Evaluating low NO hydrogen engines designed for off-road and construction applications

Area of Science:

• Internal Combustion Engines
• Environmental Science
• Automotive Engineering

Background:

• Non-road mobile machinery (NRMM) requires decarbonisation solutions.
• Hydrogen internal combustion engines (H2ICE) are a potential pathway for hard-to-electrify sectors.
• Limited research exists on H2ICEs optimized for both efficiency and air quality.

Purpose of the Study:

• To analyze tailpipe nitrogen oxides (NOx) emissions from H2ICE variants.
• To compare H2ICE emissions against a contemporary diesel engine over the Non-Road Transient Cycle (NRTC).
• To evaluate the air quality co-benefits of H2ICE adoption in NRMM.

Main Methods:

• Dynamometer testing of four spark ignition H2ICE variants (∼55 kW).
• Engine-out emissions analysis for one H2ICE variant.
• Comparison of H2ICE and diesel emissions over the NRTC.
• Evaluation of H2ICEs with and without Selective Catalytic Reduction and Particulate Filter (SCRF) aftertreatment.

Main Results:

• All H2ICE variants operating lean-burn produced substantially lower NOx than diesel over NRTC.
• H2ICE with SCRF aftertreatment achieved 1.90 mg kWh⁻¹ NOx ( >99% reduction vs. diesel).
• H2ICE with a hydrogen slip catalyst (no SCRF) emitted 63.7 mg kWh⁻¹ NOx ( >50x improvement vs. diesel).

Conclusions:

• Low-NOx H2ICEs offer significant near-term air quality improvements for NRMM, especially construction equipment.
• H2ICEs present a viable alternative to diesel, providing greater urban air quality benefits than biofuels.
• A systems-level assessment is needed to weigh the benefits of advanced aftertreatment against costs and potential ammonia slip.