A Study on Prediction of Unburned Hydrocarbons in Active Pre-chamber Gas Engine: Combustion Analysis Using 3D-CFD by Considering Wall Quenching Effects

To reproduce wall quenching phenomena using 3D-CFD, a wall quenching model was constructed based on the Peclet number. The model was further integrated with the flame propagation model. Combustion analysis showed that that a large amount of unburned hydrocarbons (UHCs) remained in the piston clevis and small gaps. Furthermore, the model was capable of predicting the increase in UHC emissions when there was a delay in the ignition time. The flame front cells were plotted on Peters' premixed turbulent combustion diagram to identify transitions in the combustion states. It was found that the flame surface transitioned from corrugated flamelets through thin reaction zones to wrinkled flamelets and further to laminar flamelets, which led to wall quenching. The turbulent Reynolds number (Re) decreased rapidly due to the increase in laminar flame speed and flame thickness and the decrease in turbulent intensity and turbulent scale. When Re < 10, the model showed that there was a sharp increase in wall quenching. In addition, wall quenching occurred when the dimensionless wall distance was less than 40 (y+ < 40) at any timing.