Experimental Investigation and Benchmark Study of Oxidation of Methane–Propane–n-Heptane Mixtures at Pressures up to 100 bar

Abstract

Dual fuel combustion exhibits a high degree of complexity due to the presence of different fuels like diesel and natural gas in initially different physical states and a spatially strongly varying mixing ratio. Optimizing this combustion process on an engine test bench is costly and time consuming. Cost reduction can be achieved by utilizing simulation tools. Although these tools cannot replace the application of test benches completely, the total development costs can be reduced by an educated combination of simulations and experiments. A suitable model for describing the reactions taking place in the combustion chamber is required to correctly reproduce the dual fuel combustion process. This is why in the presented study, four different reaction mechanisms are benchmarked to shock tube (ST) and rapid compression machine (RCM) measurements of ignition delay times (IDTs) at pressures between 60 and 100 bar and temperatures between 671 and 1284 K. To accommodate dual fuel relevant diesel-natural gas mixtures, methane–propane–n-heptane mixtures are considered as the surrogate. Additionally, the mechanisms AramcoMech 1.3, 2.0 and 3.0 are tested for methane–propane mixtures. The influence of pressure and propane/n-heptane content on the IDT based on the measurements is presented and the extent to which the mechanisms can reflect the IDT-changes discussed.

Dual Fuel Reaction Mechanism 2.0 including NOx Formation and Laminar Flame Speed Calculations Using Methane/Propane/n-Heptane Fuel Blends

“…A comparison of the simulated IDTs using MechA and MechB is shown in Figure 3. [12,13] versus model prediction (lines) using the mechanism MechA (solid lines) and MechB (dashed lines). The respective content of methane, propane, and n-heptane is given in mol% and corresponds to the values in Table 1. In the mechanism presented in [7], the Arrhenius parameters of eight reactions were adjusted, including three methane reactions and five reactions of the n-heptane sub-mechanism.…”

“…A comparison of the simulated IDTs using MechA and MechB is shown in Figure 3. [12,13] versus model prediction (lines) using the mechanism MechA (solid lines) and MechB (dashed lines). The respective content of methane, propane, and n-heptane is given in mol% and corresponds to the values in Table 1.…”

“…To better reflect the methane number (which is a measure of the knock resistance) of natural gas, a mixture of methane and propane was defined as a surrogate. In [7], in the first step, the ignition delay times (IDTs) of homogeneous methane-propane-n-heptane mixtures were investigated with a rapid compression machine (RCM) and a shock tube (ST) at PCFC (Physico Chemical Fundamentals of Combustion), RWTH Aachen [12,13], followed by the comparison of the measured values with simulation results using various n-heptane mechanisms available in the literature. For the simulations in [7], as well as the actual study, the program LOGEresearch (Version LSv1.09, LOGE AB, Lund, Sweden) [14] was used.…”

“…The effects are considered in the simulation by reading in the effective volume profile derived from the pressure profile of the associated non-reactive RCM measurement in which oxygen was replaced by an inert gas. Details on determining the effective volume curve are available in [12,15].As shown on the left side of Figure 1, the IDT is defined as the time between the point when the piston of the RCM reached its end position and the maximal pressure increase due to ignition of the mixture. The simulation of ST measurements was performed with the module "rapid compression machine" too, but with the difference that the temperature and pressure values reached in the ST after the shockwave reflection were used as starting values.…”

“…The effects are considered in the simulation by reading in the effective volume profile derived from the pressure profile of the associated non-reactive RCM measurement in which oxygen was replaced by an inert gas. Details on determining the effective volume curve are available in [12,15].…”