (EINOx) is found to be attenuated in coaxial burner with hydrogen addition. In contrast it is observed to be enhanced in bluff-body stabilized flame. The former is due to the reduction in residence time of gas mixture, whereas the latter can be explained on the basis of increased flame temperature. Besides this, NOx emission level is also found to be enhanced with increasing lip thickness due to enhanced residence time. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.