An Experimental and Computational Investigation of the Flow in Diesel Prechambers

High-speed schlieren photography was employed to study air-fuel mixing and combustion in several two-dimensional prechambers that represented a 1980 GM-oldsmobile diesel prechamber and modifications thereof. The experiments were performed in a Rapid Compression Machine. A computational study was also undertaken to model these experiments using a two-dimensional computer code. The computational study also considered a Ricardo Comet V swirl chamber, in addition to the above chambers. The computations gave predictions of the full two-dimensional transient flow field during the compression stroke in the absence of injection or combustion.

This study showed that the prechamber flow is dominated by the incoming jet. As a result the vortex, which is formed due to the nearly tangential jet entry, initially is confined to part of the chamber and not centered in the chamber. As the inflow velocity falls towards the end of the compression stroke, the vortex tends to center itself, while the vortex structure grows and more nearly fills the chamber. The implications of this flow field development on injected fuel are considered by examining velocities along the injection axis. Excellent agreement between the experiments and computations with respect to the vortex position and overall flow field structure was found.