Modeling of Engine Cyclic Variation by a Thermodynamic Model

Kantor model showing that prior-cycle effects resulting from exhaust gas residuals are a significant factor in cyclic variability of combustion in IC engines is due to a number of model assumptions that misrepresent the thermodynamic process experienced by the mixture of fresh combustible gas plus exhaust residual in important ways. In particular we show that exhaust blowdown process and variable exhaust residual gas mass fraction, neglected in the Kantor model, significantly reduce cyclic variability. However, unburned fuel not considered in the Kantor model apparently aggravates cyclic variability. These three factors cancel each other resulting in cyclic variation appeased. Using modified Kantor models, we examine the effects of all major engine operating parameters on mean and fluctuating exhaust residual temperature and indicated work. No significant cyclic variability is predicted for realistic ranges of these parameters. Only for extremely unrealistic ranges of model parameters cyclic variation reluctantly shows up. Moreover, even using the Kantor model, cyclic variability is predicted only for rather extreme, somewhat contrived choices of the model parameters.