Effects of injection timing on fluid flow characteristics of partially premixed combustion based on high-speed particle image velocimetry

Partially premixed combustion (PPC) is a promising combustion concept to meet the increasing demands of emission legislation and to improve fuel efficiency. Longer ignition delay of PPC in comparison with conventional diesel combustion provide better fuel/air mixture which decreases soot and NOx emissions. Moreover, a proper injection timing and strategy for PPC can improve the combustion stability as a result of a higher level of fuel stratification in comparison with Homogeneous Charge Compression Ignition (HCCI) concept. Different injection timings affect this level of fuel and combustion stratification which helps to control the combustion timing and the heat release behavior. The scope of the present study is to investigate the fluid flow characteristics of PPC at different injection timings. To better understand this, high-speed Particle Image Velocimetry (PIV) is implemented in a light duty optical engine to measure fluid flow characteristics inside the piston bowl as well as the squish region with a temporal resolution of 1 crank angle degree at 800 rpm. Combustion phasing is kept constant for different injection timings and flow behavior including the mean velocity, turbulent kinetic energy and cycle-resolved turbulence during the injection and combustion phenomena are measured. Two different injectors with 5 and 7 holes are also compared to see their effects on fluid flow and heat release behaviors. Formation of the vortices and turbulence enhance the air fuel interaction, changing the level of fuel stratification and combustion duration. Results well demonstrate how these different turbulent kinetic energies can correlate with heat release behaviors. Furthermore, the research provide a quantitative dataset for validation of numerical simulations.