Page 60: of Maritime Reporter Magazine (November 2026)

TECH FEATURE hydrogen. The high-speed in-cylinder pressure data was recorded using a Kistler piezoelectric transducer (Type 6045B), which was ? ush-mounted in the cylinder head.

The connected KiBox2 combustion analysis system from

Kistler prepared the data for interpretation. The tests covered both pure ammonia combustion and various ammonia-hydrogen blends (up to 60% hydrogen share).

The measured in-cylinder pressure was used as the main input, converting the pressure curve into a energy release curve, showing how quickly and at what crank angle the fuel’s energy is released during combustion. The research team compared the standard polytropic index based on gasoline combustion with a more detailed method: based on the measured pressure data and the speci? c fuel blend, the polytropic index was calculated individually for each operating point and each cycle. This allowed the Kistler team to quantify the potential error that is introduced when standard gasoline models are applied to ammonia- hydrogen combustion. Conversely, they were able to quan- tify the increase in accuracy achieved through fuel-speci? c, cycle-resolved calculations.

The Results:

Facing the Potential for Errors

Rogers and his team were stunned by the results: “We found the sheer magnitude of the potential errors surpris- ing. For some of the operational points the errors were so signi? cant that they rendered the test results borderline unusable.” Under pure ammonia operation, the polytrop- ic index deviated in compression by about four percent from the gasoline default value. The experts found out that the discrepancies primarily affected the late combus- tion phase, while the early burn phase was less sensitive.

Also, combustion accelerated and modeling discrepancies decreased as the hydrogen share increased. “Our ? ndings show that conventional gasoline-based heat release analy- sis is not universally transferable to zero-carbon fuels,” summarizes Rogers. “For accurate prediction of burn duration and combustion phasing, fuel-speci? c or cycle- resolved polytropic indices are required.”

Comparison of the late-stage

Creating More Sustainable Engines combustion duration for the

In day-to-day engine research and development, en- gineers are under a lot of pressure to quickly improve gasoline default setting (upper) engines. Here, discrepancies in the test results require re- and revised indices (lower).

peated measurements, making the whole process less ef- ? cient. With more accurate calculation models and, con- sequently, a more accurate analysis, engineering decisions 60 Maritime Reporter & Engineering News • November 2026

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