Rapid compression studies on spontaneous ignition of isopropyl nitrate art I: Nonexplosive decomposition, explosive oxidation and conditions for safe handling
✍ Scribed by P. Beeley; J.F. Griffiths; P. Gray
- Publisher
- Elsevier Science
- Year
- 1980
- Tongue
- English
- Weight
- 772 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0010-2180
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✦ Synopsis
This work relates to the effects of rapid compression on small proportions of isopropyl nitrate vapor (IPN) in inert gases or in mixtures containing oxygen. Compression is brought about in a mechanical apparatus comprising a solid piston, driven by compressed air, in a cylinder. The compression ratio ( Vinitial/Vfina 1) is 10.8:1 and the time for motion of the piston is 20 ms. Pressure-time histories are measured by transducer and gas temperatures interpreted from them.
The temperatures reached during compression depend on the ratio of principal specific heats of the reactant compositions; they fall in the range around 500°K (in CO2) to around 1000°K (in Ar). From starting pressures of about 0.5 atm the pressures reached vary between approximately 7 and 16 atm. The temperature begins to fall in nonreactive gases, immediately compression ceases; its relaxation time is about 50 ms. However, in reactive mixtures the temperature and pressure may be enhanced for a brief period ( < 10 ms) beyond those attained at the end of compression: This is due to exothermic reaction, and spontaneous ignition may be achieved. In the present circumstances it is found that the presence of oxygen is a prerequisite for the ignition of IPN vapor.
Overall extents of reaction and product abundances are measured by gas chromatography and enthalpies of reaction calculated from these. At all but the lowest temperatures (< 600°K) virtually all of the IPN reacts (i.e., less than 5% remains), whether or not oxygen is present. But even at very high temperatures (> 1000°K) very small amounts always remain: This is to be attributed to part of the IPN being confined to a cool boundary layer at the combustion chamber surface. Pyrolysis of IPN occurs in inert atmospheres and among the major products at moderate temperatures are aldehydes, nitromethane, methyl nitrite, and methanol. At temperatures beyond 1000°K, carbon monoxide and methane predominate. Overall exothermicities are modest in all circumstances (AH/kJ mol-1 < _ 150), and they are substantially lower than that associated with the self-sustained decomposition flame of IPN.
When there is insufficient oxygen for complete combustion to be possible (IPN:O 2 > 1:3.25) rather similar products are formed to those seen during pyrolysis at temperatures below 1000°K, but there are greater yields of CO, and CO 2 formation becomes possible.
When excess oxygen is present carbon oxides and formaldehyde are the predominant carbon-containing products. Now the overall exothermicity exceeds 1000 kJ tool -1 and ignition occurs at a second stage of reaction.