A Case Study Of Combustion Modeling In A Spark Ignition Engine Using Coherent Flame Model

Abstract

In this study, a computer simulation was performed, to visualize fluid flow and combustion characteristics of a single cylinder spark ignition engine. The complete engine cycle process (inlet, compression, expansion and exhaust strokes) in gasoline engine model was investigated using RAINS (Reynolds Averaged Navier-Stokes) and CFM (Coherent Flame Model) approaches offered by Star-CD/es-ice. Simulations were done for the compression ratio 8:1 and 1200 rpm engine speed. C8H18 (iso-octane) was used as the engine fuel. In the numerical simulations to model turbulent flow field, k - epsilon RING turbulence model was selected with Angelberger wall functions. Static spark advance was set at 20 CA bTDC during the simulations. Fluid flow in the cylinder was observed during all the engine strokes. Especially, just before the exhaust valve open, some numerical abnormal situations were detected. It was observed that the pressure and temperature gradients between cylinder and exhaust port caused these abnormalities at small exhaust valve lifts. Temperature distribution, velocity profiles, burnt-unburnt fuel concentrations were obtained. Courant and Mach numbers were investigated in details at the exhaust stroke. Also global engine parameters such as in cylinder pressure, temperature and heat release rates were plotted. It was observed that CFM combustion model predicts faster flame propagation speed compared to experimental ones. Due to that higher temperature and peak pressure values were obtained in the numerical simulations.