Compressed gases alkanes

In most, but not all circumstances, the core gas temperature, T, is the natural reference temperature for the compressed gas because the highest temperature at the end of compression is responsible for the development of spontaneous ignition in the shortest time [88, 95]. Exceptionally, when the compression heats the reactants to temperatures that correspond to the region of ntc for that particular mixture, combustion may be initiated in the cooler boundary layer region. That is, gases which, at the end of compression, are colder than those in the adiabatic core control the duration of the ignition delay. This was demonstrated by Schreiber and coworkers by the simulation of alkane combustion, using various reduced kinetic schemes, in computational fluid dynamic calculations [102-104]. 

Fig. 6. 21. Ignition delays as a function of compressed gas temperature for the normal alkanes, n-butane to n-heptane, i-octane (2,2,4-trimethylpentane) and toluene in stoichiometric proportions in air. The results were obtained in a rapid compression machine at a compressed gas density of 128 mol m (0.65-0.75 MPa). Ignition in the ntc and lower temperature range was not observed under these experimental conditions [50].

C1-C2 The first four alkanes (methane, ethane, propane, and butane) are gases at room temperature and atmospheric pressure. Methane and ethane are difficult to liquefy, so they are usually handled as compressed gases. Upon cooling to cryogenic (very low) temperatures, however, methane and ethane become liquids. Liquefied natural gas, mostly methane, can be transported in special refrigerated tankers more easily than it can be transported as a compressed gas. 

A four-carbon compound is named butane, with the molecular formula of 411,0. Structures, molecular formulas, and some physical characteristics of these alkane-compressed gas compounds are shown in Figure 4.8. Notice the differences in boiling points and flammable ranges. As the carbon content increases, the boiling point of the compounds increases. In addition to carbon content, polarity and branching of compounds will affect physical characteristics. This concept will be discussed in more detail in Chapter 5. For now, just be aware that there are relationships between the physical characteristics of flammable gases, which include ignition temperature, heat output, vapor content, and vapor pressure. 

Natural gas contains, of course, only the more volatile alkanes, that is, those of low molecular weight it consists chiefly of methane and progressively smaller amounts of ethane, propane, and higher alkanes. For example, a sample taken from a pipeline supplied by a large number of Pennsylvania wells contained methane, ethane, and propane in the ratio of 12 2 1, with higher alkanes making up only 3% of the total. The propane-butane fraction is separated from the more volatile components by liquefaction, compressed into cylinders, and sold as bottled gas in areas not served by a gas utility. 

Chapter 4 Compressed Gases Elammable Gases Elammable Range Vapor Density Elammable Gas Elements Hydrocarbon Eamilies Alkanes Isomers Alkenes Alkynes... 

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