Exhaust lead trap

Increased use of leaded gasoline in Canada may generate pressures to control automotive exhaust lead emissions, although there is no established health-based lead-in-air standard to serve as the basis for such control. If reduction of automotive lead emissions into the atmosphere should be required, controls should be placed on the amount of lead emitted from the tailpipe, similar to the manner by which gaseous emissions are controlled. Such action is more energy efficient than reducing the amount of lead used in gasoline. One effective way to control tailpipe lead emissions is the use of automotive exhaust lead trap that replaces the standard muffler (2). 

This report describes the two-year road test program, supported by laboratory analysis, conducted by the Canadian Combustion Research Laboratory of Energy, Mines and Resources Canada to evaluate the effectiveness of automotive exhaust lead traps. The exhaust traps were designed and built by the Du Pont Company. 

Du Pont and other major lead antiknock manufacturers have been developing automotive exhaust lead traps since the middle 1960s (3). Other road tests have shown these traps to be effective under benign climate conditions, but none have considered the wide range found in Canada. 

Automotive exhaust lead traps can reolace standard mufflers and portions of the exhaust system and can reduce automotive lead emissions by 80%. 

Automotive exhaust lead traps are equally effective over the wide range of temperatures encountered during the extremes of winter and summer driving conditions in Canada. 

The use of lead traps will not affect fuel consumption, vehicle drivability and exhaust muffling. Automotive exhaust lead traps are relatively... 

Fig. 5.9 Lead emissions from a car with a standard exhaust and a du Pont exhaust lead trap [14]. 

The test fleet consisted of eight identically-equipped 1974 four-door Chevrolet Biscaynes operated by the Department of National Defence, Canada. These cars were equipped with 5.74 litre V-8 engines having air pumps to supply secondary air to the exhaust manifolds to reduce gaseous emissions. Four vehicles were equipped with new standard muffler and exhaust pipe systems and were used as control cars. The standard mufflers and exhaust pipes of the second group of four cars were replaced with lead trap systems. 

Figure 1. Lead trap system and standard exhaust system.

Figure 3. Cutaway view of lead trap showing location of alumina pellets upstream of cyclone separators. The alumina pellets promote agglomeration and the dual parallel cyclones separate and retain the exhaust particulate matter in collection chambers.

For the lead trap cars, lead emissions were only one-third those of the standard cars over the urban cycle and one-twelfth those of the standard cars over the highway cycle. This test demonstrates that purging of previously collected exhaust particulate matter does not take place with properly designed traps when switching from sustained mild driving conditions to more severe conditions of continuous operation at highway speeds. 

Purging of previously collected lead salts occurs with standard exhaust systems, but does not occur with well-designed lead traps, such as the type tested in this program. 

Casella et al., "Evaluation of Lead Trap Performance in Exhaust Engine Control", Accordo di Ricerca (FEEMAS),... 

Despite present predictions for the number of diesel-powered cars in Europe to increase markedly, discussions on the engineering approach to the control of automobiel emissions have centered on the gasoline motor. Cylinder wall temperature, air-fuel ratios, exhaust gas catalysts, and lead traps were presented and discussed as remedies. Blended fuel, for instance gasohol or synthetic fuels, were not considered because they are used on a local basis or during transient, difficult conditions. The contribution of lubricating oil in PAH emissions exists but was not considered an important issue, and was not discussed in the meeting. 

A demonstration of the effectiveness of the du Pont trap appears in Fig. 5.9, in which the emissions from cars fitted with a standard exhaust and with the lead trap are compared. High efficiency of particle trapping is achieved, especially for the larger particle sizes (Table 5.10). Work at the Warren Spring Laboratory, England, showed that the lead emitted with standard exhausts and lead traps was respectively 70.0 and 37.5% of the lead input to the engine over a prolonged road test [15]. 

The residues deposit causes a reduction in the material permeability during the DPF life. This phenomenon leads to an increase in the exhaust back pressure, and is noticeably more marked when the soot quantity trapped in the DPF increases (see Figure 7.9). 

Overall, the NO, Trap added to the DPF in the exhaust line gives a complex and expensive after-treatment system that has an impact on the engine operation and leads to a fuel over-consumption. 

Another important catalytic technology for removal of NOx from lean-burn engine exhausts involves NOx storage reduction catalysis, or the lean-NOx trap . In the lean-NOx trap, the formation of N02 by NO oxidation is followed by the formation of a nitrate when the N02 is adsorbed onto the catalyst surface. Thus, the N02 is stored on the catalyst surface in the nitrate form and subsequently decomposed to N2. Lean NOx trap catalysts have shown serious deactivation in the presence of SOx because, under oxygen-rich conditions, SO, adsorbs more strongly on N02 adsorption sites than N02, and the adsorbed SOx does not desorb altogether even under fuel-rich conditions. The presence of S03 leads to the formation of sulfuric acid and sulfates that increase the particulates in the exhaust and poison the active sites on the catalyst. Furthermore, catalytic oxidation of NO to N02 can be operated in a limited temperature range. Oxidation of NO to N02 by a conventional Pt-based catalyst has a maximum at about 250°C and loses its efficiency below about 100°C and above about 400°C. 

This outline is not exhaustive. For example there is an increasing awareness of the role played by infection with the human immunodeficiency virus while infiltration of the marrow with fibrous tissue or tumour cells will decrease production. In much the same way massive splenomegaly, so common in tropical Africa, sequesters significant volumes of red cells while malarial infection results in their accelerated breakdown. In some cases defects are multifactorial as in chronic lymphocytic leukaemia where infiltration decreases production, splenomegaly traps large amounts of blood while immune mechanisms lead to shortened survival or haemolysis. 

The data presented above indicate that, although the metal component is not able to activate saturated hydrocarbon molecules, it is very active as a trap for free radicals generated by the oxide catalyst. As a result, reaction (5) competing with (4) leads to the apparent increase in activity of the binary catalyst, and the selectivity of the overall process is determined by the competition between reactions (3) and (5). On the other hand, the treatment in hydrogen flow causes exhaustion of this oxygen buffer , which cannot be restored in the presence of both reactants in the reaction mixture due to the high reducing activity of methyl radicals. 

The hemopoietic problems associated with a B12 deficiency are identical to those observed in a folate deficiency and, in fact, result from a folate deficiency secondary to (i.e., caused by) the B12 deficiency (i.e., the methyl trap hypothesis). As the FH4 pool is exhausted, deficiencies of the tetrahydrofolate derivatives needed for purine and dTMP biosynthesis develop, leading to the characteristic megaloblastic anemia. 

The trap system consisted of two components, as shown in Figure 1. The forward component was a tube cooler, which replaced the standard muffler. A cutaway sketch of the tube cooler is shown in Figure 2. The primary purpose of the cooler was to maintain exhaust temperatures of 300°C to 400°C in the downstream trap. Without the cooler, inlet temperatures of the trap would have been about 500°C during highway operation. Most of the lead salts in the exhaust are lead halides, which are in the vapour state at temperatures about 400°C and mostly solids below 300°C. 

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