Experimental Investigations of a Hydrogen Fueled Natural Gas Engine and Ion Current Measurement for Combustion Diagnostics in Pure Hydrogen Operationwith Water Injection

In the ongoing effort to decarbonize energy supply, a notable shift involves the conversion or retrofitting of combined heat and power plants to operate on hydrogen as an alternative to natural gas. In this transformative landscape, extensive research is underway to develop and explore innovative combustion processes for hydrogen-fueled engines, aiming to comprehend and optimize combustion processes concerning both engine performance and emissions. Among the various methods available for monitoring the combustion process and engine control, ion current sensing presents itself as a viable option. A unique feature of this research lies in utilizing the engine's spark plug itself as an electrical sensor, measuring the ion current generated during the flame development and combustion processes. Given the limited research on ion current sensing for hydrogen combustion processes, a series of experiments were conducted and presented in this work. These experiments involved sweeps of water-to-fuel ratio (WFR) on a naturally aspirated gas engine consisting of four cylinders, of which only one cylinder is being operated with pure hydrogen as fuel. The primary findings highlight the feasibility of measuring ion current even within hydrogen-air combustion under extremely lean mixtures (λ > 3). Furthermore, it is firstly presented that the levels of WFR significantly affect measured ion current signals. Using the measured data from the conducted sweeps, characteristics of the ion current signals are correlated with combustion parameters. It is foremost proven, that the first rise of the ion current signal correlates well with the calculated combustion start CA05. In essence, this research not only contributes to the evolving landscape of hydrogen-based energy solutions but also sheds light on the potential of ion current sensing as a reliable tool for monitoring and optimizing combustion processes in these engines, thereby enabling broader goals of sustainable and efficient energy systems.