Optical Diagnostics of Soot in Combusting Sprays

Doctoral thesis, 2009

Optical diagnostics in combusting diesel sprays were carried out in the Chalmers High Pressure, High Temperature (HP/HT) spray rig at conditions similar to those in an internal combustion engine, reaching up to 100 bar and 630 ◦ C. Spray development studies and combustion characterisation were done by high speed shadowgraphs that were digitally processed to measure the start of combustion, break-up, droplets and vapour penetration. In addition, flame temperature measure- ments were made, resolved in space and time up to 30,000 frames per second, using a monochromatic high speed camera and an optical arrangement. Soot formation and evolution were investigated in highly turbulent combusting sprays with simultaneous planar Laser Induced Incandescence (LII), Elastic Light Scat- tering (ELS) and Light Extinction (LE) using a laser sheet and two intensified CCD cameras. The measurements were made at different intervals after the start of ignition to obtain information on soot evolution. Results of spray behaviour studies, flame temperature measurements and two- dimensional soot laser based measurements are presented and discussed for several gas conditions, fuel types and injection pressures. Spray behaviour studies and flame temperature measurements show a correlation with the physical properties of the fuel, injection pressure and gas conditions, respect- ively. On the other hand, soot measurements made by laser based methods show that the distribution of soot is inhomogeneous across the spray and that soot is re- duced by increasing the injection pressure. Variations in the amount and location of soot particles are shown to depend strongly on the conditions inside the combustion chamber, ignition delay and injection pressure.