Controlled Auto-Ignition: Combustion Rate Shaping by Mixture Stratification

Authors

Prof. Dr.-Ing. S. Pischinger, Dipl.-Ing. K. G. Stapf, Dipl.-Ing. D. Seebach, Dipl.-Ing. C. Bücker, RWTH Aachen; Priv. Doz. Dr.-Ing. P. Adomeit, Dr.-Ing. J. Ewald, FEV Motorentechnik GmbH, Aachen

Year

2008

Print Info

Fortschritt-Berichte VDI, Reihe 12, Nr. 672

Summary

The customer requirement for increased mobility and tougher regulatory framework are the biggest challenge for research and development in combustion engines in the future. The main focus is to decrease fuel consumption and emissions at the same time. Controlled auto ignition is a promising approach to achieve both targets in future gasoline combustion engines. Due to its acoustic behaviour, this combustion process is only applicable in part load conditions and is limited to high load and high engine speed. Additionally, a more complex control system is necessary for this combustion process.

In this paper, different possibilities to regulate the stratification in the cylinder and the combustion rate of the CAI process are evaluated. Therefore, different valve timing strategies as well as the injection timing are investigated. The resulting stratification in the cylinder is quantified with numerical characteristic numbers and correlated to the burn rate from the experimental test bench investigation. Therewith, the local distribution of fuel, air and residual gas is directly correlated to the combustion start and duration. A high stratification of fuel results in a more advanced and faster combustion. Contrary to this is a high stratification of residual gas, which results in more retarded and slower combustion.

Additionally, the use of alternative fuel E85 is investigated. In test bench investigations, E85 shows the potential to increase the operation area of CAI. As a first step, a numerical simulation of the ignition delay of ethanol and iso-Octane is compared, to analyse this potential. Knowledge of the in-cylinder temperature together with the ignition delay supports the measurement from the test bench investigation.

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