Estimation of the Instantaneous In-Cylinder Pressure for Control Purposes using Crankshaft Angular Velocity

Instantaneous in-cylinder pressure, a key variable in the improvement of engine performance and reduction of emissions, is not likely to be measured directly in production type engines in the near future. As a countermeasure, a pressure estimation method based on physical first principles for the estimation of the instantaneous in-cylinder pressure of an SI engine using measured crankshaft angular velocity is presented here.

The approach consists of (a) mapping the model parameters at nominal operating conditions and (b) adapting the model parameters to current operating conditions using the instantaneous crankshaft angular velocity. The model reflects all essential effects on in-cylinder pressure, while the simulation time was reduced to 6 milliseconds per cycle on a standard PC. This makes it possible to estimate a cylinder-averaged pressure for each cycle up to an engine speed of more than 6000 rpm. The estimated in-cylinder pressure is available with a delay of one engine cycle.

The model has been compared to a benchmark pressure estimation method. Further, the model has been validated in simulation and against measured data for steady-state and transient operation. The model shows good accuracy, while the computational effort is promising for real-time applications. Furthermore, the model needs little calibration effort due to its physically based nature.