Turbocharged, direct-injection SI engines have become a mainstream solution for improving vehicle fuel economy. A central requirement is the ability to precisely estimate the pressure and gas flows in the exhaust manifold for improving the accuracy of air-charge control algorithms. Due to lack of adequate modeling capabilities, today's model-based charge and exhaust pressure estimators do not consider the influence of the high-frequency wave propagation dynamics in the manifold. This lack of physical consistency limits the robustness of the estimators, and introduces significant calibration effort to achieve acceptable accuracy. This paper presents a system dynamic approach to model the wave propagation phenomena in the exhaust system of a multi-cylinder turbocharged SI engine, to obtain a nonlinear, state-space system that is suitable for fast simulation and estimator design. A model order reduction methodology is applied to the conservation laws for unsteady compressible flows in ID pipes. Specific boundary conditions are then developed to characterize the wave reflection and transmission through various components of the exhaust system. Simulation results in steady-state and transient conditions show that the resulting reduced order model matches the accuracy of commercial ID engine simulation tools with a much simpler mathematical structure, offering an advantage in reducing calibration effort compared to the heuristic mean-value models.
All Science Journal Classification (ASJC) codes
- Control and Systems Engineering