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To address the pressing challenge of decarbonizing heavy-duty transportation, this thesis explores advanced combustion strategies using sustainable gaseous fuels, specifically hydrogen and methane, in internal combustion engines (ICEs). While electrification remains difficult to implement in long-haul applications due to energy density and infrastructure limitations, this work identifies and refines alternative pathways that retain the practicality of ICEs while mitigating their environmental impact.

A core innovation in this research is the application of advanced optical diagnostics, including high-speed imaging, natural luminosity, Schlieren imaging, and laser-induced fluorescence, to capture in-cylinder combustion phenomena in unprecedented detail. This enables a real-time, spatially resolved understanding of fuel behavior, air-fuel mixing, jet-wall interactions, and late-cycle oxidation under engine-relevant conditions.

The thesis also presents the first comprehensive optical investigation of gaseous fuel jets in the context of unconventional piston bowl geometries, specifically the wave piston. Originally developed for diesel engines, the wave piston's impact on hydrogen and methane direct injection (DI) is explored both experimentally and computationally. Through the use of custom-designed optical platforms, including a modified Volvo MD13 optical engine and a high-pressure optical chamber, the study reveals that the wave piston geometry significantly enhances fuel-air mixing and promotes flame propagation even with the lower momentum of gaseous jets.

Further contributions include the development of the “Lunda-wave” asymmetrical optical piston, which uniquely allows side-by-side comparison of waved and non-waved geometries under identical combustion conditions. This facilitated the discovery that wave structures can extend flame residence time and improve soot oxidation in low-swirl environments.

The thesis also evaluates post-injection strategies and premixed hydrogen DI techniques, revealing their respective roles in optimizing late-cycle combustion and improving efficiency. The findings offer valuable insights for injector design, injection strategies, and combustion chamber geometry optimization in future hydrogen and methane-powered engines. Overall, this work provides a foundational framework for the adaptation of ICEs to carbon-neutral operation and contributes to the scientific and technological advancements needed to realize sustainable heavy-duty transport.