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Cogeneration represents a key element within the energy transition by enabling a balancing of the long-term fluctuations of regeneratives. Regarding the expected increase of hydrogen share in natural gas pipelines in Germany, this work deals with investigations of hydrogen-associated advantages for the lean and stoichiometric operations of natural gas cogeneration engines, in relation to numerous challenges, such as the efficiency-NOx trade-off. Charge dilution is commonly regarded as one of the most effective ways for improving thermal efficiency of spark-ignition gas engines. While excess air serves as a diluent in the lean combustion process, stoichiometric combustion dilution may be obtained by exhaust gas recirculation (EGR). Combining hydrogen addition with mixture dilution is an appealing approach for a better handling of the efficiency-emissions trade-off.

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.