A New Combustion Model Based on Transport of Mean Reaction Progress Variable in a Spark Ignition Engine

In this study a new model is proposed for turbulent premixed combustion in a spark-ignition engine. An independent transport equation is solved for the mean reaction progress variable in a propagation form in KIVA-3V. An expression for turbulent burning velocity was previously given as a product of turbulent diffusivity in unburned gas, laminar flame speed and maximum flame surface density. The model has similarity with the G equation approach, but originates from zone conditionally averaged formulation for unburned gas. A spark kernel grows initially as a laminar flame and becomes a fully developed turbulent flame brush according to a transition criterion in terms of the kernel size and the integral length scale. Simulation of a homogeneous charge pancake chamber engine showed good agreement with measured flame propagation and pressure trace. The model was also applied against experimental data of Hyundai θ-2.0L SI engine. Intake flow is calculated by STAR-CD with the resulting flow field mapped as an initial condition in KIVA. Predicted pressure traces showed reasonable agreement with measurement with adjusted constants in the ignition phase. Further validation will be required in a wider range of engine geometries and operating conditions.