Knock Prediction in Reciprocating Gas-Engines Using Detailed Chemical Kinetics

Two and three-dimensional test cases were simulated using a detailed kinetic mechanism for di-methyl ether to represent methane combustion. A piston-bowl assembly for the compression and expansion strokes with combustion has been simulated at 1500 RPM. A fine grid was used for the 2-D simulations and a rather coarse grid was used for the 3-D calculations together with a k-ε subgrid-scale turbulence model and a partially stirred reactor model with three time scales. Ignition was simulated artificially by increasing the temperature at one point inside the cylinder. The results of these simulations were compared with experimental results. The simulation involved an engine with a homogeneous charge of methane as fuel. Results indicate that pressure fluctuations were captured some time after the ignition started, which indicates knock conditions. Detailed analysis of the pressure data showed that knock was present in the simulations and exhibited similar characteristics to the ones observed in experiments. The pressure oscillation frequency was around 5-14 kHz for the simulations, which is well within the in-cylinder pressure oscillation frequency range ∼3-25 kHz captured during knock via measurements. The oscillations lasted for ∼20° CA which was also experimental observed.