Transient Control of HCCI Combustion by aid of Variable Valve Timing Through the use of a Engine State Corrected CA50-Controller Combined with an In-Cylinder State Estimator Estimating Lambda

One of the main challenges with the Homogeneous Charge Compression Ignition, HCCI, combustion system is to control the Start Of Combustion, SOC, for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the SOC of previous cycles. The control can be achieved with two basic valve-timing strategies named the Overlap- and the IVC-method. The Overlap-method works by trapping of residuals while the IVC-method affects the effective compression ratio.

In an earlier paper it has been shown that if the two methods are incorporated into one controller, SOC can be controlled in a relatively large operating window although the transient performance was not sufficient. The reason is that a simple PI-controller cannot be made fast enough to cope with the transients without magnifying the cycle-to-cycle variations of the combustion into instability. It has also been shown that a controller based around a non-linear compensation extended with an engine state correction will improve the control performance. The non-linear compensation used is based on the inverse of the non-linear function from valve timings to ignition delay.

In this work an in-cylinder state estimator is added to the non-linear compensation controller in order to further improve the control performance. The in-cylinder state estimator is in the present version estimating lambda and aimed at improving load transients. Control performance from engine tests conducted on a single cylinder engine equipped with a hydraulic valve system is reported.