Cylinder pressure and combustion heat release estimation for SI engine diagnostics using nonlinear sliding observers

Cylinder pressure is an important parameter in pursuing engine combustion analysis or engine diagnosis. An approach is introduced in this paper to estimate the cylinder pressures and combustion heat releases in multi-cylinder SI engines. Because of the nonlinear nature in engines, this estimation is based on one of the nonlinear observers-the Sliding Observer. In many applications, cylinder pressure is a necessary and important system state for control systems or engine monitoring systems. Researchers have pursued various approaches to obtain the desired cylinder pressure directly or indirectly. However, cost, reliability, robustness, accuracy and convenience are important considerations in utilizing these methods. The use of nonlinear Sliding Observers in pressure and combustion heat release estimation provides an accurate, low-cost, and reliable way to acquire these desired states. In this paper the estimation of cylinder pressures and combustion heat releases of a multi-cylinder SI engine is presented first. In the application of cylinder pressure estimation, the problem of system observability arises when the cylinder piston moves to its TDC. Approaches for reducing pressure estimation errors at TDC due to the absence of observability are also described. Finally, the applications of the pressure and heat release estimation in engine diagnostics are discussed.