The Influence of Split Injection Ratio on Efficiency and NOx Emissions in a Pilot Diesel-Ignited Hydrogen Direct Injection Engine The University of New South Wales

Format:

Book

Conference/Event

Author/Creator:

Zhao, Yifan, author.

Chan, Qing Nian, author.

Kook, Sanghoon, author.

Conference Name:

WCX SAE World Congress Experience (2026-04-14 : Detroit, Michigan, United States)

Language:

English

Subjects (All):

Engine efficiency.

Nitrogen oxides.

Hydrogen fuel.

Combustion and combustion processes.

Emissions.

Pressure.

Fuel injection.

Engines.

Local Subjects:

Engine efficiency.

Nitrogen oxides.

Hydrogen fuel.

Combustion and combustion processes.

Emissions.

Pressure.

Fuel injection.

Engines.

Physical Description:

1 online resource

Place of Publication:

Warrendale, PA SAE International 2026

Summary:

This study investigates the impact of the hydrogen split injection ratio on the combustion of pilot diesel-ignited hydrogen direct-injection engines, which is expected to affect hydrogen-air mixture conditions and thus flame propagation and diffusion flame developments. Experiments were conducted on a 1-litre single-cylinder diesel engine equipped with an additional hydrogen injector operating at 35 MPa. Hydrogen accounting for 95% of total input energy was injected at 150 and 60 °CA bTDC for the first and second pulses, which were selected as high-efficiency injection timings from previous equal-split injection tests. The 5% diesel energy was injected near TDC to control CA50 at 10 °CA aTDC. While varying the split ratio between the two hydrogen injections, in-cylinder pressure/aHRR profiles, engine efficiency/power output and engine-out emissions of NOx and CO2 were evaluated. Results showed that the hydrogen split ratio does not significantly affect IMEP/efficiency, which consistently achieved a 17.2% increase over the diesel baseline. While CO2 emissions remained at a very low level due to high substitution of hydrogen energy, they showed no dependency on the split ratio. By contrast, NOx emissions were highly sensitive to the hydrogen injection split ratio. Increasing the first hydrogen injection fraction to 30% reduced NOx, attributed to decreased locally rich mixtures formed by late second hydrogen injection and increased lean mixture homogeneity from early first hydrogen injection, leading to a slower burning effect. However, further increasing the first injection fraction led to higher NO emissions due to increased hydrogen compression, which raised TDC and combustion pressure

Notes:

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