Intermediate temperature heat release in an HCCI engine fueled by ethanol/n-heptane mixtures: An experimental and modeling study
Pitz, William J.
Dibble, Robert W.
KAUST DepartmentClean Combustion Research Center
Physical Sciences and Engineering (PSE) Division
Chemical and Biological Engineering Program
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AbstractThis study examines intermediate temperature heat release (ITHR) in homogeneous charge compression ignition (HCCI) engines using blends of ethanol and n-heptane. Experiments were performed over the range of 0-50% n-heptane liquid volume fractions, at equivalence ratios 0.4 and 0.5, and intake pressures from 1.4bar to 2.2bar. ITHR was induced in the mixtures containing predominantly ethanol through the addition of small amounts of n-heptane. After a critical threshold, additional n-heptane content yielded low temperature heat release (LTHR). A method for quantifying the amount of heat released during ITHR was developed by examining the second derivative of heat release, and this method was then used to identify trends in the engine data. The combustion process inside the engine was modeled using a single-zone HCCI model, and good qualitative agreement of pre-ignition pressure rise and heat release rate was found between experimental and modeling results using a detailed n-heptane/ethanol chemical kinetic model. The simulation results were used to identify the dominant reaction pathways contributing to ITHR, as well as to verify the chemical basis behind the quantification of the amount of ITHR in the experimental analysis. The dominant reaction pathways contributing to ITHR were found to be H-atom abstraction from n-heptane by OH and the addition of fuel radicals to O2. © 2013 The Combustion Institute.
SponsorsResearchers at the King Abdullah University of Science and Technology acknowledge funding from the Clean Combustion Research Center and from Saudi Aramco under the FUELCOM program. The work at LLNL was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
JournalCombustion and Flame