Effect of Injection Timing on Piston Surface Fuel Impingement and Vaporization in Direct Injection, Spark Ignition Engines
Fuel spray imaging and PIV were used to investigate the effect of piston temperature and location on fuel spray structure and piston surface fuel impingement for three injection timings. Experiments were performed within a non-motored quartz research cylinder with in-cylinder densities and piston displacements that match those of a motored engine at the time of injection. Crank angles of 35°, 55°, and 75° before top dead center (BTDC) were considered, corresponding to in-cylinder pressures for the non-motored case of ∼5 atm, ∼3 atm, and ∼2 atm, respectively. A simulated piston was constructed of aluminum with controlled surface temperatures up to 210°C. The fuel spray was illuminated using single laser pulses formed into a sheet and passed through the cylinder with the images captured using a digital camera connected to an image acquisition board and computer. Instantaneous fuel spray imaging indicated that the heated piston had no significant impact on fuel spray structure when compared to the non-heated case for the single piston surface temperature investigated. Fuel spray imaging also revealed fuel impingement at both ambient and heated piston surface conditions for all experimental cases, which included surface temperatures from 100°C to 175°C. PIV results showed that the velocities of the impinging fuel clump for both the heated and ambient temperature cases were essentially the same within experimental uncertainties.