Simultaneous Reductions in NO x Emissions, Combustion Instability, and Efficiency Loss in a Lean-Burn CHP Engine via Hydrogen-Enriched Natural Gas

Johannes Fichtner (), Jan Ninow and Joerg Kapischke
Additional contact information
Johannes Fichtner: Faculty of Engineering, Ansbach University of Applied Sciences, 91522 Ansbach, Germany
Jan Ninow: Faculty of Engineering, Ansbach University of Applied Sciences, 91522 Ansbach, Germany
Joerg Kapischke: Faculty of Engineering, Ansbach University of Applied Sciences, 91522 Ansbach, Germany

Energies, 2025, vol. 18, issue 16, 1-15

Abstract: This study demonstrates that hydrogen enrichment in lean-burn spark-ignition engines can simultaneously improve three key performance metrics, thermal efficiency, combustion stability, and nitrogen oxide emissions, without requiring modifications to the engine hardware or ignition timing. This finding offers a novel control approach to a well-documented trade-off in existing research, where typically only two of these factors are improved at the expense of the third. Unlike previous studies, the present work achieves simultaneous improvement of all three metrics without hardware modification or ignition timing adjustment, relying solely on the optimization of the air–fuel equivalence ratio λ . 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 λ ≈ 1.6 to λ > 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 variationsfrom 2.1% to 0.7%. A defined λ window was identified in which all three key performance indicators simultaneously meet or exceed the natural gas baseline. Within this window, balanced improvements in nitrogen oxide emissions, efficiency, and stability are achievable, although the individual maxima occur at different operating points. Cylinder pressure analysis confirmed that combustion dynamics can be realigned with original equipment manufacturer characteristics via mixture leaning alone, mitigating hydrogen-induced pressure increases to just 11% above the natural gas baseline. These results 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 key result is the identification of a λ window that enables simultaneous optimization of nitrogen oxide emissions, efficiency, and combustion stability using only mixture control.

Keywords: hydrogen-enriched natural gas (H 2 NG); lean-burn combustion; spark-ignition engine; combined heat and power (CHP); nitrogen oxide (NOx) emissions; combustion stability; thermal efficiency; engine optimization (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
References: Add references at CitEc
Citations:

Downloads: (external link)
https://www.mdpi.com/1996-1073/18/16/4339/pdf (application/pdf)
https://www.mdpi.com/1996-1073/18/16/4339/ (text/html)

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:gam:jeners:v:18:y:2025:i:16:p:4339-:d:1724593

Access Statistics for this article

Energies is currently edited by Ms. Agatha Cao

More articles in Energies from MDPI
Bibliographic data for series maintained by MDPI Indexing Manager ().