Performance and Emissions of Natural Gas–Hydrogen Blends on Industrial Rich-Burn, Spark-Ignition Engines

Natural gas is increasingly used in stationary spark-ignition engines because of its abundance, high octane rating, and lower carbon dioxide emissions than conventional liquid fuels. Blending hydrogen into natural gas pipelines enables large-scale transport, but pipeline compressor engines must run directly on this blended gas. Many prior hydrogen blending studies on such engines have predominantly relied on idealized indoor testing platforms coupled with dynamometer loading to isolate the impact of hydrogen addition; however, this study experimentally evaluated hydrogen blends on a six-cylinder, four-stroke industrially representative engine-compressor unit loaded by a closed natural gas compression loop operating under open-air ambient conditions to analyze the system-level response to hydrogen addition. Additionally, emissions were characterized by using a high-resolution FTIR MKS 2030 MultiGas analyzer. Natural gas–hydrogen blends containing 0–30% hydrogen by volume were tested in 5% increments. Natural gas flow generally decreased with hydrogen addition, while brake thermal efficiency increased at all operating conditions. Relative to the natural gas baseline, methane emissions decreased by as much as 47%, volatile organic compounds by 62%, and carbon monoxide by 94%; however, NOx emissions increased by as much as 324%. Carbon dioxide emissions increased by up to 12% at lower loads and decreased by up to 13% at higher loads. At 30% hydrogen, the equivalence ratio decreased by 6.25% at the lowest tested load and 8.28% at the highest tested load. Hydrogen blending can, therefore, improve efficiency and reduce carbon-based emissions in industrial, rich-burn engines, but the accompanying NOx increase and leaner operation warrant further testing with adjusted spark timing and controlled equivalence ratio.