Effect of Water and Humidity on Hypergolic Propellant Ignition Delay
Figure 11. Photodiode IDT (a) and microphone amplitude (b) for MMH with WFNA
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| Figure 11. Photodiode IDT (a) and microphone amplitude (b) for MMH with WFNA V. Conclusions The objective of this research was to determine how ignition performance is affected by increased water presence for TEAB and MMH with WFNA. Drop-on-pool tests were completed to assess ignition and combustion. Water presence was accounted for by controlling the relative humidity of the testing environment and by adding water to WFNA. The drop-on-pool tests were able to record the time of propellant contact with video, an impact sensor, and a microphone. The video also provided validation of propellant ignition and determined the IDT. The microphone recorded the amplitude of the pressure wave released during combustion. A photodiode provided secondary measurements of IDT and was able to quantify light expulsion from combustion. The onset time and magnitude of OH and NH radical presence was quantified by a UV streak camera spectrometer. Achieved relative humidity was either below 24% or above 94% for all tests. The added water concentration in the WFNA was either 0% or 10% by weight. The effects of RH and water concentration were determined statistically by linear regression modeling. Increased water content in WFNA decreased the probability of igniting with TEAB. This is supported by increased water content causing decreased light emission on the photodiode and streak camera as well as delaying the onset of NH radicals. When using neat WFNA all tests ignited at high RH, but only 33% ignited when 10% water was added to the WFNA at high RH. Otherwise, changing the RH caused no noticeable effects on successful TEAB/WFNA reactions. Contrarily, the water concentration in WFNA did not play a major role in reactions with MMH, but RH significantly decreased IDT. To determine whether TEAB is hygroscopic or affected by extended exposure to humid environments, samples were aged in a humid air oven and compared to samples aged in dry air and dry nitrogen environments. The samples Downloaded by PURDUE UNIVERSITY on July 21, 2017 | http://arc.aiaa.org | DOI: 10.2514/6.2015-3867 American Institute of Aeronautics and Astronautics 15 aged in the humidity oven decomposed after 7 days and some samples solidified into a white powder. Samples that were exposed in the humidity oven for only 2 days or 4 days were still liquid, but became opaque. Samples aged in dry air and dry nitrogen environments did not show any signs of decomposing. All aged samples were tested in drop tests with neat WFNA. The solidified samples did not ignite but the samples exposed for only 2 days or 4 days still provided good ignition characteristics. These samples showed a significantly decreased presence of OH radicals, but all other characteristics were consistent with the neat TEAB. It is interesting that the OH presence can be dramatically decreased, but all other characteristics show no signs of change. The samples aged in dry air and dry nitrogen environments show almost no change in ignition performance. Download 0.9 Mb. Share with your friends:
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