Towards optimized spark ignition for hydrogen and biogas heavy-duty engines

Engineering notes

The use of renewable gaseous fuels such as biogas and hydrogen offers a promising pathway to significantly reduce the climate impact of ICE-based powertrains.

Chinese explanation / 中文解读

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Original abstract

Heavy-duty transport is one of the major contributors to global greenhouse gas (GHG) emissions, with internal combustion engines (ICEs) expected to remain an important propulsion technology in long-haul applications during the transition to sustainable transport. The use of renewable gaseous fuels such as biogas and hydrogen offers a promising pathway to significantly reduce the climate impact of ICE-based powertrains. Due to their high octane rating and excellent knock resisting properties, these fuels are well suited for spark ignition (SI) engines. However, achieving robust combustion in SI engines is strongly dependent on the spark ignition process, which becomes increasingly challenging under lean and highly diluted operating conditions. At the same time, excessive spark energy can accelerate spark plug wear and increase the risk of abnormal combustion, particularly in hydrogen engines. To address this, this thesis investigates spark ignition processes in ICEs operating on hydrogen and biogas.A central focus of the thesis is to improve the understanding of how electrical energy from the spark is transferred to the surrounding gas and how this governs ignitability, combustion stability, and spark plug wear. To achieve this, a combination of experimental approaches is employed, including fundamental investigations in constant-volume chambers and application-oriented studies in single-cylinder heavy-duty research engines. The results reveal that ignition performance is not determined by the total spark energy, but by how effectively the spark energy is delivered during different phases of the spark discharge. The initial breakdown and arc phases are shown to be highly efficient in transferring energy to the gas, whereas the glow phase contributes less efficiently and is associated with increased thermal losses to the spark plug electrodes.Further investigations demonstrate that ignitability in hydrogen engines is strongly governed by early flame kernel development, which is sensitive to in-cylinder flow, fuel-air mixture conditions, and heat losses to the electrodes. By systematically analyzing the interaction between spark ignition parameters, electrode geometries, and operating condition, this work identifies optimal spark ignition control strategies for both biogas and hydrogen engines. These strategies enable robust combustion while minimizing excessive spark energy discharge, thereby reducing spark plug wear and the risk of abnormal combustion phenomena such as pre-ignition.Overall, this thesis provides new insights into the fundamental physics of spark ignition and establishes a framework for optimized ignition control in heavy-duty engines operating on renewable gaseous fuels. The findings support the development of more efficient, durable, and scalable combustion technologies, contributing to a practical pathway toward sustainable heavy-duty transport.

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