Experimental study on hypergolic interaction between N,N,N′,N′ -tetramethylethylenediamine and nitric acid

The hypergolic interaction between N,N,N′,N′- tetramethylethylenediamine (TMEDA, (CH₃)₂NCH ₂CH₂N(CH₃)₂) and nitric acid was studied by several different experimental techniques. The gaseous species from condensed- and gas-phase reactions between TMEDA and nitric acid (90% HNO ₃) were analyzed by a confined interaction setup, coupled with a Fourier transform infrared (FTIR) spectrometer. The species identified include TMEDA dinitrate, dimethylnitrosamine (CH₃)₂NNO, dimethylformamide (CH₃)₂NCHO, CH₂O, H ₂O, NO₂, HONO, NO, CO₂, N₂O, and CO. The solid residue from the condensed-phase reactions between TMEDA and 90% HNO₃ was studied by using a confined rapid thermolysis (CRT) coupled with FTIR spectroscopy and time-of-flight mass spectrometry. On the basis of the product analysis, the preignition reactions between TMEDA and nitric acid are discussed. The initiation reaction is a condensed-phase, exothermic salt formation reaction. At elevated temperatures, the thermal decomposition of nitric acid produces NO₂, which abstracts a hydrogen atom from TMEDA and causes a series of further reactions involving the formation of dimethylnitrosamine and aldehydes. The acid-catalyzed decomposition of TMEDA dinitrate also plays an important role in the preignition reactions. High-speed videos were acquired to visualize the preignition, ignition and postignition events in a drop test when a fuel drop impinged on a pool of 90% HNO ₃. In addition, temperature profiles were obtained in gas and condensed phases using coated fine-wire thermocouples.