Kinetic Modeling Study of the Effect of Iron on Ignition and Combustion of n-Heptane in Counter-flow Diffusion Flames

Abstract

A kinetic modeling study of the effect of iron on the ignition and combustion characteristics of diesel, modeled as n-heptane, in compression ignition engines was carried out using CHEMKIN PRO. The ignition was simulated using the SENKIN code, and combustion was modeled using the OPPDIF code. The kinetic models incorporated n-heptane mechanisms involving 159 species and 1540 reactions and iron reaction mechanisms of 7 iron species and 46 reactions. It was found that small amounts of iron in the fuel significantly reduced the ignition delay time. The ignition delay time decreased with an increasing iron concentration. A reaction pathway analysis showed that the ignition was promoted as a result of an early injection of the OH radicals. It was also showed that the addition of iron increased the peak flame temperature of n-heptane in the counter-flow diffusion flame and reduced the maximum mole fractions of H and O in the peak flame region as a result of the catalytic recombination cycles involving FeO, Fe­(OH)2, and FeOH. The reaction rates of H + O2 ⇔ O + OH and CO + OH ⇔ CO2 + H in the peak flame region were found to increase, which is considered to be responsible for the increased peak flame temperature.

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“…The observed disagreement in the case of 3-hexene could result from missing reaction pathways involving HO2 or H2O2 in the ferrocene decomposition mechanism. The hereby developed mechanism was also tested in conditions relevant to a previous study [15], where atomic iron was added to nheptane/air mixtures. The model predicts a reduction of the ignition delay when iron atoms are added, as suggested in [15].…”

“…The hereby developed mechanism was also tested in conditions relevant to a previous study [15], where atomic iron was added to nheptane/air mixtures. The model predicts a reduction of the ignition delay when iron atoms are added, as suggested in [15]. This could be a consequence of the highest extent of Low Temperature reactivity in the case of n-heptane, in comparison with isooctane and 3-hexene.…”

“…These experimental results were simulated using the model built by Linteris et al [10] with reasonable success. Recently, Zhu et al [15] studied the kinetic effect of gaseous iron atoms on the ignition and combustion of n-heptane with a detailed model based on the work by Linteris et al [10], at T = 800K and p = 50 bar. Their work was a modeling effort, with no experimental data available to evaluate the effect of iron on the ignition delay of heptane/O2/inert mixtures, and predicted a reduction of the ignition delay time when a concentration of 100 ppm of gaseous iron atom is added.…”