Abstract
Using a 6-cylinder commercial-vehicle engine with an electronically controlled high-pressure injection system with a nominal power of 148 kW at 2300 l/min, morphological particle studies of the soot particles were carried out after the turbocharger (TC) in 2 operating points (nominal power and partial load range with 25 % load at 1400 1/min) in operation with diesel fuel with 300 ppm S-content (SDF), diesel fuel with 30 ppm S-content (RDF) and biodiesel (RME).
The exhaust was extracted at approximately 0.75 m after TC using a sampling system for morphological tests developed at the Institute Measurement Technology and Reciprocating Machines.
In the process, it was determined that evident limit values of pressure surges, caused by the outlet valve, should not be exceeded when sampling from the exhaust gas system of engines with high-pressure injection systems, since, otherwise, the very thin carbon layer (10 nm layer thickness) on the sample holding would be destroyed.
As expected, the cover density of the homogeneous carbon layer is load-dependent. At nominal power, the coverage density for SDF is approximately 2.5 times greater than in the partial load range and approximately 1.5 times greater for RDF as well as RME by use of the one and the same fuel.
At nominal power of the engine, very many small, almost round particles with a form factor (FF) of 0.86 but also particles with an FF of 0.14 are present with SDF, which indicates larger agglomerates. In contrast, almost only larger agglomerates with a FF of 0.34 are present with RDF and with RME at the same load point.
At partial load operation of the engine, relatively many medium sized agglomerates with a FF of 0.5 are present with SDF. A FF of 0.27 was ascertained at partial load operation with RDF and with RME. That means that more large agglomerates are present with RDF and with RME than with SDF and that not as many small particles are to be found as with SDF.
Apart from particles and agglomerates, droplets are also on the sample holders of SDF and RDF. The spectral analysis of the droplets shows that still significant quantities of sulfur can also be detected with RDF. The sulfur is embedded in the droplets as a vaporizable component. No droplets and no sulfur are detectable on the sampler holders of the RME samples.