Model-based methodology for estimating engine cylinder pressure imbalance for combustion feedback control applications

One of the principal issues of alternative combustion modes for Diesel engines (such as HCCI, PCCI and LTC) is related to imbalances in the distribution of air and EGR across the cylinders, which 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 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. The objective of the work in this paper is to estimating the individual in-cylinder pressure traces in a multi-cylinder engine, relying on a very restricted sensor set, namely a crankshaft speed sensor, a single production-grade pressure sensor. In doing so, a crankshaft model will be developed and a sliding mode observer will be employed to estimate the cylinder pressure using only crankshaft speed fluctuation measurement. Furthermore, as an added enhancement, the cylinder pressure signal from one cylinder will be utilized to adapt the friction and heat release parameters for more accurate estimation in all cylinders.