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To improve fuel economy and reduce regulated emissions spark-ignition engines are equipped with a large number of control actuators, motivating the use of model-based ignition timing prediction strategies. Model-based ignition timing strategies require a target combustion phasing for proper calibration, generally defined by the crank angle location where fifty percent of the air/fuel mixture is burned (CA50). When fuel type is altered the target CA50 must be updated in the ‘knock region’ to avoid engine damage while maintaining the highest possible efficiency. This process is particularly important when switching between gasoline and E85 because they have vastly different octane ratings. A semi-physical virtual octane sensor, based on an Arrhenius function combined with a quasi-dimensional turbulent flame entrainment combustion model, is described that identifies the size of the knock region for a given fuel.

The highly transient operational nature of passenger car engines makes cylinder pressure based feedback control of combustion phasing difficult. The problem is further complicated by cycle-to-cycle combustion variation. A method for fast and accurate differentiation of normal combustion variations and true changes in combustion phasing is addressed in this research. The proposed method combines the results of a feed forward combustion phasing prediction model and “noisy” measurements from cylinder pressure using an iterative estimation technique. A modified version of an Extended Kalman Filter (EKF) is applied to calculate optimal estimation gain according to the stochastic properties of the combustion phasing measurement at the corresponding engine operating condition. Methods to improve steady state CA50 estimation performance and adaptation to errors are further discussed in this research.

As engines are equipped with an increased number of control actuators to meet fuel economy targets, they become more difficult to control and calibrate. The additional complexity created by a larger number of control actuators motivates the use of physics-based control strategies to reduce calibration time and complexity. Combustion phasing, as one of the most important engine combustion metrics, has a significant influence on engine efficiency, emissions, vibration and durability. To realize physics-based engine combustion phasing control, an accurate prediction model is required. This research introduces physics-based control-oriented laminar flame speed and turbulence intensity models that can be used in a quasi-dimensional turbulent entrainment combustion model. The influence of laminar flame speed and turbulence intensity on predicted mass fraction burned (MFB) profile during combustion is analyzed.