Validation Studies of a Detailed Kinetics Mechanism for Diesel and Gasoline Surrogate Fuels 2010-01-0545
Surrogate fuels used in simulations need to capture the physical, combustion and emission characteristics of the real diesel and gasoline fuels they represent. This requirement can result in complex surrogate fuels that are blends of components representing several chemical classes, such as normal-, cyclo- and iso-alkanes, alkenes and aromatics. With a palette of around 20 potential surrogate-fuel components we can identify a blend to represent the most important physical and chemical properties of a particular real fuel. However, a detailed chemical kinetics mechanism is required to use such a surrogate in a model of the in-cylinder combustion processes. The detailed mechanism must capture the relevant kinetic pathways for all of the surrogate-fuel components. To this end, we have assembled a large comprehensive kinetic mechanism that includes several thousands of species to represent the combustion behavior of a wide range of surrogate fuels for gasoline and diesel. The gasoline surrogate mechanism consists of 1833 species and 8764 reactions, and the diesel surrogate mechanism consists of 3809 species and 15678 reactions. Validation of the reaction mechanism is an important prerequisite for its successful application in engine simulations. For this purpose, laboratory experimental data reported in the literature for a variety of operating conditions and reactors have been reviewed and catalogued. CHEMKIN zero- and one-dimensional simulations were then performed for key surrogate fuel components. This paper reports representative comparisons of simulations to the experimental data for nine surrogate fuel components, namely n-heptane, n-hexadecane, iso-octane, heptamethyl nonane (HMN), toluene, 1-pentene, 1-hexene, methyl cyclohexane (MCH) and ethanol.
Experimental data employed in this work include: ignition times under both high-temperature and low-temperature conditions, from shock tubes and rapid compression machines; laminar flame speeds; and detailed species profiles from jet-stirred reactors, flow reactors, opposed-flow flames and burner-stabilized flames. Simulations have been performed using appropriate CHEMKIN reactor models, such as the Closed Homogeneous Batch reactor, the Perfectly Stirred reactor, Premixed Laminar Flame Speed calculator, Premixed Laminar Burner-Stabilized Flame reactor and the Opposed-flow Flame reactor. The operating conditions covered include a wide range of equivalence ratios, inlet temperatures and pressures. Overall, the CHEMKIN calculations show that the comprehensive mechanism captures the important features of the experimental data for this broad range of conditions and fuel components. Sources of some discrepancies in the comparisons, as well as experimental uncertainties, are discussed.