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Evaluation of Water and EGR Effects on Combustion Characteristics of GDI Engines Using a Chemical Kinetics Approach

NAIS-Claudio Forte
University of Bologna-Giulio Cazzoli, Gian Marco Bianchi, Stefania Falfari, Matteo Ricci
  • Technical Paper
  • 2019-24-0019
Published 2019-09-09 by SAE International in United States
The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the risk of detonation, the use of dilution with the products of combustion (EGR) is an established practice that has recently improved with the use of water vapor obtained via direct or indirect injection.The application and optimization of these strategies cannot ignore the knowledge of physical quantities characterizing the combustion such as the laminar flame speed and the ignition delay, both are intrinsic property of the fuel and are function of the mixture composition (mixture fraction and dilution) and of its thermodynamic conditions.The experimental measurements of the laminar flame speed and the ignition delay available in literature, rarely report the effects of dilution by EGR or water vapor. To overcome the limitations of the experimentation is possible to predict the value of the ignition delay using numerical models based on chemical kinetics theory. The increased performance of computing systems…
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A Chemical-Kinetic Approach to the Definition of the Laminar Flame Speed for the Simulation of the Combustion of Spark-Ignition Engines

NAIS-Claudio Forte
University of Bologna-Giulio Cazzoli, Gian Marco Bianchi, Stefania Falfari
Published 2017-09-04 by SAE International in United States
The laminar burning speed is an important intrinsic property of an air-fuel mixture determining key combustion characteristics such as turbulent flame propagation. It is a function of the mixture composition (mixture fraction and residual gas mass fraction) and of the thermodynamic conditions.Experimental measurements of Laminar Flame Speeds (LFS) are common in literature, but initial pressure and temperature are limited to low values due to the test conditions: typical pressure values for LFS detection are lower than 25 bar, and temperature rarely exceeds 550 K.Actual trends in spark ignition engines are to increase specific power output by downsizing and supercharging, thus the flame front involves even more higher pressure and temperature since the beginning of combustion. The most widespread models used to extrapolate the experimental data to the engine like conditions are derived from that of Metghalchi and Keck, but they often fail to correctly predict LFS values outside the experimental space.Thanks to the development of accurate chemical kinetic models together with the increase of computer performance, it is possible to numerically predict the laminar flame…
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