An Approach for Formulating Surrogates for Gasoline with Application toward a Reduced Surrogate Mechanism for CFD Engine Modeling

Abstract

The numerical study of engine combustion requires the coupling of advanced computational fluid dynamics and accurate chemical kinetic models. This task becomes extremely challenging for real fuels. Gasoline is a mixture of hundreds of different hydrocarbons. Detailed modeling of its chemistry requires huge numbers of species and reactions and exceeds present numerical capabilities. Consequently, simpler surrogate mixtures are adopted to approximate the behavior of the real fuels. Large kinetic models for surrogates are developed to characterize their chemistry, but these models still contain thousands of species and reactions and can usually only be used for simulating simple homogeneous systems. For multidimensional engine applications, they must be reduced. In this work, we propose a methodology for the formulation of a gasoline surrogates based on the intrinsic qualities of the fuel chemical behavior. Using the proposed procedure, a candidate surrogate containing four components has been identified to match a real nonoxygenated gasoline. Starting from this formulation, the LLNL (Lawrence Livermore National Laboratory) detailed kinetic mechanism has been reduced while maintaining its ability to reproduce targets of ignition delay times and flame speeds over a wide range of operating conditions. The reduction was carried by the construction of a preliminary version of a skeletal mechanism using the Computer Assisted Reduction Mechanism (CARM) code under a set of targeted conditions. Further reduction is made with a search algorithm that sequentially tests the importance of each species, leading to a much smaller mechanism. Finally, the resulting reduced mechanism has been validated against the detailed mechanism and available experimental data.

A comprehensive combustion chemistry study of 2,5-dimethylhexane

“…The measured reactivity of the various octane isomers is similar at temperatures above 900 K, but differences are observed in the NTC region. Mehl et al [44,45] have proposed that the ignition quality of a gasoline fuel, quantified as antiknock index, can be closely correlated with its ST ignition delay time under specific conditions (e.g., 825 K and 25 atm). Figure 14 demonstrates that such a correlation exists for various octane isomers using experimental and simulated ignition delay times near 20 atm and 835 K. The logarithm of experimental shock tube ignition delay data for n-octane, 2-methylheptane, 3-methylheptane, and 2,5-dimethylhexane increases as the RON of the fuel increases.…”

Experimental and surrogate modeling study of gasoline ignition in a rapid compression machine

“…Lenhert et al [6] conducted studies in a pressurized flow reactor using a four-component surrogate consisting of n-heptane, iso-octane, toluene, and 1-pentene. In addition, there have been efforts towards the development and validation of detailed kinetic models for gasoline combustion, notably the studies of [7][8][9][10][11][12][13]. In particular, the mechanism of Mehl et al [12,13] has been validated against the experimental data of [3,5,14], showing a good agreement.…”

Analysis of exergy loss of gasoline surrogate combustion process based on detailed chemical kinetics

“…The components of gasoline surrogates are n-heptane (16%), iso-octane (57%), toluene (23%), and 2-pentene (4%). The four-component surrogate has been proved to be well matched with the fuel components of alkanes, alkenes, and aromatics and its distillation curve, H/C ratio, RON and MON values, which are corresponding to a gasoline fuel labeled RD387 [22] which has been verified by many researchers [23][24][25][26].…”