Determination of Diesel Injector Nozzle Characteristics Using Two-Color Optical Pyrometry

Ciatti, S. Determination of Diesel Injector Nozzle Characteristics Using Two-Color Optical Pyrometry. University of Wisconsin-Madison, 2001.

A study was undertaken to study several diesel injector nozzles that produced different engine emissions performance. The nozzle styles used were two VCO type nozzles that were manufactured using two different techniques, and two mini-sac nozzles that provided comparison. Fired experiments were conducted on a Detroit Diesel Series 50 engine. Optical access was obtained by substituting a sapphire window for one exhaust valve. Under high speed, high load, retarded injection timing conditions, it was discovered that each nozzle produced different specific soot and NOx emissions. Pressure and heat release data, along with high-speed film images were obtained. It was discovered that the temperature and KL factor results from the 2-color optical pyrometry showed significant differences between the nozzles.

It was also discovered that the VCO nozzles produced significantly higher hole-to-hole variation early in the injection cycle than the mini-sac nozzle. However, one VCO nozzle produced significantly higher levels of soot, coupled with slightly lower levels of NOx, than the other VCO nozzle. The mini-sac nozzle produced the lowest NOx levels coupled with the highest specific soot emissions. KL factor data shows that the soot production for each VCO nozzle corresponds to the engine out soot level. KL factor data also show that the soot luminosity extends longer into the combustion cycle for the mini-sac nozzle than for either VCO nozzle. The presented hypothesis asserts that differences in nozzle cavitation during the initial opening of the VCO needle produces the different rates of soot production. Furthermore, these different rates of soot production may have a direct impact upon the levels of specific soot measurements. Another hypothesis asserts that the high consistency of the mini-sac nozzle during the initial needle opening may assist in reducing the rate of soot formation by enhancing air entrainment. However, the specific soot emissions are then hindered by the low pressure ?dribble? of fuel out of the sac volume late in the combustion cycle, causing the specific soot numbers to be high. The study concludes that the influence of the initial conditions of injection may play a large role in determining the engine out emissions levels.