Diesel soot treatment

The evolution of Diesel standards will be discussed and the constraints and limits of Diesel after-treatment systems put in series or in development will be clarified (in particular, those dealing with NO conversion and soot particles removal). 

The first case covers for example flue-gas treatment, which requires the filtration of fly-ash and the reduction of NOx, or gasification processes, where particulates and high-boiling tars have to be removed. An example of the second case is that of combustion processes, where incomplete combustion leads to the emission of carbonaceous particulates. The most relevant topic in this category is the reduction of diesel particulate emissions ( diesel soot ) by catalytic filtration. A more exotic example is the reaction cyclone for the thermal conversion of biomass, which also combines chemical reactions and separation in one apparatus, though its separation mechanism is not filtration. 

Other systems studied are catalyst coke [56,57] and catalyst supports [58-61]. The nature of the support has a profound effect on catalyst activity. Surprisingly, the origin of the carbon, whether peat, wood or coconut shells, is reflected at all length scales from the macroscopic to the atomic level. Carbon blacks of various types and with varying treatments have also been studied [62,64], as has diesel soot [64] and carbon anodes [66-68]. 

In this work, it is shown that the copper-cerium oxide catalysts are active in the diesel soot combustion reaction. The isolated Cu ions seem to be the most active sites in such catalysts. The activity depends on the copper concentration and the pre-treatment of solids. Among all the tested catalysts, the lCulCe673 oxide, calcined at a relatively low temperature and containing the highest copper concentration, is the most active. 

The term catalytic combustion generally means a complete oxidation of hydrocarbons to C02 and H20 over solid catalysts. Catalyst technology for air-pollution control such as exhaust gas treatment, abatement of the emission of VOCs, combustion of diesel soot particles, and high temperature combustion have boosted research in catalytic combustion. 

Overall, EGR and combustion/injection systems constitute the key factors to comply with the EuroIV standards (applied in January, 2005). The EuroIV step exhibits EuroIII NO and soot particles limits divided by 2. Besides, vehicle s weight is always increasing due to the introduction of new safety systems and equipment. Therefore, pollutants emissions increase and a supplementary effort to reach the normative threshold is to be made. To comply with this target, some evolutions have been introduced, as for example multi-injection or water-cooling of the EGR system. The NO,/particle compromise adjustment remains possible for most of the applications without any after-treatment system like the Diesel particle filter (DPF). 

But the most important challenge in NO and soot removal by plasma-assisted catalysis refers to the treatment of diesel exhaust [116]. The discovery of new combinations leading to both an advanced total oxidation of unburned organic fuels and fragments, and of soot is extremely important for the near-future. According to the new regulations concerning the use of biomass in the production of fuels, the achievements in the direction NO and soot removal by plasma-assisted catalysis should be extended to the removal of tars [117]. 

Three-way catalysts are used in gasoline cars to control the emissions of hydrocarbons, carbon monoxide and nitrogen oxides. Oxidation catalysts and diesel particulate filters, DPFs, are used in diesel vehicles to control the emissions of soot particles, hydrocarbons, carbon monoxide and nitrogen oxides. All of these after-treatment devices are sensitive to additive components of the lubricant. Three-way... 

Soot emitted from Diesel engines is hazardous for human health since it is made of inhalable particles [1] and contains gases and liquids adsorbed on its smrface, some of which (Polycyclic Aromatic Hydrocarbons) are suspected to be cancerogenic [2]. Virtually, soot-free Diesel exhaust may be obtained combining reduction of soot formation in the combustion chamber with exhaust gas treatment [3]. This latter is generally performed by a ceramic wall-flow filter that collects the carbonaceous particles while the filter regeneration is achieved by post-combustion of collected soot [3, 4]. 

---