Hydrogen Enrichment in Lean-Burn Spark-Ignition Engines Improves Key Performance Metrics

Strategic Insights -

A recent study has demonstrated that hydrogen enrichment in lean-burn spark-ignition engines can simultaneously improve three key performance metrics: thermal efficiency, combustion stability, and nitrogen oxide emissions. The researchers, from the Faculty of Engineering at Ansbach University of Applied Sciences in Germany, conducted experiments on a six-cylinder engine fueled with hydrogen-natural gas blends containing up to 30% hydrogen by volume. By optimizing the air-fuel equivalence ratio, the team was able to achieve significant improvements in nitrogen oxide emissions, thermal efficiency, and combustion stability, while also reducing cycle-by-cycle variations.

Key Takeaways:

  • The researchers found that hydrogen enrichment in lean-burn spark-ignition engines can simultaneously improve thermal efficiency, combustion stability, and nitrogen oxide emissions without requiring modifications to the engine hardware or ignition timing.
  • Experiments were conducted on a six-cylinder engine for combined heat and power application, fueled with hydrogen-natural gas blends containing up to 30% hydrogen by volume.
  • By optimizing only the air-fuel equivalence ratio, it was possible to extend the lean-burn limit from 1.6 to 1.9, reduce nitrogen oxide emissions by up to 70%, enhance thermal efficiency by up to 2.2 percentage points, and significantly improve combustion stability, reducing cycle-by-cycle variations from 2.1% to 0.7%.
  • A defined "l window" was identified in which all three key performance indicators simultaneously meet or exceed the natural gas baseline.
  • The research concluded that hydrogen enrichment can position hydrogen as a performance booster for natural gas engines in stationary applications, enabling cleaner, more efficient, and smoother operation without added system complexity.
  • The study was funded by the Federal Ministry For Economic Affairs And Climate Action, and the research is published in the journal Energies under the title "Simultaneous Reductions in NO[x] Emissions, Combustion Instability, and Efficiency Loss in a Lean-Burn CHP Engine via Hydrogen-Enriched Natural Gas".

Statistics:

  • Nitrogen oxide emissions were reduced by up to 70% when hydrogen enrichment was used.
  • Thermal efficiency was enhanced by up to 2.2 percentage points.
  • Combustion stability was significantly improved, with cycle-by-cycle variations reduced from 2.1% to 0.7%.
  • The "l window" identified in the study showed simultaneous improvements in nitrogen oxide emissions, efficiency, and stability.
  • Hydrogen enrichment in lean-burn spark-ignition engines can improve thermal efficiency, combustion stability, and nitrogen oxide emissions simultaneously.

Sources:

  • Simultaneous Reductions in NO[x] Emissions, Combustion Instability, and Efficiency Loss in a Lean-Burn CHP Engine via Hydrogen-Enriched Natural Gas. Energies, 2025,18(16):4339.
  • NewsRx. New Anions Study Findings Have Been Reported from Faculty of Engineering (Simultaneous Reductions in NO[x] Emissions, Combustion Instability, and Efficiency Loss in a Lean-Burn CHP Engine via Hydrogen-Enriched Natural Gas). Energy Weekly News. September 12, 2025; p 134.