High-speed schlieren and chemiluminescence imaging showing combustion near the injector after the end of injection, or lack thereof.

Please reference SAE paper from Knox et al. (2015) for the data/movies provided above.

Conditions are the Spray A operating condition using Injector 210677 with variation in ambient gas temperature. Schlieren imaging and chemiluminescence imaging were performed simultaneously on the same injection. Time is given relative to the start of injection “ramp down”, when mixing changes are expected to begin to have an effect on combustion and lift-off location. In this schlieren imaging setup, refractive index gradients from temperature non-uniformities of gases along the boundary layer of the vessel windows are evident as a “background” signature that doesn’t change significantly with time, while the vapor and reacting sections of the jet do change. The high-temperature reaction zone appears with a smooth texture in this setup (see Lillo et al. (2012)), while in other setups (Benajes et al. (2013),Skeen et al. (2014)) the light source is intentionally made more diffused to reduce schlieren sensitivity of the ambient. These setups have shown that high-temperature combustion produces a dark appearance in the schlieren and the cool-flame causes a rather distinct “disappearance” of the schlieren where refractive index gradients (temperature) are closer to the ambient. For the chemiluminesence movies, a dynamic background correction for soot luminosity is performed as described by Bardi et al. (2012). Despite the correction, soot luminosity creates a noticeable background that moves back to the injector, but it can still be distinguished from actual chemiluminescence for results shown here. The movies shown here are displayed in false color scale with the red color the same as that defined for the lift-off length, or 50% of the mean maximum chemiluminescence in the lift-off region. The lower range is to highlight weaker, but still visible, chemiluminescence in the zone between steady lift-off and the injector.

Ambient T 800 K900 K1000 K
Schlieren description
(Same for all)
Light source is 450 nm LED.
Lens f = 85 mm, f/2.8,
450 nm filter
(50nm fwhm),
26.25 µs period,
10 µs exposure
Movies: Play or right-click to download mp4schlierenschlierenschlieren
Chemiluminescence description
(Same for all)
Chemiluminescence with dynamic
soot background correction
Lens f = 50 mm, f/1.2,
< 600 nm filter
50 µs period,
46 µs exposure
Movies: Play or right-click to download mp4chemiluminescencechemiluminescencechemiluminescence
NotesNo combustion recession or problematic soot luminosity “background”.Combustion recession by 0.4 ms after start of rampdown. Luminosity of burning “dribble” fuel by 0.8 ms.Combustion recession by 0.3 ms with strong chemiluminescence. Luminosity of burning “dribble” fuel by 0.5 ms.