Fuel mixtures

Stoichiometry is the composition of the air-fuel mixture required to obtain complete combustion. The stoichiometric ratio, r, is the quotient of the respective masses, and m, of air and fuel arranged in the stoichiometric conditions ... 

During the determination of the RON, the CFR engine operates at 600 rpm with a timing advance set at 13° TDC and with no fuel mixture preheating. The MON by contrast operates at 900 rpm, with an advance from 14 to 26° depending on compression ratio and a fuei mixture temperature of 149°C. 

Nitromethane is a very common material. Just go down to your local drag strip and pick up a gallon or two for doping your high performance cars fuel. It s also available up to 40% pure in RC model fuels. Simply fractionally distill the nitromethane (bp 101°C) out of the model fuel mixture and you re ready to go. If methanol Is present in the fuel formulation, some will azeotropically distill over with the nitromethane lowering its boiling point slightly, but this does not present a problem. 

Vehicle Emissions. Gasohol has some automotive exhaust emissions benefits because adding oxygen to a fuel leans out the fuel mixture, producing less carbon monoxide [630-08-2] (CO). This is tme both for carbureted vehicles and for those having electronic fuel injection. 

Starting in the city of Sao Paulo in 1977, and extending to the entire state of Sao Paulo in 1978, a gasohol incorporating 20% ethanol was mandated. Brazil s National Alcohol Program (Proalcool) set an initial goal of providing the 20% fuel mixture nationwide by 1980—1981 and a system of special tax, warranty, and price considerations were enacted to advance the aims of Proalcool. 

The development of combustion theory has led to the appearance of several specialized asymptotic concepts and mathematical methods. An extremely strong temperature dependence for the reaction rate is typical of the theory. This makes direct numerical solution of the equations difficult but at the same time accurate. The basic concept of combustion theory, the idea of a flame moving at a constant velocity independent of the ignition conditions and determined solely by the properties and state of the fuel mixture, is the product of the asymptotic approach (18,19). Theoretical understanding of turbulent combustion involves combining the theory of turbulence and the kinetics of chemical reactions (19—23). 

In automotive and aerospace end uses, the apphcations ate also often electrical. Polysulfones do not have as good solvent resistance as poly(phenylene sulfide). They perform well in hydrocarbons like gasoline and oil, or in antifreeze, but ate attacked by the alcohol-blend fuel mixtures. This may limit their under-the-hood apphcations. 

Hydrocarbons and carbon monoxide emissions can be minimised by lean air/fuel mixtures (Fig. 2), but lean air/fuel mixtures maximize NO emissions. Very lean mixtures (>20 air/fuel) result in reduced CO and NO, but in increased HC emissions owing to unstable combustion. The turning point is known as the lean limit. Improvements in lean-bum engines extend the lean limit. Rich mixtures, which contain excess fuel and insufficient air, produce high HC and CO concentrations in the exhaust. Very rich mixtures are typically used for small air-cooled engines, needed because of the cooling effect of the gasoline as it vaporizes in the cylinder, where CO exhaust concentrations are 4 to 5% or more. 

Catalytic Unit. The catalytic unit consists of an activated coating layer spread uniformly on a monolithic substrate. The catalyst predominantly used in the United States and Canada is known as the three-way conversion (TWC) catalyst, because it destroys aU three types of regulated poUutants HC, CO, and NO. Between 1975 and the early 1980s, an oxidation catalyst was used. Its use declined with the development of the TWC catalyst. The TWC catalytic efficiency is shown in Figure 5. At temperatures of >300° C a TWC destroys HC, CO, and NO effectively when the air/fuel mixture is close to... 

The second type is the quaUty of combustion. A misfire or partial misfire of the air/fuel charge in the combustion chamber causes the unbumed air and fuel mixture to pass to the catalyst, where combustion occurs. The temperature rise from combustion in the catalyst is considerable. Two misfiring cylinders in a four-cylinder engine could cause the catalyst to approach the melting temperature of the substrate (1465°C) (69). 

Fuel sulfur is also responsible for a phenomena known as storage and release of sulfur compounds. Sulfur oxides (S02,S02) easily react with ceria, an oxygen storage compound incorporated into most TWC catalysts, and also with alumina. When the air/fuel mixture temporarily goes rich and the catalyst temperature is in a certain range, the stored sulfur is released as H2S yielding a rotten egg odor to the exhaust. A small amount of nickel oxide incorporated into the TWC removes the H2S and releases it later as SO2 (75—79). 

The function of the oxygen sensor and the closed loop fuel metering system is to maintain the air and fuel mixture at the stoichiometric condition as it passes into the engine for combustion ie, there should be no excess air or excess fuel. The main purpose is to permit the TWC catalyst to operate effectively to control HC, CO, and NO emissions. The oxygen sensor is located in the exhaust system ahead of the catalyst so that it is exposed to the exhaust of aU cylinders (see Fig. 4). The sensor analyzes the combustion event after it happens. Therefore, the system is sometimes caUed a closed loop feedback system. There is an inherent time delay in such a system and thus the system is constandy correcting the air/fuel mixture cycles around the stoichiometric control point rather than maintaining a desired air/fuel mixture. 

The oxygen sensor closed loop system automatically compensates for changes in fuel content or air density. For instance, the stoichiometric air/fuel mixture is maintained even when the vehicle climbs from sea level to high altitudes where the air density is lower. 

One system for measuring catalyst failure is based on two oxygen sensors, one located in the normal control location, the other downstream of the catalyst (102,103). The second O2 sensor indicates relative catalyst performance by measuring the abiUty to respond to a change in air/fuel mixture. Other techniques using temperatures sensors have also been described (104—107). Whereas the dual O2 sensor method is likely to be used initially, a criticism of the two O2 sensors system has been reported (44) showing that properly functioning catalysts would be detected as a failure by the method. 

The operating air/fuel mixture of the two-stroke engine designs range from 1.3 to 2.0 stoichiometric. This lean mixture plus the characteristic internal exhaust gas recirculation lowers the peak combustion temperatures and results in low NO formation. 

The fuel flows at right angles to the air flow. Only a small amount of air is fed at the front of the stoker, to keep the fuel mixture rich, but as the coal moves toward the middle of the furnace, the amount of air is increased, and most of the coal is burned by the time it gets halfway down the length of the grate. Fuel-bed depth varies from 100 to 200 mm (4 to 8 in), depending on the fuel, which can be coke breeze, anthracite, or any noncaking bituminous coal. 

In a typical PAFC system, methane passes through a reformer with steam from the coolant loop of the water-cooled fuel cell. Heat for the reforming reaction is generated by combusting the depleted fuel. The reformed natural gas contains typically 60 percent H9, 20 percent CO, and 20 percent H9O. Because the platinum catalyst in the PAFC can tolerate only about 0.5 percent CO, this fuel mixture is passed through a water gas shift reactor before being fed to the fuel cell. 

High stack temperature can be the result of an improper air to fuel mixture. A leak of combustible material from the process side to the firetube is also a cause. It can also be the result of excessive soot deposition in the firetube. 

A variety of graphite moderated reactor concepts have evolved since the first aircooled reactors of the 1940s. Reactors with gas, water, and molten salt coolants have been constructed and a variety of fuels, and fissile/fertile fuel mixtures, have been used. The evolution and essential features of graphite moderated power producing reactors are described here, and details of their graphites cores are given. 

Urtiew, P. A. 1981. Flame propagation in gaseous fuel mixtures in semiconfined geometries. report no. UC1D-I9000. Lawrence Livermore Laboratory. 

Kraft-mehl, n. starch, amylum. -messer, m. dynamometer, -mittel, n. forceful means powerful remedy tonic, -packpapier, n. kraft (wrapping) paper, -papier, n. kraft paper, kraft. -papierstoff, m. kraft pulp, -quelle, /. source of power, -rad, n. motorcycle. -rdhre, /. (Physics) tube of force, -sammler, m. accumulator, -sitz, m. (Mach.) forced fit. -speicher, m. accumulator, -spi-ritus, m. motor spirit, -stoff, m. power fuel, motor fuel (Paper) kraft pulp, -stoffge-misch, n. fuel mixture, -stoffverbrauch, m. fuel consumption, -stoffwirtschaft, /. fuel economy, -strom, m. (Elec.) power current, -iibertragung, /. power transmission, -ver-brauch, m. power consumption, -verkehr, m. motor traffic. 

Treibstoff, m. motor fuel propellant, -alko-holgemisch, n. alcoholic motor-fuel mixture, -tank, m, motor fuel tank, "gas tank, petrol tank,... 

Liquid Pool Flames. Liquid fuel or flammable spills often lead to fires involving a flame at the surface of the liquid. This type of diffusion flame moves across the surface of the liquid driven by evaporation of the fuel through heat transfer ahead of the flame. If the liquid pool or spill is formed at ambient conditions sufficient to vaporize enough fuel to form a flammable air/fuel mixture, then a flame can propagate through the mixture above the spill as a premixed flame. 

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