Adaptive sliding mode observer for engine cylinder pressure imbalance under different parameter uncertainties

One of the principal issues of alternative combustion modes for diesel engines (such as HCCI, PCCI, and LTC) is caused by the imbalances in the distribution of air and EGR across the cylinders, which affects the combustion process and ultimately cause significant differences in the pressure trace and indicated torque for each cylinder. In principle, a cylinder-by-cylinder control approach could compensate for air, residuals, and temperature imbalance. However, in order to fully benefit from closed-loop combustion control, it is necessary to obtain feedback signals from each engine cylinder to reconstruct the pressure trace. Therefore, cylinder imbalance is an issue that can be detected in a laboratory environment, wherein each engine cylinder is instrumented with a dedicated pressure transducer. This paper describes the framework and preliminary results of a model-based estimation approach to predict the individual pressure traces in a multicylinder engine relying on a very restricted sensor set, namely, a crankshaft speed sensor, a single production-grade pressure sensor. The objective of the estimator is to reconstruct the complete pressure trace during an engine cycle with sufficient accuracy to allow for detection of cylinder to cylinder imbalances. Starting from a model of the engine crankshaft dynamics, an adaptive sliding mode observer is designed to estimate the cylinder pressure from the crankshaft speed fluctuation measurement. The results obtained by the estimator are compared with experimental data obtained on a four-cylinder diesel engine.