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Fuel effects in final phase combustion

Objective

The objective of this research project is to carry out a detailed analysis of the effect of liquid fuels on the combustion in the final phase of the combustion cycle, to propose ways for improvement and to evaluate the potential for an improved energy efficiency and for a reduction of unburned hydrocarbon emissions.
In a first phase the required experimental facilities were developed and set up. A square piston engine with full optical access by four windows was redesigned to accept an additional window in the cylinder head. Furthermore mechanical and electronical injection systems were installed on the engine to allow for direct comparisons of engine operation with gaseous or liquid fuels, respectively.

Advanced diagnostic tools, based on optical principles, were adapted for nonintrusive investigation of the flow field, mixing and combustion processes. Laser and Phase Doppler anemometry were used to measure time resolved flow field and particle data. Two different Particle Image Velocimetry systems were set up, one using a single shot and the other a high speed filming technique. Both systems have special hard-and software configurations offering high spatial and temporal resolution.

Measurements of fuel distribution and fuel air mixing in the square piston engine were accomplished by laser induced fluorescence techniques using optimized tracer materials. A fast IR-absorption technique was used to measure unburned hydrocarbon emissions from crevice volumes and wall layers.

Engine measurements were performed for a gaseous and liquid fuel, monitoring engine efficiency and UHC emissions. Results are compared to numerical prediction using an advanced CFD code with a combustion model.

For numerical simulation a 3D cold flow code was adapted to the combustion chamber geometry of the square piston engine and to inflow data as initial conditons for the computer code. Special submodels for mixing and combustion were developed and included. The complete verified 3D CFD code is now available for detailed investigations on realistic engine geometries.

During the first two phases, theoretical and experimental research carried out in parallel lead to a substantially improved understanding of cold flow, mixing phenomena and combustion processes in spark ignition engines when operated on liquid fuels.
The project is based on the results of the preceding programme (contract EN3E-0056-D). Improved Otto-cycle by enhancing the final phase of combustion. It extends the new insights gained on gaseous mixtures to the case of liquid fuels, which is more close to practical technical utilization.

Work will be focused on mixing processes and time dependent effects controlling engine combustion (local strain, rate of change in pressure and volume). These will be assessed theoretically and experimentally by our new methods for cycle and crank angle resolved length and time scale characterization of turbulent engine combustion and by the BML flamelet model.

The project will continue basic R&D on non-stationary turbulent combustion at high pressures by developing multidimensional techniques for numerical modelling, non-intrusive diagnostics and specific experimental setups for single cycle analysis.

It is planned to maintain and expand the scientific and technological lead in fundamental combustion processes in engines achieved in the transnational european cooperation between industrial and other outstanding research facilities. A strong link has been established with the nationally funded German TECFLAM programme.

Coordinator

Daimler-Benz AG
Address
Epplestraße 225
70567 Stuttgart
Germany

Participants (7)

AACHEN UNIVERSITY OF TECHNOLOGY
Germany
Address
Templergraben 64
52056 Aachen
Centre National de la Recherche Scientifique (CNRS)
France
Address

86034 Poitiers
Imperial College of Science, Technology and Medicine
United Kingdom
Address

SW7 2BX London
Institut für Physikalische Elektronik
Germany
Address

7000 Stuttgart
Institut für Technische Verbrennung
Germany
Address

7000 Stuttgart
RUPRECHT-KARLS-UNIVERSITAET HEIDELBERG
Germany
Address
Albert-überle-strasse 3-5
69120 Heidelberg
University of Cambridge
United Kingdom
Address
Trumpington Street
CB2 1PZ Cambridge