Turbulence Intensity Calculation from Cylinder Pressure Data in a High Degree of Freedom Spark-Ignition Engine

The number of control actuators available on spark-ignition engines is rapidly increasing to meet demand for improved fuel economy and reduced exhaust emissions. The added complexity greatly complicates control strategy development because there can be a wide range of potential actuator settings at each engine operating condition, and map-based actuator calibration becomes challenging as the number of control degrees of freedom expand significantly. Many engine actuators, such as variable valve actuation and flow control valves, directly influence in-cylinder combustion through changes in gas exchange, mixture preparation, and charge motion. The addition of these types of actuators makes it difficult to predict the influences of individual actuator positioning on in-cylinder combustion without substantial experimental complexity. To simplify this experimental task a data processing routine is developed that quickly estimates in-cylinder turbulence intensity in a production-style engine from commonly employed measurements. Calculation of turbulence intensity is described, the data are validated using a quasi-dimensional spark-ignition engine combustion model, and the results are discussed. Results are in good agreement with well-established models for early-combustion conditions, and the new technique proves capable of discerning small changes in engine operation. The experimental data are then used to develop a simple control-oriented turbulence intensity prediction model that could be used for model-based ignition timing prediction algorithms. The control-oriented model is capable of quickly and accurately producing turbulence intensity estimates for variations in engine speed, load, ignition timing, valve overlap, and charge motion control valve activation state. Conclusions are drawn and the prospects of using these techniques for model-based engine control applications are discussed.