Combustion, defined

The gross heat of complete combustiOTi is used to determine the net heat of complete combustion defined as the quantity of energy released when a unit mass of specimen is burned at constant pressure, with all the combustion products, including water, being gaseous. 

In practice, for motors, turbines or furnaces, the conditions of combustion are frequently far from those corresponding to stoichiometry and are characterized either by an excess or by an insufficiency of fuel with respect to oxygen. The composition of the fuel-air mixture is expressed by the equivalence ratio, (p, defined by the relation / 5 r)... 

In the expression for heating value, it is useful to define the physical state of the motor fuel for conventional motor fuels such as gasoline, diesei fuel, and jet fuels, the liquid state is chosen most often as the reference. Nevertheless, if the material is already in its vapor state before entering the combustion system because of mechanical action like atomization or thermal effects such as preheating by exhaust gases, an increase of usefui energy resufts that is not previously taken into consideration. 

This justifies all the work undertaken to arrive at fuel denitrification which, as is well known, is difficult and costly. Moreover, technological improvements can bring considerable progress to this field. That is the case with low NO burners developed at IFF. These consist of producing separated flame jets that enable lower combustion temperatures, local oxygen concentrations to be less high and a lowered fuel s nitrogen contribution to NOj. formation. In a well defined industrial installation, the burner said to be of the low NO type can attain a level of 350 mg/Nm, instead of the 600 mg/Nm with a conventional burner. 

Gas-phase reactions play a fundamental role in nature, for example atmospheric chemistry [1, 2, 3, 4 and 5] and interstellar chemistry [6], as well as in many teclmical processes, for example combustion and exliaust fiime cleansing [7, 8 and 9], Apart from such practical aspects the study of gas-phase reactions has provided the basis for our understanding of chemical reaction mechanisms on a microscopic level. The typically small particle densities in the gas phase mean that reactions occur in well defined elementary steps, usually not involving more than three particles. 

Physical Properties. Physical properties of waste as fuels are defined in accordance with the specific materials under consideration. The greatest degree of definition exists for wood and related biofuels. The least degree of definition exists for MSW, related RDF products, and the broad array of ha2ardous wastes. Table 3 compares the physical property data of some representative combustible wastes with the traditional fossil fuel bituminous coal. The soHd organic wastes typically have specific gravities or bulk densities much lower than those associated with coal and lignite. 

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 ... 

Partial Oxidation. It is often desirable to augment the supply of naturally occurring or by-product gaseous fuels or to produce gaseous fuels of well-defined composition and combustion characteristics (5). This is particularly tme in areas where the refinery fuel (natural gas) is in poor supply and/or where the manufacture of fuel gases, originally from coal and more recently from petroleum, has become well estabHshed. 

Indirect Hquefaction of coal and conversion of natural gas to synthetic Hquid fuels is defined by technology that involves an intermediate step to generate synthesis gas, CO +. The main reactions involved in the generation of synthesis gas are the coal gasification m2LC ions Combustion... 

Whereas there is no universally accepted specification for marketed natural gas, standards addressed in the United States are Hsted in Table 6 (8). In addition to these specifications, the combustion behavior of natural gases is frequently characteri2ed by several parameters that aid in assessing the influence of compositional variations on the performance of a gas burner or burner configuration. The parameters of flash-back and blow-off limits help to define the operational limits of a burner with respect to flow rates. The yeUow-tip index helps to define the conditions under which components of the natural gas do not undergo complete combustion, and the characteristic blue flame of natural gas burners begins to show yellow at the flame tip. These... 

Chemical Reaction Measurements. Experimental studies of incineration kinetics have been described (37—39), where the waste species is generally introduced as a gas in a large excess of oxidant so that the oxidant concentration is constant, and the heat of reaction is negligible compared to the heat flux required to maintain the reacting mixture at temperature. The reaction is conducted in an externally heated reactor so that the temperature can be controlled to a known value and both oxidant concentration and temperature can be easily varied. The experimental reactor is generally a long tube of small diameter so that the residence time is well defined and axial dispersion may be neglected as a source of variation. Off-gas analysis is used to track both the disappearance of the feed material and the appearance and disappearance of any products of incomplete combustion. 

The flash point of PPS, as measured by ASTM D1929, is greater than 500°C. Combustion products of PPS include carbon, sulfur oxides, and carbonyl sulfide. Specific hazards are defined by the OSHA Hazard Communication Standard (158). Based on information in 1995, PPS does not meet any of the hazard definitions of this standard. 

Thep and q denote the integral exponents of D in the respective summations, and thereby expHcitiy define the diameter that is being used. and are the number and representative diameter of sampled drops in each size class i For example, the arithmetic mean diameter, is a simple average based on the diameters of all the individual droplets in the spray sample. The volume mean diameter, D q, is the diameter of a droplet whose volume, if multiphed by the total number of droplets, equals the total volume of the sample. The Sauter mean diameter, is the diameter of a droplet whose ratio of volume-to-surface area is equal to that of the entire sample. This diameter is frequendy used because it permits quick estimation of the total Hquid surface area available for a particular industrial process or combustion system. Typical values of pressure swid atomizers range from 50 to 100 p.m. 

A minimum volatihty is frequently specified to assure adequate vaporization under low temperature conditions. It can be defined either by a vapor pressure measurement or by initial distillation temperature limits. Vaporization promotes engine start-up. Fuel vapor pressure assumes an important role particularly at low temperature. For example, if fuel has cooled to —40°C, as at arctic bases, the amount of vapor produced is well below the lean flammabihty limit. In this case a spark igniter must vaporize enough fuel droplets to initiate combustion. Start-up under the extreme temperature conditions of the arctic is a major constraint in converting the Air Force from volatile JP-4 to kerosene-type JP-8, the military counterpart of commercial Jet Al. 

TurbulentPremixedFlames. Combustion processes and flow phenomena are closely coimected and the fluid mechanics of a burning mixture play an important role in forming the stmcture of the flame. Laminar combusting flows can occur only at low Reynolds numbers, defined as... 

The combustion chamber of a modem steam generator is a large water-cooled chamber in which fuel is burned. Firing densities are important to ensure that the chamber wall metal temperatures do not exceed the limits of failure of the tubes. Firing densities are expressed in two ways volumetric combustion intensities and area firing intensities. The volumetric combustion intensity is defined by equation 23,... 

Flammability. Dimer and trimer acids, as well as monomer acids derived from dimer acid processing, are neither flammable nor combustible as defined by the Department of Transportation (DOT) and do not represent a fire ha2ard ... 

Excess Air for Combustion More than the theoretical amount of air is necessary in practice to achieve complete combustion. This excess air is expressed as a percentage of the theoretical air amount. The equivalence ratio is defined as the ratio of the actual fuel-air ratio to the stoichiometric fuel-air ratio. Equivalence ratio values less than... 

Combustible Eiquid A term used to classify certain liquids that will burn on the basis of flash points. The National Fire Protection Association (NFPA) defines a combustible liquid as having a flash point of 100°F (37.8°C) or higher. See also, Flammable Liquid. Class II liquids have flash points at or above 100°F, but below 140°F. Class III liquids are subdivided into two subclasses. 

Combustion is the most widely used, and yet one of the least understood, chemical reactions at our disposal. Combustion is defined as the rapid union of a substance with oxygen accompanied by the evolution of light and heat (2). 

The emissions from combustion processes may be predicted to some extent if the variables of the processes are completely defined. Figure 6-7 indicates how the emissions from a combustion source would be expected to vary with the temperature of the reaction. No absolute values are shown, as these will vary greatly with fuel type, independent variables of the combustion process, etc. 

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