Temperature-Dependent Thermophysical Behaviour of Bio-Based CNC Nanolubricants for Engine Applications

Abstract

The thermal management capability of engine oils is increasingly important under modern engine operating conditions characterised by high thermal loads. In this study, the effects of cellulose nanocrystals (CNC) on the specific heat capacity and density of SAE 40 engine oil were experimentally investigated over a range of temperatures and CNC volume concentrations. The results show that the specific heat capacity of CNC-enhanced engine oil increased with temperature for all samples, indicating improved thermal energy storage behaviour. Among the investigated concentrations, 0.5 vol.% CNC exhibited the highest specific heat capacity, demonstrating an optimal balance between particle–fluid interactions and dispersion quality. Density was observed to increase gradually with CNC concentration due to the contribution of solid nanoparticles; however, the magnitude of increase remained moderate and within an acceptable range for engine lubrication applications, particularly up to 0.7 vol.% CNC. The combined results indicate that the enhancement in thermal energy storage capability is not offset by adverse mass-related effects. These findings highlight the potential of renewable CNC-based nanolubricants as sustainable alternatives for improving the thermophysical performance of conventional engine oils. The findings provide new insights into the thermophysical optimisation of bio-based nanolubricants for engine thermal management applications.