Dieter Rothe

A Photoacoustic Sensor System for Time Resolved Quantification of Diesel Soot Emissions

ABCTRACT The reduction of particulate emissions limits requires new tools for the tuning of engines and exhaust aftertreatment systems. Time-resolved monitoring of low soot emissions is a key feature for such developments. The paper describes an improved photoacoustic soot sensor, and presents its applications for the characterization of transient exhaust soot emissions before and after Diesel emission after-treatment systems. The detection limit of the unit is around 5 μg/m 3 soot, which is two orders of magnitude better than conventional time-resolved transmission measurement. Additionally, a wide dynamic range of four orders of magnitude can be achieved without range switching. The photoacoustic signal is proportional to the soot mass, no significant cross-sensitivities to gaseous absorbers were detected.

Changes in Structure and Reactivity of Soot during Oxidation and Gasification by Oxygen, Studied by Micro-Raman Spectroscopy and Temperature Programmed Oxidation

Micro-Raman spectroscopy (micro-RS) and Temperature Programmed Oxidation (TPO) combined with FTIR gas analysis have been used to determine structural changes and oxidation behavior in samples of spark discharge (GfG) and heavy duty engine (EURO IV) soot upon oxidation by oxygen in a temperature range between 293 K and 873 K. Raman spectra of soot and FTIR spectra of oxidation products have been recorded before and during the oxidation process. For micro-RS analysis spectral parameters have been determined by a five band curve fitting procedure (G, D1–D4). For GfG soot the relative intensity of D3 band is decreasing and the two observed Raman peaks are getting more separated during the TPO. This suggests a rapid preferential oxidation of highly reactive amorphous carbon. The decrease of the D1 band width indicates a decrease of chemical heterogeneity and an increase of structural order upon oxidation. Changes in Raman spectroscopic parameters are in good agreement with the behavior of soot during oxidation determined by CO2 emission with FTIR. In contrast to GfG soot the spectral parameters of EURO IV soot remained mostly unchanged during the oxidation process, so that EURO IV soot shows just minor changes in structure upon oxidation. Overall Raman spectroscopic parameters provide information about changes in structural order of graphitic and amorphous carbon fractions during oxidation and can be used to analyze oxidation readiness of soot. Thus micro-Raman spectroscopy may become a rapid analytical tool for the determination of soot reactivity by analysis of the structure.

Exhaust gas aftertreatment system for Euro 4 heavy-duty engines

“Wall-flow” soot particulate filters for commercial vehicles are not a reliable means of reducing soot particulate emissions, regarding the high kilometrage of more than 1 million, in conjunction with the demand for no maintenance and as little fuel consumption as possible. To fulfil Euro 4 limits the MAN Nutzfahrzeuge Group has developed inner-engine NOx reduction and a PM-Kat system for exhaust-gas aftertreatment. The PM-Kat system with clog-free flow channels permits the reduction of soot particulate emission by continuous oxidation of the separated soot.

Ein Abgasnachbehandlungssystem für Euro 4 bei Nutzfahrzeugmotoren

Im Hinblick auf hohe Kilometerleistung von uber einer Million km, Wartungsfreiheit und geringen Kraftstoffverbrauch sind „Wall-flow“ -Ruspartikelfilter fur Nutzfahrzeuge keine zuverlassige Masnahme zur Ruspartikel-Emissionsverminderung. Zur Erfullung der Euro-4-Norm hat die MAN Nutzfahrzeuge Gruppe Motoren mit innermotorischer NOx-Reduktion und einem Ruspartikelfilter-System (PM -Kat) entwickelt. Das System mit offenen, verstopfungssicheren Stromungskanalen vermindert die Ruspartikelemission durch kontinuierliche Oxidation des Ruses.