Friction and Wear Performance Evaluation of Bio-Lubricants and DLC Coatings on Cam/Tappet Interface of Internal Combustion Engines.

Rehan Zahid,Muhammad Abul Kalam,Riaz Ahmad Mufti,Jawad Aslam,Mahendra Varman,Muhammad Usman Bhutta,Muhammad Usman Abdullah,Haji Hassan Masjuki,Mian Ashfaq Ali,Khalid Akhtar

doi:10.3390/ma14237206

Rehan Zahid, Muhammad Abul Kalam + Show 8 more

Open Access

https://doi.org/10.3390/ma14237206

Copy DOI

Abstract

The environmental concerns associated with artificially formulated engine oils have forced a shift towards bio-based lubricants. The deposition of hard coatings on engine components and migrating to environmentally friendly green lubricants can help in this regard. Chemically modified forms of vegetable oils, with better low-temperature characteristics and enhanced thermo-oxidative stability, are suitable substitutes to conventional lubricant base oils. The research presented in this manuscript was undertaken to experimentally investigate the wear and friction performance of a possible future generation of an environmentally friendly bio-based lubricant as a potential replacement for conventional engine lubricants. In order to quantify the tribological benefits which can be gained by the deposition of DLC coatings, (an (a-C:H) hydrogenated DLC coating and an (a-C:H:W) tungsten-doped DLC coating) were applied on the cam/tappet interface of a direct acting valve train assembly of an internal combustion engine. The tribological correlation between DLC-coated engine components, lubricant base oils and lubricant additives have been thoroughly investigated in this study using actual engine operating conditions. Two additive-free base oils (polyalphaolefines (PAO) and chemically-modified palm oil (TMP)) and two multi-additive-containing lubricants were used in this investigation. Real-time drive torque was measured to determine the friction force, detailed post-test analysis was performed, which involved the use of a specialized jig to measure camlobe wear. An optical profilometer was used to measure the wear on the tappet, high-resolution scanning electron microscopy was employed to study the wear mechanism and energy-dispersive X-ray spectroscopy was performed on the tested samples to qualitatively access the degradation of the coating. When using additive-free TMP, a low friction coefficient was observed for the cam/tappet interface. The presence of additives further improved the friction characteristics of TMP, resulting in reduced average friction torque values. A tremendous enhancement in wear performance was recorded with a-C:H-coated parts and the coating was able to withstand the test conditions with little or no delamination.

Highlights

Automotive manufacturers, especially those using internal combustion (IC) engines as a power source, are under immense pressure from environmental agencies and government legislators
Due to ever-increasing environmental issues, health concerns, and the scarcity of raw materials require for the production of conventional lubricants, there is a need to look for alternate sources of lubricants which are environmentally sustainable and renewable and biodegradable [16]
The study was primarily performed to investigate the potential of bio-based lubricants as potential replacements for conventional engine oils to develop environment-friendly sustainable solutions and tribological performance enhancements of the current mating engine components by experimentally simulating real engine operating conditions

Summary

Introduction

Automotive manufacturers, especially those using internal combustion (IC) engines as a power source, are under immense pressure from environmental agencies and government legislators. The main reason behind these strict legislations for automotive OEMs is the extremely high carbon footprints associated with the operation of IC-engine-based vehicles. The only way for IC-engine-based vehicles to remain relevant in the automotive industry is to reduce the associated energy losses and environmental issues by working on various facets simultaneously. Losses due to friction and associated wear can be reduced to an appreciable extent by applying surface-protective coatings and surface treatments on interacting machine parts and components [1,2,3,4]. Lubricants, used in automotive engines for the purpose of reducing the friction and wear of components, are mostly derived from non-biodegradable and non-renewable sources, such as petroleum. These shortcomings are raised by the presence of unsaturated bonds in the structure of vegetable oils, leading to high reactivity with atmospheric oxygen, resulting in oxidative degradation [21]

Objectives

Methods

Results

Conclusion