ef6b01406_si_001.txt (52.14 kB)
Investigation of Iso-octane Ignition and Validation of a Multizone Modeling Method in an Ignition Quality Tester
dataset
posted on 2016-08-18, 00:00 authored by Eric M. Osecky, Gregory
E. Bogin, Stephanie M. Villano, Matthew A. Ratcliff, Jon Luecke, Bradley T. Zigler, Anthony M. DeanAn ignition quality
tester was used to characterize the autoignition
delay times of iso-octane. The experimental data were characterized
between temperatures of 653 and 996 K, pressures of 1.0 and 1.5 MPa,
and global equivalence ratios of 0.7 and 1.05. A clear negative temperature
coefficient behavior was seen at both pressures in the experimental
data. These data were used to characterize the effectiveness of three
modeling methods: a single-zone homogeneous batch reactor, a multizone
engine model, and a three-dimensional computational fluid dynamics
(CFD) model. A detailed 874 species iso-octane ignition mechanism
(Mehl, M.; Curran, H. J.; Pitz, W. J.; Westbrook, C. K. Chemical kinetic
modeling of component mixtures relevant to gasoline. Proceedings of the European Combustion Meeting; Vienna, Austria, April 14–17, 2009) was reduced to 89 species for use in these models, and the predictions
of the reduced mechanism were consistent with ignition delay times
predicted by the detailed chemical mechanism across a broad range
of temperatures, pressures, and equivalence ratios. The CFD model
was also run without chemistry to characterize the extent of mixing
of fuel and air in the chamber. The calculations predicted that the
main part of the combustion chamber was fairly well-mixed at longer
times (> ∼30 ms), suggesting that the simpler models
might be applicable in this quasi-homogeneous region. The multizone
predictions, where the combustion chamber was divided into 20 zones
of temperature and equivalence ratio, were quite close to the coupled
CFD–kinetics results, but the calculation time was ∼11
times faster than the coupled CFD–kinetics model. Although
the coupled CFD–kinetics model captured the observed negative
temperature coefficient behavior and pressure dependence, discrepancies
remain between the predictions and the observed ignition time delays,
suggesting improvements are still needed in the kinetic mechanism
and/or the CFD model. This approach suggests a combined modeling approach,
wherein the CFD calculations (without chemistry) can be used to examine
the sensitivity of various model inputs to in-cylinder temperature
and equivalence ratios. These values can be used as inputs to the
multizone model to examine the impact on ignition delay. The speed
of the multizone model also makes it feasible to quickly test more
detailed kinetic mechanisms for comparison to experimental data and
sensitivity analysis.