Ion Current Sensing as Combustion Diagnostics for a Spark-Ignited Natural Gas-Hydrogen Engine

The use of hydrogen as an alternative fuel to power cogeneration gas engines has been a research topic over the last few decades and has currently gained importance, even more due to current circumstances related to decarbonisation efforts for the energy supply. A significant part of the research done is focused on the topic of combustion diagnostics, which can be fulfilled through different methods. This work investigates the feasibility of the ion current sensing for a pure hydrogen fueled series natural gas cogeneration engine. For this purpose, a variation of the fuel composition (from 100% natural gas to 100% hydrogen) was carried out while maintaining the indicated mean effective pressure (IMEP) and the combustion phasing (CA50). This demonstrated that the efficiency increased monotonically as the hydrogen concentration rose. Simultaneously, the duration of the ion current signals gradually dropped but was still detectable at 100% hydrogen combustion. Signals from the spark ignition interfered with the measureable ion current during the actual combustion. To further investigate this effect, a second series of experiments was conducted, where the duration of the spark ignition was varied. The results show, that a spark duration of 500 μs is sufficient to ignite a combustion with pure hydrogen and the ion current measured matches characteristic ion current signals of an engine combustion.