Atomic force microscopic measurement of a used cylinder liner for prediction of boundary friction

Abstract

Accurate simulation performs a crucial role in the design and development of new modern internal combustion engines. In the case of piston rings, simulations are used to effectively predict generated friction and power loss of proposed designs. These are consequences of viscous shear of a thin lubricant film, likewise boundary friction caused by direct interaction of piston rings with the cylinder liner/bore surface. The most commonly used model for determining boundary friction is that of Greenwood and Tripp. The model requires the pressure coefficient of boundary shear strength of asperities from the softer of the contacting surfaces as an input. This parameter needs to be measured. The paper describes the process of measurement using an Atomic Force Microscope (AFM), both for a dry surface and that wetted by the presence of a lubricant layer. For realistic results, the investigated specimen is a used, tested engine cylinder liner where boundary active lubricant additives are bonded to its surface as well as combustion products. This approach is as opposed to the previously reported works using new flat surfaces with base oil or partially formulated lubricants, and has not previously been reported in literature. The results show that for used cylinder liners, the measured boundary shear strength of asperities varies according to location along the stroke. Results are reported for the Top Dead Centre, Mid-stroke and Bottom Dead Centre locations. The measurements are subsequently used with 2D Reynolds Solution for a top compression ring-liner contact, where it is found that accurate localised predictions of generated friction and power loss can be made instead of the usual average value approach reported in literature.

Anti-wear properties evaluation of frictional sliding interfaces in automobile engines lubricated by copper/graphene nanolubricants

“…Therefore, many researchers have studied different technologies for exploring novel methods to replace environmental harmful additives that cause adverse emissions (zinc dialkyldithiophosphate) and other additives that include sulfated ash, sulfur, and phosphorous without compromising on tribological engine behavior with eco-friendly additives, such as nanomaterials and ionic liquids [5,6]. The total frictional power losses within different sliding contact interfaces contributed 20% of the overall losses within automobile engines [7,8]. Consequently, an improvement in the engine tribological performance serves to improve efficiency and fuel economy, especially the tribological performance of the ring/liner interfaces [9].…”

Numerical prediction of the frictional losses in sliding bearings during start-stop operation

“…Additionally, the utilization of advanced friction models for mixed lubrication conditions should be evaluated for further improvements, e.g., Refs. [53,54].…”

Tribological enhancement of piston skirt conjunction using graphene-based coatings

“…This causes the shear real shear strength of asperities to be in the same range of provided coating in this study. 7,67 Nano-hardness…”

“…In total, nine normal loads are applied from 10 to 80 nN, typical for measuring the nano-frictional response of coatings with these AFM probes, such as can be observed in previous works. 7,44,45,51,66,67 The lower limit of this range is usually specified by sensitivity of the machine, not being able to control lower values. The higher limit is governed by the fact that plastic deformation should be avoided in frictional measurement.…”

“…In response to this, modern research surrounding engine and vehicle efficiency improvements focus on reducing these losses, such as the one presented in the work of Morris et al 6 in which they focus on the optimisation of the piston compression ring for high-performance race engines, and Bewsher et al 7 in which the cylinder liner is examined using AFM as a way to predict boundary friction at the piston ring to cylinder liner conjunction in more realistic manner, to better control the system’s efficiency. 7 Usman and Park. 8 proposed surface texturing as practical way to enhance the system’s frictional efficiency.…”