Diesel exhaust, composition

D-4 N2O5 + Diesel Exhaust Investigate effects of NO3 on diesel exhaust composition. N2O5 decomposes to form NO2 and NO3. 

Knowing the results of epidemiology studies on the association between diesel exhaust exposure and lung cancer, and animal studies on the toxicity of two types of soot, what can we conclude concerning the toxicity to humans of soot associated with fires Combustion processes produce small, respirable size soot particles. The composition of the soot from fires can vary widely with the condi-... 

An ozone treatment (10 minutes at room temperature) of the HF-etched SiC surface before the metallization step was introduced as a very convenient processing step to produce Schottky diode gas sensors with an increased stability and reproducibility. The use of spectroscopic ellipsometry analysis and also photoelectron spectroscopy using synchrotron radiation showed that an oxide, 1-nm in thickness, was formed by the ozone exposure [74, 75]. The oxide was also found to be close to stochiometric SiO in composition. This thin oxide increased the stability of the SiC Schottky diodes considerably, without the need for any further interfacial layer such as Ta or TaSi which have been frequently used. Schottky diodes employing a porous Pt gate electrode and the ozone-produced interfacial layer have been successfully operated in both diesel exhausts and flue gases [76, 77]. 

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... 

Problems that have been solved in the risk assessment of single substances have not been solved equally well in mixture assessments. Even the most generic question in prospective risk analyses— What is a safe level —poses problems. Often the mixture composition is unknown, and the mixture problem is then that the safe level would only be applicable to that particular mixture. Even if the mixture composition is well characterized, the safe exposure or concentration level would apply only to mixtures with the same or similar concentration ratios between the mixture compounds, as in cigarette smoke, diesel exhaust, or some polychlorinated biphenyl (PCB) mixtures. One option in such cases is to set a safe level for the mixture by using one of the mixture components as an indicator compound for the whole mixture. If the concentration ratios between the mixture compounds vary, there is no unique safe mixture concentration, but an infinite number of possible safe concentration combinations. 

Sufficiently similar mixtures. Another approach is to use surrogate data on one whole mixture to conduct the risk assessment of another. This applies the concept of sufficient similarity, defined as 2 mixtures close in chemical composition where there are small differences in their components and in the proportions of their components. Key issues for similar mixtures include assessing the similarity of analytical chemistry and toxicological data for mixtures. In this case, an RfD, RfC, or slope factor could be calculated for the mixture of concern using data on a sufficiently similar mixture. This concept is also used in specific applications to groups of similar mixtures that are produced by similar processes, for example, the comparative potency method as applied to diesel exhaust emissions (Lewtas 1985,1988 Nesnow 1990). 

By virtue of the composition of the exhaust gases, mass gassings with Diesel exhaust fumes cannot have taken place. Had there really been execution chambers or gas vans operating with exhaust gas, the Germans would have used the more efficient internal combustion engines, or the even more efficient wood-gas generators. 

Particulates are another source of respiratory irritation when inhaled. In urban environments, diesel exhaust particles and fly ash residue from power plant oil combustion are the main contributors of respirable particulates of less than 10 pm diameter (PM 10). These contain mixtures of lipo-philes and hydrophiles including various metals, acid salts, aliphatic hydrocarbons, PAHs, quinones, nitroaromatic hydrocarbons, andaldehydes. 151 Diesel combustion particulates contain large surface areas that can adsorb large quantities of organic compounds and deliver these to respiratory tract tissue. Other inhaled particulates can adhere to lung surfaces and adsorb and bond other vapors that are inhaled, thereby increasing their toxicities. PM2.5 particulates (those with diameters of less than 2.5 pm) that reach the lower respiratory tract as far as the alveoli are more toxic than PM 10 particulates of the same composition. 16 ... 

Complex Mixture A combination of so many chemicals that the composition of the mixture is not fully characterized, either qualitatively or quantitatively, and may be variable (e.g., cigarette smoke, diesel exhaust, gasoline). 

The composition of PAH emissions varies with the combustion source. For example, emissions from residential wood combustion contain more acenaphthylene than other PAHs (Perwak et al. 1982), whereas auto emissions contain more benzo[g,h,i]perylene and pyrene (Rogge et al. 1993a Santodonato et al. 1981). PAHs in diesel exhaust particulates are dominated by three- and four-ring compounds, primarily fluoranthene, phenanthrene, and pyrene (Kelly et al. 1993 Rogge et al. 

D-1 Diesel Exhaust Only Determine changes in exhaust composition due to aging in chamber. 

L-1 Diesel Exhaust Only Examine effects of photolysis reactions on exhaust composition. 

The bed material consisted of a mixture of the powder sample and quartz sand in order to obtain a constant space velocity (25000 h ) for all tested catalysts. The gas composition used in the experiments was 10% O2,405 ppm NO and 911 ppm C3H6, balanced with Ar to yield a total flow of 420 ml/min. The samples were initially reduced in 5000 ppm H2 at 400°C for 15 min and stabilised in the reaction mixture at 525°C for 1 h. The samples were then cooled down to room temperature under an Ar flow. At this temperature, the catalyst was exposed to the reaction mixture under 15 min before starting the heating ramp up to 525°C, at a constant rate of 6°C/min. The steady-state experiments were performed by subsequently lowering the temperature in steps of 50°C, starting from the final ramp temperature and the products were analysed after approximately 90 min. In order to facilitate the interpretation of the flow reactor and FTIR results the model gas was simplified by omitting H O and SO2 (which would have been present if a diesel exhaust was used). 

Regarding the composition of diesel exhaust gases (containing amongst others water and SO2), developing a stable, zeolite based diesel exhaust deNOx catalyst is a challenging task. Zeolites can show dealumination under hydrothermal conditions accompanied by a loss of active material furthermore SO2 can also cause deactivation. Many authors already have reported on the hydrothermal stability of zeolite SCR catalysts [e.g. 7-9] and also some papers exist on the stabilization with respect to hydrothermal deactivation of zeolite SCR catalysts by the choice of proper cations [10-13]. A small number of articles describes the influence of SO2 on zeolite SCR catalysts [14-17]. The current paper gives the results of measurements on both the short term hydrothermal stability and the influence of SO2 on CeNa-MOR and CeH-ZSM-5 zeolite catalysts. 

The majority of the performance tests were done with an integral model gas reactor, described in a recent paper [2]. It consists of a gas mixing section, a reactor section and an analytical section. For simulation of typical diesel exhaust gas hydrocarbons several selected liquid HC-components were introduced in the exhaust gas stream by means of an HPLC-pump (Shimazu LC9A) and using an stainless steel evaporator (T>180°C). The model gas compositions used in this study are given in Table 2. 

In the early days of exhaust emissions control, it was established that, within the likely commercial range, motor gasoline and diesel fuel composition have relatively little effect on the composition of vehicle exhaust in terms of the regulated components carbon monoxide, unburnt hydrocarbons and nitrogen oxides. Legislation relating these exhaust components has therefore had little direct effect on the way in which fuels are refined and, hence, their composition. The only exception to this is where emissions controls are so severe as to demand catalytic exhaust control and hence unleaded gasoline. 

In ambient aerosols, organic compounds released in combustion processes will be incorporated into the particles through adsorption or condensation. As a result, organics are found predominantly in the accumulation mode of the aerosol, i.e. the respirable particles C<2yum) which have a large specific surface. Each aerosol particle should therefore be considered as a matrix of various shape and composition (e.g. fly-ash spherical particles built from metal oxides diesel exhaust conglomerates of carbon to which one or more surface layers of PAH are adsorbed. The chemical reactivity of" PAH will therefore be affected by two new parameters, depending on the particle matrix. 

The model of Reference (67) was later applied to evaluate the performance of an SCR catalyst with proprietary composition (124). Koebel and Elsener also compared, on a fully predictive basis, a similar model to experimental data of NO conversion and NH3 slip obtained on a diesel engine test stand (125). In this case, while the model was shown to describe qualitatively the performance of the SCR monolithic reactor, specifically with reference to the NO conversion versus NH3 slip relationship, an exact quantitative match was found impossible. According to the authors, the reasons for the discrepancies may include unaccovmted kinetic effects of the contaminants present in the diesel exhaust gases, vmcertainties due both to the extrapolation of the kinetic parameters and to the measurement of the intraporous diffusivities, and the excessive simplification involved in the assumption of a pure Langmuir isotherm for NH3 adsorption. 

As the composition and the concentration of diesel exhaust gases vary significantly depending on the engine operation, it is quite important to understand the transient behavior of NOx reduction following NH3 supply and shutoff. In this section, the effect of the periodical supply of NH3 on the NOx reduction behavior is presented. 

Some examples of SPE results are shown in Table 2. The DECSE3 diesel is a sample from another study diat was used to investigate the effeets of sulfur levels on the operation of diesel exhaust emission control devices, and the remaining samples were obtained from various refineries across Canada. These fuels were prepared for a collaborative research program Canadian Diesel Fuel Composition and Emissions . ... 

Cold composite curve, 23 191 Cold-ethanol precipitation, 22 135-136 Cold exhaust dyeing, 9 176-177 Cold flow improvers, for diesel fuel, 22 427-428... 

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