Influence of the combustion energy release on surface accelerations of an HCCI engine

Large cyclic variability along with increased combustion noise present in low temperature combustion (LTC) modes of internal combustion engines has driven the need for fast response, robust sensors for diagnostics and feedback control. Accelerometers have been shown as a possible technology for diagnostics and feedback control of advanced LTC operation in internal combustion engines. To make better use of this technology, an improved understanding is necessary of the effect of energy release from the combustion process on engine surface vibrations. This study explores the surface acceleration response for a single-cylinder engine operating with homogeneous charge compression ignition (HCCI) combustion. Preliminary investigation of the engine surface accelerations is conducted using a finite element analysis of the engine cylinder jacket along with consideration of cylindrical modes of the engine cylinder. Measured in-cylinder pressure is utilized as a load input to the FE model to provide an initial comparison of the computed and measured surface accelerations. Additionally, the cylindrical cavity resonant modes of the engine geometry are computed and the in-cylinder pressure frequency content is examined to verify this resonant behavior. Experimental correlations between heat release and surface acceleration metrics are then used to identify specific acceleration frequency bands in which characteristics of the combustion heat release process is detected with minimal structural resonant influence. Investigation of a metric capable of indicating combustion phasing is presented. Impact of variations in the combustion energy release process on the surface accelerations is discussed.