Apparatus and Procedure

The experimental apparatus used was the GALCIT Detonation Tube (Figs. 1, 2, and 3), first described in a previous report [Akbar and Shepherd (1996)]. The tube is constructed of three cast stainless steel (304) sections joined together by flanges and high-strength fasteners. The assembly is 7.3-m long and has a 280-mm inside diameter. A vacuum system is used to evacuate the tube to less than 50 mTorr before each test. A gas handling system can supply H₂, N₂O, N₂, NH₃, CH₄, O₂, Ar, and He from a cylinder farm located outside the building. Gas composition is controlled by the method of partial pressures using an electronic Heise 901a gauge, accurate to $\pm$ 0.18 kPa. Before a test, the test mixture is circulated through the tube volume with a bellows pump to ensure homogeneity.

  

Figure 1: Elevation schematic of GALCIT Detonation Tube.

  

Figure 2: Oblique schematic of GALCIT Detonation Tube.

  

Figure 3: GALCIT Detonation Tube facility. a) View along tube from driver end. b) Side view of driver end.

An oxy-acetylene driver is used to reliably initiate mixtures with a wide range of sensitivities. The driver gas is injected through a distribution manifold (4 tubes, 150-mm long) located at one end of the tube, and is a slightly lean mixture of acetylene and oxygen. Partial pressure of the driver gas is about 2 kPa, and can be controlled by varying the injection time. Initiation of the driver is achieved by a capacitor discharge through an exploding copper wire (30-mm long). A study has been carried out to measure the equivalent energy of the driver (see Appendix ). The results of this study allow control of the detonation wave strength, and a close approximation of the Chapman-Jouguet condition at the downstream end of the tube.

Table 1 summarizes the mixtures tested so far. For all mixtures except mixture 1, air was made from bottled O₂and N₂. Tests with mixture 1 (H₂+N₂O+$\beta$(O₂+3.76N₂)) used atmospheric air. We use a simplified representation of air composition as O₂ + 3.76N₂; the complete specification of all compositions used in this study are given in Table 1. Note that the mixture numbers do not correspond to the mixture numbers in the previous report [Ross and Shepherd (1996)]. To simplify the presentation, N₂ and air are treated as diluents even though air is an effective oxidizer. The amount of diluent was specified in terms of the fraction (percentage) in the figures rather than in terms of the parameter $\beta$ given in Table 1 and Appendix . For the case of nitrogen dilution, the fraction of diluent is $\beta$/N where N is the total number of moles in the mixture formula in Table 1 and in the case of air, the fraction is 4.76$\beta$/N.

Mixtures 2 to 11 represent simple mixtures of one fuel and one oxidizer that have been used to characterize the behavior of each substance individually. Mixtures 12 through 17 are best estimates of the retained gas composition in the waste tank as determined by recent tests at Hanford. A small percentage of the gas sample was not identified in those cases and was simply stated as ``unknown.'' In those cases, we have increased the amount of N₂ to preserve the actual percentages of the other species. For instance, mixture 12 was originally specified with 2% unknown, so the original 33% N₂ was replaced with 35% N₂. In each series, as the dilution was increased, the initial pressure was increased such that predicted detonation pressures were just below the tube design limit, up to 1 atm initial pressure. The purpose of this strategy was to acquire as much data at 1 atm initial pressure (field conditions) as possible while deviating as little as possible when required by structural limitations. The largest cell sizes possible are about 50% to 100% of the tube diameter (280 mm). Only one test was carried out for each mixture type 3 and 4 and no cell data were obtained.

 

Table 1: Experimentally Studied Mixtures

Mixture	Composition	Initial Pressure	Note
1	H2+N2O+$\beta$(O2 + 3.76N2)	100 kPa
2	H2+N2O+$\beta$N2	100 kPa
3	14H2+14N2O+71N2+O2	100 kPa
4	H2+4O2	98 kPa
5	CH4+2O2+$\beta$N2	72-102 kPa
6	CH4+4N2O+$\beta$N2	57-102 kPa
7	CH4+4N2O+$\beta$(O2 + 3.76N2)	86-97 kPa
8	NH3+0.75O2+$\beta$N2	66-91 kPa
9	NH3+1.5N2O+$\beta$N2	56-81 kPa
10	NH3+1.5N2O+$\beta$(O2 + 3.76N2)	61-101 kPa
11	42H2+21NH3+36N2O+CH4+$\beta$(O2 + 3.76N2)	76-101 kPa	SY-1011
12	29H2+11NH3+24N2O+35N2+CH4+$\beta$(O2 + 3.76N2)	94-101 kPa	SY-101
13	31H2+0.02NH3+4.3N2O+63.08N2+1.6CH4+$\beta$(O2 + 3.76N2)	101 kPa	AW-101
14	63H2+0.02NH3+11N2O+25.28N2+0.7CH4+$\beta$(O2 + 3.76N2)	101 kPa	AN-105
15	47H2+0.02NH3+19N2O+33.08N2+0.9CH4+$\beta$(O2 + 3.76N2)	101 kPa	AN-104
16	61H2+0.05NH3+3.8N2O+35.14N2+0.01CH4+$\beta$(O2 + 3.76N2)	101 kPa	AN-103
17	75H2+2.4NH3+5.6N2O+16.3N2+0.7CH4+$\beta$(O2 + 3.76N2)	101 kPa	A-101

¹Mixture 26 from [Ross and Shepherd (1996)], see Appendix 

Detonation cell widths are measured by the soot foil technique. The cell width is determined by physical measurements of the spacing, transverse to the detonation propagation direction, between triple point tracks inscribed on soot foils placed within the detonation tube. The foils are 61 cm x 91.4 cm x 0.5 mm aluminum sheets, rolled into cylinders to conform to the detonation tube inner diameter. Soot is deposited on the inside surface of each foil by burning a kerosene-soaked cloth strip inside a closed vertical tube containing the foil. Each foil is normally sooted twice, in both vertical orientations, to cancel convection-induced gradients. The upstream edge of the foil is riveted to an aluminum ring (3-mm thick by 51-mm wide) to secure it as the detonation passes. The downstream end (adjacent to the end flange) is clamped at two points to the tube wall. The cell widths are measured on flattened foils, as the transverse distance between triple point tracks. Since this distance can vary significantly over a foil, minimum and maximum values are reported. Note that for small cells (relative to the tube diameter), this is a unique measure of the cell width, but for cell widths on the order of the tube diameter, this measure may not be comparable to measurements in other facilities or by other techniques. In this case, the effect of the tube geometry on the cells should be considered. Currently, cell widths are measured manually. The inherent variation of cell size across the foil and the difficulty of identifying cell boundaries are significant sources of uncertainty and impose serious limitations on efforts to characterize and predict cell size. Typically, 10 cell-width measurements are made and representative minimum and maximum values are reported. In general, the uncertainty in cell-width measurements, reflected in the reported ranges, can be up to 50%.