Results

Appendix  summarizes the results of tests involving the mixtures listed in Table 1. The initial pressure listed for each shot includes the pressure added by the driver gas. Detonation initiation or failure of each shot is recorded under ``Go''. Chapman-Jouguet detonation speeds, as predicted by STANJAN [Reynolds (1986)], are reported under D$_{\rm CJ}$ while the measured (average) wave speeds between pressure transducers 1 and 2, and 2 and 3 are reported under D_1-2 and D_2-3, respectively. $\lambda_{\rm min}$ and $\lambda_{\rm max}$ represent the range of cell widths recorded by the soot foil technique for shots where cells were measurable. One conclusion to be reached from the data in Appendix  is that equilibrium predictions of detonation speed are quite accurate. This relates to the performance of the driver (Section ) as well as the accuracy and relevance of equilibrium calculations. Of the shots with promptly initiated detonations, the apparent velocity between pressure transducers 1 and 2 was slightly above the CJ velocity (0.14% on average), and the apparent velocity between transducers 2 and 3 exhibited a slight velocity deficit (0.27% on average). The average drop in velocity was 7.92 m/s. Several photographic examples of soot foils are given in Appendix  and a number of pressure traces are provided in Appendix G.

  

Figure 4: Cell width vs. percent dilution for stoichiometric H₂-N₂O-diluent mixtures.

Figures 4 through 11 show the cell-width measurements along with data from the literature. These data are also shown in different form in Section 3.3. Figure 4 shows cell-width measurements of H₂-N₂O-diluent mixtures from the present work and from a previous report [Akbar and Shepherd (1993)]. Cases with dilution by air and N₂ are presented together. Figure 5 shows cell-width measurements of CH₄-O₂-N₂from the present work and a number of other publications ([Moen et al. (1984)], [Manzhalei et al. (1974)], [Knystautas et al. (1984)], [Beeson et al. (1991)]). Note that the data points around 0% N₂ have been artificially spread out so they are distinguishable, but they all represent the undiluted case. The data points at 71.5% N₂ also represent stoichiometric CH₄-air. As described in Section 2.1, higher initial pressures were generally used at higher dilutions, but some data points at low pressure (70 kPa) are shown for both low and high dilution. Figure 6 shows cell-width measurements of CH₄-N₂O-diluent mixtures from the present work only. No comparable data have been found in the published literature. Five of the tests shown in Fig. 6 used air dilution and the rest were with N₂ dilution. Within the range of dilution studied experimentally, little difference is seen between N₂ and air dilution. Again, data from a number of initial pressures are shown together.

  

Figure 5: Cell width vs. percent N₂ for stoichiometric CH₄-O₂-N₂ mixtures.

  

Figure 6: Cell width vs. percent dilution for stoichiometric CH₄-N₂O-diluent mixtures.

  

Figure 7: Cell width vs. percent dilution for stoichiometric NH₃-O₂-N₂ mixtures.

  

Figure 8: Cell width vs. percent dilution for stoichiometric NH₃-N₂O-Diluent mixtures.

  

Figure 9: Cell width vs. percent air dilution for model SY-101 mixtures.

  

Figure 10: Cell width vs. percent air dilution for model tank mixtures.

  

Figure 11: Cell width vs. percent CH₄ for mixture 12.

Some data were available from unpublished sources for cell widths in stoichiometric NH₃-O₂ mixtures diluted by N₂ [Bennett (1986)] and these data are shown along with some from the current work in Fig. 7. Figure 8 shows data for stoichiometric NH₃-N₂O mixtures diluted with N₂ and air. As seen in the CH₄-N₂O data (Fig. 6), little difference is apparent between N₂ and air dilution at the levels tested.

A large number of tests were performed with two versions of SY-101 model tank mixtures with variable air dilution, and these results are shown in Fig. 9. At the lower dilution levels, the initial pressure varied below 1 atm. These data are interesting for the slow increase (and slight decrease for mixture 12) of cell width with increasing air concentration at low dilution. A selection of air dilution cases were tested in other model tank mixtures, and these data are shown together in Fig. 10.

A notable feature of the model tank mixtures under study is the small concentrations of CH₄ present. In all experiments and calculations performed so far, the CH₄ has been included as specified. However, analysis of the mixtures would be greatly simplified if it were omitted, particularly for chemical kinetics calculations. The number of reactions to be considered could be dramatically reduced (79 reactions and 20 species vs 201 reactions and 45 species) for one standard mechanism. Possible strategies for omitting CH₄ from the study include ignoring it, replacing it with a comparable species, or developing some correction scheme based on modeling results. Considering this, a set of experiments with one of the model tank mixtures were performed (without air) with various CH₄ concentrations. These results are shown in Fig. 11 which shows a slight increase in cell width with methane concentration in the range of 0-2% CH₄.

Some of the model tank mixtures contain very small quantities of NH₃, which may be insignificant. However, since some mixtures do contain substantial concentrations of NH₃, any gains made by omitting it would be limited.