Liquid Nitrous Oxide BLEVE Tests

Abstract

A series of tests to characterize the behavior of nitrous oxide at conditions to initiate a BLEVE (Boiling Liquid Expanding Vapor Explosion) spanned the expected temperature range for nitrous oxide storage, transfer, and feed in commercial rocket systems. The behavior of the liquid upon instantaneously relieving the pressure in a storage vessel with a burst diaphragm was observed and visually recorded through a window in the test vessel, in an attempt to distinguish if homogeneous nucleation of bubbles (the defining characteristic of a BLEVE) occurred at the predetermined test temperature. High-speed piezoelectric pressure transducers at the inside of the exhaust duct, above the burst disc, recorded a secondary pressure pulse that is believed to result from a rapid phase transition of the liquid nitrous oxide, releasing large quantities of N2O vapor in a very short time interval. Close-up videos of the window showed that in all tests, nitrous oxide “ice” crystals were formed in the test vessel. Based upon the review of free-field high-speed pressure data, a BLEVE with the formation of a shock wave did occur when liquid nitrous oxide temperatures were 29.1 o F and 25.1 o F. A BLEVE was not evidenced when the liquid nitrous oxide temperatures were +1.5 o F and -8.1 o F. The strength of the shock wave decreased as the liquid nitrous oxide temperature decreased. Even without a shock wave that may indicate a BLEVE event, a large volume of rapidly expanding gas was generated for all tests at all liquid nitrous oxide temperatures, between -8.1 o F and +29.1 o F. The rapid phase change from liquid to vapor within 400 milliseconds might have occurred via homogeneous bubble nucleation (characterizing a true BLEVE), or alternatively via heterogeneous nucleation promoted by nitrous oxide crystals.