Diesel engine exhausts application

The applications of isokinetic sampling cover but are not limited to the sampling of aerosols such as flu gas in chimney, soots (unbumed carbons) from diesel engine exhaust, dusts suspended in the atmosphere, and fumes from various sprayers measurements of particulate mass fluxes in pneumatic transport pipelines and other particulate pipe flows solid fuel (also some liquid fuels) distributions in furnaces, engines, and other types of combustors and calibrations of instruments for the measurements of particle mass concentrations. Isokinetic sampling can also be applied to flows with liquid droplets. In this case, the droplet sample is usually collected by an immiscible liquid (Koo et al., 1992 Zhang and Ishii, 1995). 

Extruded cordierite honeycombs also have applications in other fields because of their unique material and structural properties such as high porosity, low thermal expansion, high geometric surface area, and low gas flow restriction [2]. Utilizing their porous ceramic wall as filters, extruded honeycombs can be used as trap oxidizers to eliminate toxic particulate matter from diesel engine exhaust. 

In this chapter, the use of gas chromatography-mass spectrometry (GC-MS) in the field of occupational and environmental health is discussed with emphasis on the detection of traces of nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) from complex source emissions (diesel engine exhaust) in the ambient atmosphere and in personal air samples (workplace atmosphere). The uptake, and distribution, covalent binding to proteins, and excretion of urinary metabolites are addressed in terms of specific MS-applications. The analysis of drinking water and foodstuffs for contaminants or residues is not discussed these topics are presented elsewhere in this book. 

The PAG system utilizes plasma to oxidize NO to NO2, which then reacts with a suitable reductant over a catalyst. LNC, NSR, and PAG systems have still several challenging tasks to be solved. Gonsequently, all these technologies are not yet appropriate for commercial applications to diesel and lean-burn engine exhausts [47]. 

Emission control from heavy duty diesel engines in vehicles and stationary sources involves the use of ammonium to selectively reduce N O, from the exhaust gas. This NO removal system is called selective catalytic reduction by ammonium (NH3-SGR) and it is additionally used for the catalytic oxidation of GO and HGs.The ammonia primarily reacts in the SGR catalytic converter with NO2 to form nitrogen and water. Excess ammonia is converted to nitrogen and water on reaction with residual oxygen. As ammonia is a toxic substance, the actual reducing agent used in motor vehicle applications is urea. Urea is manufactured commercially and is both ground water compatible and chemically stable under ambient conditions [46]. 

The small particles are reported to be very harmful for human health [98]. To remove particulate emissions from diesel engines, diesel particulate filters (DPF) are used. Filter systems can be metallic and ceramic with a large number of parallel channels. In applications to passenger cars, only ceramic filters are used. The channels in the filter are alternatively open and closed. Consequently, the exhaust gas is forced to flow through the porous walls of the honeycomb structure. The solid particles are deposited in the pores. Depending on the porosity of the filter material, these filters can attain filtration efficiencies up to 97%. The soot deposits in the particulate filter induce a steady rise in flow resistance. For this reason, the particulate filter must be regenerated at certain intervals, which can be achieved in the passive or active process [46]. 

For similar motivations, there are limited incentives to develop an alternative SCR process for stationary sources based on methane (CH4-SCR) or other HCs, or based on NTP technologies, if not for specific, better applications. The situation is instead quite different for mobile sources, and in particular for diesel engine emissions. The catalytic removal of NO under lean conditions, e.g. when 02 during the combustion is in excess with respect to the stoichiometric one (diesel and lean-burn engines, natural gas or LPG-powered engines), is still a relevant target in catalysis research and an open problem to meet future exhaust emission regulations. 

Analysis and modelling of the dynamic behaviour of the catalyst is useful to closely describe the performance during start up, shut down and load variation of stationary applications, and of critical relevance for SCR-NH3 of mobile diesel engine emissions. Use of dynamic models for exhaust transients has not been extensively reported in the literature for the design of improved catalysts, although it is a very valuable method. On the contrary, as will be discussed later, use of this tool to derive mechanistic implications is much less convincing. 

The previous section has evidenced that NH3-SCR technology has been used successfully for more than two decades, to reduce NOx emissions from power stations fired by coal, oil and gas, from marine vessels and stationary diesel engines. NH3-SCR technology for high-duty diesel (HDD) vehicles has also been developed to the commercialization stage and is already available as an option in the series production of several European truck-manufacturing companies starting from 2001. For mobile source applications, the preferred reductant source is aqueous urea, which rapidly hydrolyses to produce ammonia in the exhaust stream. 

Dimethyl ether was first proposed as an alternative fuel for direct-injected (DI) diesel applications in 1995. Since that time, engine testing has shown DME to be as effective as CNG, LPG, and methanol in producing low levels of engine exhaust emissions. Results of an engine study completed in Austria using a Navistar V8 diesel engine are provided in TABLE 12-13. 

However, there are several major drawbacks that hinder practical application of this NOx reduction method in automobile exhaust aftertreatment (i) The NO reduction activity is typically limited to a certain temperature window, for NM-based catalysts it is around the light-off—cf. Fig. 14 and Ansell et al. (1996), Jirat et al. (1999b), Burch et al. (2002) and Joubert et al. (2006). (ii) With low HC concentrations and the exhaust composition met in modern diesel engines, the achieved NOx conversions in real driving cycles are quite low (typically around 5-10%, cf., e.g., Kryl et al, 2005). (iii) The selectivity of NOx reduction is problematic, N20 may form up to 50% of the product (Burch et al., 2002 Joubert et al., 2006). Alternative (Cu-, Co-, Ag-, etc., based) catalysts may provide a wider temperature window or better selectivity for... 

Structured catalysts are also essential in diesel exhaust gas purification. State-of-the-art solutions are marketed by PSA and by Johnson Matthey. The truck market is dominated by diesel engines. In that application, space requirement is a major issue, and intensification is badly needed. Space velocities exceeding 100,000 h 1 arc demanded. Reactive structured filters are the way to go. 

Alternatively it may take the form of a ceramic or metallic monolith, of which a variety of physical shapes is available monoliths are now widely used as supports for the active catalyst, which lines the channels which permeate the structure. They find particular application for the control of exhaust from vehicles powered by internal combustion or diesel engines. If the catalyst particles are small enough, a fast flow of reactants causes the bed to expand and the particles to move about like molecules in a liquid. We then have a fluidised bed reactor, which affords a more uniform temperature profile than is possible in fixed bed reactors, and is therefore more apposite to strongly exothermic reactions. 

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