Combustion characteristics

The various types of hydrocarbons in gasoline behave differently in their preflame reactions and thus, their tendency to knock. It is difficult to find any precise relationship between chemical structure and antiknock performance in an engine. Members of the same hydrocarbon series may show very different antiknock effects. For example, normal heptane and normal pentane, both paraffins, have antiknock ratings (octane numbers) of 0 and 61.9, respectively (Table 5.5). Very generally, aromatic hydrocarbons (e.g., benzene and toluene), highly branched iso-paraffins (e.g., iso-octane), and 

The knock rating of a gasoline is expressed as octane number and is the percentage by volume of o-octane (octane number 100, by definition) in admixture with normal heptane (octane number 0, by definition) that has the same knock characteristics as the gasoline being assessed. 

To avoid the confusion arising from the use of two separate octane number scales, one below and one above 100, an arbitrary extension of the octane number scale was selected so that the value in terms of automotive engine performance of each unit between 100 and 103 was similar to those between 97 and 100. The relationship between the octane number scale above 100 and the performance number scale is  

An alternative criterion of energy content is the aniline gravity product (AGP), which is fairly accurately related to calorific value but more easily determined. It is the product of the gravity at 60°F (expressed in degrees API) and the aniline point of the gasoline in °F (ASTM D-611, IP 2). The aniline point is the lowest temperature at which the gasoline is miscible with an equal volume of aniline and is inversely proportional to the aromatic content and related to the calorific value (ASTM D-1405, IP 193). 

As with naphtha, the number of potential hydrocarbon isomers in the gasoline boiling range (Table 5.2) renders complete speciation of individual hydrocarbons impossible for the gasoline distillation range, and methods are used that identify the hydrocarbon types as chemical groups rather than as individual constituents. 

---

N. Kubota, "Survey of Rocket PropeUants and Their Combustion Characteristics," in K. K. Kuo and M. Summerfield, eds.. Fundamentals of Solid Propellant Combustion, Vol. 90, Progress in Astronautics and Aeronautics, AJAA, 1984. 

Combustion characteristics of consequence include the overall mechanism of soHd waste combustion, factors governing rates of waste fuels combustion, temperatures associated with waste oxidation, and pollution-formation mechanisms. 

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. 

An alternative method of produciag hydrocarbon fuels from biomass uses oils that are produced ia certaia plant seeds, such as rape seed, sunflowers, or oil palms, or from aquatic plants (see Soybeans and other oilseeds). Certain aquatic plants produce oils that can be extracted and upgraded to produce diesel fuel. The primary processiag requirement is to isolate the hydrocarbon portion of the carbon chain that closely matches diesel fuel and modify its combustion characteristics by chemical processiag. 

VFO works well in gas turbines. In a nine-month test program, the combustion properties of VFO were studied in a combustion test module. A gas turbine was also operated on VFO. The tests were conducted to study the combustion characteristics of VFO, the erosive and corrosive effects of VFO, and the operation of a gas turbine on VFO. The combustion tests were conducted on a combustion test module built from a GE Frame 5 combustion can and liner. The gas turbine tests were conducted on a Ford model 707 industrial gas turbine. Both the combustion module and gas turbine were used in the erosion and corrosion evaluation. The combustion tests showed the VFO to match natural gas in flame patterns, temperature profile, and flame color. The operation of the gas turbine revealed that the gas turbine not only operated well on VFO, but its performance was improved. The turbine inlet temperature was lower at a given output with VFO than with either natural gas or diesel fuel. This phenomenon is due to the increase in exhaust mass flow provided by the addition of steam in the diesel for the vaporization process. Following the tests, a thorough inspection was made of materials in the combustion module and on the gas turbine, which came into contact with the vaporized fuel or with the combustion gas. The inspection revealed no harmful effects on any of the components due to the use of VFO. 

Many methods have been evolved in recent years for assessing flame retardants and the combustion characteristics of plastics and these have been the subject of comprehensive reviews. " ... 

Among the various selection considerations are specific combustion characteristics of different fuels. One of the combustion characteristics of gaseous fuels is their flammability limit. The flammability limit refers to the mixture proportions of fuel and air that will sustain a premixed flame when there is either limited or excess air available. If there is a large amount of fuel mixed with a small amount of air, then there is a limiting ratio of fuel to air at which the mixture will no longer sustain a flame. This limit is called the rich flammability limit. If there is a small amount of fuel mixed with excess air, then there is a limiting ratio of the two at which the flame will not propagate.This limit is called the lean flammability limit. Different fuels have different flammability limits and these must be identified for each fuel. 

The combustion characteristics of liquid fuels are similarly determined by measures of their ability to sustain a flame. Two measures of the combustion characteristics of liquid fuels especially related to safety are flash point and autoignition temperature. The flash point is the maximum temperature at which a liquid fuel can be maintained in an open vessel exposed to air before which it will sustain a flame... 

The importance of coal as an energy source motivates further research into the combustion characteristics and chemical kinetics of both coal and the material that remains after devolatization, char. Furrher research will aid in making coal a cleaner and more efficient energy source. 

Oxygenate is an oxygen-containing hydrocarbon. The term is used for oxygen-containing molecules blended into gasoline to improve its combustion characteristics. 

Owing to the differing combustion characteristics and calorific values of the gaseous fuels which are commonly available [natural gas, liquefied petroleum (bottled) gas], slight variations in dimensions, including jet size and aeration controls, are necessary for maximum efficiency it is essential that, unless the burner is of the All Gases type which can be adjusted, the burner should be the one intended for the available gas supply. 

Since an understanding of the combustion characteristics of composite propellants requires information on the chemical behavior of the individual oxidizer and fuel, a discussion of these areas is presented as a prelude to the discussion of propellant combustion. 

Powling (P7) recently reported on the results of an extensive study of the combustion characteristics of ammonium perchlorate-based composite propellants. The nature of the chemical processes taking place at the solid-gas interface and the possibility of heat release in the condensed phase were considered. Although the evidence is that some heat release is likely to occur within the solid surface, Powling found that the combustion in all pressure regions appears to be dominated by gas-phase reactions. 

Because any such behavior causes the motor to fail in its mission objective, these peculiar operational effects have received considerable research attention. The results of these research studies have shown that these various forms of instability result from a coupling between the transient combustion characteristics of the propellant and the transient ballistics of the combustion chamber. These instabilities are termed pressure-coupled, velocity-coupled, and bulk-coupled, and will be described below. 

When the propellant burning rate is espressed by Eq. (5b), the parameter p /e can be considered as the transient sensitivity of the burning rate to pressure. This parameter depends on the transient combustion characteristics, and its evaluation depends on the particular model of the combustion process. Thus, the acoustic admittance provides the link between experimental observation and theoretical prediction. 

Table 9-1 Combustible Characteristic Constant for the Swift-Epstein Equation1...

Koseki, H., Combustion characteristics of hazardous materials, in The Symposium for the NRIFD 56th Anniversary, Mitaka, Tokyo, National Research Institute of Fire and Disaster, 1 June 1998. 

Determine the worst-case gas mixture combustion characteristics, system pressure, and permissible pressure drop across the arrester, to help select the most appropriate element design. Not only does element design impact pressure drop, but also the rate of blockage due to particle impact, liquid condensation, and chemical reaction (such as monomer polymerization) can make some designs impractical even if in-service and out-of-service arresters are provided in parallel. 

---