Leaded fuels

In every part of the world, the same type of classification as above is found for fuels premium or regular, with or without lead. The octane numbers can be different from one country to another depending on the extent of development of their car populations and the capabilities of their local refining industries. The elimination of lead is becoming the rule wherever there are large automobile populations and severe anti-pollution requirements. Thus the United States, Japan and Canada no longer distribute leaded fuels. (... 

However, in some countries such as Germany there is considerable reservation to adding scavengers because of their possible contribution to dioxin emissions. Furthermore, for lead contents of 0.15 g/1, the need for scavengers is questionable. It is possible that the leaded fuels sold in the coming years will contain neither chlorine nor bromine. 

Would you expect to find the same chemical composition of the hydrocarbons from the exhaust of a gasoline-powered automobile as that of gasoline in the vehicle s tank Why What would be the effect on emissions from a gasoline-powered vehicle if it was designed to be operated on leaded fuel and an unleaded fuel was used ... 

What would be the effect on emissions from a gasoline-powered vehicle if it was designed to be operated on unleaded fuel and a leaded fuel was used ... 

Sodium and potassium are restricted because they react with sulfur at elevated temperatures to corrode metals by hot corrosion or sulfurization. The hot-corrision mechanism is not fully understood however, it can be discussed in general terms. It is believed that the deposition of alkali sulfates (Na2S04) on the blade reduces the protective oxide layer. Corrosion results from the continual forming and removing of the oxide layer. Also, oxidation of the blades occurs when liquid vanadium is deposited on the blade. Fortunately, lead is not encountered very often. Its presence is primarily from contamination by leaded fuel or as a result of some refinery practice. Presently, there is no fuel treatment to counteract the presence of lead. 

Unbumt gasoline and cracked hydrocarbons such as ethylene and propylene are also substantial constituents of exhaust. Gasoline contains additives such as benzene, toluene and branched hydrocarbons to achieve the necessary octane numbers. The direct emission of these volatile compounds, e.g. at gas stations, is a significant source of air pollution. Leaded fuels, containing antiknock additions such as tetra-ethyl-lead, have been abandoned because lead poisons both human beings and the three-way exhaust catalyst, especially for the removal of NO by rhodium. 

The public loved leaded fuel for its pep, not its efficiency. Interest in fuel conservation faded when new oil deposits were discovered. Reassured about lead s dangers, Americans reveled in unprecedented personal mobility and used tetraethyl lead to expand their reliance on automobiles. Surprisingly, Midgley did not think his discovery would increase passenger car ownership. Nevertheless, tetraethyl lead and the engine improvements it permitted helped form America s car-dependent society. Fuel-efficient cars and public transportation were no longer top priorities. 

Used industrially as a chemical intermediate in the manufacture of dyes, pharmaceuticals, and polymers as a special solvent, as an exhaust system scavenger for leaded fuels, and in gauge fluids used in agriculture as a fumigant. 

Increases in Pb concentrations of 30 times have been measured in Lake Washington caused mainly through the burning of leaded fuel in internal combusion engines. Significant increases in the concentrations of Zn (6 times), Pb (13 times), and Cu (8 times) have been introduced by man s activity near Sinclair Inlet, probably as a result of shipyard s activities. 

Leaded fuels are now banned across Canada. In unleaded gasoline, simple organic compounds are added instead of lead compounds. These octane-enhancing compounds include methyl-t-butyl ether, t-butyl alcohol, methanol, and ethanol. Like lead catalysts. 

This section provides a brief description of the various, "leading" fuel cell technologies currently under development. 

This was calculated in the same manner as that described by Cass, Boone and Macias (9). The carbon to lead ratio determined from this inventory can be examined for several limiting cases ranging from the output of an automobile using leaded fuel (C/Pb /2) to aerosol in the well mixed LA air basin with significant secondary conversion of carbon (C/Pb>7). This approach assumes, of course, that lead is present only as a primary pollutant. For highway traffic composed of vehicles and fuel types in the same proportions as for the entire urban area, the ratio of aerosol carbon to lead was calculated to be about 4. 

This is about a factor of 2 lower than that calculated for 1980 due to the large number of automobiles which used unleaded fuel and the lower lead content in leaded fuel in 1980 (9 ). For the other extreme where primary emissions from all sources become well mixed, a situation which is possible because of the long... 

Analytical data on combustion chamber deposits accumulated from leaded fuel show the presence of both carbonaceous material and lead salts. An analysis of the extreme outer layer of deposits which have been causing surface ignition, however, shows that very little carbon is present and that nearly all the deposit is made up of lead salts (24, 41) This observation suggests that the carbonaceous portion of the deposit is consumed in the process of ignition, which is in agreement with the idea that glowing carbonaceous material is an important source of surface ignition (14). 

Another approach to the problem of relative resistance to surface ignition of various hydrocarbons has been to compare the fuels being rated with the occurrence of ignition caused by the deposits they form 39), These experiments were run with leaded fuels in an effort to simulate practical conditions, and tests were made under conditions of both cyclic operation and constant speed and load. Without exception, less surface ignition occurred under the constant speed and load conditions, with very great reductions in the case of toluene and benzene. This result was not unexpected, as aromatic compounds are known to produce carbon deposits rapidly under conditions of idling and deceleration 39), Table III presents data for conditions of cycling and constant speed and load. 

Effect of Additives. One of the first attempts to solve the preignition problem by additives was the use of tributyl phosphite, claimed in a patent by Campbell (14) This compound inhibited the catalytic activity of lead compounds in promoting the glowing of carbon. A later patent issued to Withrow claimed that trimethyl phosphate and trimethyl phosphite also are effective as fuel additives in inhibiting surface ignition due to leaded deposits (94). Street, in 1952, ran tests with tricresyl phosphate as an additive in leaded fuel and reported that the phosphorus compound affected the occurrence of lead compounds in the end-gas region of the combustion chamber (80). 

The most useful tool for the study of penetration is the electron microprobe, which was first used for this purpose by Cannon and Welling (14). They have shown the buildup of relatively thick layers of lead compounds around pellets exposed to exhaust originating from heavily leaded fuels. More recently, penetration profiles in pellets have been published for exhaust produced by fuels with lower amounts of lead. Figure 8 shows such a profile in a pellet exposed to exhaust with 0.5 g Pb/gal for 400 hr. Note, that at the exterior of the pellet, lead concentration (by weight) has... 

The material used for the electrolyte determines many of the fuel cell s properties, including its operating temperature, and thus is used to distinguish the different types of fuel cells. All the leading fuel cells are discussed in the sections that follow. 

Heavy metals concentration generally decreases in urban soils away from the main road network and with increasing depth of sampling. This can be explained by the strong dependence of these contaminants on the use of motor vehicles—leaded fuels for Pb, tire wear for Zn and Cd, brake pads for Sb, converters and exhaust systems for platinum group elements (PGEs). 

Direct and indirect evidence indicates that motor vehicles are a source of environmental PCDD/Fs, with leaded gasoline emitting higher levels of PCDD/Fs into the environment than unleaded gasoline.20-23 Leaded fuel-powered vehicles... 

The American 1970 Clean Air Act defined ambient air quality standards (NAAQS) in the United States for atmospheric ozone, NO, lead, carbon monoxide, sulfur oxides, and PM-10 (particulate matter less than 10 p.m). The strategy to reduce levels of lead, NOx, PM-10, and to some extent carbon monoxide was to control emissions from automobiles that included the phasing-out of leaded fuel. As previously noted, ozone is a product of the photochemical reaction of volatile organic compounds with NOx (photochemical smog), so the balance between organic compounds and NOx pollutants is important in meeting target ozone levels (e.g., 0.12 ppm). Emissions from stationary sources is an important factor, and limits have been set for them. Because of low pressure drop requirements, coated monolithic catalysts... 

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