Combustion timing determination based on vibration velocity in HCCI engines

Combustion timing is one of the most important feedback parameters for combustion control of homogeneous charge compression ignition (HCCI) engines. It is well known that the variation of combustion affects the engine outer surface vibration. Hence, the present work aims at investigating the possibility of using cylinder headʹs vibration response as a means to determine the combustion timing of HCCI engines. This paper proposes a new combustion timing identification method based on measured vibration velocity. In order to provide a clearer insight into the relationship between cylinder headʹs vibration velocity and the combustion timing, a finite element model (FEM) of a 295 HCCI engine is established. Based on the FEM simulation, the vibration velocity excited by combustion is simulated and results show that the cylinder headʹs vibration velocity and the rate of in-cylinder pressure rises have similar trend before the peak pressure occurs. The turning point of the cylinder head vibration velocity curve during the compression stroke corresponds to the combustion timing. Experiments are conducted on the 295 HCCI engine to compare and verify with the FEM results. Test results confirm that when the combustion begins, a turning point will occur in the cylinder headʹs vibration velocity curve. Therefore the combustion timings can be detected by the turning point of the cylinder headʹs vibration velocity during the compression stroke. Comparison is made between the combustion timings that are determined from the vibration velocity and from the rate of cylinder pressure rise. Compared to the combustion timings determined from the rate of cylinder pressure rise, the accuracy of that from the turning point of the cylinder head vibration velocity is within ± 0.5°CA.