Liquid Fuel Flow in the Vicinity of the Intake Valve of a Port-Injected SI Engine 982471
Liquid fuel flow into the cylinder an important source of hydrocarbon (HC) emissions of an SI engine. This is an especially important HC source during engine warm up. This paper examines the phenomena that determine the inflow of liquid fuel through the intake valve during a simulated start-up procedure. A Phase Doppler Particle Analyzer (PDPA) was used to measure the size and velocity of liquid fuel droplets in the vicinity of the intake valve in a firing transparent flow-visualization engine. These characteristics were measured as a function of engine running time and crank angle position during four stroke cycle. Droplet characteristics were measured at 7 angular positions in 5 planes around the circumference of the intake valve for both open and closed-valve injection. Additionally the cone shaped geometry of the entering liquid fuel spray was visualized using a Planar Laser Induced Fluorescence (PLIF) setup on the same engine. The data allowed detailed analysis of the spatial variation of the liquid fuel flow into the cylinder and of the development of the liquid fuel spray geometry emerging from the intake valve throughout the engine cycle. By combining the quantitative PDPA fuel droplet measurements and the qualitative information of the geometry of the liquid fuel cone entering the cylinder obtained from PLIF images, a procedure was developed to estimate the volume of liquid fuel entering the cylinder as a function of time during warm up. Using this procedure, the mass flow of liquid fuel into the cylinder as a function of time during start-up could be assessed. The mass flow distribution in the vicinity of the intake valve and important cycle phases of fuel inflow were identified.
The results clearly identify 4 transport mechanisms of liquid fuel into the cylinder during the intake stroke: First forward flow atomization, spray contribution, high speed intake flow transport, and fuel film squeezing. The spatial and temporal variation of in-cylinder liquid fuel occurrence in the vicinity of the intake valve is described for open and closed valve injection. Liquid fuel mass flow into the cylinder during start-up shows distinctly different behavior for open and closed valve injection. On open valve injection the amount of liquid fuel in the cylinder decreases steadily during warm-up.
On closed valve injection the occurrence of an inflow maximum about 15 seconds after start-up was observed due to significant wall film build-up in the port.