Stoichiometric Combustion Ratios

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 ... 

The diesel engine operates, inherently by its concept, at variable fuel-air ratio. One easily sees that it is not possible to attain the stoichiometric ratio because the fuel never diffuses in an ideal manner into the air for an average equivalence ratio of 1.00, the combustion chamber will contain zones that are too rich leading to incomplete combustion accompanied by smoke and soot formation. Finally, at full load, the overall equivalence ratio... 

Thermal energy in flame atomization is provided by the combustion of a fuel-oxidant mixture. Common fuels and oxidants and their normal temperature ranges are listed in Table 10.9. Of these, the air-acetylene and nitrous oxide-acetylene flames are used most frequently. Normally, the fuel and oxidant are mixed in an approximately stoichiometric ratio however, a fuel-rich mixture may be desirable for atoms that are easily oxidized. The most common design for the burner is the slot burner shown in Figure 10.38. This burner provides a long path length for monitoring absorbance and a stable flame. 

Where T)is flame temperature in K MC is moisture content of the waste, expressed on a total weight basis SR is defined as stoichiometric ratio or moles O2 avadable/moles O2 required for complete oxidation of the carbon, hydrogen, and sulfur in the fuel, ie, 1/SR = equivalence ratio and is temperature of the combustion air, expressed in K. In Fnglish units, this equation is as follows ... 

Figure 4 illustrates the trend in adiabatic flame temperatures with heat of combustion as described. Also indicated is the consequence of another statistical result, ie, flames extinguish at a roughly common low limit (1200°C). This corresponds to heat-release density of ca 1.9 MJ/m (50 Btu/ft ) of fuel—air mixtures, or half that for the stoichiometric ratio. It also corresponds to flame temperature, as indicated, of ca 1220°C. Because these are statistical quantities, the same numerical values of flame temperature, low limit excess air, and so forth, can be expected to apply to coal—air mixtures and to fuels derived from coal (see Fuels, synthetic). 

Fuel Heat of Combustion (288 K, 1 atm) (MJIm ) Stoichiometric Volume Ratio (%) Heat of Combustion Stoichiometrically Mixed with Air (MJ/m )... 

For conventional gasoline, the stoichiometric ratio is approximately 14.7. Its precise value varies slightly with the composition of the gasoline. Maximum power is achieved with a slightly rich air/fuel ratio— say, 12.5. Maximum efficiency is achieved with a slightly lean mixture—say, 16—although this best-economy mixture ratio is somewhat dependent on combustion quality. 

Hydrocarbon-rich conditions imply that oxygen is the limiting reactant, due to the high oxygen-to-hydrocarbon stoichiometric ratio in n-hexane ammoxidation. Therefore, the conversion of the hydrocarbon is low this should favour, in principle, the selectivity to products of partial (amm)oxidation instead of that to combustion products. 

Stoichiometric combustion air requirement, 72 322t Stoichiometric concentration, 27 840 Stoichiometric organic synthesis, metal carbonyls in, 76 72 Stoichiometric parameters, in reactor technology, 27 337-338 Stoichiometric ratios, epoxy/curing agent, 70 418-420... 

As the combustion proceeded, the bed surface regressed downwards and reached the first thermocouple (Tl), and after some time the second one (T2), and then the third one (T3). Since the time elapsed for the combustion front to regress between the thermocouples was measured (derived from temperature curves), and the distances between the thermocouples were fixed, the regression rate could be calculated. From the ratio between the air flow and regression rate the bed stoichiometric ratio could be obtained. 

The stoichiometric ratio is the proportion of fuel and oxidizer that results in optimal combustion and maximum heat release. The optimal ratio is deter-... 

A mixture below it stoichiometric ratios is described as "lean." A mixture above its stoichiometric ratio is described as "rich." A "lean" mixture has extra oxygen along with the combustion products and a "rich" mixture has fuel remaining with the combustion products. 

A theoretical analysis of combustion synthesis of refractory nitrides was presented by Munir and Holt in 1987.37 They predicted the existence of an activation energy due to chemical reaction or mass-transport. Glassman et al. in 1987,38 in their thermodynamic analysis of TiN formation, examined the possibility of creating TiN by a self-sustained reaction of the metal particles and nitrogen gas in a rocket motor. They reported that for the stoichiometric ratio of 0.5 mole N2/mole titanium, the reaction has... 

Thus, for rapid combustion of non-premixed gases, in the reaction zone we obtain exactly the same concentration of combustion products as if we had mixed the burning gases in a stoichiometric ratio and carried out the chemical combustion reaction without any diffusion exchange. 

This is called the stoichiometric ratio of the combustion system. 

On the contrary, for propane combustion on Pd/AljOj modified by ceria addition, Shyu and co-workers observed that ceria allows to maintain Pd in a more stable oxidised state less prompt to react with propane [78], Catalytic oxidation which occurred from 200°C to 350°C is now delayed to higher temperature by 50°C to 100°C from 250°C to 450°C. More dramatically is the decrease of the conversion at 350°C from 100% to 20% as the partial pressure of oxygen increases beyond the stoichiometric ratio up to 8 times. They concluded from their studies that ceria and palladium are in close interaction, may be in a Pd-O-O-Ce-0 model via a O2 species. 

The reduction of fuel-N to molecular nitrogen in air staging is favored in the fuel rich primary combustion zone ( Fig. 3 ). Investigations on fixed bed wood furnaces have shown that a minimum of the Total Fixed Nitrogen (TFN = HCN+NH3+NO+ NO2+2N2O emission from the primary combustion zone is reached for a stoichiometric ratio of 0.7 to 0.8 and a temperature of 1100 C to 1200 °C and providing a mean residence time of 0.5 s. After the reduction zone the combustion is completed in the burnout zone by injection of the excess air. 

The injection of burnout air completes the combustion after the reduction zone. The amount of burnout air is controlled the way that complete burnout is achieved at a stoichiometric ratio between 1.5 and 2,0. The oxygen content in the flue gas is also continuously measured with a second gas sensor. A flue gas ventilator controls the pressure in the facility and guarantees safe operation. 

Fi%. 8 Influence of stoichiometric ratio in the reduction zone in air staged combustion of wood chips and UF-chipboard. 

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