HCCI Operation - Closed loop combustion control using VVA or dual fuel

Abstract: The current technology within combustion engines have the possibility of handling the more stringent legislative demands on combustion engines. However the required solutions are getting more expensive and technically challenging. One possible way towards a more simple exhaust aftertreatment system is the use of the Homogeneous Charge Compression Ignition (HCCI) engine cycle. The main advantage of the HCCI engine is its low output of NOx exhaust emissions. Because of its indirect combustion initiation the main disadvantage is that it requires closed loop control of its combustion process. Two methods for engine timing control were used, dual fuels or variable valve actuation(VVA). With dual fuels the timing change was achieved by changing the autoignition properties of the homogeneous charge and with VVA, timing control was achieved by changing the effective compression ratio. This thesis focuses on the control of the HCCI engine. For the purpose of studying control of the HCCI engine, special engine control software was developed. This software aimed towards engine cycle-to-cycle control and actuation. Another aid in the development was the use of Matlab/Simulink for the design of powerful control algorithms. Successful system identification control design has been shown. Different control strategies were tested, amongst the most successful was the use of Model Predictive Control (MPC), which is a control strategy that can take care of the nonlinear behavior of the dynamic engine system and its actuators. It was concluded that low order models were sufficient for capturing the important HCCI engine dynamics. The use of ion current for detection and control of the HCCI combustion was also shown. A method for obtaining combustion timing from the ion current was defined and investigated. Closed-loop control using ion currents on an HCCI engine was demonstrated.