Development of a Turbulence Controlled Rapid Compression Machine for HCCI Combustion

This paper presents the development of an innovative rapid compression machine (RCM) designed to study the homogeneous charge compression ignition (HCCI) combustion process. This RCM has been developed to reproduce conditions relevant to homogeneous charge compression ignition engine operating regimes while trying to match the real working engine conditions in terms of aerodynamic features. A high compression ratio (16) can be achieved within a very short compression time (29 ms). This fast compression is powered by a hydraulic system and mastered by a multistage servovalve, making the piston motion control accurate. The design of the combustion chamber includes the turbulence characteristics control through a grid, fastened between the pre-compression and combustion chambers. This design also allows a very large optical access. The performances of this new RCM are presented in detail. The experimental results using reactive mixtures demonstrate the capability of the designed RCM in obtaining highly repeatable test data and capturing the essential features of combustion phenomena. Different parameters (compression ratio, air fuel ratio, fuels) have been varied to assess their influence on the ignition timing and the pressure time history. A high speed digital camera was used to monitor the ignition process. Subsequent image processing allows for an apparent propagation speed evaluation, which is correlated to the heat release rate. This discussion sheds light on the nature of the combustion modes inside the chamber. A discussion on the application of these trends to real engines is proposed, showing the high potential of the observations extracted from the rapid compression machine.