Oxidation of Methane/n-Heptane Mixtures in a High-Pressure Flow Reactor

To evaluate the use of diesel as a pilot fuel in natural gas combustion in two-stroke maritime engines, research on high-pressure oxidation of methane/n-heptane mixtures is of interest. In this study, laminar flow reactor experiments were conducted at pressures of 21 and 100 bar, temperatures in the range 450–900 K, and under stoichiometric and fuel-lean conditions. For all conditions, the n-heptane conversion starts below 600 K. A pronounced negative temperature coefficient region was observed at 21 bar. The n-heptane was depleted at all conditions before reaching 900 K. Methane oxidation was initiated once n-heptane was consumed. Compared to the oxidation of pure n-heptane and NH₃/n-heptane mixtures, the presence of methane promoted n-heptane oxidation in the full temperature range. The model from Zhang et al. provided overall a good agreement with the experimental data. However, the low-temperature conversion of n-heptane at 21 bar and stoichiometric conditions is underpredicted, possibly because some chemical coupling between n-heptane and methane is missing in the model.