Domestic research projects


Research projects (co)funded by the Slovenian Research Agency.


  • Member of University of Ljubljana: UL Faculty of Mechanical Engineering
  • Project code: Z2-1868
  • Project title: Novel design of EHL contacts by employing solid-liquid interface phenomena
  • Period: 01.07.2019 - 30.06.2021
  • Range on year: 0,5 FTE
  • Head: doc. dr. Marko Polajnar
  • Research activity: Engineering sciences and technologies 
  • Research Organisation: Link
  • Researchers: Link
  • Citations for bibliographic records: Link

The project focuses on the design of novel and innovative elasto-hydrodynamic (EHD) contacts that provide remarkably low energy losses due to significantly reduced friction at the solid-liquid interfaces in fully-realistic lubrication conditions.

Namely, in the last years, we succeeded to make one of the major lubrication step-changes and present an immensely reduced friction due to a completely new lubrication phenomena at the macro-scale EHD contacts; i.e. the lubricant slip at the surface wall. We were the first to report on almost 50 % reduction of friction in EHL contacts – by changing the wetting and polar surface energy of solid surfaces and tailoring them for a lubricants surface tension. This paramount achievement gained great attention in scientific and industrial community. However, this breath-taking phenomenon has only been confirmed in pure base oils, while for the success in industrial and automotive applications, it has to be confirmed in realistic oils, namely fully formulated oils. Due to additives competition and even stronger “passivation” of the surfaces, the outcome of this project is very promising and may completely change the future additive technology and result in an immensely reduced energy consumption due to friction, which in total accounts for 25 % of all energy produced world-wide.

In this project, we will innovatively design extremely-efficient EHD contacts, with taking into an account interactions and phenomena at the solid-liquid interface that significantly effect EHD friction. To achieve this, low-surface energy, slip-inducing DLC coatings will be combined with formulated-oils by employing both, the coatings and oils that are commonly used in automotive and industrial applications. To provide proof-of-concept for this project, we already possess supporting results with some DLC coatings and some formulated oils, but this has to be systematically and scientifically confirmed in a broad range of contact conditions and materials used. Therefore, for actual industrial implementation, this concept should be proven for several commonly used formulated oils, DLC and other surfaces, together with complete and in-depth understanding of the effect of all the additives in formulation on solid-liquid interactions. Proposed project will thus address a paramount scientific goal: to find fundamental understanding and synergistic effect of additives and DLC coatings, on lubricant-DLC interactions to achieve solid-liquid slip that will provide significant EHD friction reduction in real-engineering contacts.




The phases of the project and their realization:

WP1: Selection, preparation and characterization of the oils

Task 1.1: Selection of base oils

This task has been realized.

Task 1.2: Selection of additives and preparation of oils oil-additive mixtures

This task has been realized.

Task 1.3: Selection of fully-formulated oil

This task has been realized.

Task 1.4: Characterization of oils

This task is in realization (estimated realization is 50 %).       


WP2: Selection and preparation of materials

Task 2.1: Selection of reference material and preparation of samples

This task has been realized.

Task 2.2: Selection and deposition of DLC coatings

This task has been realized.


WP3: Initial characterization of interface properties                         

Task 3.1: Surface tension experiments

This task has been realized.

Task 3.2: Surface energy experiments

This task has been realized.  

Task 3.3: Wetting experiments

This task is in realization (estimated realization is 35 %).       


WP4: Thermal tests

Task 4.1: Experiments at 25 °C

This task has been realized.

Task 4.2: Experiments at 100 °C

This task has been realized.


WP5: Tribological tests

Task 5.1: Definition of testing conditions

This task has been realized.

Task 5.2: Tribological experiments

This task is in realization (estimated realization is 50 %).       

Task 5.3: Tribometric analyses

This task is in realization (estimated realization is 40 %).       


WP6: Confirmation of boundary films and final characterization of interface properties                                                             

Task 6.1: Confirmation of adsorbed layers

This task has not started yet according to Gantt chart.

Task 6.2: Surface energy and wetting experiments after tribological and thermal tests

This task has not started yet according to Gantt chart. 


WP7: EHD friction modelling for thermal effect

This task is in realization (estimated realization is 10 %).       


WP8: Mechanism of EHD friction reduction and optimal solid-liquid interface design

Task 8.1: Revealing the contribution of solid-liquid slip and thermal effect for EHD friction reduction

This task has not started yet according to Gantt chart. 

Task 8.2: Revealing optimal solid-liquid interface design

This task has not started yet according to Gantt chart. 


WP9: Management

This WP is running all the time.


WP10: Dissemination and exploitation

The tasks within this WP are running in terms of preparation of original scientific paper, while the presentation of results on international conferences is despited of accepted abstracts at this moment due to health issues impossible.