A refined two-zone heat release model for combustion analysis in SI engines

A refined two-zone heat release model for combustion diagnostics in spark-ignition (SI) engines was developed and assessed. The novelty of the model includes the following improvements. A more general complex-variable formulation of Newton's convection law was applied for modeling the instantaneous surface-averaged heat flux so as to take the unsteadiness of gas-wall temperature difference into account. A CAD procedure was introduced to estimate the heat-transfer wall areas of the burned and unburned-zone for assigned geometric features of the flame front. The energy conservation law was applied to the unburned-gas zone instead of the isentropic law that is commonly used to evaluate the temperature of the unburned gas. The calibration of the cumulative mass-fraction burned at the end of the flame propagation process was carried out through an overall energy balance of the whole cylinder charge during combustion. The unreleased energy predicted at the end of the flame propagation was related to the combustion efficiency stemming from the exhaust-gas composition. The new heat release model was shown to be an accurate means of combustion diagnostics for SI engines through its application to the analysis of combustion in a multivalve engine fueled by either natural gas or gasoline under a significant sample of operating conditions.