Hydrogen-compressed natural gas blend (HCNG) engines can extend the lean burn limit because of the wide flammability range of hydrogen. Lean combustion helps facilitate high efficiency and fundamentally reduces NOx emission. Increasing the compression ratio (CR) of an HCNG engine was reported to improve its thermal efficiency. However, the high risk of knock occurrence and the increase in NOx emission can hinder CR increase. To reduce NOx emission, an ignition timing retard strategy was considered for an HCNG engine with an increased CR. The thermal efficiency and emission characteristics at maximum power operation were investigated by retarding the ignition timing from minimum spark advance for best torque (MBT) timing. The results showed that the condition of HCNG30, a CR of 11.5, lambda of 1.8, and retarding the ignition timing by 10 CAD from the MBT timing could produce 2.0% higher thermal efficiency, 61.7% lower NOx emission, and 6.7% higher CH4 emission compared to the base CNG engine condition. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.