Search Results

Validation of the Ford General Engine SIMulation program (GESIM) with measured firing data from a modified single cylinder Ricardo HYDRA research engine is described. GESIM predictions for peak cylinder pressure and burn duration are compared to test results at idle operating conditions over a wide range of valve overlap. The calibration of GESIM was determined using data from only one representative world-wide operating point and left unchanged for the remainder of the study. Valve overlap was varied by as much as 36° from its base setting. In most cases, agreement between model and data was within the accuracy of the measurements. A cycle simulation computer model provides the researcher with an invaluable tool for acquiring insight into the thermodynamic and fluid mechanical processes occurring in the cylinder of an internal combustion engine.

A computer simulation for the performance of a four-stroke spark-ignition engine is used to assess the effects of in-cylinder flow processes on engine efficiency. The engine simulation model is a thermodynamic model coupled to submodels for the various physical processes of in-cylinder swirl, squish and turbulent velocities, heat transfer and flame propagation. The swirl and turbulence models are based on an integral formulation of the angular momentum equation and a K-ε turbulence model, These models account for the effects of changes in geometry of the intake system and the chamber design on in-cylinder flow processes. The combustion model is an entrainment burn-up model applicable to the mixing controlled region of turbulent flame propagation. The flame is assumed to propagate spherically from one or two spark plug locations. A heat transfer model that is dependent upon the turbulence level is used to compute the heat loss from the unburned and burned gases.

An Engine Simulation Model was used to study the effect of in-cylinder swirl level on turbulence intensity and burn rate while holding the inducted kinetic energy constant. Experimental measurements of burn rate for three different swirl levels were obtained and compared with model predictions. The turbulence model used previously did not include wall shear effects and showed little enhancement of turbulence due to swirl, causing small changes in predicted burn rate when the swirl level was changed. An improved turbulence model is proposed which includes production of turbulence due to wall shear effects. Turbulence intensity predictions from the improved model resulted in excellent agreement between the measured and predicted burn rates as swirl level was changed. In addition, the model was used to predict the effect of swirl levels on ISFC. Results showed that ISFC changes were overall small for the range of swirl levels considered.