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

Cylinder pressure is an important parameter in engine combustion analysis or engine diagnosis. An approach is introduced to estimate cylinder pressure and combustion heat release in multicylinder SI engines based solely on engine speed measurements. Because of the nonlinear nature of engines, this estimation employs a nonlinear observer: the sliding observer. In many applications, cylinder pressure is critical for control or engine monitoring systems. Researchers have pursued various approaches to obtain the desired cylinder pressure directly or indirectly. However, these approaches vary in cost, reliability, robustness, accuracy and convenience. The use of nonlinear sliding observers in pressure and combustion heat release estimation based on measurements of engine speed 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 multicylinder SI engine is presented. Since a problem of system observability arises in pressure estimation when the cylinder piston moves to its TDC, means of reducing estimation errors in this condition are described. Finally, the applications of this approach in engine diagnostics are discussed