HCCI Timing Control Using Iterative Feedback Tuning

Abstract: The Homogeneous Charge Compression Ignition (HCCI) is an engine which combines some of the characteristics of the Diesel and Otto engines. As a result an engine with a high efficiency and low emissions is constructed. Unfortunately, there is not a direct way to control its start of combustion (SOC). One way to phase the SOC is using valve timings. There are two main methods, the Overlap, which consists in trapping more or less residual gas, and the IVC method, which acts affecting the effective compression ratio. Iterative Feedback Tuning (IFT) is a control method that appeared in 1994, which has presented good performances in the tuning of PID and more complex controllers. The tuning is done by using data of closed loop experiments with the controller that is being tuned in the loop. Therefore, knowledge of the system and disturbances is not required. That is one of the principal advantages of this method. At the department of Machine Design at the Royal Institute of Technology (KTH) there is a single cylinder HCCI engine. It is based on a SCANIA truck engine and it includes an Active Valve Train System. In this equipment a control system based on non-linear compensation is used. Furthermore, a model of the real engine is available. In this project a procedure which allows the application of IFT in the HCCI has been developed. The method was tested, first, on a model and, secondly, in the test bed of the HCCI engine explained above. Controllers were tuned for three different operating points of the engine. The overlap method was used in two of them and the IVC method in the third one. However, more experience is required to determine how much improvement can be gained with the method. It was also noted that speed transients were very difficult to control due to long time delays.