Abstract
Keywords - Particle size distribution, number concentration, injection pressure, calibration, NOx
Abstract - The influence of the injection pressure on the particle size distribution was measured with a scanning mobility particle sizer. Measurements were carried out on a stationary test bench with a 3 l, 6 cylinder, common rail direct injection engine from a passenger car, by varying the pressure in the rail. The sulphur content of the diesel fuel was < 10 ppm, and the sampling point was the tailpipe or the outlet of a transfer line.
First of all, the size distribution was measured with the standard engine calibration. In a second step, only the torque was set to the value of the original operating point (the one with the original rail pressure, etc.) after changing the pressure. This was done by adapting the end of injection. In a third step, the engine was set to the emissions level of the original calibration by varying the EGR rate to set the soot emission (measured in terms of the Bosch Smoke Number, SN), and the start of injection for the NOx level. Finally, the size distribution was measured in this configuration but with the sampling point at the outlet of a transfer line.
If the original injection pressure of 550 bar is varied in a range of 250-1600 bar and the engine torque is kept at 82 Nm, a slight decrease in the count median diameter (CMD) with increasing rail pressure can be found; on the other hand, the total number concentration (N) is reduced quite significantly. In the step three configuration, the same emissions as the original calibration, both particle size and concentration are almost constant with changing injection pressure. If the residence time of the aerosol prior to dilution is increased by employing a transfer line, a smaller number of slightly larger particles can be measured.
With the test procedure and measurement conditions used in this investigation, no negative effect of high injection pressure on the particle size distribution could be found.