Flame speed measurement techniques

For a long time there was no interest in flame speed measurements. Sufficient data and understanding were thought to be at hand. But as lean bum conditions became popular in spark ignition engines, the flame speed of lean limits became important. Thus, interest has been rekindled in measurement techniques. 

The temperature at which the flame speed is measured is calculated as follows. For the approach gas temperature, one calculates what the initial temperature would have been if there were no heat extraction. Then the velocity of the mixture, which would give the measured mass flow rate at this temperature, is determined. This velocity is SL at the calculated temperature. Detailed descriptions of various burned systems and techniques are to be found in Ref. [22],... 

Reported flame speed results for most fuels vary somewhat with the measurement technique used. Most results, however, are internally consistent. Plotted in Fig. 4.21 are some typical flame speed results as a function of the stoichiometric mixture ratio. Detailed data, which were given in recent combustion symposia, are available in the extensive tabulations of Refs. [24-26], The flame speeds for many fuels in air have been summarized from these references and are listed in Appendix F. Since most paraffins, except methane, have approximately the same flame temperature in air, it is not surprising that their flame speeds are about the same (—45 cm/s). Methane has a somewhat lower speed (<40 cm/s). Attempts [24] have been made to correlate flame speed with hydrocarbon fuel structure and chain length, but these correlations... 

A similar flat flame technique—one that does not require a heat loss correction—is the so-called opposed jet system. This approach to measuring flame speeds was introduced to determine the effect of flame stretch on the measured laminar flame velocity. The concept of stretch was introduced in attempts to understand the effects of turbulence on the mass burning rate of premixed systems. (This subject is considered in more detail in Section 4.E.) The technique uses two... 

The burning velocity, Sa, can be determined by a technique that measures the speed of a spherical flame in a soap bubble. This process is shown below. 

Other reports deal with individual elements, such as Ni [1, 86, 87] or Fe [11,84]. The efficiency [71—73] of flame methods (AAS) has been compared with flameless techniques (NFAAS) (Table 6). Because of their significance there have been attempts to determine the elements P [38] and S [78] directly with AAS. This, however, requires a device which can measure ultraviolet lines (ca. 180 nm) with sufficient sensitivity. Good results can also be achieved by gas chromatographic separation and successive AAS determination [92] and simultaneous multielement analysis with a Vidicon-detector has been tried [68] because the speed with which the information is gained can be very important in practice. Some work [39, 53] reports on the problem of molecular bands which can appear when working with... 

Although originally FIA was conceived as a special technique for delivery of a sample segment into the instrument, the combination of flow injection as a sample pretreatment tool with atomic spectrometry has been shown to be of great potential for enhancing the selectivity and sensitivity of the measurements. Moreover, contamination problems are reduced due to the closed system used, making this interface suitable for ultratrace determination of metal species. Hyphenated techniques such as FIA/ SIA with flame atomic absorption spectrometry, inductively coupled plasma (ICP)-optical emission spectrometry, and ICP-mass spectrometry (MS) have been exploited extensively in recent years. The major attraction of FIA-ICP-MS is its exceptional multi-elemental sensitivity combined with high speed of analysis. In addition, the possibility of... 

Low-dispersion flow injection techniques (dispersion values of 1-3) have been used for high-speed sample introduction to such detector systems as inductively coupled plasma atomic emission, flame atomic absorption, and specific-ion electrodes. The justification for using flow injection methods for electrodes such as pH and pCa is the small sample size required ( 25 pL) and the short measurement time ( 10 s). That is, measurements are made well before steady-state equilibria are established, which for many specific-ion electrodes may require a minute or more. With flow injection measurements, transient signals tor sample and standards provide excellent accuracy and precision. For example, it has been reported that pH measurements on blood serum can be accomplished at a rate of 240/h with a precision of 0.002 pH. 

A crucial factor affecting analytical measurements, especially in intensive care situations, is speed—clearly an advantage of these electrode systems. The development of the ion-selective electrode technique has reached such a state that flame photometry is likely to disappear from clinical laboratories within a few years. There is no doubt that carrier membrane electrodes based on crown compounds will also become an applicable tool in other fields of chemical analysis. 

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