Numerical evaluation of heat transfer effects on the improvement of efficiency of a spark ignition engine characterized by cylinder variability

In this work, the effects of in-cylinder heat transfer on indicated thermal efficiency of a spark ignition engine showing a cylinder-to-cylinder variation are numerically analyzed. A 1D CFD model of engine is developed and integrated with a turbulent combustion sub-model and with a refined thermal sub-model for cylinders and exhaust pipes. The model is validated against the engine measurements. Thermal sub-model includes a Finite Element (FE) approach to predict the temperatures of cylinders and of exhaust pipes. The model correctly reproduces the thermodynamic behavior of cylinders at varying the operating condition. Simulations at low load and speed indicate that in-cylinder heat transfer represents a relevant percentage on total fuel energy entering the cylinder. Therefore, heat transfer exerts an important influence on the improvement of engine indicated thermal efficiency when considering the sole combustion phasing optimization of cylinders and the suppression of cylinder-to-cylinder variation.