Visualization of ignition processes in high-pressure sprays with multiple injections of n-dodecane (SAE15PFL-0911)
The high-speed movies, still images, and rate-of-injection (ROI) data available in this page are intended to provide support to a manuscript entitled “Visualization of ignition processes in high-pressure sprays with multiple injections of n-dodecane” by Skeen et al. (2015). The operating conditions for this work explore the split-injection Spray A variant (0.5/0.5 dwell/0.5 ms) injection schedule at ambient temperatures of 750 K, 800 K, and 900 K. We used ECN Spray A injector: 210370. The table of movies and images below are referenced by figure number and panel number where applicable. The axial and radial distances are given in millimeters and the times are with respect to the start of injection and are given in microseconds (µs).
The high-speed schlieren movies were acquired at 150,000 frames per second with a 2 µs exposure time and a resolution of 0.21 mm/pixel. A high-intensity, short-pulse (1 µs) LED was used for illumination. Formaldehyde PLIF was excited with a 355 nm laser sheet and images were acquired at select timings with an intensified CCD camera having a 250 ns gate time.
The rate of injection (ROI) data for the ECN recommended split-injection schedule is provided in comma-delimited format in the link to the right.
The raw schlieren movie in the link to the right shows that during the 0.5 ms hold time between injections, the schlieren effect attributed to the first injection has diminished in the near injector region. Consequently, the penetration of the second injection is clearly distinguished.
|Non-Reacting Schlieren Movie|
(Spray A Split Injection) The raw schlieren movie in the link to the right shows the softening of the schlieren effect during first-stage ignition, the darkening contrast of the schlieren during second-stage ignition, and the darkening contrast in the near-injector region during combustion recession. The chemiluminescence movie shows luminosity at the lift-off location after ignition of the first injection, luminosity in the near-injector region during combustion recession, early high-temperature ignition near the liquid length for the second injection, and luminosity in the near-injector region from combustion recession following the end of the second injection.
(800 K Split Injection) The raw schlieren movie in the link to the right shows the softening of the schlieren effect during first-stage ignition much later and farther downstream than observed at the Spray A (900 K) condition. The darkening contrast of the schlieren during second-stage ignition is also observed. Because there is no combustion recession at this ambient temperature, the near-injector region does not darken after the end of the first or second injection. An arrow appears near 1200 µs indicating a softening of the schlieren effect along the radial periphery of the second injection.
(750 K Split Injection) The raw schlieren movie in the link to the right shows the softening of the schlieren effect due to mixing of the first injection with the ambient gases, not due to cool-flame heat release. First-stage ignition instead appears as a mild darkening of the schlieren image for the first injection. High-temperature ignition appears to take place first in the head of the second injection as it penetrates into cool-flame products from the first injection.