Challenges in Measuring Lube Oil Consumption of Internal Combustion Engines Using Deuterium As a Tracer

Lube oil emission is thought to have a negative influence on hydrocarbon and particle emissions, autoignition and the life-cycle cost of internal combustion engines. Thus, one of the major goals of combustion engine research and development is to optimize lube oil consumption, for example by optimizing the tribological behavior of the piston group (interaction between piston rings and cylinder liner). This requires the application of a fast and accurate lube oil consumption measurement method. Methods such as gravimetric and volumetric measurement are outdated for R&D applications because of measurement time, absolute accuracy as well as repeatability, however some OEMs are still applying this method. At present, the use of tracer methods for measuring lube oil consumption is considered the most promising in terms of decreasing measurement time and increasing accuracy. For example, sulfur as a tracer is one of the most established methods for measuring lube oil consumption, but previous publications have revealed downsides and future challenges of its use. This publication, however, highlights the challenges of using the stable hydrogen isotope deuterium as a tracer which are still to overcome, in order to become a viable and reliable method for measuring lube oil consumption on internal combustion engines. In the introduction, a novel concept of measuring lube oil consumption with deuterated engine oil and the test bench setup are explained. Following laboratory experiments, test bench runs on a heavy-duty diesel engine and long-term studies on a field engine, three major challenges facing the new approach are identified and potential solutions are proposed. First, the long-term stability of the tracer in the lube oil and potential changes in the physical and chemical properties of the oil due to deuteration are discussed in light of the results of tests on a field engine that uses deuterated engine oil. Second, the hydrogen-deuterium exchange process to mark the oil with the tracer is examined and potential approaches for reducing cost and duration are highlighted. The universal applicability of the deuteration process to several base oil groups is also explained. Finally, the detection of deuterium in the gas of the engine exhaust and potential cross-sensitivities to trace gases as well as other crucial limitations of the detector in analyzing engine exhaust are addressed. The summary presents the requirements for converting the experiments with a deuterium tracer into a reliable method for lube oil consumption measurement providing crucial properties such as high accuracy, short measurement time, effort and ease of use.