CNG (Compressed natural gas) and HCNG (Hydrogen enriched compressed natural gas) have not been investigated extensively for particulate emissions, when they are used as fuel in the internal combustion (IC) engines. This study investigated the particulate emissions from spark ignition HCNG fuelled engine with varying fractions of hydrogen (0%, 10%, 20% and 30% v/v). Experiments were performed on a prototype single cylinder (1 l) port fuel injected HCNG engine at varying loads (BMEP), while maintaining identical fuel injection conditions, engine speed and ignition timing. At each operating point, exhaust samples were collected from the engine tail pipe and particle size-number distribution was determined using engine exhaust particle sizer (EEPS). Similar trend was observed for each HCNG composition. Results showed higher particulate numbers in nano-particle size range, but their corresponding mass contribution was rather small. On the other hand, accumulation and coarse mode particles were lower in particulate size-number distribution but they contributed dominatingly to the particulate size-mass distribution. Among the tested HCNG compositions, 30HCNG showed highest number of nano-particles emitted at each engine load amongst with corresponding higher contributions to size-mass and size-surface area distributions. (C) 2015 Elsevier Ltd. All rights reserved.