Computational comparison of the conventional diesel and hydrogen direct-injection compression-ignition combustion engines

Rafig Babayev, Arne Andersson, Albert Serra Dalmau, Hong G. Im, Bengt Johansson

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


Most research and development on hydrogen (H2) internal combustion engines focus on premixed-charge spark ignition (SI) or diesel-hydrogen dual-fuel technologies. Premixed charge limits the engine efficiency, power density, and safety, while diesel injections give rise to CO2 and particulate emissions. This paper demonstrates a non-premixed compression-ignition (CI) neat H2 engine concept that uses H2 pilots for ignition. It compares the CI H2 engine to an equivalent diesel engine to draw fundamental insights about the mixing and combustion processes. The Converge computational fluid dynamics solver is used for all simulations. The results show that the brake thermal efficiency of the CI H2 engine is comparable or higher than diesel, and the molar expansion with H2 injections at TDC constitutes 5–10 % of the total useful work. Fuel-air mixing in the free-jet phase of combustion is substantially higher with H2 due to hydrogen's gaseous state, low density, high injection velocity, and transient vortices, which contribute to the 3 times higher air entrainment into the quasi-steady-state jet regions. However, the H2 jet momentum is up to 4 times lower than for diesel, which leads to not only ineffective momentum-driven global mixing but also reduced heat transfer losses with H2. The short H2 flame quenching distance may also be inconsequential for heat transfer in CI engines. Finally, this research enables future improvements in CI H2 engine efficiency by hypothesizing a new optimization path, which maximizes the free-jet phase of combustion, hence is totally different from that for conventional diesel engines.
Original languageEnglish (US)
Pages (from-to)121909
StatePublished - Sep 9 2021

Bibliographical note

KAUST Repository Item: Exported on 2021-09-20
Acknowledgements: This work was sponsored by the King Abdullah University of Science and Technology (KAUST) and the Combustion Engine Research Center (CERC) at the Chalmers University of Technology. All simulations were performed on Shaheen II supercomputer operated by KAUST Supercomputing Laboratory (KSL). Convergent Science provided CONVERGE licenses, as well as technical support for this work.

ASJC Scopus subject areas

  • Energy Engineering and Power Technology
  • Organic Chemistry
  • General Chemical Engineering
  • Fuel Technology


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