In-cylinder Quantitative Soot Concentration Measurement By Laser-Induced Incandescence

Some methods to quantify the soot concentration by Laser-Induced Incandescence were developed using a flat flame burner in our previous work [1]. Those methods take the following points into consideration. (1)a correction of the LII signal intensity profile distorted by the laser attenuation due to soot clouds on the laser path, (2)a correction of the LII signal intensity attenuated by soot clouds between a camera and a measurement plane, (3)soot particle sizing up using 2-color LII signals and (4)conversion from a signal intensity to a soot concentration based on a calibration data. Using the methods, the accuracy of less than 10% was achieved in soot concentration measurement by a flat flame burner.

In this study, the above methods were applied to an optically accessible single-cylinder diesel engine to measure in-cylinder soot concentration quantitatively. The detailed investigations based on the sequences of spatial and temporal quantitative images reveal the following points.

1. 1
   The 2-color LII method shows that the particle sizes are increasing with time from the ignition timing and particle sizes are smaller in high-pressure injection than in low-pressure injection.
2. 2
   The soot along the cavity wall was oxidized promptly due to strong mixing by swirl flow. On the contrary, the soot near the nozzle orifice remained longer because mixing effect around the center of the cavity was relatively small.
3. 3
   The soot was formed only downstream along the spray jet in the high-pressure case (120MPa) because the soot field with higher temperature and higher equivalence ratio are carried away downstream or toward the cavity wall due to the strong bulk flow along the spray jet in this case.
4. 4
   The average soot volume fraction over all the cavity is remarkably decreased in the high injection pressure case.