In this study, the microstructure and oxidation behaviour of soot from the raw exhaust of a Euro IV test heavy duty (HD) diesel engine is investigated and compared to that of spark discharge soot and hexabenzocoronene (HBC, C 42 H 18 ). We find a microstructure-controlled reactivity toward oxidation of all three samples in 5% O 2 in N 2 . The spark discharge soot with its fine primary particles and fullerenoid structure has an onset temperature of 423 K for combustion, while the hexabenzocoronene with its well-ordered crystallites has a high onset temperature of 773 K. Due to an improved combustion process in the Euro IV HD diesel engine, the soot emitted consists of more fullerenoid-like or onion-like particles agglomerated in a chain-like secondary structure. The onset temperature of the Euro IV HD engine soot combustion is 573 K. Oxidation of the three samples produces only CO 2 and H 2 O. The different H 2 O production profiles can be assigned to the functionalised surface of the samples and depend on the soot structures and preparation route.

No abstract

The deactivation of NO oxidation by SO 2 was studied with the use of commercial diesel oxidation catalysts (DOC) and Pt/Al 2 O 3 as reference material, coated on cordierite monolith. Despite their slightly different elemental compositions, the NO conversion rates of the fresh commercial catalysts were very similar. The maximum NO conversion was 38% at 350 °C, and above this temperature conversion started to be limited by the thermodynamics of the reaction. The rates of NO conversion strongly decreased with the start of SO 2 dosing. For analysis of SO 2 conversion and uptake, SO 2 and SO 3 /H 2 SO 4 were determined separately in the gas phase by absorption and titration. Under typical exhaust gas conditions (1 ppm SO 2 , 250 °C), the catalysts functioned as sulfur traps and stored a large part of the emitted SO 2 . The SO x storage was divided into two phases: a fast saturation of the catalyst surface with sulfuric acid, which hampered NO conversion, and a slow, long-lasting sulfation of the washcoat. The storage capacities of the oxidation catalysts reached their maxima at 250 °C due to the temperature dependency of sulfur adsorption and desorption. Adsorbed sulfuric acid desorbed between 350 and 400 °C, whereas more stable compounds, such as aluminum sulfate, were decomposed at higher temperatures. Deactivated catalysts could be completely regenerated within a few minutes at temperatures above 350 °C. However, repeated or lengthier thermal treatments resulted in a reduced sulfur storage capacity and irreversible activity losses for NO oxidation due to a reduction of the active surface by sintering.

Soot particulates from an EuroIV diesel engine are sampled and investigated by high-resolution electron microscopy (HRTEM) and thermal gravimetry (TG). The experiments reveal a drastic reduction of primary particle size down to less than 20 nm, much smaller than that emitted by earlier diesel engines. HRTEM reveals primary particles with deformed fullerenoid structures. The defective fullerenoid soot is more prone to oxidation than the soot of a black smoking diesel engine. Our findings may initiate a critical review of the current strategy for the reduction of soot emission from diesel engines. The newly developed engines reduce the quantity of soot emitted, they also emit smaller soot particles with a fullerene-like structure into the exhaust.

Heavy duty EURO 4 diesel engine exhaust particle and ion size distributions were measured atthetailpipe using dynamometer testing. Measurements of particle volatility and electrical charge were undertaken to clarify diesel exhaust nucleation mode characteristics with different exhaust after-treatment systems. Nucleation mode particle volatility and charging probability were dependent on exhaust after-treatment particles were volatile and uncharged when the engine was equipped with diesel particulate filter and partly volatile and partly charged in exhaust without any after-treatment or with an oxidation catalyst only. The absence of charged particles in the nucleation mode of diesel particulate filtered exhaust excludes the ion mediated process as a nucleation particle formation mechanism.