Abstract: Estimating combustion timing in homogenous charge compression ignition (HCCI) engines based on cylinder head’s vibration acceleration is presented. The relationship between the vibration acceleration and the second derivative of cylinder pressure is analyzed on a 295 engine model. Results indicate that the vibration acceleration and the second derivative of cylinder pressure has similar trend before the appearance of the peak pressure. Combustion timing can be estimated by the first zero-crossing point before the location of the peak vibration acceleration of cylinder head. Experiments are conducted on a 295 HCCI engine. Results show that the combustion timing obtained on the basis of the cylinder surface vibration acceleration signal lags behind that characterized by the second derivative of cylinder pressure. The lag angle is in the range of 2.5°～4.5°. The average value 3.5° is regarded as system lag. The fluctuation of combustion timing obtained from the vibration acceleration signal is 1.0 relative to the combustion timing characterized by the second derivative of cylinder pressure.

Key words: Combustion timing, Cylinder head vibration acceleration, Homogenous charge compression ignition (HCCI)