Visualization of EGR Influence on Diesel Combustion With Long Ignition Delay in a Heavy-duty Engine

The effects of EGR on diesel combustion were visually examined in a single-cylinder, heavy-duty research engine with a low compression ratio, low swirl, a CR fuel injection system and an eight-orifice nozzle. Optical access was primarily obtained through the cylinder head. The effects of EGR were found to be significant. NOx emissions were reduced from over 500 ppm at 0% EGR to 5 ppm at 55% EGR. At higher levels of EGR (approximately 35% or more) there was a loss in efficiency. Constant fuel masses were injected. Results from the optical measurements and global emission data were compared in order to obtain a better understanding of the spray behavior and mixing process. Optical measurements provide fundamental insights by visualizing air motion and combustion behavior. The NOx reductions observed might be explained by reductions in oxygen concentration associated with the increases in EGR.