Fuel composition

Real Driving Emissions (RDE) and soot formation

Short description

In addition to the reduction of greenhouse gas emissions, air pollution control is a key mobility issue. From the EURO 6b exhaust emission standard, the limit value for the number of particles is 6×1011 particles/ km. Modern gasoline engines are therefore equipped with gasoline particulate filters as standard in order to comply with current and future limits even under difficult boundary conditions, such as in the RDE test (Real Driving Emissions). Another approach is to formulate the fuel in such a way that as few particulates as possible are produced during operation. To design such fuels, a method for predicting soot formation is needed.

The state of the art in predicting soot emissions are empirically determined indices based on selected physicochemical material values of the fuels (JAMA PN Index, Honda PMI, MW PN Index, …).

The current methods for characterizing soot formation tendencies have the following drawbacks:

  • The studies were conducted on individual engines and manufacturers. This means that the results are not universally applicable to other engine variants.
  • Indirect correlations were established between individual fuel properties and emission behavior. The totality of a substance’s properties cannot be captured by these methods.
  • The exact processes of soot formation during combustion, in particular possible interactions between the individual fuel components, are not taken into account in the correlation equations.

In summary, no direct analytical method with suitable robustness for non-scientific laboratory use currently exists.

In the fundamental field of combustion research, the use of the Yield Sooting Index (YSI) is an established method for evaluating the sooting potential of fuels. The YSI is an index to be determined experimentally that encompasses the entire sequence of fuel/air mixing, combustion, and pollutant formation. To determine YSI, the test fuel is doped in a methane flame and the maximum soot volume fraction is measured using optical measurement techniques.

In one study, the YSI measurements were correlated with exhaust emissions, so the potential of this index for predicting soot RDE should be investigated more deeply.

Aims of the project

The objective of the research project is to develop a novel method for predicting soot emission performance in RDE cycles. In addition to confirming the suitability of the YSI as an evaluation criterion for Real Driving Emissions, the correlation of a novel, simplified laboratory test method (coflow burner) with RDE investigations will be established. This is to work out the applicability of the method for simpler and faster investigations. This methodology is based on the evaluation of spectral intensities as well as flicker frequencies of the doped methane flame. The method could reduce the testing effort many times over and thus lower the costs for the automotive industry as well as the fuel producing and developing industry.

Works tasks OWI

  • Selection of 20 to 30 different fuels or fuel mixtures for tests with a coflow burner and an engine test bench.
  • Design and installation of the test setup as well as test execution with the coflow burner for the determination of the Yield Sooting Index (YSI).
  • Development and evaluation of a robust methodology for estimating the soot formation potential. It should reduce the effort of the complex, established, optical measurements of the soot content and allow the use of the test methodology in simple laboratories (fuel manufacturers, engine manufacturers, …).

Research institutions

  • OWI Science for Fuels gGmbH
  • Institute of Internal Combustion Engines at the Karlsruhe Institute of Technology

Project funding

Forschungsvereinigung Verbrennungskraftmaschinen e.V. (FVV)

The letters FVV and dots arranged in a semicircle around the last V.

Project duration

09/ 2021 bis 08/ 2023


M. Sc. Sergej Warkentin
Tel.: 02407/ 9518-134