New Approaches to Lube Oil Consumption Measurement Based on the Tracer Method

In the research and development of internal combustion engines, there are several drivers for developing an accurate online lube oil consumption (LOC) measurement system. Lube oil consumption is considered to be a root cause of hydrocarbon and particle emissions and lubricating oil autoignition. It also negatively influences the life cycle cost for engine operators. Highly accurate measurement of lube oil consumption must be possible before it can be reduced - or rather optimized - to levels stakeholders will require in the future. State-of-the-art methods such as gravimetric and volumetric measurements are not fully satisfactory for several reasons. Generally, offline LOC measurement is no longer suitable for fast and accurate measuring cycles, oil condition monitoring and wear monitoring. At present, tracer methods are considered to be the most promising approach. However, current tracer methods have their downsides as well. This paper will first discuss the advances, optimizations and remaining challenges of state-of-the-art tracer methods. Next, it will examine a novel approach that uses a newly developed tracer and measurement setup based on the stable isotope deuterium. While tests have confirmed the efficacy of this approach, improvements are still being made. Oil consumption measurements are conducted offline and online on both passenger car and truck engines at the engine test bench and compared to the results of the SO₂ tracer method. Friction measurement data and oil consumption measurement will provide a comprehensive tribological assessment of these engines. Furthermore, the process of spiking the engine oil with the tracer, its challenges and potentials will be discussed. In conclusion, the outlook will show that further optimization of the oil spiking process and the long-term stability of the tracer in the oil in particular are required before the method can be applied cost-effectively to large engines.