A detailed model of in-cylinder heat transfer in spark ignited engines has been developed. The model is based on a well established boundary layer representation which is driven by a flow model which describes all of the major in-cylinder fluid motions: swirl, squish, axial piston-driven motion and turbulence, The flow model allows for bowl-in-piston and recessed head geometries, divided into four flow regions. The convective heat transfer coefficients are calculated from Colburn analogy using the local effective flow velocities. The coefficients thus vary from surface to surface within the combustion chamber, reflecting the effects of local flow conditions.
During the combustion, the model simulates flame propagation as a spherically growing region originating at the spark location. This sphere intersects combustion chamber surfaces, and the flame area is defined as the area of the sphere which intersects the combustion gases. The rate of mass burned is proportional to this flame area and to the flame speed. The flame speed is calculated from a turbulence-based entrainment model, which also accounts for the effects of gas composition, pressure and temperature on the laminar burnup behind the entrainment front. The instantaneous flame position calculated by this model feeds directly into the heat transfer model, which resolves the combustion chamber surfaces in a detailed manner.
The model was applied to a well documented experimental data set obtained by other investigators. These data include measurements of heat fluxes at different engine speeds, spatial locations, intake pressures (volumetric efficiency), and spark timing. The results of these comparisons showed a good agreement across the whole data set.