An Experimental Investigation of the Turbulence Effect on the Combustion Propagation in a Rapid Compression Machine

The role of different combustion modes that govern the combustion propagation inside a rapid compression machine is discussed. Aiming at the control of the compression generated turbulence, the careful design of the UPMC-RCM is described. A methodology is then proposed to investigate the influence of the residual post-compression turbulence level on the visible combustion propagation process. Through the fuel type, the main parameter varied is the ratio of the ignition delay time to the characteristic decay time for the post-compression turbulence. A high-speed camera images the visible combustion. Particle Image Velocimetry provides two-dimensional velocity fields of the post-compression flow prior to ignition. The residual turbulence level is shown to influence the combustion propagation phenomenology, highlighting the coexistence of both volumetric and frontlike combustion modes for the shorter aforementioned ratios. This conclusion could contribute to an explanation of the experimental discrepancies among the ignition delays measured in different RCMs as the residual turbulence level is highly set-up dependent.