Experimental study on emissions of a spark-ignition engine fueled with natural gas - Hydrogen blends

An experimental investigation on the influence of the excess air ratio and hydrogen fraction on the emissions characteristics of a spark-ignition engine fueled with natural gas - hydrogen blends was conducted. The results indicate that the excess air ratio has a significant effect on the hydrocarbon (HC), NO_x, CO, and CO₂ concentration for both pure natural gas and natural gas - hydrogen blends. For a specified excess air ratio, HC emissions decrease with the increase of hydrogen fraction; the behavior is more obvious under the lean burn operation. The NO_x concentration increases with the increase of hydrogen fraction, and NO_x gets its peak value at an excess air ratio of 1.1. CO₂ emissions decrease with increasing hydrogen fraction. Meanwhile, the addition of hydrogen into natural gas can extend the lean burn limit of a mixture. Thus, an engine fueled with natural gas - hydrogen blends operating under lean mixture conditions can get low emissions of HC, CO, CO₂, and NO_x.