Application of hydrogen enriched natural gas in spark ignition IC engines: from fundamental fuel properties to engine performances and emissions

This review offers a summary of the recent research progress on hydrogen enriched compressed natural gas (HCNG) engines. Spark ignition IC engines fueled by HCNG have been shown to be advantageous over traditional gasoline engines in terms of fuel efficiencies and pollutant emissions. Further taking into account the vast availability of natural gas and the renewability of hydrogen, HCNG is considered to be a promising alternative fuel for large-scale applications in spark ignition engines. The past decade has witnessed significant progress in the research and development of HCNG engines. In this work, we intend to provide a comprehensive survey of recent studies on the power, efficiency and combustion & emission characteristics of HCNG engines. Additionally, we also focus on correlating fuel properties with experimentally observed HCNG engine performances, providing fundamental insights in the effects of hydrogen addition on engine working processes. To reach this goal, the physicochemical properties of hydrogen and its mixture with natural gas were firstly analyzed, followed by the detailed presentation and analysis of notable experimental results on HCNG engine performances. Numerical models for HCNG engines, which serve as an efficient way for engine parameter optimization, were also discussed. Apart from HCNG, the usage of other hydrogen-enriched fuels, such as hydrogen-gasoline, hydrogen-diesel, biogas and hydrogen-ethanol/methanol in IC engines were also briefly discussed.