In this paper, the effect of hydrogen (H-2) addition on the pollutant emissions of an IDF (inverse diffusion flame) burning LPG (liquefied petroleum gas) has been studied. Pollutant emission behavior was intensively investigated at fuel lean condition, and CO2, CO, HC, and NOx emitted from the flame were measured with their emission indices reported. HC and CO emissions are highly dependent on overall equivalence ratio, and both HC and CO are very high at fuel lean condition while reduce to nearly zero at equivalence ratio larger than 0.8 in LPG-H-2 IDF. NOx emission follows the trend of HC due to N2O-intermediate and Fenimore mechanisms at fuel lean condition while NOx emission increases with equivalence ratio at fuel rich condition due to thermal NOx mechanism. Hydrogen addition is found to promote the conversion of CO and HC into CO2, and there exists a threshold fraction of hydrogen over which a significant reduction of CO and HC occurs. High air jet Reynolds number tends to induce poor combustion and thus increasing HC, CO and NOx emissions. Compared to LPG IDF, LPG-H-2 IDF starts to generate noticeably CO and HC emissions earlier, and both CO and HC emissions are heavier. (C) 2016 Elsevier Ltd. All rights reserved.