High-Speed Particle Image Velocimetry Measurement of Partially Premixed Combustion (PPC) in a Light Duty Engine for Different Injection Strategies

It has been proven that partially premixed combustion (PPC) has the capability of high combustion efficiency with low soot and NOx emissions, which meet the requirements of increasingly restricted emission regulations. In order to obtain more homogenous combustion and longer ignition delay in PPC, different fuel injection strategies were employed which could affect the fuel air mixing and control the combustion. In the present work, a light duty optical diesel engine was used to conduct high speed particle image velocimetry (PIV) for single, double and triple injections with different timings. A quartz piston and a cylinder liner were installed in the Bowditch configuration to enable optical access. The geometry of the quartz piston crown is based on the standard diesel combustion chamber design for this commercial passenger car engine, including a re-entrant bowl shape. The severe image distortions caused by the optical piston shape are minimized through recordings of reference targets and an image dewarping algorithm. To the authors knowledge this is the first time the flow field inside such realistic re-entrant piston bowl has been mapped through high speed PIV. PRF 70 was used as fuel in these measurements. The in-cylinder flow field was evaluated and investigated with high temporal and spatial resolution to provide additional understanding of the fuel air mixing process. Formation of the vortices and turbulence enhance the air fuel interaction. The vector field of 40 consecutive cycles, mean velocity, and turbulence kinetic energy were calculated and evaluated. All the results based on PIV experiment also provide a quantitative dataset being useful for model validation of the computational fluid dynamics (CFD) simulation of this PPC engine.