Kinetic Effects of n -Heptane Addition on Low and High Temperature Oxidation of Methane in a Jet-Stirred Reactor

The kinetic effects of n-heptane addition on low and high temperature oxidations of methane were experimentally investigated over a range of temperatures from 800 to 1200 K, at the equivalence ratio of 0.5 in an atmospheric jet-stirred reactor (JSR). The n-heptane content in the methane/n-heptane mixture was varied between 0 and 100%. The mole fractions of CH₄, nC₇H₁₆, O₂, CO, CO₂, CH₂O, and C₂H₄ were determined respectively in the present experiments, and the NUI mechanism was employed to perform the numerical studies under the same conditions by using the perfectly stirred reactor model. The results show that the onset temperature of the oxidation of methane decreases with the increase of the n-heptane content in methane/n-heptane mixture significantly, and that even a small amount of n-heptane can cause an obvious shift of high temperature oxidation of methane to lower temperature. According to the reaction path analysis, the initial kinetic enhancement reactions of n-heptane in the oxidation of methane are identified. It is shown that the kinetic enhancement of methane oxidation by n-heptane addition increases at low temperature. The sensitivity analysis of the mole fraction of methane indicate that the methane oxidation is mainly sensitive to those relevant reactions involving OH, HO₂, and other radicals produced by n-heptane at low temperature, and especially at low n-heptane content through the radical pool enrichment. The present study indicates the potential of n-heptane-assisted methane combustion in diesel and marine engine applications.