Diesel Particulate Combustion

The exhaust gases of diesel engines are known to be a hazard to human health. 

A promising alternative to reduce soot emission is the development of a multifunctional catalytic filter that combines filtration and oxidation of the emitted particulate matter. Consequently, several authors have carried out studies of catalysts such as perovskite (La-Li-Cr or lanthanum cobaltite)-t)q)e oxides in a temperature-programmed combustion microreactor ( 600 °C) offering the best compromise between satisfactory catalytic activity and stability [17,18]. 

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Effects of Support and Noble Metal on C3H0 Oxidation During Diesel Particulate Combustion... 

Fino, D., Russo, N., Cauda, E., Saracco, G and Specchia, V. (2006) La-Li-Cr perovskite catalysts for diesel particulate combustion. Catal. Today, 114, 31-39. 

Sidhu S, Gullet B, Striebich R, Klosterman JR, Contreras J, DeVito M (2005) Endocrine disrupting chemical emissions from combustion sources diesel particulate emissions and domestic waste open bum emissions. Atmos Environ 39 801-811... 

The NSR technology has been also applied to diesel engines, and is most reliable and attractive method for lean-burn combustion vehicles. Diesel particulate-NOx reduction system (DPNR) method is used to realize the simultaneous and continuous reduction of particulate and NOx is also recommended. This catalyst system is DPF combined with NSR catalyst. Soot on catalyst is removed during NOx reduction by occasional rich engine modification. Many other catalyst systems with NSR catalyst have been also developed. With decreasing S content in fuel and successive development of... 

The simultaneous removal of NOx and soot on Pt-Ba/Al203 NSRC was investigated by Castoldi et al. (2006). They concluded that the presence of soot does not affect the NOx reduction activity of the NSRC, while the soot combustion is enhanced by the presence of N02. This principle has been already utilized by Toyota in the integrated DPNR (diesel particulate and NOx reduction) system (Nakatani et al., 2002). 

Diesel particle filters are a very efficient means of reducing PM mass emissions from diesel vehicles, but do not directly target NOx. However, most diesel particulate filter (DPF) systems contain catalytic materials which assist in the DPF regeneration (the combustion of PM accumulated on the filter to clean the DPF and prevent blockage). Such catalytic materials can have a similar impact to DOCs... 

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. 

Many working groups have modeled the performance of diesel particulate traps during the past few decades. Concentrated parameter models (CSTR assumption) have been applied for the evaluation of formal kinetic models and model parameters. The formal kinetic parameters lump the heat and mass transfer effects with the reaction kinetics of the complicated reaction network of diesel soot combustion. Those models and model parameters were used for the characterization of the performance of different filter geometries and filter materials, as well as of the performance of a variety of catalytically active coatings and fuel additives [58],... 

Fig. 15.5. Typical pressure drop and concentration-time curves of a diesel particulate trap in a closed gas-loop experiment with constant heating rate for the characterization of catalyst or filter performance for the combustion of diesel soot. Sintered SiC ceramic filter, without catalyst coating or fuel additive (from Ref. [46]).

McCabe, R.W. Sinkevitch, R.M. A laboratory combustion study of diesel particulates containing metal additives. SAE paper 860011, 1986. 

Bensaid, S., Marchisio, D. L. Fino, D. 2010 Numerical simulation of soot filtration and combustion within diesel particulate Alters. Chemical Engineering Science 65, 357-363. 

The most convenient way to remove particulates from the exhaust gas is combustion. Diesel particulates are, however, relatively unreactive and oxidation occurs moderately at normal exhaust temperatures for both passenger cars and heavy-duty trucks. In the non-catal3rtic as well as the catal3rtic oxidation of soot the reaction rate under all circumstances is rather slow in comparison to the residence time in the exhaust system. To achieve complete oxidation, the reaction... 

Diesel particulates are a health hazard and legislation has been established (in the U.S.A.) to reduce diesel particulate emissions. Particulate traps have been developed which can filter (up to 90%) of these particulates [Ref. 1], but require some external means to burn the collected particulates. One way to ignite these particulates effectively at low temperatures is to use traps which initiate soot combustion catalytically. 

Once the particulates are trapped, the next problem is conversion of these particulates into innocuous substances. Since the combustion temperature of diesel particulates is about 650°C in the absence of catalysts and since the exhaust temperature in diesel passenger vehicles is often no higher than 300-450°C, the particulates will not spontaneously ignite. Alternate ways are needed to burn the particulates so that excessive back-pressure due to trap plugging does not occur. Two ways have been proposed to burn the particulates ... 

This paper will focus on the catalytic combustion of diesel particulates. The majority of the work on catalyzed diesel traps has focused on engine or vehicle measurements. However, some work has been done to quantify the catalytic combustion of diesel particulates. For example Otto, et al. [Ref. 7] collected particulates and then burned them in the laboratory. They determined the effect of temperature, oxygen pressure, and step-wise combustion on reactivity. 

Watabe, Y. Irako, K. Miyajima, T. Yoshimoto, T. and Murakami, Y., "Trapless Trap" - A catalytic combustion system of diesel particulates using ceramic foam, SAE Paper 830082 (1983). 

One attractive method to meet the regeneration challenge is to dose diesel fuel with a Ceria-based fuel-home catalyst at low concentration. Combustion of the resulting fuel leads to in-cylinder generation of ceria particles (a highly effective catalyst for soot combustion) intimately mixed with the diesel particulates which are... 

The other path would be to lower the engine-out NOx to the legislated value with later injection timing and cooled EGR. This would lead to higher soot from the combustion and higher fuel consumption. A DOC (diesel oxidation catalyst) and/or a DPF (diesel particulate filter) are then used in order to reduce the particulates to the legislated value (Fig. 3.2). 

Diesel exhaust is a mixture of gases and particulates produced during the combustion of diesel fuel. The very small particles are known as diesel particulate matter (DPM), which consists primarily of solid elemental carbon (EC) cores with organic carbon (OC) compounds adhered to the surfaces. The organic carbon includes polyaromatic hydrocarbons (PAH), some of which cause cancer when tested in animals. Workers exposed to diesel exhaust face the risk of health effects ranging from irritation of the eyes and nose, headaches and nausea, to respiratory disease and lung cancer. 

Core-shell catalysts have also been studied for catalytic soot combustion, a gas-phase oxidation reaction used for the removal of diesel particulate matter in internal combustion engines. The Ag Ce02 rice-ball system discussed in Section 7.2.1 was employed for this purpose. Conventional Ag/Ce02 systems generally show low activity below 300 °C and exhibit only limited thermal stability. The results reported for Ag Ce02 indicated that the core-shell catalyst showed good activity for soot oxidation at temperatures below... 

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