Reduction and validation of a chemical kinetic mechanism including necessity analysis and investigation of CH4/C3H8 oxidation at pressures up to 120 bar using a rapid compression machine

Abstract

Cost efficiency and the ecological footprint are becoming more important in the locomotive and maritime business. To overcome these needs, manufacturers are forced to develop highly efficient internal combustion engines suitable for alternative fuel, such as biogas. In the development process of a new engine, simulation tools offer economic benefits compared to engine bench tests. To manage the trade-off between enhanced efficiency by increasing the compression ratio and knocking combustion, a reaction mechanism is necessary to capture the ignition behavior of various fuel blends and conditions during the simulation. Since previous studies only investigated methane/propane oxidation at pressures up to 50bar, experimental investigations have been conducted to include pressure regimes, which are similar to those of a knocking combustion. Therefore, rapid compression machine (RCM) experiments were performed using methane/propane mixtures at lean conditions with air-to-fuel ratios of 1.5, 1.7 and 1.9. Furthermore a range of compression temperatures from 800 to 1000K at pressures of 80, 100 and 120bar were conducted. The experiments for mixtures containing 30mol% propane showed a negative temperature coefficient (NTC) behavior, which is consistent with experiments for other alkane fuels presented in the literature. In addition, the experimental results were compared with the recently published detailed chemical mechanism Aramco Mech 1.3. This mechanism was used to simulate the ignition delay times with consideration of the facility effects of the rapid compression machine. The simulation results, based on a zero-dimensional homogeneous batch reactor showed good agreement with the measurements over a wide range of the investigated conditions. In a further step the detailed mechanism has been reduced by necessity analysis in order to minimize computational efforts for future combined CFD (Computational Fluid Dynamics) and kinetic simulations. The results of this novel work show the first set of high pressure screening experiments in a RCM for CH4/C3H8 mixtures combined with a systematic method for mechanism reduction.