Influence of Engine Oils on Pre-Ignition Tendency in a Hydrogen–Kerosene Dual-Fuel Engine

Reducing CO2 emissions is an increasingly important goal in general aviation. The dual-fuel hydrogen–kerosene combustion process has proven to be a suitable technology for use in small aircraft. This robust and reliable technology significantly reduces CO2 emissions due to the carbon-free combustion of hydrogen during operation, while pure kerosene or sustainable aviation fuel (SAF) can be used in safety-critical situations or in the event of fuel supply issues. Previous studies have demonstrated the potential of this technology in terms of emissions, performance, and efficiency, while also highlighting challenges related to abnormal combustion phenomena, such as knocking and pre-ignition, which limit the maximum achievable hydrogen energy share. However, the causes of such phenomena—especially regarding the role of lubricating oils—have not yet been sufficiently investigated in hydrogen engines, making this a crucial area for further development. In this paper, investigations at the TU Wien, Institute of Powertrain and Automotive Technology, concerning the role of different engine oils in influencing pre-ignition tendencies in a hydrogen–kerosene dual-fuel engine are described. A specialized test procedure was developed to account for the unique combustion characteristics of the dual-fuel process, along with a detailed purge procedure to minimize oil carryover. Multiple engine oils with varying compositions were tested to evaluate their influence on pre-ignition tendencies, with a particular focus on additives containing calcium, magnesium, and molybdenum, known for their roles in detergent and anti-wear properties. Additionally, the study addressed the contribution of particles to pre-ignition occurrences. The results indicate that calcium and magnesium exhibit no notable impact on pre-ignition behavior; however, the addition of molybdenum results in a pronounced reduction in pre-ignition events, which could enable a higher hydrogen energy share and thus decrease CO2 emissions in the context of hydrogen dual-fuel aviation applications.