Emissions from diesel engine exhaust

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]. 

BaP, benzo[g/z/]perylene, benzo[6]fluoranthene, in-deno[l,2,3-cd]pyrene, and benzo[/c]fluoranthene, contribute the major portion of the identifiable mutagenicity of the extract of the whole unfractionated sample, accounting for 8.6, 2.5, 1.7, 1.4, 1.2, and 0.8%, respectively, of the total mutagenicity of the whole sample. Two semipolar mutagenic PACs were also present at significant levels 2-nitrofluoranthene, a product of atmospheric reactions, and 6//-benzo[c<7]pyren-6-one, a primary O-PAC pollutant present in exhaust emissions from diesel engines and non-catalyst-equipped cars (see Sections E and F). These account for an additional 0.8 and 1.6%, respectively, of the identified whole sample mutagenic potency (see Table 10.26). 

Karonis, D., E. Lois, S. Stournas, and F. Zannikos, Correlations of Exhaust Emissions from Diesel Engine with Diesel Fuel Properties, Energy Fuels, 12, 230-238 (1998). 

Japan does not currently regulate exhaust particulate emissions from diesel engines. However, smoke standards have applied to both new and in-use vehicles since 1972 and 1975, respectively. The maximum permissible limits for both are 50 percent opacity however, the new vehicle standard is the more stringent because smoke is measured at full load, while in-use vehicles are required to meet standards under the less severe no-load acceleration test. 

Smoke emission from diesel engines is controlled by operation of the engine within its design limits. (Most smoke emission occurs when the engine is overloaded.) Filters for diesel engine exhaust are under development. 

Schuetzle, D., and J. A. Frazier, Factors Influencing the Emission of Vapor and Particulate Phase Components from Diesel Engines, in Carcinogenic and Mutagenic Effects of Diesel Engine Exhaust (N. Ishinishi, A. Koizumi, R. O. McClellan, and W. Stober, Eds.), pp. 41-63, Elsevier, Amsterdam/New York, 1986. 

A great effort is underway to develop reliable aftertreatment systems for lowering NOx emissions from diesel and LB engines. A variety of approaches have been proposed for NOx aftertreatment of advanced vehicles including lean NOx catalysts (LNC), NOx storage and reduction (NSR) catalysts, selective catalytic reduction with urea (urea-SCR), and plasma-assisted catalysis (PAC). Lean NOx catalysts are mainly designed to reduce NOx with unburned hydrocarbons already included in the exhaust stream in the presence of O2 but result in... 

Several experiments have shown that most PAH mixtures are considerably less potent than individual PAHs. Various combustion emissions and benzo[a]pyrene have been examined for carcinogenic potency and tumor initiation activity on mouse skin. In all cases, PAH mixtures were much less potent than benzo[a]pyrene. The authors calculated relative potency estimates that ranged from 0.007 for coke oven emissions extract to less than 0.002 for diesel engine exhaust extract, using papillomas per mouse per milligram of the mixture as the end point (Slaga et al. 

Diesel engines are reliable, fuel efficient, and relatively dean. Since the application of three-way catalysts for otto engines, the emissions of diesel engines are subject to discussion. The emissions that are the main topics of concern are those of NOx and particulates. In this paper, the removal of particulates from diesel exhaust gas will be discussed. 

A major difference between diesel engines and gasoline powered engines is that the potential for controlling hydrocarbons in diesel exhaust through exhaust catalysts is very poor. The most that can be expected is some form of trap to contain diesel particulates. This may also be effective in controlling PNA, since a substantial part of the PNA emission from diesels is associated with the solid material. 

Another approach to the problem of NOx emissions from diesel vehicles is the use of NOx traps. NO2 is acidic and is adsorbed by basic oxide, such as BaO, to form Ba(N03)2. The NO2 is released and reduced to N2 during the periodic engine rich excursion. Basic oxides will, of course, bind sulfur oxides as well, and high temperature intervals with rich exhaust gas must be included in the engine control strategy to desulfate the catalyst. The lean-NOx-trapping concept is currently not in wide commercial use while development efforts are continuing. 

Nevertheless, secondary measures are mostly still needed to reduce exhaust emissions of cars to meet current emission standard in most countries. These so-called end-of-pipe solutions are based on the catalytic conversion of all HCs, CO and NO (three-way catalyst). The success of the monolithic catalytic converter (which has a lower pressure drop than a fixed bed) is up to now limited to gasoline powered engines. However, in recent years progress has been made in the development of catalytic filters for the cleaning of exhaust gas (e.g., particulate matter) from diesel engines. 

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