Ph.D. Defense | Rafig Babayev


Hydrogen Combustion versus Diesel Isobaric Combustion in the Double Compression-Expansion Engine



Rafig Babayev, Ph.D. Candidate Supervised by Prof. Bengt Johansson


Monday, December 14, 2020


01:00 PM - 02:00 PM




In light of humanity's recent efforts to decarbonize the world economy, energy conversion efficiency and emissions have become among the most important subjects of research. As one of the most widely used energy conversion devices, the internal combustion engine (ICE) remains the focal point of much of the research in the field. This thesis aims to contribute to the research and development of a new highly efficient split-cycle engine concept – the double compression-expansion engine (DCEE) – by expanding the knowledge of combustion processes suitable for this, and potentially, other modern engines, via experimental and computational studies. In this thesis, first, the importance of continued improvement of ICEs is demonstrated by comparing the life-cycle CO2 emissions of different modes of transport. Then, an isobaric combustion concept is proposed for use in modern high-pressure combustion engines, such as the DCEE. It is shown that isobaric combustion is capable of reducing cylinder wall heat transfer losses by 20 %, simultaneously improving the NOx emissions by a factor of two. An in-situ injection rate measurement technique is developed and applied to improve the understanding of the complex injection strategies required for isobaric combustion. It is also shown that isobaric combustion is possible to achieve with a single fuel injector at a wide range of engine load conditions, but using multiple injectors may offer additional benefits of even lower heat losses, better heat release control, and improved soot and NOx trade-off. Then, an alternative combustion system to the diesel isobaric is proposed – a hydrogen direct-injection (DI) compression-ignition (CI) combustion concept, which has the advantage of eliminated CO2 and soot emissions. It is shown that the non-premixed DICI H2 combustion can be used more efficiently than premixed spark-ignition concepts in an engine. DICI H2 combustion is found to differ significantly from diesel non-premixed combustion, thus a completely different optimization path must be taken for H2 engines. This path is then hypothesized, tested in computational investigations, and proven effective. Finally, hydrogen combustion is compared to the diesel in the context of the DCEE, where brake thermal efficiencies in the range of 56 % are demonstrated for the entire powertrain. The results of this thesis outline a path for future high-efficiency and zero-emission combustion engine development, which is expected to involve hydrogen isobaric combustion with multiple fuel injectors per cylinder in double compression-expansion engines.


Rafig Babayev earned his Bachelor's degree in 2016 from the Qafqaz University in Baku, Azerbaijan. He then joined the MS/PhD program at KAUST in Mechanical Engineering with Prof. Bengt Johansson. Rafig's research efforts focused on reducing the negative impacts of the transport sector by developing and investigating state-of-the-art combustion systems and different fuels using experimental and computational techniques. His research also aided in the development of modern automotive powertrains. In 2019, Rafig was a member of the Student Advisory Committee, serving the people of the CCRC.

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Event Quick Information

14 Dec, 2020
13:00 PM – 14:00 PM