Interaction of fuel and lubricating oil – Fuel in oil

Fuel post injection is an efficient measure for the regeneration of exhaust gas treatment in diesel vehicles. However, it can lead to fuel entering the lubricating oil and thus to undesirable oil dilution. This results in the lubricating effect of the oil being reduced, which in turn can seriously damage the engine. In the FVV research cluster "Fuel in Oil", oil dilution was investigated and quantified both experimentally and numerically. The investigations focused on the following aspects: the processes of fuel entering lubricating oil wall coatings, the transport of oil and fuel through piston rings and the blow-by in the oil sump as well as the change of the fuel-oil composition in the crankcase. In order to bring together all findings relating to the different processes and to be able to apply these, the detailed results were fed into a simulation tool which, aided by simplified physical models, adequately describes oil dilution precisely.

» The FVV research cluster ›Fuel in Oil‹ provides groundbreaking insights into oil dilution in combustion engines. The new simulation tool makes an important contribution to improving the design of diesel engines. «
Dr.-Ing. Marcus Gohl (APL Automobil-Prüftechnik Landau GmbH)


Oil dilution occurs in combustion engines because of fuels entering the lubricating oil. This is an extremely undesirable effect. For this reason, it is essential to have a detailed understanding of the connections that can lead to oil dilution. To this end simulation tools should be developed in order to quantitatively measure in advance oil dilution in early engine development phases and to realistically appraise the influence of different parameters like engine and injector geometry, fuel injection strategy and load spectrum on oil dilution.


This complex issue was divided into the sub-areas combustion chamber, transport, oil sump and whole simulation. Particular attention was given to the fuel drops/spray interaction with the lubricating oil wall coatings or film. On the basis of experiments and numerical simulations a routine for modelling the drop-film interaction was developed. It formed the basis for 3D computational fluid (CFD) simulation of fuel entry in the combustion chamber. Through the measurement of lubricating film concentration and height in the combustion chamber, this fuel entry could be recorded. A further focus was the exploration of fuel and oil transport through piston rings from the combustion chamber to the crankcase. Measurements of the lubricating film concentration and thickness at different positions on the cylinder wall of the engine as well as multi-body system calculations and 3D CFD simulations served to make this possible. To investigate the phenomena in the oil sump, fuel entry and discharge were determined through online measurements of the fuel concentration in the oil sump and the crankcase ventilation. The calculation of processes in the crankcase was based on 3D CFD simulations. Based on the simulation results of the sub-areas, a model-based simulation method for calculating the total oil dilution was created.


The project developed methods for describing the phenomenon of diesel-engine oil dilution. This includes the description of injection spray lubricating film interaction as well as the interaction of fuel drops and the lubricating film. Fuel and oil transport through the piston rings was calculated using piston ring dynamic simulations as well as detailed CFD simulations. It is thus now possible to observe the mass transport (blow-by), the piston ring dynamic, the ring land pressure and the friction (liquid and mixed friction). Aided by CFD simulations, flow in the crank chamber can be illustrated, including drop movement and fuel evaporation. For the metrological investigation of oil dilution, a method for mass spectrometry analysis of fuel concentrate in the oil sump is available. All findings were fed into the simulation tool which, with the help of simplified physical models, depicts the individual phenomena of oil dilution in the combustion chamber, piston ring package and crank chamber. Building on the findings of the fuel-lubricating oil interaction in diesel engines, the FVV has initiated a follow-up project that has the goal of identifying and quantifying possible oil sources in the combustion chamber of direct-injection combustion engines.


Fuel in Oil - General Overview | Investigation of the fuel lubrication oil interaction on oil dilution during particulate filter/ Nox storage catalyst regeneration | Project No. 1084

Fuel in Oil II - Sources of Oil in Combustion Chamber of SI Engines | Quantification of increased oil concentrations of piston and cylinder-liner, the associated oil-discharge and its influence on the SI engine combustion | Project No. 1225



Public & FVV Funding

3.200.000,00 EUR

Time Period
2011-10-01 to 2015-02-28 Part I
2016-04-01 to 2018-09-30 Part II

Research Association for Combustion Engines (FVV) eV

Lyoner Strasse 18
60528 Frankfurt am Main

German Federation of Industrial Research Associations (AiF) e. V.

Bayenthalgürtel 23
50968 Cologne

German Research Foundation (DFG) eV

Kennedyallee 40
53175 Bonn

Federal Ministry for Economic Affairs and Energy (BMWi)

Scharnhorststrasse 34-37
10115 Berlin


Dr.-Ing. Marcus Gohl
APL Automobil-Prüftechnik Landau GmbH

RTD Performer

1 | Institute for Combustion Engines (vka) - RWTH Aachen University | I + II

Head of research:
Univ.-Prof. Dr.-Ing. Stefan Pischinger

2 | Institut für Analytische Messtechnik Hamburg - IAM-Hamburg e.V. | II

Head of research:
Prof. Dr.-Ing. Gerhard Matz

3 | Institut für Messtechnik (UMT) - Technische Universität Hamburg | I

Head of research:
Prof. Dr.-Ing. Gerhard Matz

4 | Institute for Powertrain and Automotive Technology (iaf) - University of Kassel | I

Head of research:
Prof. Dr.-Ing. Adrian Rienäcker

5 | Institute of Machine Design, Chair of Machine Elements and Tribology (LMT) - Otto-von-Guericke University Magdeburg (OVGU) | I

Head of research:
Prof. Dr.-Ing. habil. D. Bartel

6 | Institute of Internal Combustion Engines (LVK), Department of Mechanical Engineering - Technical University of Munich (TUM) | I

Head of research:
Prof. Dr.-Ing. Georg Wachtmeister

Technical University of Munich (TUM)

Institute of Internal Combustion Engines (LVK)

Arcisstrasse 21
80333 Garching

University of Kassel

Institute for Powertrain and Automotive Technology (iaf)/Department of Machine Elements and Engineering Design (MT)

Mönchebergstrasse 7
34125 Kassel

University of Stuttgart

Institute of Aerospace Thermodynamics

Pfaffenwaldring 31
70569 Stuttgart

RWTH Aachen University

Chair of Thermodynamics of Mobile Energy Conversion Systems (tme)

Forckenbeckstrasse 4
52074 Aachen

Hamburg University of Technology (TUHH)

Institute of Measurement Technology

Harburger Schloßstr. 20
21079 Hamburg

Hamburg University of Technology (TUHH)

Institut für Analytische Messtechnik Hamburg - IAM-Hamburg e.V.

Peutestraße 53A
20539 Hamburg

Otto von Guericke University Magdeburg (OVGU)

Institut für Maschinenkonstruktion (IMK)/Chair of Machine Elements and Tribology (LMT)

Universitätsplatz 2
39106 Magdeburg

Project Management

Ralf Thee

+49 (0) 69 6603 1349
+49 (0) 69 6603 2349


Lyoner Strasse 18
60528 Frankfurt am Main
T +49 69 6603 1345