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Analysis of Cyclic Variability of Heat Release for High-EGR GDI Engine Operation with Observations on Implications for Effective Control
Journal Article
2013-01-0270
ISSN: 1946-3936, e-ISSN: 1946-3944
Sector:
Topic:
Citation:
Kaul, B., Wagner, R., and Green, J., "Analysis of Cyclic Variability of Heat Release for High-EGR GDI Engine Operation with Observations on Implications for Effective Control," SAE Int. J. Engines 6(1):132-141, 2013, https://doi.org/10.4271/2013-01-0270.
Language:
English
Abstract:
Operation of spark-ignition (SI) engines with high levels of
charge dilution through exhaust gas recirculation (EGR) achieves
significant engine efficiency gains while maintaining
stoichiometric operation for compatibility with three-way
catalysts. Dilution levels, however, are limited by cyclic
variability - including significant numbers of misfires - that
becomes more pronounced with increasing dilution. This variability
has been shown to have both stochastic and deterministic
components. Stochastic effects include turbulence, mixing
variations, and the like, while the deterministic effect is
primarily due to the nonlinear dependence of flame propagation
rates and ignition characteristics on the charge composition, which
is influenced by the composition of residual gases from prior
cycles.
The presence of determinism implies that an increased
understanding of the dynamics of such systems could lead to
effective control approaches that allow operation near the edge of
stability, effectively extending the dilution limit. This nonlinear
dependence has been characterized previously for homogeneous
charge, port-fuel-injected (PFI) SI engines operating fuel-lean as
well as with inert diluents such as bottled N₂ gas. In this paper,
cyclic dispersion in a modern boosted gasoline direct injection
(GDI) engine using a cooled external EGR loop is examined, and the
potential for improvement with effective control is evaluated
through the use of symbol sequence statistics and other techniques
from chaos theory. Observations related to the potential
implications of these results for control approaches that could
effectively enable engine operation at the edge of combustion
stability are noted.