Combustion and emission characteristics of a port-injection SI turbocharged engine fueled with several H-2/CNG blend ratios (0-50vol%) under various ignition timings were investigated. The results show that with the increase of hydrogen addition, the maximum brake toque timing decreases and the indicated thermal efficiency increases; the MBT gets close to the top dead center and the indicated thermal efficiency increases with decreased load. The combustion duration is reduced by increasing the hydrogen fraction in HCNG (hydrogen enriched compressed natural gas) mixture. The NOx, CO and HC emissions all descend with the increase of spark advance angle, and ascend with the increase of the load. Under the same ignition timing NOx and CO emissions rises with the increase of hydrogen blend ratio, and the HC emission presents an opposite trend. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.